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At least 1,765 records · Page 98
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

SU-E-T-49: A Multi-Institutional Study of Independent Dose Verification for IMRT

Purpose: AAPM TG114 does not cover the independent verification for IMRT. We conducted a study of independent dose verification for IMRT in seven institutes to show the feasibility. Methods: 384 IMRT plans in the sites of prostate and head and neck (HN) were collected from the institutes, where the planning was performed using Eclipse and Pinnacle3 with the two techniques of step and shoot (S&S) and sliding window (SW). All of the institutes used a same independent dose verification software program (Simple MU Analysis: SMU, Triangle Product, Ishikawa, JP), which is Clarkson-based and CT images were used to compute radiological path length. An ion-chamber measurement in a water-equivalent slab phantom was performed to compare the doses computed using the TPS and an independent dose verification program. Additionally, the agreement in dose computed in patient CT images between using the TPS and using the SMU was assessed. The dose of the composite beams in the plan was evaluated. Results: The agreement between the measurement and the SMU were −2.3±1.9 % and −5.6±3.6 % for prostate and HN sites, respectively. The agreement between the TPSs and the SMU were −2.1±1.9 % and −3.0±3.7 for prostate and HN sites, respectively. There was a negative systematic difference with similar standard deviation and the difference was larger in the HN site. The S&S technique showed a statistically significant difference between the SW. Because the Clarkson-based method in the independent program underestimated (cannot consider) the dose under the MLC. Conclusion: The accuracy would be improved when the Clarkson-based algorithm should be modified for IMRT and the tolerance level would be within 5%.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-57: A Novel Method to Improve Dose Heterogeneity of Target and Organs at Risk Sparing in the Intensity-Modulated Radiotherapy for Stage III Lung Cancer

Purpose: Intensity-modulated radiotherapy (IMRT) treatment for lung cancer is difficult due to the heterogeneous dose distribution and excessive dose to the organs at risk (OARs). We introduce a simple method based on the base dose function (BDF) in Eclipse treatment planning system to overcome the difficulties. Methods: Thirteen patients suffered from stage III non-small cell lung cancer (NSCLC) were enrolled in the study. Three kinds of approaches were applied to obtain clinically acceptable treatment plans: 1) conventionally optimizing method with hot and cold spots re-optimization (CO); 2) target-divided optimizing method (TDO) in which the optimization objective in the lung density of planning target volume (PTV) was set to 2 to 4 Gy higher than in the soft tissue density; 3) base dose function (BDF) in which the treatment plan was produced based on the original plan for re-optimization. CO, TDO and BDF methods were then compared in terms of conformity index (CI), homogeneity index (HI), OARs sparing and monitor units (MUs). Additionally, delta4, portal dosimetry and IMSure were used to measure the dose delivering accuracy. Results: The BDF technique provided more superior CI and HI than the other two methods. Moreover, the new method also reduced the lung, esophagus, heart and spinal cord dose. However, the BDF plans needed extra 15% and 10% MUs than the CO and TDO methods. Dose verification results demonstrated good and comparable γ pass rates among the three methods. Conclusion: The proposed BDF method greatly improves the dose homogeneity and OARs sparing in the IMRT treatment for lung cancer.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-61: A Practical Process for Fabricating Passive Scatter Proton Beam Modulation Compensation Filters Using 3D Printing

