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Purpose Vaginal applicators for a novel miniature x-ray tube were developed using three-dimensional (3D) printing to be used in brachytherapy of endometrial cancers. Methods Cylindrical vaginal applicators with various diameters, lengths, and infill percentages (IFPs) were fabricated using a 3D printer. X-ray dose distributions and depth-dose profiles were calculated using a Monte Carlo simulation. The performances of the applicators were evaluated by measuring and analyzing the dosimetric characteristics of x rays generated from the miniature x-ray tube equipped with the applicators. Results Quite uniform dose distributions around the applicators were achieved by optimizing the dwell positions and the dwell times of the miniature x-ray tube inside the applicators. In addition, identical absolute dose and depth-dose profiles were obtained through the control of the IFP values even though different-sized applicators are used. Conclusion The presented 3D printing technique provides an efficient approach to provide vaginal applicators with optimal IFPs that allow consistent treatment time for patients of varying vaginal canal size.

Purpose: The authors investigated the potential of optimized noncoplanar irradiation trajectories for volumetric modulated arc therapy (VMAT) treatments of nasopharyngeal patients and studied the trade-off between treatment plan quality and delivery time in radiation therapy. Methods: For three nasopharyngeal patients, the authors generated treatment plans for nine different delivery scenarios using dedicated optimization methods. They compared these scenarios according to dose characteristics, number of beam directions, and estimated delivery times. In particular, the authors generated the following treatment plans: (1) a 4π plan, which is a not sequenced, fluence optimized plan that uses beam directions from approximately 1400 noncoplanar directions and marks a theoretical upper limit of the treatment plan quality, (2) a coplanar 2π plan with 72 coplanar beam directions as pendant to the noncoplanar 4π plan, (3) a coplanar VMAT plan, (4) a coplanar step and shoot (SnS) plan, (5) a beam angle optimized (BAO) coplanar SnS IMRT plan, (6) a noncoplanar BAO SnS plan, (7) a VMAT plan with rotated treatment couch, (8) a noncoplanar VMAT plan with an optimized great circle around the patient, and (9) a noncoplanar BAO VMAT plan with an arbitrary trajectory around the patient. Results: VMAT using optimized noncoplanar irradiation trajectories reduced the mean and maximum doses in organs at risk compared to coplanar VMAT plans by 19% on average while the target coverage remains constant. A coplanar BAO SnS plan was superior to coplanar SnS or VMAT; however, noncoplanar plans like a noncoplanar BAO SnS plan or noncoplanar VMAT yielded a better plan quality than the best coplanar 2π plan. The treatment plan quality of VMAT plans depended on the length of the trajectory. The delivery times of noncoplanar VMAT plans were estimated to be 6.5 min in average; 1.6 min longer than a coplanar plan but on average 2.8 min faster than a noncoplanar SnS plan with comparable treatment plan quality. Conclusions: The authors’ study reconfirms the dosimetric benefits of noncoplanar irradiation of nasopharyngeal tumors. Both SnS using optimized noncoplanar beam ensembles and VMAT using an optimized, arbitrary, noncoplanar trajectory enabled dose reductions in organs at risk compared to coplanar SnS and VMAT. Using great circles or simple couch rotations to implement noncoplanar VMAT, however, was not sufficient to yield meaningful improvements in treatment plan quality. The authors estimate that noncoplanar VMAT using arbitrary optimized irradiation trajectories comes at an increased delivery time compared to coplanar VMAT yet at a decreased delivery time compared to noncoplanar SnS IMRT.

Purpose: To analyze and report prostate intrafractional motion recorded online during external beam radiotherapy and to provide guidance for advanced prostate IMRT.Methods: Prostate intrafractional motion during IMRT and RapidARC treatments was tracked and recorded using a Calypso 4D‐localization system. Data for 8600 treatment fractions of 230 prostate patients was analyzed. The percentage of treatment fractions, the fractional treatment time, and the fractional time of any individual minute were analyzed separately for prostate movements greater than the thresholds (2, 3, 5 and 7mm). Results: The percentages of fractions in which prostate shifted more than the thresholds for a duration >10 seconds are 66.2%, 34.9%, 8.9% and 2.6% (57.9%, 27.9%, 5.2% and 0.8% for >30 seconds duration), respectively. For 10 patients who exhibited the largest motion, the percentages are 95.2%, 76.0%, 43.2% and 14.7% (91.3%, 72.4%, 36.3% and 6.0% for >30 seconds duration). The fractional time for motion larger than the thresholds is 27.8%, 10.7%, 1.6% and 0.3% (56.2%, 33.7%, 11.2% and 2.1% for these patients). The posterior‐direction motion is significantly higher than those in other directions. The fractional time of an individual minute with shift >3mm is higher at the 10th minute than at the 5th minute (20% vs. 10%) after the initial setup. For treatments completed within 5 minutes, the average fractional time with motion >3mm was lower than those within 10 minutes (4% vs. 12%). Irregular movements were observed most likely in the first minute after patient's setup, which were 12% and 7% among all fractions with movements >2mm and >3mm, respectively. Conclusions: The prostate intrafractional motion was within 3mm for most treatment fractions. However, larger movements were observed for some patients, who require real‐time corrections or larger treatment margins. The results indicate that it is beneficial if the treatment can be completed within 5 minutes.

Purpose: To compare and analyze the characteristics of intensity‐modulated arc therapy(IMAT) versus fixed‐gantry intensity‐modulated radiotherapy(IMRT) in treatment of non‐small‐cell lungcancer.Methods: Twelve patients treated in our radiotherapy center were selected for this study. The patient subsequently underwent 4D‐CT simulation.Margins of 5 mm and 10mm were added to the ITV to generate the CTV and PTV respectively. Three treatment plans (IMRT,one single arc (RA1),double arcs (RA2))were generated with Eclipse ver.8.6 planning systems. Using a dose level of75Gy in 15fractions to the ITV ,60Gy in 15fractions to the CTV and 45Gy in 15fractions to the PTV respectively. The target and normol tissue volumes were compared, as were the dosimetry parameters. Results: There were no significant differences in CI of ITV,PTV, HI of ITV,CTV and PTV, V5,V10,V15,V20,V25,V30,V45,V50 of total‐lung and mean lungdose (all p>0.05). However, the differences were significant in terms of CI of CTV, V5 of B‐P (all p

Purpose: The fraction duration of robotic radiosurgery treatments can be reduced by generating more time-efficient treatment plans with a reduced number of node positions, beams, and monitor units (MUs). Node positions are preprogramed locations where the robot can position the focal spot of the x-ray beam. As the time needed for the robot to travel between node positions takes up a large part of the treatment time, the aim of this study was to develop and evaluate a node reduction technique in order to reduce the treatment time per fraction for robotic radiosurgery. Methods: Node reduction was integrated into the inverse planning algorithm, developed in-house for the robotic radiosurgery modality. It involved repeated inverse optimization, each iteration excluding low-contribution node positions from the planning and resampling new candidate beams from the remaining node positions. Node reduction was performed until the exclusion of a single node position caused a constraint violation, after which the shortest treatment plan was selected retrospectively. Treatment plans were generated with and without node reduction for two lung cases of different complexity, one oropharyngeal case and one prostate case. Plan quality was assessed using the number of node positions, beams and MUs, and the estimated treatment timemore » per fraction. All treatment plans had to fulfill all clinical dose constraints. Extra constraints were added to maintain the low-dose conformality and restrict skin doses during node reduction. Results: Node reduction resulted in 12 residual node positions, on average (reduction by 77%), at the cost of an increase in the number of beams and total MUs of 28% and 9%, respectively. Overall fraction durations (excluding patient setup) were shortened by 25% (range of 18%-40%), on average. Dose distributions changed only little and dose in low-dose regions was effectively restricted by the additional constraints. Conclusions: The fraction duration of robotic radiosurgery treatments can be reduced considerably by node reduction with minimal changes in dosimetrical plan quality. Additional constraints are required to guarantee low-dose conformality and to avoid unacceptable skin dose.« less

An algorithm, which combines the scanning beam with dynamic collimation to generate any arbitrary intensity profile, is presented. The desired intensity profile is assumed to be piecewise linear. The dynamic collimation method used is the ‘‘sliding window.’’ The algorithm can be used either for a given scanning beam profile or to simultaneously determine the scanning beam profile and the leaf motions required to generate the desired intensity profile, which minimize the total treatment time. The limitations imposed by the physics of an elementary beam are taken into account. The algorithm is an iterative one, with typical calculation times being of the order of a few milliseconds.

