bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐E‐T‐257: Output Constancy: Reducing Measurement Variations in a Large Practice Group
Authors: Hedrick K , Fitzgerald T , Miller R 
Published: July 2014

Purpose:To standardize output constancy check procedures in a large medical physics practice group covering multiple sites, in order to identify and reduce small systematic errors caused by differences in equipment and the procedures of multiple physicists.Methods:A standardized machine output constancy check for both photons and electrons was instituted within the practice group in 2010. After conducting annual TG‐51 measurements in water and adjusting the linac to deliver 1.00 cGy/MU at Dmax, an acrylic phantom (comparable at all sites) and PTW farmer ion chamber are used to obtain monthly output constancy reference readings. From the collected charge reading, measurements of air pressure and temperature, and chamber Ndw and Pelec, a value we call the Kacrylic factor is determined, relating the chamber reading in acrylic to the dose in water with standard set‐up conditions. This procedure easily allows for multiple equipment combinations to be used at any site. The Kacrylic factors and output results from all sites and machines are logged monthly in a central database and used to monitor trends in calibration and output.Results:The practice group consists of 19 sites, currently with 34 Varian and 8 Elekta linacs (24 Varian and 5 Elekta linacs in 2010). Over the past three years, the standard deviation of Kacrylic factors measured on all machines decreased by 20% for photons and high energy electrons as systematic errors were found and reduced. Low energy electrons showed very little change in the distribution of Kacrylic values. Small errors in linac beam data were found by investigating outlier Kacrylic values.Conclusion:While the use of acrylic phantoms introduces an additional source of error through small differences in depth and effective depth, the new standardized procedure eliminates potential sources of error from using many different phantoms and results in more consistent output constancy measurements.
SU‐E‐T‐263: Point Dose Variation Using a Single Ir‐192 HDR Brachytherapy Plan for Two Treatments with a Single Tandem‐Ovoid Insertion for Cervical Cancer
Authors: Liang X , Morrill S , Hardee M , Han E , Penagaricano J , Zhang X , Vaneerat R 
Published: July 2014

Purpose:To evaluate the point dose variations between Ir‐192 HDR treatments on two consecutive days using a single tandem‐ovoid insertion without replanning in cervical cancer patients.Methods:This study includes eleven cervical cancer patients undergoing HDR brachytherapy with a prescribed dose of 28 Gy in 4 fractions. Each patient had two tandemovoid insertions one week apart. Each insertion was treated on consecutive days with rescanning and replanning prior to each treatment. To study the effect of no replanning for day 2 treatments, the day 1 plan dwell position and dwell time with decay were applied to the day 2 CT dataset. The point dose variations on the prescription point H (defined according to American Brachytherapy Society), and normal tissue doses at point B, bladder, rectum and vaginal mucosa (based on ICRU Report 38) were obtained.Results:Without replanning, the mean point H dose variation was 4.6 ± 10.7% on the left; 2.3 ± 2.9% on the right. The mean B point variation was 3.8 ± 4.9% on the left; 3.6 ± 4.7% on the right. The variation in the left vaginal mucosal point was 12.2 ± 10.7%; 9.5 ± 12.5% on the right; the bladder point 5.5 ± 7.4%; and the rectal point 7.9 ± 9.1%.Conclusion:Without replanning, there are variations both in the prescription point and the normal tissue point doses. The latter can vary as much as 10% or more. This is likely due to the steep dose gradient from brachytherapy compounded by shifts in the positions of the applicator in relationship to the patients anatomy. Imaging prior to each treatment and replanning ensure effective and safe brachytherapy are recommended.
SU‐E‐T‐267: Proton Pencil Beam Scanning for Mediastinal Lymphoma: 4‐Dimensional Feasibility Study
Authors: Zeng C , Plastaras J , Tochner Z , Hill‐Kayser C , Hahn S , Both S 
Published: July 2014