Purpose: The purpose of this project was to devise a practical fabrication process for passive scatter proton beam compensation filters (CF) that is competitive in time, cost and effort using 3D printing. Methods: DICOM compensator filter files for a proton beam were generated by our Eclipse (Varian, Inc.) treatment planning system. The compensator thickness specifications were extracted with in-house software written in Matlab (MathWorks, Inc.) code and written to a text file which could be read by the Rhinoceros 5, computer-aided design (CAD) package (Robert McNeel and Associates), which subsequently generated a smoothed model in a STereoLithographic also known as a Standard Tesselation Language file (STL). The model in the STL file was subsequently refined using Netfabb software and then converted to printing instructions using Cura. version 15.02.1. for our 3D printer. The Airwolf3D, model HD2x, fused filament fabrication (FFF) 3D printer (Airwolf3D.com) was used for our fabrication system with a print speed of 150mm per second. It can print in over 22 different plastic filament materials in a build volume of 11” x 8” x 12”. We choose ABS plastic to print the 3D model of the imprint for our CFs. Results: Prints of the CF could be performed at a print speed of 70mm per second. The time to print the 3D topology for the CF for the 14 cm diameter snout of our Mevion 250 proton accelerator was less than 3 hours. The printed model is intended to subsequently be used as a mold to imprint a molten wax cylindrical to form the compensation after cooling. The whole process should be performed for a typical 3 beam treatment plan within a day. Conclusion: Use of 3D printing is practical and can be used to print a 3D model of a CF within a few hours.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2015

SU-E-T-78: A Study of Dose Falloff Gradient in RapidArc Planning of Lung SBRT

Purpose: Rapid dose falloff beyond PTV is an important criterion for normal tissue sparing in SBRT. RTOG protocols use D2cm and R50% for plan quality evaluation. This study is aimed at analyzing the dose falloff gradient beyond the PTV extending into normal tissue structures and to ascertain the impact of PTV geometry and location on the dose falloff gradient in RapidArc planning of lung SBRT Methods: In this retrospective study, we analyzed 39 clinical RapidArc lung SBRT treatment plans that met RTOG-0915 criteria. Planning was done on Eclipse 8.9 for delivery on either Novalis NTx or TrueBeam STx equipped with HD MLCs. PTV volumes ranged between 5.3 and 113 cc (2.2 to 6 cm sphere equivalent diameter respectively) and their geographic locations were distributed in both lungs. 6X, 6X-FFF, 10X, and 10X-FFF energies were used for planning. All of these SBRT plans were planned using either 2 or 3 full or hemi arcs, with moderate couch kicks. Dose falloff gradients were obtained by generating 7 concentric 5 mm rings beyond PTV surface. Mean dose in each ring is used to evaluate percentage dose falloff gradient as a function of distance from the PTV surface. Results: The mean percentage dose falloff beyond PTV surface in all plans followed an exponential decay and the data was modeled with double exponential decay fit. Photon energy selection in the plan had a minimal impact on the mean percentage dose fall off beyond PTV surface. Conclusion: Dose falloff beyond PTV surface as a function of distance can be ascertained by the use of the double exponential decay fit coefficients in RapidArc planning of lung SBRT. This will help also in plan quality evaluation in addition to D2cm and R50% defined by RTOG.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-81: A Study On Correlation Between Gamma Analysis for Midline and Lateralized Tumors Using VMAT

Purpose: To evaluate the fluence for the midline and lateralized tumors for VMAT technique using 2D seven29 detector array combined with the Octavius phantom. Methods: 60 cases that are already being treated with volumetric modulated arc therapy (VMAT) have selected for this study. This includes tumors situated at the medial and lateral. Medial refers to the tumor situated at the midline of the body and lateral means toward the side or away from the midline of the body. Verification plans were created for each treatment plan in Varian Eclipse treatment planning system (version10, Varian medical systems, Palo Alto,CA) with the 2D Seven29 detector array and the Octavius phantom(PTW, Freiburg, Germany). Measurements were performed on a Varian Clinac 2100 iX, linear accelerator equipped with a millennium 120 leaf collimator. Analysis was done by comparing the fluence measured for the tumors situated on the midline and tumors situated laterally. Results: Fluence measured for all the delivered plans were analyzed using Verisoft software (PTW, Freiburg, Germany). The gamma pass percentage for midline tumors were found to be higher compared with the lateralized ones. The standard deviation between gamma values for midline and lateralized tumors is 2.18 and 3.5 respectively. Also the standard deviation between the point doses for midline and lateralized tumors is 0.38 and 0.29 respectively. The average gamma passing rate for midline tumors is 96.55% and for lateralized tumors are 94.94% for 3%DD and 3mm DTA criteria. From the T test, it was found that there is no significant difference between the gamma pass percentage between midline and lateralized tumors with p value of 0.28. Conclusion: There is no particular correlation found in the gamma pass criteria for midline and lateralized tumors.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-82: A Study On Enhanced Dynamic Wedge (EDW) Dosimetry Using 2D Seven29 Ion Chamber Array Detector

