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Abstract Background For cervical cancer patients treated with MR-guided high dose rate brachytherapy, the accuracy of radiation delivery depends on accurate localization of both tumors and the applicator, e.g. tandem and ovoid. Standard T2-weighted (T2W) MRI has good tumor-tissue contrast. However, it suffers from poor uterus-tandem contrast, which makes the tandem delineation very challenging. In this study, we evaluated the possibility of using proton density weighted (PDW) MRI to improve the definition of titanium tandems. Methods Both T2W and PDW MRI images were obtained from each cervical cancer patient. Imaging parameters were kept the same between the T2W and PDW sequences for each patient except the echo time (90 ms for T2W and 5.5 ms for PDW) and the slice thickness (0.5 cm for T2W and 0.25 cm for PDW). Uterus-tandem contrast was calculated by the equation C = (Su-St)/Su, where Su and St represented the average signal in the uterus and the tandem, respectively. The diameter of the tandem was measured 1.5 cm away from the tip of the tandem. The tandem was segmented by the histogram thresholding technique. Results PDW MRI could significantly improve the uterus-tandem contrast compared to T2W MRI (0.42±0.24 for T2W MRI, 0.77±0.14 for PDW MRI, p=0.0002). The average difference between the measured and physical diameters of the tandem was reduced from 0.20±0.15 cm by using T2W MRI to 0.10±0.11 cm by using PDW MRI (p=0.0003). The tandem segmented from the PDW image looked more uniform and complete compared to that from the T2W image. Conclusions Compared to the standard T2W MRI, PDW MRI has better uterus-tandem contrast. The information provided by PDW MRI is complementary to those provided by T2W MRI. Therefore, we recommend adding PDW MRI to the simulation protocol to assist tandem delineation process for cervical cancer patients.

Purpose: The Calypso medical four-dimensional localization system uses AC electromagnetics, which do not require ionizing radiation, for accurate, real-time tumor tracking. This investigation compared the static and dynamic tracking accuracy of this system to that of an on-board imaging kilovoltage X-ray system for concurrent use of the two systems.Methods and Materials: The localization accuracies of a kilovoltage imaging system and a continuous electromagnetic tracking system were compared. Using an in-house developed four-dimensional stage, quality-assurance fixture containing three radiofrequency transponders was positioned at a series of static locations and then moved through the ellipsoidal and nonuniform continuous paths. The transponder positions were tracked concurrently by the Calypso system. For static localization, the transponders were localized using portal images and digitally reconstructed radiographs by commercial matching software. For dynamic localization, the transponders were fluoroscopically imaged, and their positions were determined retrospectively using custom-written image processing programs. The localization data sets were synchronized with and compared to the known quality assurance fixture positions. The experiment was repeated to retrospectively track three transponders implanted in a canine lung.Results: The root mean square error of the on-board imaging and Calypso systems was 0.1 cm and 0.0 cm, respectively, for static localization, 0.22 mm and 0.33 mm for dynamic phantom positioning, and 0.42 mm for the canine study.Conclusion: The results showed that both localization systems provide submillimeter accuracy. The Calypso and on-board imaging tracking systems offer distinct sets of advantages and, given their compatibility, patients could benefit from the complementary nature of the two systems when used concurrently. [ABSTRACT FROM AUTHOR]

Background and Purpose: High BMI is a reason for medical inoperability in patients with endometrial cancer in the United States. Definitive radiation is an alternative therapy for these patients; however, data on patterns of failure after definitive radiotherapy are lacking. We describe the patterns of failure after definitive treatment with 3-D image-based high dose rate (HDR) brachytherapy for medically inoperable endometrial cancer., Materials and Methods: Forty-three consecutive patients with endometrial cancer FIGO stages I-III were treated definitively with HDR brachytherapy with or without external beam radiation therapy. Cumulative incidence of failures was estimated and prognostic variables were identified, Results: Mean follow up was 29.7 months. Median BMI was 50.2 kg/m(2) (range: 25.1-104 kg/m(2)). The two-year overall survival was 65.2%. The two-year cumulative incidence of pelvic and distant failures was 8.3% and 13.5%, respectively. Grade 3 disease was associated with a higher risk of all-failures (Hazard Ratio [HR]: 4.67, 95% CI: 1.04-20.9, p=0.044). The incidence of acute Grade 3 GI/GU toxicities was 4.6%., Conclusions: Pelvic failure at two years was less than 10%. Patients with grade 3 disease were more likely to experience disease failure and may warrant closer follow up., (Copyright © 2015 Elsevier Ireland Ltd. All rights reserved.)