Introduction: Couch-gantry trajectory based deliveries are capable of producing high quality Stereotactic Radiosurgery (SRS) treatments in a time efficient manner. In this work we present two methods for treatment time optimization of these deliveries. Methods: Dosimetrically optimal plans were calculated by optimizing MLC and dose rates along a trajectory which encapsulates 4π geometry. This trajectory was used to benchmark time optimization methods. Two methods of treatment time optimization were developed in this study. The first of which relies on a trajectory which samples phase space variably dependent on a selected sampling frequency. Treatment plans were created with decreased sampling frequencies until the treatment quality was deleteriously effected and the most time efficient delivery was selected. The second method uses a gradient descent algorithm to remove time inefficient sections of a trajectory and subsequently re-optimizes the MLC and dose rates to form a new, time optimized trajectory. Results: Both methods were capable of producing treatment plans which were dose equivalent to the benchmark 4π geometry plan. The methods reduced treatment time of 12Gy fractions by 18% and 13% for the first and second method respectively. Both methods had a more pronounced time saving benefits for 2Gy fractions, for which delivery time was decreased by 53% and 34% for the first and second method respectively. Conclusion: The methods presented were capable of producing highly conformal SRS treatment plans. These treatments took an average time of 109 seconds for fractionated deliveries and 394 seconds as single fraction deliveries.

Purpose: A new development in linac-based intracranial radiosurgery is treatment of multiple targets using single isocenter VMAT, which dramatically reduces treatment time while maintaining high conformality and dose gradient. Our purpose is to translate this technique to extracranial SBRT of oligometastases and address additional challenges such as interplay from motion and setup uncertainties. Methods: We propose SIDO (Single Isocenter with Distinct Optimizations) planning in which all VMAT arcs share an isocenter but each arc treats only one target. Setup uncertainties from rotations and deformations are mitigated by applying a couch translation between VMAT arcs, while interplay is minimized by using dynamic conformal arcs (DCAs) as the starting point for VMAT optimization. We compared SIDO to single (VMAT) and dual (VMAT & DCA) isocenter plans for phantom and patient (N=2) cases. Dose statistics included conformity index (CI), gradient index (GI), and modulation factor (MLC opening & total MU). Finally, we determined likelihood of needing a translational shift between SIDO arcs to correct rotational uncertainties using CBCTs from eleven previous SBRT cases. Results: For phantoms with target separations of 5–15cm, CI was 0.87±0.02, 0.89±0.05, and 0.91±0.02, for SIDO, single, and dual-isocenter VMAT respectively. GI was 6.83±1.0, 7.45±1.0 and 5.94±0.7 respectively. SIDO conformity did not trend with increasing distance between PTVs, while gradient decreased for all planning techniques. Using DCAs as the starting point of VMAT optimization decreased modulation, with a 39.4% reduction in monitor units. SIDO had 4.9% and 39% less MU than single and dual-isocenter VMAT respectively. A translational shift between SIDO arcs would be required in 10–28% of cases due to rotational uncertainties to stay within a 5mm margin, for targets separated by ≥10cm. Conclusion: SIDO for extracranial oligometastases has comparable dosimetry to traditional VMAT with low modulation similar to DCAs. Future work will quantify decrease in dosimetric interplay.

Purpose: To compare the Accelerated Partial Breast Irradiation (APBI) plan with the normalized basal dose points and 5mm box prescription. Methods: Five patients of APBI were planned twice in Oncentra Master planning TPS (Version 4.3) using TG-43 algorithm. The number of catheters for all the patients was 10 to 16 and implant plane 2 to 3. For planning all catheters were reconstructed. Source loading was done as per HR-CTV contoured. The HR-CTV volume range was from 75cc to 182cc. Plans were normalized in two methods. First all plans were normalized on Basal dose points (PlanA) and second all the plan were normalized on 5mm box (PlanB). The prescription dose (PD) was 35Gy in 10 fractions. All the plans were completely based on normalization and without optimization. Plan evaluation was based on certain parameters coverage Index (CI), dose homogeneity index (DHI), conformity index (COIN), over dose volume index (OI). Results: The average and median of CI for planA was 0.835 and 0.8154, for planB 0.82 and 0.799 respectively. The median and average of DHI for planA was 0.66 and 0.6062, for planB 0.67 and 0.62 respectively. The range of COIN for planA and planB was from 0.58 to 0.65 respectively. The range of OI was from 0.083 to 0.169 for planA and planB. The treatment time in planA was in average 1.13 times more than planB as V150% of HR_CTV in planA was 4–6% more. The ipsilateral lung was getting 30% of PD which was 0.6% to 3.5%. Conclusion: Treatment Planning should be individualized based on implants characteristics. Planning with prescription to basal dose points should be preferred to 5mm box prescription, in order to achieve better DHI and less treatment time.

Purpose: To present treatment statistics of a Varian Novalis Tx using more than 90,000 Varian Dynalog files collected over the past 2 years. Methods: Varian Dynalog files are recorded for every patient treated on our Varian Novalis Tx. The files are collected and analyzed daily to check interfraction agreement of treatment deliveries. This is accomplished by creating fluence maps from the data contained in the Dynalog files. From the Dynalog files we have also compiled statistics for treatment delivery times, MLC errors, gantry errors and collimator errors. Results: The mean treatment time for VMAT patients was 153 ± 86 seconds while the mean treatment time for step & shoot was 256 ± 149 seconds. Patient’s treatment times showed a variation of 0.4% over there treatment course for VMAT and 0.5% for step & shoot. The average field sizes were 40 cm2 and 26 cm2 for VMAT and step & shoot respectively. VMAT beams contained and average overall leaf travel of 34.17 meters and step & shoot beams averaged less than half of that at 15.93 meters. When comparing planned and delivered fluence maps generated using the Dynalog files VMAT plans showed an average gamma passing percentage of 99.85 ± 0.47. Step & shoot plans showed an average gamma passing percentage of 97.04 ± 0.04. 5.3% of beams contained an MLC error greater than 1 mm and 2.4% had an error greater than 2mm. The mean gantry speed for VMAT plans was 1.01 degrees/s with a maximum of 6.5 degrees/s. Conclusion: Varian Dynalog files are useful for monitoring machine performance treatment parameters. The Dynalog files have shown that the performance of the Novalis Tx is consistent over the course of a patients treatment with only slight variations in patient treatment times and a low rate of MLC errors.

Purpose: To report cranio-spinal irradiation (CSI) planning experience, compare dosimetric quality and delivery efficiency with Tomotherapy from different institutions, and to investigate effect of planning parameters on plan quality and treatment time. Methods: Clinical helical tomotherapy IMRT plans for thirty-nine CSI cases from three academic institutions were retrospectively evaluated. The planning parameters: field width (FW), pitch, modulation factor (MF), and achieved dosimetric endpoints were cross-compared. A fraction-dose-delivery-timing index (FDTI), defined as treatment time per fraction dose per PTV length, was utilized to evaluate plan delivery efficiency. A lower FDTI indicates higher delivery efficiency. We studied the correlation between planning quality, treatment time and planning parameters by grouping the plans under specific planning parameters. Additionally, we created new plans using 5cm jaw for a subset of plans that used 2.5cm jaw to exam if treatment efficiency can be improved without sacrificing plan quality. Results: There were significant dosimetric differences for organ at risks (OARs) among different institutions (A,B,C). Using the lowest average MF (1.9±0.4) and 5cm field width, C had the highest lung, heart, kidney, liver mean doses and maximum doses for lens. Using the same field width of 5cm, but higher MF (2.6±0.6), B had lower doses to the OARs in the thorax and abdomen area. Most of A's plans were planned with 2.5cm jaw, the plans yielded better PTV coverage, higher OAR doses and slightly shorter FDTI compared to institution B. The replanned 5cm jaw plans achieved comparable PTV coverage and OARs sparing, while saving up to 44.7% treatment time. Conclusion: Plan quality and delivery efficiency could vary significantly in CSI planning on Tomotheapy due to choice of different planning parameters. CSI plans using a 5cm jaw, with proper selection of pitch and MF, can achieve comparable/ better plan quality with shorter delivery time compared to 2.5cm jaw plans.

Purpose: To assess the variation in dose received by the organs at risk (OARs) due to inter-fractional motion by SAVI to determine the importance of providing proper immobilization Methods: An analysis of 15 patients treated with SAVI applicators were considered for this study. Treatment planning teams did not see significant changes in their CT scans through scout images and initial treatment plan was used for the entire treatment. These scans, taken before each treatment were imported in to the treatment planning system and were fused together with respective to the applicator, using landmark registration. Dosimetric evaluations were performed. Dose received by skin, ribs and PTV(Planning target volume) respect to the initial treatment plan were measured. Results: Contours of the OARs were not similar with the initial image. Deduction in volumes of PTV and cavity, small deviations in displacements from the applicator to the OARs, difference in doses received by the OARs between treatments were noticed. The maximum, minimum, average doses varied between 10% to 20% 5% to 8% and 15% to 20% in ribs and skin. The 0.1cc doses to OARs showed an average change of 10% of the prescribed dose. PTV was receiving a different dose than the estimated dose Conclusion: The variation in volumes and isodoses related to the OARs, PTV receiving a lesser dose than the prescribed dose indicate that the estimated doses are different from the received dose. This study reveals the urgent need of improving the immobilization methods. Taking a CT scan before each treatment and replanning is helpful to minimize the risk of delivering undesired high doses to the OARs. Patient positioning, motion, respiration, observer differences and time lap between the planning and treating can arise more complications. VacLock, Positioning cushions, Image guided brachytherapy and adjustable registration should be used for further improvements.