Purpose: To study the dosimetric properties of Enhanced Dynamic Wedge (EDW) using PTW Seven29 ion chamber array Methods: PTW Seven29 ion chamber array and Solid Water phantoms for different depths were used for the study. The study was carried out in Varian Clinac ix with photon energies, 6MV & 15MV. Primarily the solid water phantoms with the 2D array were scanned using a CT scanner (GE Optima 580) at different depths. These scanned images were used for EDW planning in an Eclipse treatment planning system (version 10). Planning was done for different wedge angles and for different depths for 6MV & 15MV. A dose of 100 CGy was delivered in each cases. For each delivery, calculated the Monitoring Unit (MU) required. Same set-up was created before delivering the plans in Varian Clinac-ix. For each clinically relevant depth and for different wedge angles, the same MU was delivered as calculated. Different wedged dose distributions where reconstructed from the measured 2D array data using the in-house developed excel program. Results: It is observed that the shoulder like region in the profile which reduces as depth increases. For the same depth and energy, the percentage difference between planned and measured dose is lesser than 3%. For smaller wedge angles, the percentage difference is found to be greater than 3% for the largest wedge angle. Standard deviation between measured doses at shoulder region for planned and measured profiles is 0.08 and 0.02 respectively. Standard deviations between planned and measured wedge factors for different depths (2.5cm, 5cm, 10cm, and 15cm) are (0.0021, 0.0007, 0.0050, 0.0001) for 6MV and (0.0024, 0.0191, 0.0013, 0.0005) for 15MV respectively. Conclusion: The 2D Seven29 ion chamber array is a good tool for the Enhanced Dynamic Wedge (EDW) dosimetry.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-83: A Study On Evaluating the Directional Dependency of 2D Seven 29 Ion Chamber Array Clinically with Different IMRT Plans

Purpose: To evaluate the directional dependency of 2D seven 29 ion chamber array clinically with different IMRT plans. Methods: 25 patients already treated with IMRT plans were selected for the study. Verification plans were created for each treatment plan in eclipse 10 treatment planning system using the AAA algorithm with the 2D array and the Octavius CT phantom. Verification plans were done 2 times for a single patient. First plan with real IMRT (plan-related approach) and second plan with zero degree gantry angle (field-related approach). Measurements were performed on a Varian Clinac-iX, linear accelerator equipped with a millennium 120 multileaf collimator. Fluence was measured for all the delivered plans and analyzed using the verisoft software. Comparison was done by selecting the fluence delivered in static gantry (zero degree gantry) versus IMRT with real gantry angles. Results: The gamma pass percentage is greater than 97 % for all IMRT delivered with zero gantry angle and between 95%–98% for real gantry angles. Dose difference between the TPS calculated and measured for IMRT delivered with zero gantry angle was found to be between (0.03 to 0.06Gy) and with real gantry angles between (0.02 to 0.05Gy). There is a significant difference between the gamma analysis between the zero degree and true angle with a significance of 0.002. Standard deviation of gamma pass percentage between the IMRT plans with zero gantry angle was 0.68 and for IMRT with true gantry angle was found to be 0.74. Conclusion: The gamma analysis for IMRT with zero degree gantry angles shows higher pass percentage than IMRT delivered with true gantry angles. Verification plans delivered with true gantry angles lower the verification accuracy when 2D array is used for measurement.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-91: Accuracy of Dose Calculation Algorithms for Patients Undergoing Stereotactic Ablative Radiotherapy