Purpose: The purpose of this consensus statement from the American Brachytherapy Society (ABS) is to summarize recent advances and to generate general guidelines for the management of medically inoperable endometrial cancer patients with radiation therapy., Methods: Recent advances in the literature were summarized and reviewed by a panel of experts. Panel members participated in a series of conference calls and were surveyed to determine their current practices and patterns. This document was reviewed and approved by the full panel, the ABS Board of Directors and the ACR Commission on Radiation Oncology., Results: A transition from two-dimensional (2D) to three-dimensional (3D) treatment planning for the definitive treatment of medically inoperable endometrial cancer is described. Magnetic resonance (MR) imaging can be used to define the gross tumor volume (GTV), clinical target volume (CTV), and the organs at risk (OARs). Brachytherapy alone can be used for medically inoperable endometrial cancer patients with clinical Stage I cancer with no lymph node involvement and no evidence of deep invasion of the myometrium on MR imaging. In the absence of MR imaging, a combined approach using external beam and brachytherapy may be considered., Conclusions: Recent advances support the use of MR imaging and 3D planning for brachytherapy treatment for medically inoperable endometrial cancer., (Copyright © 2015 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

Accelerated partial breast irradiation (APBI) is an excellent treatment option for many women with early stage breast cancer. Patient selection criteria include age over 40, status post lumpectomy, breast cancer (invasive or in situ disease) measuring <3 cm, negative margins (at least 2 mm), negative lymph nodes, and no lymphovascular space invasion. APBI is effective, well tolerated, and convenient. Women with early stage breast cancer and theii caregivers should be aware of this potential treatment option.

Purpose: Dose accumulation of split-field external beam radiotherapy (EBRT) and brachytherapy (BT) is challenging because of significant EBRT and BT dose gradients in the central pelvic region. We developed a method to determine biologically effective dose parameters for combined split-field intensity-modulated radiation therapy (IMRT) and image-guided BT in locally advanced cervical cancer., Methods and Materials: Thirty-three patients treated with split-field-IMRT to 45.0-51.2 Gy in 1.6-1.8 Gy per fraction to the elective pelvic lymph nodes and to 20 Gy to the central pelvis region were included in this study. Patients received six weekly fractions of high-dose rate BT to 6.5-7.3 Gy per fraction. A dose tracker software was developed to compute the equivalent dose in 2-Gy fractions (EQD2) to gross tumor volume (GTV), organs-at-risk and point A. Total dose-volume histogram parameters were computed on the 3D combined EQD2 dose based on rigid image registration. The dose accumulation uncertainty introduced by organ deformations between IMRT and BT was evaluated., Results: According to International Commission on Radiation Unit and Measurement and GEC European Society for Therapeutic Radiology and Oncology recommendations, D98, D90, D50, and D2cm3 EQD2 dose-volume histogram parameters were computed. GTV D98 was 84.0 ± 26.5 Gy and D2cc was 99.6 ± 13.9 Gy, 67.4 ± 12.2 Gy, 75.0 ± 10.1 Gy, for bladder, rectum, and sigmoid, respectively. The uncertainties induced by organ deformation were estimated to be -1 ± 4 Gy, -3 ± 5 Gy, 2 ± 3 Gy, and -3 ± 5 Gy for bladder, rectum, sigmoid, and GTV, respectively., Conclusions: It is feasible to perform 3D EQD2 dose accumulation to assess high and intermediate dose regions for combined split-field IMRT and BT., (Copyright © 2015 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

Purpose: To evaluate outpatient-based high-dose-rate (HDR) interstitial brachytherapy (ISBT) in the treatment of gynecologic malignancies., Methods and Materials: Between December 2006 and July 2012, 50 patients were treated with twice-daily outpatient-based HDR iridium-192 ISBT at our institution. Thirty-two patients had vaginal cancers, 13 vulvar, 3 urethral, and 2 cervical cancers. The most common histologies were squamous cell carcinoma (58%) and endometrioid adenocarcinoma (26%). Twenty-six patients were treated with definitive radiation therapy with or without platinum-based chemotherapy, 16 were treated for recurrent disease, 5 were treated in the postoperative setting, and 3 were treated palliatively. Forty patients received external beam radiation therapy before ISBT., Results: Median followup was 13.7 months. Median interstitial dose was 18 Gy in 2.25 Gy twice-daily fractions prescribed to the implant volume. Median external beam dose was 50.4 Gy in 1.8 Gy daily fractions prescribed to the primary disease site. Eight patients (16%) were seen in the emergency room or were admitted to the hospital during treatment. Six patients (17%) experienced significant complications after treatment (3 ulcerations at the primary site, 1 vaginal necrosis, 1 vaginal abscess, and 1 patient with urinary obstruction). Larger volume encompassing 100% of the prescribed dose was correlated with significant complications on multivariate analysis (p = 0.039). Actuarial local control at 1 year was 72%, with univariate analysis demonstrating worse local control for nonendometrioid adenocarcinoma compared with squamous cell carcinoma (20% vs. 84%, p = 0.044)., Conclusions: Outpatient-based HDR ISBT is feasible and safe, with toxicity and local control rates consistent with historical outcomes., (Copyright © 2015 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.)