Purpose: To compare three-dimensional conformal radiotherapy (3D CRT) and volumetric-modulated arc therapy (VMAT) in lung stereotactic body radiation therapy (SBRT) Methods: A retrospective study of clinically treated lung SBRT cases treated between 2010 and 2015 at our hospital was performed. All treatment modalities were included in this evaluation (VMAT, 3D CRT, static IMRT, and dynamic conformal arc therapy). However, the majority of treatment modalities were either VMAT or 3D CRT. Treatment times of patients and dosimetric plan quality metrics were compared. Treatment times were calculated based on the time the therapist opened and closed the patient's treatment plan. This treatment time closely approximates the utilization time of the treatment room. The dosimetric plan quality metrics evaluated include ICRU conformity index, the volume of 105% prescribed dose outside PTV, the ratio of volume of 50% prescribed dose to the volume of PTV, the percentage of maximum dose at 2 cm away from PTV to the prescribed dose, and the V20 (percentage of lung volume receiving 20 Gy or more). Results: Treatment time comparisons show that on average VMAT has shorter treatment times than 3D CRT. Dose conformity, defined by the ICRU conformity index, and high dose spillage, defined by the volume of 105% dose outside the PTV, is reduced when using VMAT compared to 3D CRT. V20 and intermediate dose spillage/fall-off metrics of VMAT and 3D are not significantly different. Conclusion: Clinically treated lung SBRT cases indicate VMAT is superior to 3D with regard to shorter treatment times, plan dose conformity, and plan high dose spillage.

Purpose: Spine SBRT treatments require high dose to PTV, located close to OAR. Treatment time should be short due to patient condition. The objective of this work is to compare HybridARC (HA) with sliding windows IMRT treatment modality Methods: A 6MV photon beam with 1000MU/min (SRS beam) produced by a NovalisTX (Varian/BrainLAB) equipped with HDMLC was used. The TPS was iPlan v4.5.3 (BrainLAB). Treatment plans comparison was done for 5 patients. Dose prescription was 27Gy in 3 fractions. HA used 1 arc plus 3 (HA), 5 (HA5) and 8 (HA8) IMRT fields. HA plans used OAR high. Between 60–40% of the prescribed dose was given by the arc. IMRT plans used 15 beams. Treatment times, MU, CI, V50% and V20% was used for plans comparisons. Results: Assuming IMRT plan as reference, the treatment time was reduced by −14.6% with HA8, −8.6% with HA5 and −23% with HA3. Increasing arc dose proportion in HA (arc MU > 2000) requires 2 or more arcs which increments treatment time. HA3 and HA5 exhibits beam hold off for fixed IMRT fields which in some cases need to be split in 2 segments. MU varied +4% with HA8, +3.7% with HA5 and −5% with HA3. CI increased +5% with HA8, +23% with HA5 and +37% with H3. V50% increased +5% with HA8, +43% with HA5 and +62% with HA3. V20% increased +13.2% with HA8, +7.6% with HA5 and +1% with HA3. OARs doses were keep within tolerances in all plans. Conclusion: HybridARC for spine SBRT with 8 fix IMRT gantry angle shows a treatment time reduction, comparable MU and similar dose conformation to dMLC IMRT. HybridARC with 5 or 3 fix IMRT fields produce undesirable beam hold off, worse dose conformation and increments the total volume with 50% of the prescribed dose.

Purpose: The purpose of this work was to generate a tabular nomogram of treatment times for strut-based APBI applicators. The nomogram is intended to provide guidance and a quality assurance check for clinics establishing new treatment techniques or transitioning from balloon-based applicators. Methods: A retrospective analysis was conducted of 486 patients receiving APBI using strut-based applicators at three separate institutions. Strut-based applicators are composed of a central channel surrounded by 6 close-range (“mini”), 6 mid-range, 8, or 10 peripheral channels. Patient data was organized based on applicator size (a surrogate of treatment volume) and number of organs at risk. Three organs at risk categories were determined based on the proximity of the device to the patient’s skin and/or chest wall (0, 1, or 2 OARs). The proximity criterion was defined as being < 5 mm from the cavity wall/peripheral struts. A tabular nomogram of treatment time (based on nominal 10 Ci source strength) was generated from descriptive statistics of each combination of applicator size and organs at risk category. Results: The average treatment time was observed to be directly related to applicator size and, to a lesser extent, inversely related to the number of nearby organs at risk. Distributions of treatment times observed for each combination of applicator size and organs at risk category are depicted in Figure 1. The tabular nomogram featuring average treatment times with standard deviations is presented in Table 1. Conclusion: Strutbased APBI treatment times were observed to depend in a consistent manner on applicator size and number of nearby organs at risk. Information provided in the nomogram presented here represents several hundred treatments performed at multiple institutions. This data can serve as guidance or quality assurance for institutions with limited experience using strut-based APBI applicators.

Purpose: To introduce double‐ends quasi‐breath‐hold (DE‐QBH) technique and evaluate its feasibility. Methods: It was previously demonstrated QBH, a hybrid technique combining free‐breathing‐gating (FBG) and breath‐hold, could provide less motion uncertainty and shorter treatment time than conventional FBG. While QBH uses only one phase, either end‐of‐exhalation (EOE) or end‐of‐inhalation (EOI), DE‐QBH utilizes both phases to further improve delivery efficiency. DE‐QBH is realized using an audiovisual biofeedback system (AVBFS) and a respiratory motion management program (RMMP). The in‐house developed AVBFS, consisting of two infrared stereo cameras and a head mounted display, provides dynamic feedback to patients. The RMMP establishes a personalized DE‐QBH model by adding a short quasi‐breath‐hold period to both EOI and EOE phase. Then the patient is guided to follow the model. A simulation study for 6 different maneuvers (2−2, 3−3, 4−4, 5−5, 7−5, and 9−5 sec for EOI‐EOE combination) was performed with 3 volunteers. External motion signals were analyzed to obtain mean absolute error (MAE) between the measured and guided. Duty cycle was also estimated. Results: MAEs were smaller than 1 mm for all maneuvers except 9−5 combination [0.9(+/−)1.3, 0.7(+/−)1.2, 0.6(+/−)1.1, 0.7(+/−)1.1, 0.6(+/−)1.0, and 1.1(+/−)0.8 mm for 2−2, 3−3, 4−4, 5−5, 7−5, and 9−5 combination, respectively]. Estimated duty cycles were 43, 52, 57, 62, 64, and 71% for 2−2, 3−3, 4−4, 5−5, 7−5, and 9v5 combination, respectively. Conclusion: The proposed DE‐QBH technique was feasible for respiratory motion management. It showed excellent feasibility with minimal motion uncertainty and significantly improved delivery efficiency, reaching up to 70% duty cycle.

Purpose: To compare step&shoot and dynamic MLC‐based IMRT for prostate treatment. Methods: Patient data with prostate cancer was selected. Same beam geometries and energy were used. Treatment plan includes simultaneous irradiation of prostate to 82Gy and seminal vesicles to 64Gy (41 fractions). Plans were normalized to achieve 82Gy minimum dose to prostate. Step&shoot was delivered using Primus linac (Optifocus MLC, 10mm leaf‐width, 200MU/min) and Konrad v2.2 TPS (Siemens). MLC step‐size of 0.5cm, minimum of 3 MU per segment and 15 intensity levels was used. Dynamic was delivered using Clinac 21EX (Millenium MLC, 0.5cm leaf‐width, 300MU/min) and Eclipse v8.1 TPS (Varian). MLC step‐size was 0.2cm. Plans dose distributions were compared in PCRT3D TPS (TRF). Optimization and dose calculation time, treatment time, MUs, PTVs and OAR DVH analysis and treatment plan QA were compared for both techniques. Results: Optimization and dose calculation time was 220seg for S&S and 360seg for dynamic. Total MU was 508 for S&S and 577 for dynamic. D98% (V82Gy) for PTV prostate were 81.5Gy (95.7%) for step&shoot and 80.1Gy (84.6%) for dynamic respectively. D98% (V64Gy) for PTV seminal vesicle were 64.2Gy (98.2%) for S&S and 62Gy (92.3%) for dynamic respectively. Rectum, V40Gy, V65Gy and EUD were 56.6cc, 21.2cc and 65.1Gy for S&S and 55.7cc, 19.7cc and 63.3Gy for dynamic respectively. Bladder V65Gy and EUD were 27.4cc and 47.9Gy for S&S and 24.4cc, and 46.2Gy for dynamic. Femoral head D10% were 40.4Gy for S&S and 39.3Gy for dynamic. Treatment time was 531seg for S&S and 271 seg for dynamic. Both treatment plans QA are within tolerances. Conclusions: Both IMRT modalities could be used for prostate treatment. Calculation time and MU are lower with S&S. D98%, V82Gy and V64Gy are slightly better using S&S. OAR doses are few percent better using dynamic. Treatment time is 50% less with dynamic.