Purpose: The purpose of this study was to investigate and quantify the variation in dose distributions in small field lung cancer radiotherapy using seven different dose calculation algorithms. Methods: The study was performed in 21 lung cancer patients who underwent Stereotactic Ablative Body Radiotherapy (SABR). Two different methods (i) Same dose coverage to the target volume (named as same dose method) (ii) Same monitor units in all algorithms (named as same monitor units) were used for studying the performance of seven different dose calculation algorithms in XiO and Eclipse treatment planning systems. The seven dose calculation algorithms include Superposition, Fast superposition, Fast Fourier Transform ( FFT) Convolution, Clarkson, Anisotropic Analytic Algorithm (AAA), Acurous XB and pencil beam (PB) algorithms. Prior to this, a phantom study was performed to assess the accuracy of these algorithms. Superposition algorithm was used as a reference algorithm in this study. The treatment plans were compared using different dosimetric parameters including conformity, heterogeneity and dose fall off index. In addition to this, the dose to critical structures like lungs, heart, oesophagus and spinal cord were also studied. Statistical analysis was performed using Prism software. Results: The mean±stdev with conformity index for Superposition, Fast superposition, Clarkson and FFT convolution algorithms were 1.29±0.13, 1.31±0.16, 2.2±0.7 and 2.17±0.59 respectively whereas for AAA, pencil beam and Acurous XB were 1.4±0.27, 1.66±0.27 and 1.35±0.24 respectively. Conclusion: Our study showed significant variations among the seven different algorithms. Superposition and AcurosXB algorithms showed similar values for most of the dosimetric parameters. Clarkson, FFT convolution and pencil beam algorithms showed large differences as compared to superposition algorithms. Based on our study, we recommend Superposition and AcurosXB algorithms as the first choice of algorithms in lung cancer radiotherapy involving small fields. However, further investigation by Monte Carlo simulation is required to confirm our results.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-97: An Analysis of Knowledge Based Planning for Stereotactic Body Radiation Therapy of the Spine

Purpose: Creating high quality SBRT treatment plans for the spine is often tedious and time consuming. In addition, the quality of treatment plans can vary greatly between treatment facilities due to inconsistencies in planning methods. This study investigates the performance of knowledge-based planning (KBP) for spine SBRT. Methods: Treatment plans were created for 28 spine SBRT patients. Each case was planned to meet strict dose objectives and guidelines. After physician and physicist approval, the plans were added to a custom model in a KBP system (RapidPlan, Varian Eclipse v13.5). The model was then trained to be able to predict estimated DVHs and provide starting objective functions for future patients based on both generated and manual objectives. To validate the model, ten additional spine SBRT cases were planned manually as well as using the model objectives. Plans were compared based on planning time and quality (ability to meet the plan objectives, including dose metrics and conformity). Results: The average dose to the spinal cord and the cord PRV differed between the validation and control plans by <0.25% demonstrating iso-toxicity. Six out of 10 validation plans met all dose objectives without the need for modifications, and overall, target dose coverage was increased by about 4.8%. If the validation plans did not meet the dose requirements initially, only 1–2 iterations of modifying the planning parameters were required before an acceptable plan was achieved. While manually created plans usually required 30 minutes to 3 hours to create, KBP can be used to create similar quality plans in 15–20 minutes. Conclusion: KBP for spinal tumors has shown to greatly decrease the amount of time required to achieve high quality treatment plans with minimal human intervention and could feasibly be used to standardize plan quality between institutions. Supported by Varian Medical Systems.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-108: An Investigation of Cerenkov Light Production in the Exradin W1 Scintillator Under Various Measurement Conditions

