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Purpose To compare the fixed-beam intensity-modulated radiotherapy (IMRT) with the volumetric-modulated arc therapy (VMAT) plans for different cancers using the biologically effective dose (BED). Methods Recruited patients were divided into three groups in terms of tumor anatomic site, including head and neck, thoracic, and abdominal cancers. All of plans were generated using the fixed-beam IMRT and the VMAT techniques. The qualities of the plans were assessed using the conformity index (CI) and the homogeneous index (HI) with respect to the dose delivered to the tumors. Some selected organs-at-risk (OARs) were analyzed. For the efficiency of the plan, monitor units (MUs) were compared between the paired plans. All parameters were collected and evaluated based on the conventional dose-volume histogram (DVH) of the paired plans. All BED were calculated from the physical dose. Results For CI and HI, the fixed-beam IMRT and the VMAT gained significant differences (p Conclusion There is no difference in the data comparison of the paired plans using the BED values compared with the physical doses.

Purpose To evaluate the impacts of different leaf-width of multileaf collimator (MLC) on the fixed-beam intensity-modulated radiotherapy (IMRT) planning for prostate cancer patients with intermediate risk factors. Materials and methods Sixteen prostate cancer patients with intermediate risk factors were retrospectively recruited. For each patient, the two IMRT plans using MLC leaf width of 10 mm and 4 mm (sIMRT and mIMRT) were compared. All of plans were generated with the same setup and optimized parameters and methods. Homogeneity index (HI), conformity index (CI), dose distribution for planning tumor volume (PTV) and organs at risk (OARs) were analyzed to evaluate the quality of the plans. Delivery time (DT), monitor units (MUs) and control points (CPs) were used to assess the efficiency of treatment. Results For the target dose distribution, the mean HI values of the two plans for 16 patients are similar (sIMRT vs. mIMRT: 1.120±0.13 vs. 1.103±0.099, p>0.05). The mean CI of the mIMRT plans was significantly better than that of the sIMRT plans (sIMRT vs. mIMRT: 0.648±0.11 vs. 0.688±0.10, p Conclusions For the IMRT of the prostate cancer patients with intermediate risk factors, the plans with the narrower leaf-width MLC failed to promote the quality of plans, OARs dose sparing and the efficiency of treatment, and could only improve the conformity of the plans.

Volumetric‐modulated arc therapy (VMAT) is emerging as a leading technology in treating early‐stage, non‐small cell lung cancer (NSCLC) with stereotactic ablative radiotherapy (SABR). However, two other modalities capable of delivering intensity‐modulated radiation therapy (IMRT) include fixed‐beam and helical TomoTherapy (HT). This study aims to provide an extensive dosimetric comparison among these various IMRT techniques for treating early‐stage NSCLC with SABR. Ten early‐stage NSCLC patients were retrospectively optimized using three fixed‐beam techniques via nine to eleven beams (high and low modulation step‐and‐shoot (SS), and sliding window (SW)), two VMAT techniques via two partial arcs (SmartArc (SA) and RapidArc (RA)), and three HT techniques via three different fan beam widths (1 cm, 2.5 cm, and 5 cm) for 80 plans total. Fixed‐beam and VMAT plans were generated using flattening filter‐free beams. SS and SA, HT treatment plans, and SW and RA were optimized using Pinnacle v9.1, Tomoplan v.3.1.1, and Eclipse (Acuros XB v11.3 algorithm), respectively. Dose‐volume histogram statistics, dose conformality, and treatment delivery efficiency were analyzed. VMAT treatment plans achieved significantly lower values for contralateral lung V5Gy(p≤0.05) compared to the HT plans, and significantly lower mean lung dose (p