Purpose:To assess the feasibility of proton pencil beam scanning (PBS) for the treatment of mediastinal lymphoma.Methods:A group of 6 patients were planned using an anterior field with PBS. Spots with ∼5 mm σ were used for all patients, while large spots (∼10 mm σ) were employed for patients with motion perpendicular to the beam (≥5 mm). We considered volumetric repainting such that, in each fraction, the same field would be delivered twice. Four‐dimensional dose was calculated on initial and verification 4‐dimensional computed tomography (4D‐CT) scans (2—3) based on respiratory trace and beam delivery sequence. This was implemented by binning the spots into separate plans on each 4D‐CT phase respectively. Four starting phases were sampled for each painting and 4 energy switching times (0.5 s, 1 s, 3 s, and 5 s) were tested, resulting in 2560 dose distributions for the cohort. Plan robustness was measured for target and critical structures in terms of the percentage difference between delivered dose and planned dose.Results:For 5 of the 6 patients, the ITV (internal target volume) D<sub>98%</sub> was degraded by <3% (standard deviations ∼ 0.1%) when averaged over the whole course (up to 5% per fraction). Deviations of mean lung dose, heart maximum dose, and cord maximum dose were within 5% of prescribed dose. For one patient with motion perpendicular to the beam (up to 5 mm), the degradation of ITV D<sub>98%</sub> was 9% over the whole course (12% per fraction), which was mitigated to 1% (3% per fraction) by employing large spots and repainting. No significant difference in coverage was observed for different energy switching times.Conclusion:This feasibility study demonstrates that, for mediastinal lymphoma, the PBS plan robustness can be maintained during delivery when target motion is measured and volumetric repainting and/or large spots are employed.This work was supported by Ion Beam Application.
SU‐E‐T‐268: Proton Radiosurgery End‐To‐End Testing Using Lucy 3D QA Phantom
Authors: Choi D , Gordon I , Ghebremedhin A , Wroe A , Schulte R , Bush D , Slater J , Patyal B 
Published: July 2014

Purpose:To check the overall accuracy of proton radiosurgery treatment delivery using ready‐made circular collimator inserts and fixed thickness compensating boluses.Methods:Lucy 3D QA phantom (Standard Imaging Inc. WI, USA) inserted with GaFchromicTM film was irradiated with laterally scattered and longitudinally spread‐out 126.8 MeV proton beams. The tests followed every step in the proton radiosurgery treatment delivery process: CT scan (GE Lightspeed VCT), target contouring, treatment planning (Odyssey 5.0, Optivus, CA), portal calibration, target localization using robotic couch with image guidance and dose delivery at planned gantry angles. A 2 cm diameter collimator insert in a 4 cm diameter radiosurgery cone and a 1.2 cm thick compensating flat bolus were used for all beams. Film dosimetry (RIT114 v5.0, Radiological Imaging Technology, CO, USA) was used to evaluate the accuracy of target localization and relative dose distributions compared to those calculated by the treatment planning system.Results:The localization accuracy was estimated by analyzing the GaFchromic films irradiated at gantry 0, 90 and 270 degrees. We observed 0.5 mm shift in lateral direction (patient left), ±0.9 mm shift in AP direction and ±1.0 mm shift in vertical direction (gantry dependent). The isodose overlays showed good agreement (<2mm, 50% isodose lines) between measured and calculated doses.Conclusion:Localization accuracy depends on gantry sag, CT resolution and distortion, DRRs from treatment planning computer, localization accuracy of image guidance system, fabrication of ready‐made aperture and cone housing. The total deviation from the isocenter was 1.4 mm. Dose distribution uncertainty comes from distal end error due to bolus and CT density, in addition to localization error. The planned dose distribution was well matched (>90%) to the measured values 2%/2mm criteria. Our test showed the robustness of our proton radiosurgery treatment delivery system using ready‐made collimator inserts and fixed thickness compensating boluses.
SU‐E‐T‐272: Radiation Damage Comparison Between Intensity Modulated Radiotherapy and Field‐In‐Field Technique in Breast Cancer Treatments
Authors: Ai H , Zhang H 
Published: July 2014