There is a clear need for established standards for medical physics residency training. The complexity of techniques in imaging, nuclear medicine, and radiation oncology continues to increase with each passing year. It is therefore imperative that training requirements and competencies are routinely reviewed and updated to reflect the changing environment in hospitals and clinics across the country. In 2010, the AAPM Work Group on Periodic Review of Medical Physics Residency Training was formed and charged with updating AAPM Report Number 90. This work group includes AAPM members with extensive experience in clinical, professional, and educational aspects of medical physics. The resulting report, AAPM Report Number 249, concentrates on the clinical and professional knowledge needed to function independently as a practicing medical physicist in the areas of radiation oncology, imaging, and nuclear medicine, and constitutes a revision to AAPM Report Number 90. This manuscript presents an executive summary of AAPM Report Number 249.

Purpose: To assess the impact on local tumor control of intraoperative ultrasonographic plaque visualization and selective application of transpupillary thermotherapy (TTT) in the treatment of posterior uveal melanoma with iodine-125 (I-125) episcleral plaque brachytherapy (EPB)., Methods and Materials: Retrospective analysis of 526 patients treated with I-125 EPB for posterior uveal melanoma. Clinical features, dosimetric parameters, TTT treatments, and local tumor control outcomes were recorded. Statistical analysis was performed using Cox proportional hazards and Kaplan-Meier life table method., Results: The study included 270 men (51%) and 256 women (49%), with a median age of 63 years (mean, 62 years; range, 16-91 years). Median dose to the tumor apex was 94.4 Gy (mean, 97.8; range, 43.9-183.9) and to the tumor base was 257.9 Gy (mean, 275.6; range, 124.2-729.8). Plaque tilt >1 mm away from the sclera at plaque removal was detected in 142 cases (27%). Supplemental TTT was performed in 72 patients (13.7%). One or 2 TTT sessions were required in 71 TTT cases (98.6%). After a median follow-up of 45.9 months (mean, 53.4 months; range, 6-175 months), local tumor recurrence was detected in 19 patients (3.6%). Local tumor recurrence was associated with lower dose to the tumor base (P=.02)., Conclusions: Ultrasound-guided plaque localization of I-125 EPB is associated with excellent local tumor control. Detection of plaque tilt by ultrasonography at plaque removal allows supplemental TTT to be used in patients at potentially higher risk for local recurrence while sparing the majority of patients who are at low risk. Most patients require only 1 or 2 TTT sessions., (Copyright © 2014 Elsevier Inc. All rights reserved.)

Purpose: A multi-institutional phase 2 trial assessed the utility of dose-painted intensity modulated radiation therapy (DP-IMRT) in reducing grade 2+ combined acute gastrointestinal and genitourinary adverse events (AEs) of 5-fluorouracil (5FU) and mitomycin-C (MMC) chemoradiation for anal cancer by at least 15% compared with the conventional radiation/5FU/MMC arm from RTOG 9811., Methods and Materials: T2-4N0-3M0 anal cancer patients received 5FU and MMC on days 1 and 29 of DP-IMRT, prescribed per stage: T2N0, 42 Gy elective nodal and 50.4 Gy anal tumor planning target volumes (PTVs) in 28 fractions; T3-4N0-3, 45 Gy elective nodal, 50.4 Gy ≤ 3 cm or 54 Gy >3 cm metastatic nodal and 54 Gy anal tumor PTVs in 30 fractions. The primary endpoint is described above. Planned secondary endpoints assessed all AEs and the investigator's ability to perform DP-IMRT., Results: Of 63 accrued patients, 52 were evaluable. Tumor stage included 54% II, 25% IIIA, and 21% IIIB. In primary endpoint analysis, 77% experienced grade 2+ gastrointestinal/genitourinary acute AEs (9811 77%). There was, however, a significant reduction in acute grade 2+ hematologic, 73% (9811 85%, P=.032), grade 3+ gastrointestinal, 21% (9811 36%, P=.0082), and grade 3+ dermatologic AEs 23% (9811 49%, P<.0001) with DP-IMRT. On initial pretreatment review, 81% required DP-IMRT replanning, and final review revealed only 3 cases with normal tissue major deviations., Conclusions: Although the primary endpoint was not met, DP-IMRT was associated with significant sparing of acute grade 2+ hematologic and grade 3+ dermatologic and gastrointestinal toxicity. Although DP-IMRT proved feasible, the high pretreatment planning revision rate emphasizes the importance of real-time radiation quality assurance for IMRT trials., (Copyright © 2013 Elsevier Inc. All rights reserved.)