Purpose: Accurate TomoTherapy treatment is dependent on multiple parameters, including the accuracy of couch velocity during beam delivery and gantry rotation. The recent TG‐148 protocol recommends quarterly film tests to verify the constancy of couch velocity. We determined the feasibility of using TomoDose, a quality assurance device, to detect the variation in couch velocity from baseline by a deviation of one or two percent. Methods: The TomoDose unit was rotated 90 degrees clockwise so that the long axis, consisting of 107 detectors, would translate across the TomoTherapy ‘Y’ jaws. The collimatorfield size used was the 1 cm mode and the table velocity was set to 0.5 mm/sec to establish a baseline. The velocity was then varied by 1% or 2% from nominal. The five tested velocities were 0.495, 0.490, 0.500, 0.505 and 0.510 mm/sec. The total translation time was kept at a constant 400 sec. The field was progressively painted during the scans and was shortened if table velocity was decreased, and lengthened as velocity was increased. Results: The baseline field size was 20.03 cm (400 sec × 0.05 cm/sec). A 2% increase in velocity translated to an increase in the field size to 20.39 cm and a 2% decrease in velocity resulted in a decrease in field size to 19.64 cm. Similarly, a 1% increase in velocity increased the field to 20.18 cm, and a 1% decrease velocity decreased the field to 19.76 cm. Conclusions: An increase or decrease in the couch velocity, for a fixed beam delivery time, resulted in an altered radiation field size. The field size results are approximately as expected for both the baseline scans as well as the modified velocity scans. This study demonstrates that, under these conditions, TomoDose can be used to determine small variations in table velocity as small as 1 %.

Purpose: To compare prostate radiation planning using four VMAT techniques and IMRT on plan quality and dosedelivery efficiency. Methods: The four VMAT techniques are: 1) Monaco VMAT (Version 2.03.01, CMS Inc., MO); 2) RapidArc (Eclipse Version 10.0, Varian Medical System Inc., CA); 3) SmartArc (Pinnacle Version 9.0, Philips RadiationOncology Systems, WI) and 4) helical TomoTherapy (TomoTherapy Version 3, Accuray Inc., CA). The IMRT planning employed 7‐field fixed gantry on Pinnacle. Single full‐arc plan using each technique was generated for five prostate cases. All plans were prescribed to 70 Gy (2.5 Gy/fx) to 95% PTV using 6 MV photon beams to achieve same PTV coverage and similar OAR sparing. The quality of dosimetric plans was evaluated using metrics: target coverage, heterogeneity index (HI), target/organ mean/max/min doses, EUD, dose‐volume histogram, etc. Results: All VMAT plans are capable of delivering adequate target dose with equal or better OAR sparing than IMRT plans. The average mean PTV doses were 72.8, 73.1, 71.0 and 72.5 Gy with HIs of 1.10, 1.08, 1.03 and 1.05 for the Monaco, RadipArc, SmartArc and TomoTherapy plans respectively. In low dose range, TomoTherapy resulted in the highest V10 and V20 while V70 and V60 were generally lower compared to other plans. Generated on the same platform, the SmartArc plans were slightly more conformal (CI=1.04 vs 1.08) and less heterogeneous (HI=1.02 vs 1.04) with better OAR sparing compared to IMRT plans. The average required MUs were 817 (Monaco), 735 (RapidArc), 798 (SmartArc) and 4986(TomoTherapy), compared to 876 MUs for the IMRT plans. Conclusions: All single‐arc VMAT techniques under study improve normal tissue sparing with more efficient dosedelivery compared to prostate IMRT plans. RapidArc plans require least MUs while SmartArc provided most homogenous plans. All VMAT plans demonstrate significantly reduced MUs to achieve comparable dosimetric plans compared to Tomotherapy.

Purpose To report on a universal bolus (UB) designed to replace the range shifter (RS); the UB allows the treatment of shallow tumors while keeping the pencil beam scanning (PBS) spot size small. Methods and Materials Ten patients with brain cancers treated from 2010 to 2011 were planned using the PBS technique with bolus and the RS. In-air spot sizes of the pencil beam were measured and compared for 4 conditions (open field, with RS, and with UB at 2- and 8-cm air gap) in isocentric geometry. The UB was applied in our clinic to treat brain tumors, and the plans with UB were compared with the plans with RS. Results A UB of 5.5 cm water equivalent thickness was found to meet the needs of the majority of patients. By using the UB, the PBS spot sizes are similar with the open beam ( P >.1). The heterogeneity index was found to be approximately 10% lower for the UB plans than for the RS plans. The coverage for plans with UB is more conformal than for plans with RS; the largest increase in sparing is usually for peripheral organs at risk. Conclusions The integrity of the physical properties of the PBS beam can be maintained using a UB that allows for highly conformal PBS treatment design, even in a simple geometry of the fixed beam line when noncoplanar beams are used.