Purpose:To compare normal tissue complications between IMRT and FIF treatment in breast cancer.Methods:16 patients treated with IMRT plan and 20 patients treated with FIF plan were evaluated in this study. Both kinds of plans were generated using Eclipse treatment planning system by dosimetrist following clinical radiotherapy treatment guidelines. The plans were reviewed and approved by radiation oncologist. The average survival fraction (SF) for three different normal tissue cells of each concerned structure can be calculated from differential dose volume histogram (DVH) using linear quadratic model. The three types of normal tissues include radiosensitive, moderately radiosensitive and radio‐resistant that represents 70%, 50% and 30% survival fractions, respectively, for a 2‐Gy open field. Equivalent uniform doses (EUD) for corresponding normal tissues of each structure were calculated.Results:The EUDs of the lungs, heart, healthy breast and spinal cord with both IMRT and FIF treatments were calculated. Considering the average value of all IMRT plans, the lung of treated side absorbed 16.0% of dosage prescribed to the tumor if the radiosensitivity of the lung is similar to the radiosensitive cell line. For moderately radiosensitive and radio‐resistant lung tissue, the average EUDs can be 18.9% and 22.4% of prescription. In contrast, patients treated with FIF plans were delivered 6.0%, 7.5% and 10.3% of prescribed dose for radiosensitive, moderately radiosensitive and radio‐resistant lung tissue, respectively. Comparing heart EUDs between IMRT and FIF plans, average absorbed doses in IMRT treatment were 7.7%, 8.7% and 9.7% of prescription for three types of heart normal tissue cell lines while FIF treatments delivered only 1.3%, 1.5% and 1.6% of prescription dose. For the other organs, the results were similar.Conclusion:The results indicated that breast cancer treatment using IMRT technique had more normal tissue damage than FIF treatment. FIF demonstrated more effective normal tissue dose reduction in breast cancer treatment.
SU‐E‐T‐273: Radiation Shielding for a Fixed Horizontal‐Beam Linac in a Shipping Container and a Conventional Treatment Vault
Authors: Hsieh M , Balter P , Beadle B , Chi P , Stingo F , Court L 
Published: July 2014

Purpose:A fixed horizontal‐beam linac, where the patient is treated in a seated position, could lower the overall costs of the treatment unit and room shielding substantially. This design also allows the treatment room and control area to be contained within a reduced space, such as a shipping container. The main application is the introduction of low‐cost, high‐quality radiation therapy to low‐ and middle‐income regions. Here we consider shielding for upright treatments with a fixed‐6MV‐beam linac in a shipping container and a conventional treatment vault.Methods:Shielding calculations were done for two treatment room layouts using calculation methods in NCRP Report 151: (1) a shipping container (6m × 2.4m with the remaining space occupied by the console area), and (2) the treatment vault in NCRP 151 (7.8m by 5.4m by 3.4m). The shipping container has a fixed gantry that points in one direction at all times. For the treatment vault, various beam directions were evaluated.Results:The shipping container requires a primary barrier of 168cm concrete (4.5 TVL), surrounded by a secondary barrier of 3.6 TVL. The other walls require between 2.8–3.3 TVL. Multiple shielding calculations were done along the side wall. The results show that patient scatter increases in the forward direction and decreases dramatically in the backward direction. Leakage scatter also varies along the wall, depending largely on the distance between the gantry and the wall. For the treatment room, fixed‐beam requires a slightly thicker primary barrier than the conventional linac (0.6 TVL), although this barrier is only needed in the center of one wall. The secondary barrier is different only by 0–0.2 TVL.Conclusion:This work shows that (1) the shipping container option is achievable, using indigenous materials for shielding and (2) upright treatments can be performed in a conventional treatment room with minimal additional shielding.Varian Medical Systems
SU‐E‐T‐276: Radiochromic Film Dosimetry: Solving the Lateral Response Puzzle
Authors: Lewis D , Chan M 
Published: July 2014

Purpose:A known factor affecting the accuracy of radiochromic film dosimetry is the lateral response artifact induced by off‐center placement of film on flatbed scanners. This work reports a practical solution to eliminate such artifacts for IMRT dose QA.Methods:EBT3 film calibration strips (3.5×32cm2) were exposed at a depth of 5cm on a Varian Trilogy to a 40×40cm2 open field at six doses between 120 and 900cGy using 6MV photons. A sheet of film was similarly exposed with a large IMRT field. Together with a strip of unexposed film from the same lot the films were digitized at different lateral positions on an Epson 10000XL scanner. The calibration strips covered nearly the full width of the scanner window. Calibration and response data were used to generate the IMRT dose map using multi‐channel dosimetry. The scanner response was determined as a function of lateral position of the scanned film. The response at any lateral position L is related to the response at the center, C, of the scanner by Response(C,D) = aL+bL*Response(L,D) where D is dose and the coefficients aL and bL are constant for each lateral location. The coefficients aL and bL were determined by measuring films exposed to different doses at the center of the scanner and various lateral positions.Results:Applying this relationship to raw calibration responses, the values at any lateral position can be corrected to an equivalent response as if that film was located centrally. Our study found that calibration curves at the different lateral positions are correlated by a simple two‐point re‐scaling and thereby the correction could be made.Conclusion:The work reported elaborates on the process and demonstrates improvements in radiochromic film dosimetry using this simple procedure to eliminate the lateral response artifact. Acknowledgements: Supported in part by a grant from Ashland Inc.D Lewis is an employee of Ashland Inc., the manufacturer of radiochromic film; M Chan is supported in part by a grant from Ashland Inc.
SU‐E‐T‐279: Realization of Three‐Dimensional Conformal Dose Planning in Prostate Brachytherapy
Authors: Li Z , Jiang S , Yang Z , Bai H , Zhang X 
Published: July 2014