Purpose: To compare [(18)F]fluorodeoxyglucose (FDG)/positron emission tomography (PET)/computed tomography (CT) and magnetic resonance imaging (MRI) for evaluating patients with cervical cancer. We compared tumor characteristics on FDG-PET and apparent diffusion coefficient (ADC) maps on diffusion-weighted MRI (DWI) to evaluate concordance of two functional imaging techniques., Materials and Methods: Twenty women with cervical cancer underwent pretreatment FDG-PET/CT and pelvic MRI. Images were rigidly fused by pelvic anatomy using coregistration software. Tumor contours on PET images were generated by autosegmentation of the region containing at least 40% of the maximum standardized uptake value (SUV). DWI contours were generated by manual segmentation. Tumor volume similarity was evaluated using the [PET]/[ADC] volume proportion, Dice's coefficient, and the mean SUV isothreshold at the surface of each ADC contour. Tumor subvolume similarity was evaluated with analysis of variance (ANOVA)., Results: The [PET]/[ADC] volume proportion was 0.88 ± 0.14. Dice's coefficient between PET and ADC tumor contours was 0.76 ± 0.06. The mean SUV isothreshold at the ADC-delineated tumor surface was 34 ± 4%. Subvolumes with increased metabolic activity on FDG-PET also had more restricted diffusion on DWI (P < 0.0001, ANOVA)., Conclusion: Concordance of functional imaging was observed between FDG-PET and DWI for cervical cancer. Tumor subvolumes with increased metabolic activity on FDG-PET also have greater cell density by DWI., (Copyright © 2012 Wiley Periodicals, Inc.)

Purpose: T2-weighted (T2W) magnetic resonance imaging (MRI) has been used for target delineation in cervix cancer brachytherapy. The objective of this study was to examine the feasibility of using diffusion-weighted magnetic resonance imaging (DWI) for target delineation as compared against T2W imaging., Material and Methods: Fifteen cervix cancer patients, implanted with tandem and ovoid applicators, underwent T2W turbo-spin echo imaging and DWI with a maximum diffusion factor of 800 sec/mm(2) on a 1.5-T MR scanner. Apparent diffusion coefficient (ADC) maps were derived from the DWI. The gross tumor volume was manually delineated on the T2W and ADC datasets for each patient. The agreement between T2W- and ADC-delineated volumes was assessed using the Dice similarity coefficient (DSC). An algorithm was developed to compare the edge contrast of the delineated volumes on T2W images and ADC maps by calculating the percentage difference in the intensity values of selected regions of pixels inside versus outside the target contour., Results: ADC-delineated volumes were generally smaller than T2W-delineated volumes, yielding a low DSC of 0.54 ± 0.22. ADC maps were found to display superior definition of the target volume edge relative to T2W images, yielding a statistically significant difference between the mean edge contrast on ADC (12.7 ± 7.7%) versus that on T2W images (4.6 ± 3.2%; p = 0.0010)., Conclusions: These results suggest that incorporating the use of DWI for cervix cancer brachytherapy may yield gross tumor volumes that are different from those based on T2W images alone.

Purpose: As experience with the MammoSite device for accelerated partial breast irradiation (APBI) has increased, more centers are starting to use three-dimensional (3D) treatment planning to generate plans with multiple nonequally weighted dwell positions. This report presents the use of serial computed tomography (CT) imaging, in addition to planar or ultrasound imaging, for the quality assurance of an APBI treatment using the elliptical MammoSite., Methods and Materials: CT images of a patient implanted with a 4cmx6cm elliptical MammoSite balloon were acquired. A treatment plan using multiple, nonequally weighted dwells was generated and delivered on Day 1 of a 10-fraction, twice-daily treatment. Before morning treatments on Days 2-5, the patient was reimaged on CT. Treatment plans on repeat CTs were generated two ways: using the decay-corrected plan from Day 1 (unadapted) vs. modifying the plan to account for changes in implant geometry (adapted). Adapted and unadapted plans on repeat CTs were compared with one another, and to the Day 1 plan., Results: The use of unadapted plans led to increased doses to normal tissues, particularly the skin. Adaptive planning on the repeat CTs was effective for maintaining acceptable dosimetry throughout treatment., Conclusions: Serial CT imaging was shown to provide a useful tool for the quality assurance of an elliptical balloon implant during the course of treatment. Serial CT imaging, as opposed to planar or ultrasound imaging, was necessary to evaluate skin dose and to facilitate adaptation of the treatment plan to satisfy limits for skin dose.