This preliminary work compared a new optimization technique, modulated photon radiotherapy (XMRT), with IMRT in a treatment planning study for a cohort of eight prostate cancer patients. XMRT differs from IMRT in that it allows the typically fixed beam energy to vary such that the optimizer finds a dose distribution by simultaneously optimizing photon beamlet fluence and energy. Plans were comprised of a seven-coplanar beam arrangement, with IMRT restricted to 6 MV while XMRT used both 6 and 18 MV beams. Both IMRT and XMRT optimization were based on a linear programming model with partial-volume constraints implemented via the conditional variable at risk (cVaR) approach. XMRT and IMRT provided similar coverage to 95% of the target (PTV) with the prescribed dose (78 Gy), however XMRT improved the target dose homogeneity. XMRT was able to reduce the dose to a large volume (p

Purpose: A fixed-beam room could be underutilized in a multi-room proton center. We investigated the use of proton pencil beam scanning (PBS) on a fixed-beam as an alternative for posterior fossa tumor bed (PF-TB) boost treatments which were usually treating on a gantry with uniform scanning. Methods: Five patients were treated with craniospinal irradiation (CSI, 23.4 or 36.0 Gy(RBE)) followed by a PF-TB boost to 54 Gy(RBE) with proton beams. Three PF-TB boost plans were generated for each patient: (1) a uniform scanning (US) gantry plan with 4–7 posterior fields shaped with apertures and compensators (2) a PBS plan using bi-lateral and vertex fields with a 3-mm planning organ-at-risk volume (PRV) expansion around the brainstem and (3) PBS fields using same beam arrangement but replacing the PRV with robust optimization considering a 3-mm setup uncertainty. Results: A concave 54-Gy(RBE) isodose line surrounding the brainstem could be achieved using all three techniques. The mean V95% of the PTV was 99.7% (range: 97.6% to 100%) while the V100% of the PTV ranged from 56.3% to 93.1% depending on the involvement of the brainstem with the PTV. The mean doses received by 0.05 cm3 of the brainstem were effectively identical: 54.0 Gy(RBE), 53.4 Gy(RBE) and 53.3 Gy(RBE) for US, PBS optimized with PRV, and PBS optimized with robustness plans respectively. The cochlea mean dose increased by 23% of the prescribed boost dose in average from the bi-lateral fields used in the PBS plan. Planning time for the PBS plan with PRV was 5–10 times less than the US plan and the robustly optimized PBS plan. Conclusion: We have demonstrated that a fixed-beam with PBS can deliver a dose distribution comparable to a gantry plan using uniform scanning. Planning time can be reduced substantially using a PRV around the brainstem instead of robust optimization.

The purpose of this study is to compare the dose distribution, monitor units (MUs) and radiation delivery time between volumetric-modulated arc (VMAT) and fix-beam intensity modulated radiotherapy (FB-IMRT) in skull-base and non-skull-base head and neck cancer (HNC). CT datasets of 8 skull-base and 7 non-skull-base HNC were identified. IMRT and VMAT plans were generated. The prescription dose ranged 45–70 Gy (1.8–2.2 Gy/fraction). The VMAT delivery time was measured when these plans were delivered to the patients. The FB-IMRT delivery time was generated on a phantom. Comparison of dose-volume histogram data, MUs, and delivery times was performed using T-test. Our results show that both plans yield similar target volume coverage, homogeneity, and conformity. In skull-base cases, compared to FB-IMRT, VMAT generated significantly smaller hot-spot inside PTV (2.0% vs. 4.5%, p = 0.031), lower maximum chiasm dose (32 ± 11 Gy vs. 41 ± 15 Gy, p = 0.026), lower ipsilateral temporal-mandibular joint dose (D33: 41.4 Gy vs. 46.1 Gy, p = 0.016), lower mean ipsilateral middle ear dose (43 ± 9 Gy vs. 38 ± 10 Gy, p = 0.020) and a trend for lower optic nerve, temporal lobe, parotid, and oral cavity dose. In non-skull-base cases, doses to normal tissues were similar between the two plans. There was a reduction of 70% in MUs (486 ± 95 vs. 1614 ± 493, p < 0.001) and 73% in delivery times (3.0 ± 0.6 vs. 11.0 ± 3.3 min, p < 0.001) favoring VMAT. We conclude that VMAT appears to spare more normal tissues from high radiation dose for the tested skull-base tumors. Dosimetrically, both approaches were equivalent for non-skull-base tumor with VMAT using fewer MUs and shorter delivery time.