Purpose:Successful clinical treatment in prostate brachytherapy is largely dependent on the effectiveness of pre‐surgery dose planning. Conventional dose planning method could hardly arrive at a satisfy result. In this abstract, a three‐dimensional conformal localized dose planning method is put forward to ensure the accuracy and effectiveness of pre‐implantation dose planning.Methods:Using Monte Carlo method, the pre‐calculated 3‐D dose map for single source is obtained. As for multiple seeds dose distribution, the maps are combined linearly to acquire the 3‐D distribution. The 3‐D dose distribution is exhibited in the form of isodose surface together with reconstructed 3‐D organs group real‐timely. Then it is possible to observe the dose exposure to target volume and normal tissues intuitively, thus achieving maximum dose irradiation to treatment target and minimum healthy tissues damage. In addition, the exfoliation display of different isodose surfaces can be realized applying multi‐values contour extraction algorithm based on voxels. The needles could be displayed in the system by tracking the position of the implanted seeds in real time to conduct block research in optimizing insertion trajectory.Results:This study extends dose planning from two‐dimensional to three‐dimensional, realizing the three‐dimensional conformal irradiation, which could eliminate the limitations of 2‐D images and two‐dimensional dose planning. A software platform is developed using VC++ and Visualization Toolkit (VTK) to perform dose planning. The 3‐D model reconstruction time is within three seconds (on a Intel Core i5 PC). Block research could be conducted to avoid inaccurate insertion into sensitive organs or internal obstructions. Experiments on eight prostate cancer cases prove that this study could make the dose planning results more reasonable.Conclusion:The three‐dimensional conformal dose planning method could improve the rationality of dose planning by safely reducing the large target margin and avoiding dose dead zones for prostate cancer treatment.1) National Natural Science Foundation of People's Republic of China (No. 51175373); 2) New Century Educational Talents Plan of Chinese Education Ministry (NCET‐10‐0625); 3) Scientific and Technological Major Project, Tianjin (No. 12ZCDZSY10600).
SU‐E‐T‐280: Reconstructed Rectal Wall Dose Map‐Based Verification of Rectal Dose Sparing Effect According to Rectum Definition Methods and Dose Perturbation by Air Cavity in Endo‐Rectal Balloon
Authors: Park J , Park H , Lee J , Kang S , Lee M , Lee B , Suh T 
Published: July 2014

Purpose:Dosimetric effect and discrepancy according to the rectum definition methods and dose perturbation by air cavity in an endo‐rectal balloon (ERB) were verified using rectal‐wall (Rwall) dose maps considering systematic errors in dose optimization and calculation accuracy in intensity‐modulated radiation treatment (IMRT) for prostate cancer patients.Methods:When the inflated ERB having average diameter of 4.5 cm and air volume of 100 cc is used for patient, Rwall doses were predicted by pencil‐beam convolution (PBC), anisotropic analytic algorithm (AAA), and AcurosXB (AXB) with material assignment function. The errors of dose optimization and calculation by separating air cavity from the whole rectum (Rwhole) were verified with measured rectal doses. The Rwall doses affected by the dose perturbation of air cavity were evaluated using a featured rectal phantom allowing insert of rolled‐up gafchromic films and glass rod detectors placed along the rectum perimeter. Inner and outer Rwall doses were verified with reconstructed predicted rectal wall dose maps. Dose errors and extent at dose levels were evaluated with estimated rectal toxicity.Results:While AXB showed insignificant difference of target dose coverage, Rwall doses underestimated by up to 20% in dose optimization for the Rwhole than Rwall at all dose range except for the maximum dose. As dose optimization for Rwall was applied, the Rwall doses presented dose error less than 3% between dose calculation algorithm except for overestimation of maximum rectal dose up to 5% in PBC. Dose optimization for Rwhole caused dose difference of Rwall especially at intermediate doses.Conclusion:Dose optimization for Rwall could be suggested for more accurate prediction of rectal wall dose prediction and dose perturbation effect by air cavity in IMRT for prostate cancer.This research was supported by the Leading Foreign Research Institute Recruitment Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (MSIP) (Grant No. 200900420)
SU‐E‐T‐281: Reduction of Treatment Times in CyberKnife Prostate SBRT Using a Water Filled Rectal Balloon
Authors: Desai P , Caroprese B , McKellar H 
Published: July 2014