The Calypso Medical 4D localization system utilizes alternating current electromagnetics for accurate, real-time tumor tracking. A quality assurance program to clinically implement this system is described here. Testing of the continuous electromagnetic tracking system (Calypso Medical Technologies, Seattle, WA) was performed using an in-house developed four-dimensional stage and a quality assurance fixture containing three radiofrequency transponders at independently measured locations. The following tests were performed to validate the Calypso system: (a) Localization and tracking accuracy, (b) system reproducibility, (c) measurement of the latency of the tracking system, and (d) measurement of transmission through the Calypso table overlay and the electromagnetic array. The translational and rotational localization accuracies were found to be within 0.01 cm and 1.0 degree, respectively. The reproducibility was within 0.1 cm. The average system latency was measured to be within 303 ms. The attenuation by the Calypso overlay was measured to be 1.0% for both 6 and 18 MV photons. The attenuations by the Calypso array were measured to be 2% and 1.5% for 6 and 18 MV photons, respectively. For oblique angles, the transmission was measured to be 3% for 6 MV, while it was 2% for 18 MV photons. A quality assurance process has been developed for the clinical implementation of an electromagnetic tracking system in radiation therapy.

Purpose: To describe a more aggressive treatment technique allowing dose escalation to positive para-aortic lymph nodes (PALN) in patients with cervical cancer, by means of positron emission tomography (PET)/computed tomography (CT)-guided intensity-modulated radiation therapy (IMRT). Here, we describe methods for simulation and planning of these treatments and provide objectives for target coverage as well as normal tissue sparing to guide treatment plan evaluation., Methods and Materials: Patients underwent simulation on a PET/CT scanner. Treatment plans were generated to deliver 60.0 Gy to the PET-positive PALN and 50.0 Gy to the PALN and pelvic lymph node beds. Treatment plans were optimized to deliver at least 95% of the prescribed doses to at least 95% of each target volume. Dose-volume histograms were calculated for normal structures., Results: The plans of 10 patients were reviewed. Target coverage goals were satisfied in all plans. Analysis of dose-volume histograms indicated that treatment plans involved irradiation of approximately 50% of the bowel volume to at least 25.0 Gy, with less than 10% receiving at least 50.0 Gy and less than 1% receiving at least 60.0. With regard to kidney sparing, approximately 50% of the kidney volume received at least 16.0 Gy, less than 5% received at least 50.0 Gy, and less than 1% received at least 60.0 Gy., Conclusions: We have provided treatment simulation and planning methods as well as guidelines for the evaluation of target coverage and normal tissue sparing that should facilitate the more aggressive treatment of cervical cancer.

Purpose: This prospective study investigates gynecologic malignancy online treatment setup error corrections using planar kilovoltage/megavoltage (KV/MV) imaging and helical MV computed tomography (MVCT) imaging., Methods and Materials: Twenty patients were divided into two groups. The first group (10 patients) was imaged and treated using a conventional linear accelerator (LINAC) with image-guidance capabilities, whereas the second group (10 patients) was treated using tomotherapy with MVCT capabilities. Patients treated on the LINAC underwent planar KV and portal MV imaging and a two-dimensional image registration algorithm was used to match these images to digitally reconstructed radiographs (DRRs). Patients that were treated using tomotherapy underwent MVCT imaging, and a three-dimensional image registration algorithm was used to match planning CT to MVCT images. Subsequent repositioning shifts were applied before each treatment and recorded for further analysis. To assess intrafraction motion, 5 of the 10 patients treated on the LINAC underwent posttreatment planar imaging and DRR matching. Based on these data, patient position uncertainties along with estimated margins based on well-known recipes were determined., Results: The errors associated with patient positioning ranged from 0.13 cm to 0.38 cm, for patients imaged on LINAC and 0.13 cm to 0.48 cm for patients imaged on tomotherapy. Our institutional clinical target volume-PTV margin value of 0.7 cm lies inside the confidence interval of the margins established using both planar and MVCT imaging., Conclusion: Use of high-quality daily planar imaging, volumetric MVCT imaging, and setup corrections yields excellent setup accuracy and can help reduce margins for the external beam treatment of gynecologic malignancies.