Purpose A study was performed to assess dosimetric characteristics of volumetric modulated arcs (RapidArc, RA) and fixed field intensity modulated therapy (IMRT) for Whole Abdomen Radiotherapy (WAR) after ovarian cancer. Methods and Materials Plans for IMRT and RA were optimised for 5 patients prescribing 25 Gy to the whole abdomen (PTV_WAR) and 45 Gy to the pelvis and pelvic nodes (PTV_Pelvis) with Simultaneous Integrated Boost (SIB) technique. Plans were investigated for 6 MV (RA6, IMRT6) and 15 MV (RA15, IMRT15) photons. Objectives were: for both PTVs V90% > 95%, for PTV_Pelvis: Dmax < 105%; for organs at risk, maximal sparing was required. The MU and delivery time measured treatment efficiency. Pre-treatment Quality assurance was scored with Gamma Agreement Index (GAI) with 3% and 3 mm thresholds. Results IMRT and RapidArc resulted comparable for target coverage. For PTV_WAR, V90% was 99.8 ± 0.2% and 93.4 ± 7.3% for IMRT6 and IMRT15, and 98.4 ± 1.7 and 98.6 ± 0.9% for RA6 and RA15. Target coverage resulted improved for PTV_Pelvis. Dose homogeneity resulted slightly improved by RA (Uniformity was defined as U5-95% = D5%-D95%/Dmean). U5-95% for PTV_WAR was 0.34 ± 0.05 and 0.32 ± 0.06 (IMRT6 and IMRT15), 0.30 ± 0.03 and 0.26 ± 0.04 (RA6 and RA15); for PTV_Pelvis, it resulted equal to 0.1 for all techniques. For organs at risk, small differences were observed between the techniques. MU resulted 3130 ± 221 (IMRT6), 2841 ± 318 (IMRT15), 538 ± 29 (RA6), 635 ± 139 (RA15); the average measured treatment time was 18.0 ± 0.8 and 17.4 ± 2.2 minutes (IMRT6 and IMRT15) and 4.8 ± 0.2 (RA6 and RA15). GAIIMRT6 = 97.3 ± 2.6%, GAIIMRT15 = 94.4 ± 2.1%, GAIRA6 = 98.7 ± 1.0% and GAIRA15 = 95.7 ± 3.7%. Conclusion RapidArc showed to be a solution to WAR treatments offering good dosimetric features with significant logistic improvements compared to IMRT.

There is concern about dose along the matchline when upper head-and-neck fields are treated with IMRT and the lower (supraclavicular) field is treated with a conventional fixed beam. An anatomical phantom was scanned and planned with IMRT upper head-and-neck fields and a fixed-beam supraclavicular field. The plans were fused and dose was calculated to points along the matchline. These doses were compared with thermolaminescent dosimetry measurements in the phantom, as the phantom was treated according to the plans.