Purpose: This study is to compare volumetric arc therapy (VMAT) with intensity modulated radiotherapy(IMRT) for stereotactic body radiation therapy(SBRT) of the adrenal metastases. Methods: For 13 patients who have completed SBRT with conventional IMRT technique, new VMAT plans were generated. Plans were optimized with the aim to protect organs at risk and spare healthy tissue while enforcing highly conformal target coverage of clinical prescriptions. IMRT and VMAT plans were designed on Pinnacle3 Version 9.0. All treatment plans were delivered on Elekta's Synergy machine. Plan quality and treatment efficiency for VMAT vs. conventional IMRT were evaluated. Results: all plans designed for conventional IMRT and VMAT techniques fulfilled the specific dose constraints. Both VMAT and IMRT resulted in equivalent target coverage but VMAT had an improved conformity index (CI=0.83±0.02 for VMAT and 0.81±0.02 for IMRT, p=0.025). Normal tissue sparing was comparable in both treatment techniques. The mean dose of the unilateral kidney was 10.5±4.6Gy for VMAT and 10.8±4.8Gy for IMRT (p=0.11). The VMAT reduced the total MUs per fraction by 13.1% (1192±261MU for VMAT and 1371±224MU for IMRT, p

Purpose: A common practice, in proton therapy, is to deliver a rotating subset of fields from the treatment plan for the daily fractions. This study compares the impact this practice has on the biological effective dose (BED) versus delivering all planned fields daily. Methods: For two scenarios (a phantom with a geometry approximating the anatomy of a prostate treatment with opposing lateral beams, and a clinical 3-field brain treatment), treatment plans were produced in Eclipse (Varian) to simulate delivery of one, two, and three fields per fraction. The RT-Dose file, structure set, and α/β ratios were processed using in-house MATLAB code to return a new RT-Dose file containing the BED (including a proton RBE of 1.1) which was imported back into Eclipse for analysis. Results: For targets and regions of field overlap in the treatment plan, BED is not affected by delivery regimen. In the phantom, BED in the femoral heads showed increased by 20% when a single field was used rather than two fields. In the brain treatment, the minimum BED to the left optic nerve and the pituitary gland increased by 13% and 10% respectively, for a one-field regime compared to three-fields per fraction. Comparing the two-field and threefield regimes, the optic nerve BED was not significantly affected and the minimum pituitary BED was 4% higher for two fields per day. Conclusion: Hypo-fractionation effects, in regions of non-overlap of fields, significantly increase the BED to the involved tissues by as much as 20%. Care should be taken to avoid inadvertently sacrificing plan effectiveness in the interest of reduced treatment time.

Purpose: To compare the dosimetric differences between intensity-modulated arc therapy (ARC) and intensity-modulated tadiotherapy (IMRT) plans for cervical carcinoma. Methods: 15 cervical carcinoma cases were sdudied. All plans were prescribed 50 Gy in 25 fractions.Two treatment plans (ARC and IMRT) were generated using Varian Eclipse treatment planning system. Evaluate the dose parameters of targets, organs at risk (OAR), monitor units and treatment time, using dose-volume histogram (DVH). Results: The CI and HI of PTV was better in ARC plan than IMRT plan,but there were no statistical differences (P>0.05). There were statistical differences between V20,V25,V30,V35of health tissues. There were statistical differences between V15,V20,V25of femurs. There were statistical differences between V20,V25,V30of small bowel. The V35,V40,V45 of bladder and rectum increased in ARC plan but there were statistical differences. The number of MU resulted to be MUIMRT=1677±212, MUARC=894±213. The MU of ARC plan were 47% less on average than IMRT plan. The mean treatment time for ARC was decreased 40% compared with IMRT. Conclusion: The ARC was equal to IMRT on the target coverage and the dose of OAR. The ARC plan has fewer machine monitor units and lesss treatment time and significantly improves the treatment efficiency.

Purpose: One of the advanced features of Tomotherapy HDA is that the jaws move dynamically at the cephalocaudal ends of the target to make shaper dose fall-off. The purpose of this project is to determine the dosimetric efficacy of volumetric dose shaping using dynamic jaw vs. fixed jaw. Methods: To evaluate the improvement offered by dynamic jaw collimation, five different cases were planned using both dynamic and fixed jaw collimation. Dose profiles and statistics for PTV and OARs were compared for each treatment site. The treatment plans were then delivered to a PTW 2D array and to a SunNuclear ArcCheck for volumetric dose comparison. The total delivered dose of one patient plan using dynamic jaw was reconstructed based on MVCTs of Tomotherapy and compared with the original plan by Tomotherapy Plan Adaptive. Plans using different jaw sizes and total treatment time from dynamic jaw vs. fixed jaw were dosimetrically evaluated. Results: Cephalocaudal dose profiles using dynamic jaw vs. fixed jaw show large differences but the lateral dose profiles are similar. A plan using dynamic jaw reduced mean doses to spinal cord(42.6%), kidney(42.7%), liver(60.4%) and bowel(51%) comparing to a plan with fixed jaw while the PTV dose coverage is similar. The largest dose discrepancy occurs when comparing plans with 5cm dynamic jaws vs. 5cm fixed jaws. The 2.5cm dynamic jaw produced the sharpest dose fall off. Plans using the 5cm dynamic Jaw can produce better yet similar results compared to the plan using 2.5cm fixed jaw. There were no significant differences between the reconstructed delivered doses vs. dose from the original plan. Conclusion: The use of dynamic jaws in Tomotherapy planning largely spare doses to OARs adjacent to the PTV. When this planning option is not available, planners should use < 2.5cm fixed jaw when critical OARs are located cephalocaudally to the PTV.

Purpose: To assess the correlation between mean lethal radiation doses (Do) with NMR water proton spin lattice relaxation time (T1) in different phases of Hela cells. Methods: Analysis of T1 with Do was assessed in M, G1, G2 and S-phase at energies of 220 kVp, 280 kVp and 1.25 MeV (Co-60). Results: T1 against Do in M, G1, G2, and S phase at 220 kVp yield a correlation of 0.80. At 280 kVp and 1.25 MeV the correlation is 0.77 and 0.82 respectively. Conclusion: It appears that T1 value decreases from M phase (1020 ± 84 ms) to S phase (534 ± 43 ms). The Do values increases from M phase to S phase. The variation in T1 and Do in different phases of the cell cycles provide a clue to time the mitotic phase at the radiation treatment time. It appears that T1 value decreases from M phase (1020 ± 84 ms) to S phase (534 ± 43 ms). The Do values increases from M phase to S phase. The variation in T1 and Do in different phases of the cell cycles provide a clue to time the mitotic phase at the radiation treatment time.

Purpose: Modern IMRT relies on computers to generate treatment plans of varied complexity. A highly complex treatment plan may use a large number of small and irregular beam apertures in order to achieve high dose conformity. However, excessive beam complexity can increase dosimetric uncertainty, prolong treatment time, and increase susceptibility to target or organ motion. In this study we sought to develop metrics to assess the complexity of IMRT beams and plans. Methods: Based the information of leaf positions and MU for each beam segment, we calculated the following beam complexity metrics: aperture area, shape irregularity, and beam modulation. Then these beam complexity metrics were averaged to obtain the corresponding plan complexity metrics, using the beam MUs as weighting factors. We evaluated and compared the beam and plan complexity scores for 65 IMRT plans from 3 sites (prostate, head and neck, and spine). We also studied how the plan complexity scores were affected by adjusting inverse planning parameters. Results: For prostate IMRT, the lateral beams had large MUs and smaller shape irregularity, while the anterior or posterior beams had larger modulation values. On average, the prostate IMRT plans had the smallest shape irregularity and beam modulation; the HN IMRT plans had the largest aperture area, shape irregularity, and beam modulation; and the spine stereotactic IMRT plans often had small aperture area, which may be associated with relatively large discrepancies between calculated and measures doses. The plan complexity increased as the number of optimization iterations and the number of beam segments increased and as the minimum segment area decreased. Conclusion: Complexity of IMRT beams and plans were quantified in terms of aperture area, shape irregularity and beam modulation. The complexity metrics varied among IMRT plans for different disease sites and were affected when the planning parameters were adjusted.