Purpose: Computed tomography (CT)/positron emission tomography (PET)-guided intensity-modulated radiotherapy of the paraaortic lymph nodes (PALNs) has been proposed for patients with cervical carcinoma and paraaortic metastasis. This investigation attempted to determine the guidelines regarding the selection of appropriate treatment parameters (e.g., number of beams, beam geometry) and organ-specific parameters (e.g., importance weighting and tolerance dose) for intensity-modulated radiotherapy planning for the PALNs., Methods and Materials: Patients underwent imaging using CT and PET. The images were registered, and the structures were contoured. A goal dose of 50.4 Gy and 59.4 Gy was assigned to the clinical target volume (lymph node bed) and gross tumor volume (PET-delineated PALNs), respectively. For each patient, multiple treatment plans using various beam geometries and planning parameters were executed and evaluated in terms of the dose-volume histograms of the target and critical structures., Results: Acceptable sparing of the stomach, liver, and colon was achieved, regardless of the number of beams used. Sparing of the spinal cord was strongly dependent on the number and arrangement of the beams. Varying the number and arrangement of the beams affected small intestine sparing, but the amount of sparing was limited because the small intestine overlapped the target volumes, and, therefore, received the prescription dose. Adjusting the number of beams, beam angles, and prescription parameters provided minimal improvement in kidney sparing., Conclusion: We successfully developed treatment plans that deliver 59.4 Gy to the positive PALNs and 50.4 Gy to the paraaortic region using CT/PET-guided intensity-modulated radiotherapy.

Understanding head scatter characteristics of photon beams is vital to properly commission treatment planning (TP) algorithms. Simultaneously, having definitive surface and buildup region dosimetry is important to optimize bolus. The Elekta Precise linacs have unique beam flattening filter configurations for each photon beam (6, 10, and 18 MV) in terms of material and location. We performed a comprehensive set of surface and buildup dose measurements with a thin window parallel-plate (PP) chamber to examine effects of field size (FS), source-to-skin distance (SSD), and attenuating media. Relative ionization data were converted to fractional depth dose (FDD) after correcting for bias effects and using the Gerbi method to account for chamber characteristics. Data were compared with a similar vintage Varian linac. At short SSDs the surface and buildup dose characteristics were similar to published data for Varian and Elekta accelerators. The FDD at surface (FDD(0)) for 6, 10, and 18 MV photons was 0.171, 0.159, and 0.199, respectively, for a 15x15 cm2, 100 cm SSD field. A blocking tray increased FDD(0) to 0.200, 0.200, and 0.256, while the universal wedge decreased FDD(0) to 0.107, 0.124, and 0.176. FDD(0) increased linearly with FS (approximately 1.16%/cm). FDD(0) decreased exponentially for 10 and 18 MV with increasing SSD. However, the 6 MV FDD(0) actually increased slightly with increasing SSD. This is likely due to the unique distal flattening filter for 6 MV. The measured buildup curves have been used to optimize TP calculations and guide bolus decisions. Overall the FDD(0) and buildup doses were very similar to published data. Of interest were the relatively low 10 MV surface doses, and the 6 MV FDD(0)'s dependence on SSD.

Purpose: To evaluate a treatment planning method for dose escalation to the para-aortic lymph nodes (PALNs) based on positron emission tomography (PET) with intensity-modulated radiotherapy (IMRT) for cervical cancer patients with PALN involvement. One goal of this process was not to modify the traditional treatment of the pelvic region., Methods and Materials: PET images for 4 cervical cancer patents with PALN involvement were registered with their corresponding CT scans. Positive PALNs were identified on PET images, and the surrounding critical structures were delineated on CT images. The treatment machine central axis (CAX) was placed at the level of the L4-L5 vertebral body interspace. There were two distinct treatment regions: the para-aortic bed superior to the CAX and the whole pelvis region inferior to the CAX. IMRT was used for treatment planning of PALN bed irradiation. The positive PALNs identified on PET images were defined as the gross target volume, and the para-aortic bed was defined as the clinical target volume. The radiation doses were escalated from the conventional 45 Gy to 59.4 Gy for the gross target volume and 50.4 Gy for the clinical target volume in 33 fractions. The pelvis area was treated with conventional treatment methods, AP-PA beams to 50.4 Gy in 28 fractions with a brachytherapy implant boost. The placement of the CAX allowed the two treatment regions to be abutted using the treatment machine's independent jaws., Results: Dose escalation to positive PALNs, as identified on PET images, and the PALN bed is feasible with IMRT. Treatment plans for 4 patients revealed that escalated prescription doses could be delivered to target volumes while maintaining acceptable doses to the surrounding critical structures. Strategic placement of the treatment isocenter allows the IMRT region (PALN bed) and whole pelvis fields to be treated with a relatively uniform dose distribution in the abutment region., Conclusion: This study indicates that PET-guided IMRT could be used in a clinical trial in an attempt to escalate doses delivered to patients with cervical cancer who have positive PALNs.