Purpose: The purpose of this study is to inter-compare and find statistically significant differences between flattened field fixed-beam (FB) IMRT with flattening-filter free (FFF) volumetric modulated arc therapy (VMAT) for stereotactic body radiation therapy SBRT. Methods: SBRT plans using FB IMRT and FFF VMAT were generated for fifteen SBRT lung patients using 6 MV beams. For each patient, both IMRT and VMAT plans were created for comparison. Plans were generated utilizing RTOG 0915 (peripheral, 10 patients) and RTOG 0813 (medial, 5 patients) lung protocols. Target dose, critical structure dose, and treatment time were compared and tested for statistical significance. Parameters of interest included prescription isodose surface coverage, target dose heterogeneity, high dose spillage (location and volume), low dose spillage (location and volume), lung dose spillage, and critical structure maximum- and volumetric-dose limits. Results: For all criteria, we found equivalent or higher conformality with VMAT plans as well as reduced critical structure doses. Several differences passed a Student's t-test of significance: VMAT reduced the high dose spillage, evaluated with conformality index (CI), by an average of 9.4%±15.1% (p=0.030) compared to IMRT. VMAT plans reduced the lung volume receiving 20 Gy by 16.2%±15.0% (p=0.016) compared with IMRT. For the RTOG 0915 peripheral lesions, the volumes of lung receiving 12.4 Gy and 11.6 Gy were reduced by 27.0%±13.8% and 27.5%±12.6% (for both, p

Purpose: To identify persistent characteristics of IMRT, helical tomotherapy and IMPT across the range of potential applications. Method and Materials: The comparison of optimized treatment plans from different planning systems is difficult because treatment objective definitions and dose algorithms differ. Here, the techniques were implemented in the same optimization algorithm and Monte Carlo dose computation was available. Each of the techniques may offer benefits for certain cases and be less suitable for others. Five cases of different classes were selected including prostate, pediatric, lung and head‐and‐neck. The optimization employs biologically‐based objectives and enforces constraints for normal tissue doses. For each case, the same prescription and constraints were used. Results: For the clinical dose levels of this study, no treatment modality produced significantly superior plans. IMPT spared larger parts of the OAR. However, the EUD was mostly similar to that reached by photon techniques as it is mostly determined by the extent of the high dose volume. Tomotherapy provided generally better target coverage and higher homogeneity compared to fixed‐beam IMRT. However, the difference was mainly caused by the translation of the fully modulated fluence into static MLC segments. OAR irradiation was equivalent for both photon modalities, with higher mean doses for the tomo. Thus, the advantage of helical irradiation was mostly offset by the finer resolution of the MLC leaves (4 mm), once sufficiently chosen beams were used. On the other hand, noncoplanar beams did not provide a clear benefit. Conclusion: All modalities were optimized with the same planning system, thereby eliminating differences caused by the TPS. The differences between modalities were rarely significant. The quality of the dose distribution is governed by the particle type (mean dose) and the ability to deliver the ideal dose accurately (MLC leaf width, sequencing, number of beams, scanning grid).

Purpose: To discover the number of beams required in fixed‐beam IMRT to achieve similar plan quality to SmartArc in prostate cancertreatment.Method and Materials: Previous study showed that IMRT with as many as 24, uniformly‐distributed, beams still could not exceed SmartArc. In this work, we first studied the dose distributions of IMRT and SmartArc plans in a cylindrical water phantom, which provided guidelines for the beam‐angle‐selection in the patient study. Then, IMRT with respectively 8 to 16 beams and a SmartArc plan were generated for each of five prostate‐cancer patients. The 8‐beam plan used our Institution's standard configuration; other IMRT plans applied re‐selected gantry angles for better rectum sparing. All plans were generated using our in‐house developed automatic inverse‐planning algorithm and were optimized to at least similar quality as the clinical plan for each patient. Dose distributions in the OARs from each plan were compared. Results: The phantom study shows that SmartArc produced generally uniform penumbra in dose profile all around the target; in contrast, the fixed‐beam plans resulted in narrower penumbra perpendicular to beam directions whereas wider penumbra at other directions, which indicates that, for IMRT to achieve better sparing of OAR, beams along the tangent direction of the connection between the OAR and PTV should be included. The IMRT plans in the patient study shows obvious dose reduction in the rectum when more beams were selected based on such principle; when the number of beams reaches 16, the rectum starts to receive comparable dose to SmartArc with similar PTV coverage. Conclusion: Fixed‐beam IMRT is capable of exceeding the performance of SmartArc in prostate cancertreatment as long as 16 or more beams with properly selected gantry angles are used. Considering the superior delivery efficiency of SmartArc, however, SmartArc may still be preferable in clinical applications.