Purpose: Flattening-filter-free (FFF) beam mode offered on TrueBeam™ linac enables delivering IMRT at 2400 MU/min dose rate. This study investigates the benefit and delivery accuracy of using high dose rate in the context of prostate SBRT. Methods: 8 prostate SBRT patients were retrospectively studied. In 5 cases treated with 600-MU/min dose rate, continuous prostate motion data acquired during radiation-beam-on was used to analyze motion range. In addition, the initial 1/3 of prostate motion trajectories during each radiation-beam-on was separated to simulate motion range if 2400-MU/min were used. To analyze delivery accuracy in FFF mode, MLC trajectory log files from an additional 3 cases treated at 2400-MU/min were acquired. These log files record MLC expected and actual positions every 20ms, and therefore can be used to reveal delivery accuracy. Results: (1) Benefit. On average treatment at 600-MU/min takes 30s per beam; whereas 2400-MU/min requires only 11s. When shortening delivery time to ~1/3, the prostate motion range was significantly smaller (p

Purpose: To compare and analyze the characteristics of static intensity-modulated radiotherapy (IMRT) plans designed on Elekta and Varian Linac in different esophageal cancer(EC), exploring advantages and disadvantages of different vendor Linac, thus can be better serve for clinical. Methods: Twenty-four patients with EC were selected, including 6 cases located in the cervical, upper, middle and the lower thorax, respectively. Two IMRT plans were generated with the Oncentra planning system: in Elekta and Varian Linac, prescription dose of 60Gy in 30 fractions to the PTV. We examined the dose-volume histogram parameters of PTV and the organs at risk (OAR) such as lungs, spinal cord and heart, and additional Monitor units(MU), treatment time, Homogeneity index(HI), Conformity index(CI) and Gamma index comparisons were performed. Results: All plans resulted in abundant dose coverage of PTV for EC of different locations. The doses to PTV, HI and OAR in Elekta plans were not statistically different in comparison with Varian plans, with the following exceptions: in cervical, upper and lower thoracic EC the PTV's CI, and in middle thorax EC PTV's D2, D50, V105 and PTV-average were better in Elekta plans than in Varian plans. In the cervical, upper and the middle thorax EC, treatment timemore » were significantly decreased in Varian plans as against Elekta plans, while in the lower thoracic EC treatment time were no striking difference. MUs and gamma index were similar between the two Linac plans. Conclusion: For the the middle thorax EC Varian plans is better than Elekta plans, not only in treatment time but in the PTV dose; while for the lower thorax EC Elekta plans is the first choice for better CI; for the other part of the EC usually Elekta plans can increase the CI, while Varian plans can reduce treatment time, can be selected according to the actual situation of the patient treatment.« less

Purpose: Commissioning of a skin applicator for a 50kVp electronic source for an expeditious IORT treatmentMethod and Materials: A single applicator cone (50mm diameter, 31.4mm SSD) was used with a 50kVp source to produce a circular field. The field was collimated using disposable cutouts (0.5mm lead equivalent) between 1cm × 1cm and 1cm × 4.9cm. Treatment margins were derived to ensure a 5% dose deviation, using GAFChromic film. Cutout factors, chamber stem effect, and the effect of imperfect Cone‐Skin contact were investigated using a soft x‐ray chamber. Results: Without the cutout, the treatment margin was found to be 0.9mm. Adding cutouts, the margin was 0.4mm for a 10mm field, and 2.1mm for a 45mm field. The stem effect was as high as 0.8% for elongated cutouts. A 10% dose rate decrease was measured 1mm away from the end cap. The cutout factors range was 3.7%. Physical abutment of two fields on the skin could increase dose up to 44%, while a 1mm gap/overlap caused −60%/+60% dose variations, respectively. Conclusion: In an IORT setting, it is necessary to provide proper cutout and treatment time as quickly as possible. Based on our measurements, a cutout can be produced on the fly in the OR by conservatively adding 2mm around the measured scar. It is not necessary to measure individual cutout factors, as the dose delivered using an averaged cutout factor should be within 5% of the measured value. Given the 10%/mm dose rate drop away from the applicator, it is imperative to position the lesion at a known and stable treatment position for maintaining contact between cutout and skin. When treating areas greater than 5cm, the overlap region could experience ∼60% dose variations. Study partially supported by a Xoft, Inc. grant.

Purpose: Varian RapidArc™ is a new treatment technique that delivers conformal dose distributions to the target in one single gantry rotation. The segments in the treatment arc are allowed to have different monitor unit (MU) weightings requiring variable dose‐rate (VDR) for delivery. An alternative delivery approach for (VDR) RapidArc plans that utilizes constant dose‐rate (CDR) was developed. Method and Materials: For four patient cases (two head‐and‐neck (HN), one brain, one prostate), RapidArc plans were generated using the Eclipse treatment planning system. The resultant VDR treatment plans were converted into CDR plans by re‐distributing the equi‐spaced segments in the VDR arc such that the segments with larger MU weighting occupy a greater angular interval. To minimize perturbation from the optimized dose distribution, the angular deviation of the segments was restricted to 5°. This restriction requires the treatment arc to be broken into multiple sectors such that the local MU fluctuation within each sector is reduced, thereby lowering the angular deviation of the segments during re‐distribution. The converted broken‐sector CDR (b‐CDR) plans were delivered with a single gantry sweep as in the VDR plans but each sector was delivered with different values of CDR. Results and Conclusion: For plans with complex angular MU distribution, the number of broken sectors may increase in the b‐CDR plans in order to maintain the original plan quality. All b‐CDR plans produced similar dose distributions to the VDR plans by dissecting the arc up to 5 sectors. On average, the delivery times of the b‐CDR plans were 1 minute longer than that in the VDR plans. Since the majority of treatment time is spent on the patient setup, these results show that VDR RapidArc plans can be delivered using CDR without significantly compromising the plan quality or treatment efficiency. Research sponsored by Varian Medical Systems.

Purpose: To compare two commercial TPS systems for 2D HDR planning. Method and Materials: The Nucletron Plato System (NPS) version BPS13.7 is a well established TPS for Brachytherapy procedures and has been used clinically for more than 20 years. New softwares have been released for 2D and 3D calculation using new optimization methods. In this work we intercompare the dose at prescription points calculated by the NPS and by Simuplan Planning System (SPS) version 8.2d, with the same dwell position times. The input data for both systems was done minimizing the geometric error in the final reconstruction. Plannings were done in both systems for several configurations, varying the length of active path (point source, 2, 3, 4 and 5 cm). For each active path calculation distances were changed from 10 to 30 mm from the catheter). The same prescription points were defined in both systems. The optimized plans were generated with the SPS system, adjusting the dwell times aiming a maximum dose difference around ±2% among the prescription points. The total treatment time was verified by manual calculation. The dwell times obtained by SPS system were input into NPS system, to compare the dose at the prescription points. The error at the source and points coordinate positions was evaluated for both systems. Results and Discussion: The dose difference at the prescription points, changing the active length ranged from 0.24% to 0.66%. Keeping the length fixed and varying the treatment distances, these differences ranged from 0.25% to 0.65%. The overall average difference was 0.45%±0.19%. The error in positioning the source and the points was 0.21 mm for SPS and 0.61mm for NPS. All the manual calculations were within ±5% difference.

Purpose: The planning process for helical tomotherapy plans is governed by three basic planning parameters: field length, pitch ratio, and modulation factor. The purpose of this work is to evaluate the influence of each parameter on the achievable plan. Method and Materials: Using commercial treatment planning software (TomoTherapy, Inc.) the same head and neck case was re‐planned by the same person using different planning parameters. The standard settings (field length of 25 mm, pitch of 0.287 and modulation factor of 2.5) were used to generate a baseline plan. Using the standard settings for two parameters the third parameter was varied for different plans. Three field lengths (10, 25, 50 mm), four pitch ratios (0.2, 0.287, 0.5, 1) and seven modulation factors were used (1.5, 2, 2.5, 4, 6, 8, 10). The plans were evaluated in terms of treatment time, target coverage, conformity, and sensitive structure sparing. Results: Increasing the pitch ratio leads to an increase in the volume of unspecified tissues that receives prescription dose (less conformal plans) and an increase in the dose to sensitive structures. The treatment time did not significantly reduce with increasing pitch (there are fewer gantry rotation but the gantry rotation period increases). Similarly, an increased modulation reduces the dose to unspecified tissue and sensitive structures. However the cost is an increased treatment time. Using a larger field length increases the dose to unspecified tissue and sensitive structures while reducing the treatment time. All plans achieved acceptable target coverage and homogeneity. Conclusions: Changing the planning parameters mainly affects plan conformity. It appears that with respect to our standard settings a slight reduction of the pitch or a slight increase in the modulation factor should improve plan quality with a modest increase in treatment time. Conflict of Interest: One co‐author is employed by TomoTherapy, Inc.