For intensity modulated radiation therapy (IMRT) dose distribution verification, multidimensional measurements are required to quantify the steep dose-gradient regions. High resolution, two-dimensional dose distributions can be measured using radiographic film. However, the photon energy response of film is known to be a function of depth, field size, and photon beam energy, potentially reducing the accuracy of dose distribution measurements. The dosimetric properties of the recently developed Kodak EDR2 film were investigated and compared to those of Kodak XV film. The dose responses of both film types to 6 MV and 18 MV photon beams were investigated for depths of 5 cm, 10 cm, and 15 cm and field sizes of 4x4 cm2 and 15x15 cm2. This analysis involved the determination of sensitometric curves for XV and EDR2 films, the determination of dose profiles from exposed XV and EDR2 films, and comparison of the film-generated dose profiles to ionization chamber measurements. For the combinations of photon beam energy, depth, and field size investigated here, our results indicate that the sensitometric curves are nearly independent of field size and depth of calibration. For a field size of 4x4 cm2, a single sensitometric curve for either EDR2 and XV film can be used for the determination of relative dose profiles. For the larger field size, the sensitometric curve for EDR2 film is superior to XV film in regions where the dose falls below 20% of the central axis dose, due to the effects that the increased low energy scattered photon contributions have on film response. The limited field size and depth dependence of sensitometric data measured using EDR2 film, along with the inherently wide linear dose-response range of EDR2 film, makes it better suited to the verification of IMRT dose distributions.

The American Association of Physicists in Medicine Task Group 36 (AAPM TG-36) data can be used to estimate peripheral dose (PD) distributions outside the primary radiation field. However, the report data does not apply to linear accelerators equipped with a multileaf collimator (MLC) and universal wedge (UW). Tertiary multileaf collimators have been shown to significantly affect PD distributions and TG-36 reported data. Measurements were performed to evaluate PD distributions for a linear accelerator equipped with a secondary MLC, backup diaphragms, and UW. This data can be used to compliment the TG-36 report for estimation of doses to critical structures outside primary radiation fields. For the evaluated linear accelerator, an MLC is incorporated in the upper secondary collimator jaws. Backup shielding diaphragms are located underneath the MLC. At the nominal collimator position, the MLC and the backup diaphragm provide collimation primarily in the transverse direction. Conventional, solid tungsten-alloy jaws, located underneath the backup diaphragms, provide secondary collimation in the longitudinal direction. The universal wedge provides dose modulation in the direction of the conventional jaws. Measurements were made with an ionization chamber inserted into a 20x40x120 cm(3) water-equivalent plastic phantom with the secondary collimator and MLC settings of 5x5, 10x10, 15x15, and 25x25 cm(2) with and without UW. Data was acquired along the machine's longitudinal axis for 6, 10, and 18 MV photons. Peripheral dose distributions were measured with the collimator rotated to 0 degrees and 270 degrees for open field measurements and to 0 degrees, 180 degrees, and 270 degrees for wedged fields (IEC 1217). This allowed evaluation of peripheral dose distributions as a function of collimator rotation. Wedged fields were normalized to deliver the same dose at the depth of maximum dose on the central axis as open fields. The measured PD distributions were generally comparable to data reported by TG-36. At distances close to the field edge (less than 30 or 40 cm), the measured PD distributions were lower when the measurement point was shielded by solid jaws than with MLC and backup diaphragm. At longer distances, this trend reversed for all energies and evaluated field sizes. However, the difference in PD distribution with collimator rotation was not large enough to warrant strategic positioning of the collimator to reduce dose to critical structures outside the primary radiation field. Because internal scatter dominates close to the field edge, wedged PD distributions were comparable to open field doses at distances closer than 30 cm. However, at distances larger than 30 cm from the field edge, wedged PD distributions were significantly grater than those for open fields due to increased contribution of leakage radiation. Increased leakage radiation is due to the increase in wedged field monitor units, which is related to a small wedge factor (0.27 to 0.29).

With the increasing number and complexity of therapeutic coronary interventions, there is an increasing need for accurate quantitative measurements. These interventions and measurements may be facilitated by accurate and reproducible magnifications and orientations of the vessel structures, specifically by accurate 3D vascular tree centerlines. A number of methods have been proposed to calculate 3D vascular tree centerlines from biplane images. In general, the calculated magnifications and orientations are accurate to within approximately 1-3% and 2-5 degrees, respectively. Here, we present a complete system for determination of the 3D vessel centerlines from biplane angiograms without the use of a calibration object. Subsequent to indication of the vessel centerlines, the imaging geometry and 3D centerlines are calculated automatically and within approximately 2 min. The system was evaluated in terms of the intra- and inter-user variations of the various calculated quantities. The reproducibilities obtained with this system are comparable to or better than the accuracies and reproducibilities quoted for other proposed methods. Based on these results and those reported in earlier studies, we believe that this system will provide accurate and reproducible vascular tree centerlines from biplane images while the patient is still on the table, and thereby will facilitate interventions and associated quantitative analyses of the vasculature.