Purpose: Volumetric modulated arc therapy is an attractive treatment approach primarily due to potential decreases in treatment time affecting immobilization, patient comfort and throughput. However, this time savings must be weighed against plan quality and subsequent outcomes. We have compared the Varian RapidArc delivery method to fixed‐gantry step‐and‐shoot IMRT for the treatment of prostate cancer as we have a large experience and well defined acceptance criteria for this patient population. Method and Materials: For a series of patients, 10MV fixed‐beam IMRT, single and dual arc RapidArc plans were generated. In all cases the fixed beam plans were generated first with strict adherence to our clinical acceptance criteria. The arc plans were generated in an iterative manner to assure that they are at least dosimetrically equivalent to the routine IMRT plans where possible with respect to the aforementioned criteria, and allow for a faster delivery time. Results: As compared with fixed‐gantry IMRT, single arc plans resulted in average increases of 2.3% and 9.1% of the rectum receiving 65Gy and 40Gy, respectively. Dual arc plans resulted in 0.6% and 0.4% decreases in these cut‐points. Average total MU decreased by 392 and 261 with treatment time decreases from approximately 5min to 70sec and less than 2.5min for single and dual arc plans, respectively. The high‐dose conformity index (CI) was equivalent for the three methods while the low‐dose CI reduced from 4.94 to 4.68 and 4.63 for single and dual arc plans, respectively. Conclusions: While single‐arc plans demonstrate the greatest decrease in treatment time the increases in rectal dose, particularly in the low‐dose regions, are of concern with respect to potential secondary rectal cancers. The average improvement in low‐dose CI for dual arc plans, combined with the decrease in treatment time demonstrates the efficacy of this modality for this disease site.

Trials of the prior immobilization and positioning (PIP) system were carried out for pion patients at the Los Alamos Scientific Laboratory, Los Alamos, N.M., to demonstrate a more efficient method of beam utilization. In the trials patients entered the staging area, where they were placed in immobilizing casts in a treatment module. Localizing lasers identical to those in the treatment room defined the treatment portal and aligned bolus and collimator. Patients thus positioned and immobilized with necessary bolus and collimating devices in place were transported by stretcher into the treatment room and keyed by laser coordinates under the beam, which can be activated immediately. The PIP prototype at Los Alamos has reduced from 20 min to 4 min the interval required to position successive patients under the vertical fixed beam. Using the PIP system with current supervoltage generators and treatment couches, approximately 10 patients could be treated per hr as compared with 4 or 5 patients currently managed. This would reduce the cost per treatment by approximately half. PIP also makes feasible the use of computerized treatment. Any room of reasonable size near the treatment room could accommodate PIP procedures.

(1965). Dose Planning for Irradiation of Thorax with 60Co in Fixed-Beam Teletherapy. Acta Radiologica: Therapy, Physics, Biology: Vol. 3, No. 5, pp. 342-352.

Compared to kilovoltage radiation, megavoltage radiation has important advantages for external radiation therapy, but the much higher costs of the machines and treatment rooms have prevented more general use. Figure 1 shows an arrangement which greatly lowers the costs of megavoltage therapy. Two identical treatment rooms are served from one double-headed machine mounted in the wall between the two rooms. The teletherapy source, either cobalt 60 or cesium 137, is in the middle in the “off” position and can be moved into either head by a steel cable operated manually by a control wheel. Automatic return of the source to the “off” position at the end of the treatment time is provided by a spring. While one patient is treated in one room, the next patient is set up in the adjoining room, an arrangement similar to Failla's layout for the Memorial Hospital 4 g radium bomb. The radiation beam is always directed straight down. Its size and shape are adjusted with shielding blocks placed on a tray below each head...