Purpose: To study the feasibility of treating multiple‐brain metastass with stereotactic radiosurgery using the tomotherapy Hi‐Art machine, and to compare tomotherapy stereotactic radiosurgerytreatment plans with conventional linac‐based stereotactic radiosurgery plans. Method and Materials: Five previously treated patients with multiple brain metastases ranging from 1 to 5 metastases were selected for the study. These five patients were treated with linacstereotactic radiosurgery. The same structures and prescription doses used for linacradiosurgery were also used to produce stereotactic radiosurgerytreatment plans on the tomotherapy planning system. In order to compare the tomotherapy plans to the linac‐based plans, the homogeneity of the target volumes, as well as the PITV, the volume of normal braintissue receiving at least 10Gy and treatment time were considered. Results: Analysis of the five plans shows that the target dose uniformity, target dose conformality, and the treatment time for each plan is much improved for tomotherapy. The plans show that on average using tomotherapy planning system increases the dose uniformity by 70%, increases the target‐dose conformality by 42% while it reduces the normal tissue volume receiving at least 10 Gy by about 40% for large metastases. On the other hand, for metastases smaller than 1cc tomotherapy increases the 10.0 Gy volume over that for a conventional linac plan by about 60%. Conclusion: These results show that tomotherapy could be used for treating patients with multiple brain metastases using stereotactic radiosurgey.

Purpose: To investigate the effect of microbubble‐induced microstream on the sonoporation during drug‐delivery. Methods: In the present work, MCF‐7 cells mixed with polyethylenimine: Deoxyribonucleic acid (DNA) complex and microbubbles were exposed to 1‐MHz ultrasound with low acoustic driving pressures (0.05−0.3 MPa). The sonoporation pores generated on the cell membrane were examined with scanning electron microscopy. Results: The results show that larger sonoporation pores would be generated with the increasing acoustic pressure or longer treatment time, which could be useful for the enhancement of DNA transfection efficiency, the mean diameters of pores ranged from 100nm to 1.25um. Conclusion: The microstreaming‐induced shear stress might be involved in the mechanisms of the low‐intensity ultrasound induced sonoporation.

Purpose: For some patients to be treated with IMRT, extremely low tolerances of critical organs(such as lens, ovaries and testicles) could not be met during treatment planning. The aim of this work is to introduce a new planning method to overcome this problem. Methods: In current planning practice, jaw positions are automatically set to cover all target volumes by planning system(eg, Pinnacle3 system). Because of such setting, critical organs may be fully blocked by MLC, but sit in the field shaped by collimator jaws. These critical organs receive doses from MLC leaf transmission and leakage. To reduce their doses further, we manually fixed jaw positions to block them. This method has been used for different treatment sites in our clinic. Here we take 8 patients with radical hysterectomy plus ovarian transposition as example, to demonstrate its performance. For each patient, two treatment plans were generated with the same optimization parameters: the original plan(called O‐plan), and the plan with fixed jaw positions(named F‐plan). In F‐plan, the jaws were manually fixed to block the ovaries. Results: For target coverage, the mean CI of F‐plan was remarkable lower than O‐plan(p

Purpose: Traditionally, cervical HDR planning was done using standard loading techniques, and prescription points defined in 2D. Currently, widespread availability of 3D imaging allows for structure contouring, inverse plan optimization, and structure based dose prescriptions. However, many institutions still use traditional techniques for some portion of HDR planning. The goal of this research is to compare inverse‐optimized plans with structure based dose prescriptions, to forward‐optimized plans with point A based prescriptions. Methods: 41 clinical cervical HDR plans (12 patients), originally optimized using forward‐planning techniques, were retrospectively optimized using Oncentra MasterPlans (Nucletron, Veenendal, the Netherlands) inverse planning simulated annealing (IPSA) algorithm. Dose objectives for the high risk CTV (HRCTV) and Organs at risk (OARs) were used in the inverse optimization. The inverse optimization plans were normalized to match the HRCTV D90 dose with their forward‐planned counterparts. For each plan, the following values were recorded: the dose to Point A, D90 for intermediate risk CTV (IRCTV); D2cc, D0. 1cc for OARs (rectum, bladder, sigmoid colon, small bowel) and total treatment time. Results: Inverse optimization changed the dose to point A and IRCTV D90 by −12.77+/−32.86% and −17.17+/−31.52%, respectively. Changes in the OARs [D2cc, D0.1cc] were: [−15.89+/−27.10%,−12.87 +/− 31.40%] for rectum, [−14.88+/−23.70%, −11.50+/−27.69%] for bladder, [− 18.32+/−38.81%, −17.52+/−41.35%] for sigmoid colon, and [−24.10+/− 36.61%,−22.47+/−39.64%] for small bowel. The treatment time changed by — 25.49 +/−24.44%. Conclusion: On average, the IPSA optimized plans decreased the dose to the IRCTV, point A, and OARs. However, the large standard deviations in the dosimetric changes indicate that the performance of the IPSA optimization is highly case dependent. Further IPSA studies are needed to determine whether dose can be increased to IRCTV and point A, while maintaining OAR sparing.

Purpose: In Gamma Knife radiosurgery, an efficient plan is one that achieves dosimetric quality while minimizing treatment time. Although minimization of treatment time to improve throughput and benefit patient comfort is a common and important goal of radiosurgery planning, to date no studies have attempted to specifically quantify efficiency. The aim of this study was to define simple index to score efficiency, and by quantifying time savings achieved by replanning those cases identified as least efficient, so demonstrate the efficacy of the index. Methods: To quantify efficiency, it is necessary to determine treatment times expected for specified lesions. However, because of numerous case-specifics, efficiency cannot be quantified in terms of treatment times alone. This study defines a new quantity, the attenuation-corrected normalized treatment time-dose rate product,nTRPcorr, to account for differing dose rates, prescriptions, and attenuation. A plan efficiency index (PEI) is then defined for lesions of similar volume and shape in terms of expected and planned nTRPcorr. nTRPcorr was retrospectively calculated for metastatic lesions of comparable shape. A curve fitted to data describing how nTRPcorr typically varied with volume for these lesions was then used to determine expected nTRPcorr. For each lesion, PEI was calculated as the ratio of expected-to-planned nTRPcorr. Plans with the lowest PEI were replanned, with the aim of maintaining dosimetric quality while minimizing treatment time. Dosimetric quality was defined in terms of coverage, conformity, and gradient index. Statistical significance of differences between original and replans was quantified via paired t-tests. Results: The mean(standard deviation) PEI of all reviewed lesions was 1.08(0.28). The 14 least efficient plans across the range of investigated volumes (45–19 800 mm3) had a mean PEI of 0.64, versus 1.18 when replanned (p 0.05) change in dosimetric quality. Conclusions: The PEI is a viable metric for identifying those plans that benefit from a more efficient planning strategy.

Purpose: This limited study determines the fraction of prostate IMRT patients who do not need setup adjustments, following initial setup, for their first 5 and last 5 fractions. For patients needing setup adjustments during their first or last 5 fractions, the average time to the first adjustment is established for each interrupted fraction. Methods: The Calypso System (Varian Medical Systems, Palo Alto, CA) tracks the position of three implanted fiducials in the prostate. The treatment is manually interrupted if excursions >3mm occur over a time period >5 seconds. Post treatment reports were examined from 18 patients to determine the number of setup changes needed during their first and last 5 fractions and the time of the first setup change for each interrupted fraction. Results: Three of the 18 patients in their first 5 fractions and 5 of the 18 patients in their last 5 fractions did not require setup changes. On average, 7.6 (+/− 7.4) setup changes were needed per patient for the first 5 fractions and 5.9 (+/− 8.5) setup changes for the last 5 fractions. Over the 18 patients, there were a total of 137 setup changes in the first 5 fractions and 106 in the last 5 fractions and only 1 patient with no setup changes. For those patients requiring setup changes, the first setup change occurred, on average, after 6.3 (+/− 4.4) minutes for the first 5 fractions and 5.4 (+/− 2.5) minutes for the last 5 fractions. Conclusions: The majority of prostate patients required adjustments multiple times over the first and last 5 fractions. Using the Calypso System to monitor target motion appears to be beneficial for the majority of prostate patients. Treatment techniques decreasing treatment time, such as VMAT, can be helpful in decreasing the number of interruptions, but still require motion management systems.