A technique is developed that will calculate accurate and reliable imaging geometries and three-dimensional (3D) positions from biplane images of a calibration phantom. The calculated data provided by our technique will facilitate accurate 3D analysis in various clinical applications. Biplane images of a Lucite cube containing lead beads 1 mm in diameter were acquired. After identifying corresponding beads in both images and calculating their image positions, the 3D positions of the beads relative to each focal spot were determined. From these data, the transformation relating the 3D configurations were calculated to give the imaging geometry relating the biplane views. The 3D positions of objects were determined from the biplane images along with the corresponding imaging geometries. In addition, methods are developed to evaluate the quality of the calculated results on a case-by-case basis in the clinical setting. Methods are presented for evaluating the reproducibility of the calculated geometries and 3D positions, the accuracy of calculated object sizes, and the effects of errors due to time jitter, variation in user-indication, centering, and distortions on the calculated geometries and 3D reconstructions. The precision of the translation vectors and rotation matrices of the calculated geometries were within 1% and 1 degree, respectively, in phantom studies, with estimated accuracies of approximately 0.5% and 0.4 degree, respectively, in simulation studies. The precisions of the absolute 3D positions and orientations of the calculated 3D reconstructions were approximately 2 mm and 0.5 degree, respectively, in phantom studies, with estimated accuracies of approximately 1.5 mm and 0.4 degree, respectively, in simulation studies. This technique will provide accurate and precise imaging geometries as well as 3D positions from biplane images, thereby facilitating 3D analysis in various clinical applications. We believe that the study presented here is unique in that it represents the first steps toward understanding and evaluating the reliability of these 3D calculations in the clinical situation.

In vitro and in vivo analyses of stress on pacemaker leads and their components during the heart cycle have become especially important because of incidences of failure of some of these mechanical components. For stress analyses, the three-dimensional (3D) position, shape, and motion of the pacemaker leads must be known accurately at each time point during the cardiac cycle. We have developed a method for determination of the in vivo 3D positions of pacemaker leads during the entire heart cycle. Sequences of biplane images of patients with pacemakers were obtained at 30 frames/s for each projection. The sequences usually included at least two heart cycles. After patient imaging, biplane images of a calibration object were obtained from which the biplane imaging geometry was determined. The centerlines of the leads and unique, identifiable points on the attached electrodes were indicated manually for all acquired images. Temporal interpolation of the lead and electrode data was performed so that the temporal nonsynchronicity of the image acquisition was overcome. Epipolar lines, generated from the calculated geometry, were employed to identify corresponding points along the leads in the pairs of biplane images for each time point. The 3D positions of the lead and electrodes were calculated from the known geometry and from the identified corresponding points in the images. Using multiple image sets obtained with the calibration object at various orientations, the precision of the calculated rotation matrix and of the translation vector defining the imaging geometry was found to be approximately 0.7 degree and 1%, respectively. The 3D positions were reproducible to within 2 mm, with the error lying primarily along the axis between the focal spot and the imaging plane. Using data obtained by temporally downsampling to 15 frames/s, the interpolated data were found to lie within approximately 2 mm of the true position for most of the heart cycle. These results indicate that, with this technique, one can reliably determine pacemaker lead positions throughout the heart cycle, and thereby it will provide the basis for stress analysis on pacemaker leads.

A new technique is developed for accurate determination of the three-dimensional position and orientation of known sparse objects, e.g., a configuration of points, from a single-perspective projection. In this technique, a computer model of the known object is translated and rotated so as to align it optimally in a least-squares sense with the projection lines connecting the image points with the focal spot by using a modification of the projection-Procrustes technique. The translational and rotational adjustments are repeated iteratively until the angular change between iterations is less than 0.25 degree. Simulations indicate that, for rms input image errors of 0.03 cm, the three-dimensional positions and orientations can be determined to within approximately 0.2 cm and 0.3 degree for a wide range of initially guessed positions and orientations, and positions can be determined with an accuracy of approximately 0.3 cm for objects having as few as four points. In phantom experiments, three-dimensional positions and orientations of a cube phantom were reproducibly determined to within 0.23 cm and 0.13 degree. The entire calculation requires only 10 s on a VAX 3500 to converge to the solution. The accuracy, precision, and speed of the technique indicate that it will be a useful tool for determination of three-dimensional positions and orientations of known sparse objects.