Purpose:To illustrate 25% reduction in CyberKnife prostate SBRT treatment times using a water filled rectal balloon.Methods:We perform prostate SBRT using a 3800cGy in 4 fraction regimen prescribed between 51% 59% iso‐dose lines to 95% of PTV using a CyberKnife System. The resultant heterogeneous dosimetry is analogous to HDR dosimetry. Our patients are treated in a feet first supine position to decrease treatment couch sag and also to position the prostate anatomy closer to the robot. CT imaging is performed with a Radiadyne Immobiloc rectal balloon filled with 45‐50cc water placed firmly inside the patient's rectum. A treatment plan is developed from this CT study using Multiplan. The patient is treated every other day for 4 days using the rectal balloon for each fraction. Gold fiducials previously implanted inside the prostate are used for tracking by the CyberKnife system.Results:Critical structures comprise the usual GU anatomy of bladder, rectum, urethra, femoral‐heads along with emphasis on doses to anterior rectal wall and rectal mucosa. The water filled rectal balloon localizes the rectum, which enables the physician to accurately contour both anterior rectal wall, and rectal mucosa. The balloon also has a gas release valve enabling better patient comfort. Rectum localization enables the CyberKnife system to make fewer corrections resulting in fewer treatment interruptions and time lost to re‐adjustment for rectal motion, bowel filling and gas creation. Effective treatment times are reduced by 25% to approximately 45 minutes. Adoption of the balloon has required minimal change to our planning strategy and plan evaluation process.Conclusion:Patient follow‐up comparisons show no difference in effectiveness of treatment with and without balloons We conclude that rectal balloons enhance patient comfort and decrease effective treatment times.
SU‐E‐T‐283: Research of the Irradiation Damage to the Skin Cell by the Contaminative Electron in External Radiotherapy
Authors: Xiong Z , Lin H , Jing J , Cai J , Dai Y 
Published: July 2014

Purpose:To investigate the micro‐damage mechanism of the contaminative electron to the skin cell in external radiotherapy, the cell damage yield was simulated.Methods:The physical interaction and the energy deposited events of contaminative electrons in the cell DNA were modeled based on Geant4‐DNA low energy physical model. The densitybased cluster mining algorithm was used to analyze the micro‐damage yield and obtain its detailed compositive information. By taking the irradiation sensitive parameter and the clinical feature dose threshold of the skin cell into consideration, the damage features of the low energy contaminative electron to the skin cell were studied. The DSB and SSB yield and ratio, the cluster size and the root mean square radius, the cell SF and the lethal coefficient ε of the complex cDSB were researched.Results:For some very low energy electrons such as 20keV and 100keV, the cluster size can be more than 5 SSBs. The irradiation protection will be more crucial for the later response and the high α tissue. The lethal coefficient ε of the complex cDSB will increase with the incident electron number and the accumulative dose increasing for the dose square term in LQ model. However, the ε increment will increase 3%∼15% when the incident electron increases up to 100000.Conclusion:The simulation of the direct physical damage of the cell can be adjusted by a probability parameter to offset the simulation of the indirect biochemical damage. Thus the micro‐damage mechanism of the contaminative electron to the skin cell can be detected at a certain extent by Monte Carlo physical simulation. This damage model of the low energy electron to DNA and these simulated results could be used to evaluate the damage effect of the low energy contaminative electron to the skin cells in the external radiotherapy.Strategic Priority Research Program of the Chinese Academy of Sciences (XDA03040000), Fundamental Research Funds for the Central Universities (2012HGXJ0057,2013HGXJ0193), Seed Foundation of Hefei University of Technology (2012HGZY0007) and Hefei University of Technology undergraduate innovative experiment project(2012CXCY431)