Purpose: This study shows that there is no clear dosimetric benefit of biological‐based optimization for either fixed‐beam IMRT or VMAT. Other than shorter delivery times, even VMAT does not offer additional advantage to fixed‐beam IMRT.Methods: A small number of patients for lung, pancreas, spine and brain CA were planned with fixed‐beam IMRT, optimized with (gEUD) and without (DV) biological objectives and, also planned for VMAT with and without gEUD, for comparison. For the lung and brain cases, a non‐coplanar 7–11 beam arrangement was used for fixed‐ beam IMRT and a coplanar ‘hybrid’ arc simulated VMAT with beams set every 5° spacing. For the other treatment sites, all beams were coplanar. For each case, the fixed‐beam IMRT and VMAT plans were optimized with the same objectives. It is important to note that, only 2 segments/beam were allowed for each plan, in order to create small fluence modulation, appropriate for small target volumes during SBRT.Results: For all plans we noticed that there were minor or no dosimetric differences between fixed‐ beam IMRT and VMAT, whether DV or gEUD objectives were used or whether fixed‐beam IMRT or VMAT is used. Keeping the level of beam modulation as‐low‐as possible, for small SBRT targets, one can show that VMAT with or without gEUD optimization does not offer any dosimetric advantage against fixed‐beam IMRT with multiple non‐coplanar beams. This is against the expectation that gEUD‐optimization can Result superior plans than DV‐optimization. The difference is that, for small target volumes like those encountered in SBRT, the complexity of the fluence is not as high as in large field intensity modulated cases. Conclusions: The fact that VMAT with or without gEUD can produce as good plans as fixed‐IMRT does not make VMAT a preferred treatment modality, other than the fact that requires reduced treatment time.

Purpose: To quantify intrafraction prostate motion between patient groups treated with and without daily endorectal balloon (ERB) employed during prostate radiotherapy and establish the effectiveness of the ERB. Methods: Real time intrafraction prostate motion from 29 non‐ERB (1061 sessions) and 30 ERB (1008 sessions) patients was evaluated based on three‐dimensional (3D), left, right, cranial, caudal, anterior and posterior displacements. The average percentage of time with 3D and unidirectional prostate displacements > 2, 3, 4, 5, 6, 7, 8, 9, and 10mm in 1 minute intervals was calculated for up to 6 minutes of treatment time. The Kolmogorov‐Smirnov method was used to evaluate the intrafraction prostate motion pattern between both groups. Results: 3D motion >=1 cm was observed for the non‐ERB group only. The motion increased as a function of elapsed time for displacements > 2 to 8mm for the non‐ERB group and > 2 to 4 mm for the ERB group (p 5 mm (p < 0.05). The 3D internal margin (IM) covering 95% treatment time can be reduced from 5 to 3 mm (40% reduction) while the asymmetrical IM can be reduced from 3 to 2 mm (33% reduction) in cranial, caudal, anterior, and posterior for 6 minutes treatment, when ERB is employed. Beyond 6 minutes, the 3D and cranial, caudal, anterior, and posterior IMs can be reduced from 9, 4, 7, 7, and 8 to 5, 2, 5, 3, and 4 mm, respectively (up to 57% reduction). The calculated IMs apply to the worst case scenario patient as well. Conclusions: The ERB effectively reduces prostate motion and allows for smaller IMs. Therefore, daily ERB has the potential to further improve toxicity profiles in prostate radiotherapy.

Purpose: The purpose was to analyze the influence of the step size during head&neck IMRT treatments. Methods: Ten patients with head&neck IMRT treatment plan were selected. Treatment plans were done using nine 6MV photon‐beams on a Primus linac (Siemens) with Optifocus MLC (10mm leaf width) and a dose rate of 200MU/min. The TPS used was Konrad v2.2 (Siemens) with leaves step size of 10, 5 and 3mm. For each step‐size, plans were evaluated in terms of MU, segments number, treatment time, PTV's (66Gy and 50Gy) dose uniformity and OAR (parotids and spinal cord) doses. Variations between measured and calculated total plan doses were obtained using solid water phantom and PTW PinPoint ionization chamber. Results: The MU number for 10mm step‐size plans was 624 [495,770] and increased 51% [36%, 87%] for 5mm and 124% [93%, 171%] for 3mm. The segments number for 10mm step‐size plans was 111 [99,129] and increased 41% [27%, 52%] for 5mm and 102% [71%, 125%] for 3mm. The treatment time for 10mm step‐size plans was 11.47min [11.08min, 12.45min] and increased 24% [9%, 33%] for 5mm and 65% [27%, 74%] for 3mm. Reducing the step‐size from 10mm to 5mm leads to better PTV_66Gy dose uniformity within ICRU50 tolerance (no difference observed between 5mm and 3mm). Step‐size diminution from 10mm to 3mm leads to a better coverage of PTV_50Gy especially in patient surface regions. For all the studied plans there are no differences in the parotids mean doses and spinal cord maximum dose. The variation between measured and calculated doses was 1.1% for 10mm step‐size. It increased 1.7% and 2.4% for 5mm and 3mm respectively. Conclusions: Using 10mm step‐size produces plans with adequate OAR doses. PTV Dose uniformity and volume coverage could be improved by 5mm step‐size whereas 3mm step‐size produces larger treatment times without advantages in dose distribution.

Purpose: We developed an algorithm to minimize total inter‐segment time (TIST) for the MLC‐based real‐time tumor tracking with step‐and‐shoot IMRT. This algorithm optimizes a starting phase of tumor motion for each segment to minimize TIST. Methods: The optimizing algorithm consists of four steps: (1) implementation of feathering motion for the closed leaves that will be opened at the next segment, (2) calculation of inter‐segment time for all segments, (3) reordering segments to minimize TIST, and (4) optimization of the starting phase of tumor motion for each segment to minimize TIST. Thirty step‐and‐shoot IMRT fields from five patients with lung and abdominal cancer were used to test the algorithm. Tumor motion was varied with a period (2.0 to 4.0 s) and a peak‐to‐peak distance (0.5 to 4.0 cm). TIST and duty cycle for each field were compared to those from the strategy of starting each segment at end‐of‐exhale. Results: The TIST was reduced by 54.0% on average (from 30.2 ± 16.9 to 13.9 ± 10.6 s) and, the effective duty cycle was increased from 32 ± 10% to 52 ± 15% for a tumor motion with 4 s and 1.0 cm peak‐to‐peak. More reduction in the TIST was observed from 45.1 to 72.1% with an increase of the period from 2 to 8 s; effect of reduction was degraded by 54.5 to 46.2% when the peak‐to‐peak increased from 0.5 to 4.0 cm. The TIST increased when a field size formed by x‐jaws increased (correlation coefficient: 0.7). Conclusions: : Total treatment time was reduced noticeably with the algorithm presented in this study so that real‐time tumor tracking can be delivered with step‐and‐shoot IMRT with an increased duty cycle. This research was supported in part by a NIH grant 1R01CA133539‐01A2 and in part by the Intramural Research Program of the NIH, NCI.

Purpose: Proton planning techniques of the in‐field matching and the range‐ compensator‐volume (RCV) were investigated to improve dosimetry on treating oropharynx tumors of head and neck cancers. Methods: Irregularities of oropharynx tumors are dictated by patterns of contiguous and lymphatic spread over anatomical peculiarities. Proton plans with complex target volumes can result large dose non‐uniformity to target and exceeding the tolerance of organs at risk (OARs). Proton boost plans, delivering an additional 20Gy to 95% PTV and 100% CTV volumes on escalating the IMRTdose of 50.4Gy to 70.4Gy, were performed over nine patients. Typical approach is using PTV with 6mm margin on forming the aperture and constructing the compensator with 5mm smearing; including 3mm patient‐positioning error and irregularity of PTV. New approach is using techniques of the in‐field matching and the RCV. The RCV was by copying and manually expanding of PTV and then used on constructing compensator. In‐field matching technique allows for treating primary target with larger modulation and neck node with small modulation by sharing same compensator. Results: Nine patients were cataloged into single‐target‐ volume (STV) cases with no or homo‐lateral node and multiple‐target‐ volumes (MTV) cases with bi‐lateral nodes. Plans using typical approach on complex PTV including single or both neck nodes in STV and MTV cases, the maximum doses to PTV can be over 30% of prescription. Maximum doses to PTV occur at regions between primary target and neck node where a gap or large volumetric change is seen. By applying new approach, the uniformity of PTV is within 13% for all of nine patients while OARs doses are reduced without largely increasing treatment time. Conclusions: Although new approach on boost plans achieves clinical requirements, the uncertainty on proton beam ranges induced patient‐positioning error on using in‐filed matching and RCV need be investigated.

Purpose: Bulky (>40 cc) cervical cancerbrachytherapy (BT) tumordose conformity is often poor since symmetric BT dose is limited by the presence of the nearby bladder, rectum, and sigmoid. Rotating shield intensity modulated brachytherapy (RS‐IMBT) can theoretically improve tumordose conformity, but at the cost of significantly increased treatment times. We developed a time efficient method of improving cervical cancerdose distributions with multi‐rotating‐shield IMBT (MRS‐IMBT) that drastically reduces the delivery times relative to RS‐IMBT. Methods: We developed a shield sequencing method that optimally divides a set of finely sampled IMBT shielding patterns into a combination of coarse and fine shields that delivers the same dose distribution but with a reduced treatment time. The resulting MRS‐IMBT method was applied to eight cervical cancer patients who were treated with MRI‐guided conventional BT. The treatment planning was done with an in‐house treatment planning system. Results: The MRS‐IMBT method significantly reduced treatment times relative to finely‐sampled IMBT without losing tumor coverage. When using shields that provided adequate coverage (22.5°), the sequencing method on average decreased the treatment time by a factor of 4. For the finest shields considered (5.625°), MRS‐IMBT decreased the treatment time by a factor of 12 on average. Conclusions: While RS‐IMBT causes treatment times to rise exponentially with the number of emission directions when a single shield emission angle is used, treatment times for the MRS‐IMBT method increase linearly with the number of emission directions. MRS‐IMBT makes IMBT delivery clinically feasible, which could lead to mean better tumordose conformity and improved outcomes.

Introduction Reducing the beamlet size during step&shoot IMRT planning may lead to improve dose conformity. The beamlet length can be adjusted in the treatment planning system (TPS) with the leaf step‐size along the MLC travel direction. The aim of this paper was to analyse the step‐size influence during prostate treatments.Materials and methods Ten patients treated for prostate cancer with 6MV‐IMRT fields were selected. Each treatment was calculated with the Konrad v2.2, Siemens, TPS using leaves step sizes of 3, 5 and 10mm, and delivered with a Primus, Siemens, linac associated to an Optifocus MLC (10mm leaf width). For each step‐size, the plans were calculated so as to equal the dose received by 95% of the PTV. Plans were compared in terms of PTV dose uniformity, organ‐at‐risk doses, treatment time and MU number. For each plan, the beams were imported in a water‐equivalent phantom and the doses calculated were compared with Farmer (0.6cc) and Pinpoint (0.015cc) ion chambers measurements. Results Reducing the step‐size from 10 to 5 or 3mm leads to a better PTV dose uniformity (31.2% and 35.8% dose standard deviation increase) and higher prostate minimum dose (+0.2% and +0.6%). Rectum V40 (V65) decreased of 3.2% (3.6%) and 6.9% (12%) for 5mm and 3mm. Bladder V65 and femoral heads V50 decreased of 9.5% and 26% for 5mm and 18% and 42% for 3mm. The treatment time and MU number increased of about 10% and 27% for 5mm and 20% and 48% for 3mm. The dose measurement verification showed that both chambers can be used for all step‐sizes with errors less than 1.3%. However, the PinPoint chamber use for 3mm beamlet sizes decreases the error from 1.3% to 0.3%. Conclusion Using 5mm step‐size seems to be a good compromise by improving the IMRT plan quality without treatment time increase.

Intensity modulated arc therapy (IMAT) was proposed in 1995 by Yu as an alternative to Tomotherapy. Due to the lack of an efficient planning algorithm, wide clinical adoption of IMAT as a major form of radiation treatment delivery did not happen until a 2007 when multiple new planning methods were developed and commercial interests in IMAT were intensified due to competition. Specifically, a commercial product, RapidArc, based on the Volumetric Modulated Art Therapy (VMAT) developed by Otto, was developed and marketed by Varian in 2007. VMAT is a single arc form of IMAT that delivers apertures of varying weightings with a single arc rotation. The intense commercial promotion and fast clinical adoption caused much confusion and controversy. There is a lack of a general understanding of how such arc treatments are planned, and what delivery limitations and compromises are made. It is therefore the purpose of this presentation to provide a summary of this technology and some guidelines on its clinical implementation. A historical review of all the works leading to the wide clinical adoption will be provided. Different planning methods will be described by a companion presentation in the same session. Issues related to clinical implementations, including commissioning and quality assurance will also be described. We will also hope to provide some perspectives on its further development in the context of increased clinical use of image guidance. Because there has been vast experience in IMRT using multiple intensity modulated fields, comparisons between IMAT and IMRT will also be made in the review to illustrate its advantages and limitation in the areas of planning, delivery and quality assurance. The research is partially supported by Varian Medical Systems, Inc., and by NIH grant RO1 CA117997.

Purpose: The CyberKnife robotic radiosurgery unit uses small circular beams that can be targeted from 117 node positions to obtain highly conformal dose distributions. Typically a large number of node positions, beams and monitor units (MUs) are used, resulting in long treatment times per fraction. The aim of this study was to develop and evaluate node reduction techniques to reduce the long treatment times for robotic radiosurgery. Method and Materials: Two node reduction techniques were implemented in our inverse planning algorithm developed in‐house. This algorithm uses ‘resampling’: repeated inverse optimization, each time replacing candidate beams with zero weight by new candidate beams. In the first reduction technique (passive reduction), node positions that were not ascribed any dose after inverse optimization were excluded from successive resampling iterations. This process was repeated until the number of node positions remained constant. In the second method (active reduction), node positions were reduced by forced exclusion of node positions with the lowest contribution until a valid solution could no longer be found. Both techniques were evaluated for two lung cases of different complexity, one prostate and one oropharynx case. Obtained plans were compared with plans without node reduction by the number of node positions, beams and MUs. All plans fulfilled the clinical dose constraints. Results: Compared to no node reduction, both passive and active node reduction resulted in a lower number of node positions (passive:−23%, active:−68%) and MUs (passive:−3%, active:−3%). The number of beams increased during node reduction (passive:+3%, active:+13%). Increasing complexity lowered the reduction in node positions. Conclusion: Results showed a dramatic reduction in the number of node positions while still fulfilling clinical dose constraints. The most efficient treatment plans were obtained by active node reduction. This technique could be used to shorten the treatment time per fraction.

Purpose: To develop efficient single and partial arc VMAT plans in terms of dosimetric accuracy and mechanical stability. Methods and Materials: Delivery efficiency of single and partial arc plans for various treatment sites (2 HN, 3 Hypolung, 2 SRS and 1 Hypoprostate) optimized with SmartArc in Pinnacle3 ™ 9.0 were tested on Elekta synergy and Axesse machines. Mechanical accuracy was evaluated using an application that records real‐time VMAT delivery information using the MLC log files. Dosimetric accuracy was performed using Delta4 and Arccheck cylindrical QA phantoms. Results: Results based on various treatment sites showed that single and partial arc VMAT plans satisfied all the re‐planning objectives. For Elekta machines, dose rate fluctuated significantly for plans with higher leaf motion, and dynamic leaf gap of 2 mm and leaf speed of 0.46 cm/deg were optimum for all the plans. Constraining the leaf motion resulted in a longer delivery time for all the plans. Lowering the control points by choosing partial arcs 6° spacing saved MUs up to 25% compared to full arc 4° spacing. Segment shapes were typically not very smooth. Gantry and leaf positions were within tolerance for all delivered plans. Compared to IMRT, PTV coverage and OAR sparing were better or comparable in all cases. MUs were reduced by 40% and 27% for HN and SRS plans. Delivery times for HN and Hypoprostate cases were within 2 mins (5 mins for HypoLung). Dosimetric analysis with Delta4 and Arccheck QA resulted in 98% and 96.5% of detectors with a gamma index (3%/2mm) < 1 respectively for all cases. Conclusion: SmartArc generated efficient single and partial arc VMAT plans in terms of lower MUs, shorter treatment time and better target coverage and OAR sparing compared to IMRT. The dosimetric and mechanical accuracy of these plans were within QA and machine tolerances.

Purpose: RapidArc has the advantage of reducing the MUs in dose delivery. This study reports the comparison of the beam arrangement and MU reductions of RapidArc (RA) and IMRT based radiosurgery (IMRS) for the treatment of multiple intracranial metastases. Method and Materials: Twelve patients with multiple brain metastases treated with IMRS were re‐planned with RapidArc. All the IMRS were delivered in a single fraction, single‐isocenter approach using 8–11 static beams. The prescribed dose was 18–20 Gy and the normalization as 100% of prescription dose covering 98% of PTV. Across patients, all the RA‐plans used 2‐coplanar arcs and followed systematic strategies in optimization objectives and MU limits. For each patient, two or more RapidArc plans were generated, and the plan with lower MU and higher conformity was chosen for comparison. Results: It is found that the MU reduction by RapidArc is more predominant for larger number of brain lesions, as the MU‐ratio of RA and IMRS was reduced from 92% to 39% as lesion number increased from 2 to 12. Also, the strategy of using only two coplanar arcs was based on the realization that it has a better dose conformity with comparable amount of total MUs as compared with a single‐arc approach. The 2‐coplanar‐arcs is also favorable as compared to more arcs as adding vertical or oblique arcs actually increases the dose to the normal brain and brainstem with little benefit to the PTV dose conformity. Conclusion: The MU reduction of RapidArc is more significant in intracranial radiosurgery. RapidArc uses much fewer MUs in radiosurgery as compared to those in the static 9‐beam IMRS treatment. The total treatment time is reduced even more, as two co‐planar arcs with zero couch position further reduced the beam setup time as compared to 6–9 couch positions normally used in the IMRS treatment..