Purpose: To investigate the effects of depth, fiber-optic cable bends, and incident radiation angle on Cerenkov production in the Standard Imaging Exradin W1. Methods: Measurements were completed using a Varian Clinac 21EX linear accelerator with an Exradin W1 scintillator as well as a cable-only scintillator (no scintillation material) to isolate the Cerenkov signal. The effects of cable bend radius and location were investigated by bending the fiber-optic cable into a circle with radii ranging from 1.0 to 10.8 cm and positioning the center of the coil at distances ranging from 10.0 to 175.0 cm from the photodiode. The effects of depth and incident radiation angle were investigated by performing measurements in water at depths ranging from 1.0 cm to 25.0 cm and angles ranging from 0° to 80°. Eclipse treatment-planning software was utilized to ensure a consistent dose was delivered to the W1 regardless of depth or angle. Results: Measured signal in both channels of the cable-only scintillator decreased as the bend radius decreased and as the distance between the bend and photodiode increased. A fiber bend of 1.0 cm radius produced a 17.1% decrease in the green channel response in the cable-only scintillator. The effect of depth was less severe; a maximum increase of 6.6% in the green channel response was observed at a depth of 25.0 cm in the W1. In the angular dependence investigation, the signal in both channels of the W1 peaked at an angle of 40°; which is in agreement with the nominal Cerenkov emission angle of 45°. Conclusion: The green channel response in the W1 (mainly Cerenkov signal) varied with depth, fiber-optic cable bends, and incident radiation angle. Fully characterizing Cerenkov production is essential to ensure it is properly accounted for in scintillator measurements. Research funding and materials received by Standard Imaging, Inc. (Middleton WI)

07 ISOTOPE AND RADIATION SOURCES↗
DOE OSTI2015

SU-E-T-115: Analysis of Patient Specific QA for VMAT by Disease Site and Planning-Delivery System Using the ScandiDos Delta4 Phantom

Purpose: To evaluate patient specific quality assurance (PSQA) for the delivery of volumetric modulated arc therapy (VMAT) by disease site. To compare planning-delivery system (PDS) PSQA pass rates in a dual vendor institution. Methods: PSQA is performed for VMAT plans using a ScandiDos Delta4 phantom. Verification plans are calculated using Varian Eclipse and Elekta Monaco treatment planning systems (TPS) for patients treated using Varian Truebeam and Elekta linear accelerators respectively. Individual arcs are delivered to the Delta4 phantoms and assessed using the gamma index pass criterion(3% Dose Deviation(DD%), 3mm Distance to Agreement(DTA),10% dose threshold and 90% gamma index). Results: A total of 287 VMAT plans and 680 arcs were analyzed. The passing rates for VMAT QA plans were 95% and 98% for head/neck and pelvis/prostate plans respectively, and 100% for chest/abdomen, spine, lung Stereotactic Body Radiotherapy (SBRT) and Stereotactic Radiosurgery(SRS) plans. Average gamma indices were: (99 ± 2) % for pelvis/prostate, chest/abdomen and lung SBRT plans, (97 ± 4) % for head and neck plans and (98 ± 3) % for spine plans. The average DD% and DTA pass rates ranged from 82% to 90% and 98% to 99% respectively for plans in different disease sites. Paired t-test analysis (two tails) indicated no significant differences in the gamma indices between plans delivered using different PDS; the P values were: 0.08, 0.45, and 0.94 for lung SBRT, head/neck and pelvis/prostate plans respectively. The statistical power for comparing PDS in different disease sites with an alpha of 0.05 is 1. Conclusion: The Gamma indices based on 3% DD%, 3 mm DTA and 10% dose threshold for the VMAT QA plans in all disease sites were well above 90%, suggesting the possibility of using a more stringent PSQA criterion. No significant differences were observed in the QA of VMAT plans delivered using different PDS.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-142: Automatic Linac Log File: Analysis and Reporting

Purpose: End to end QA for IMRT/VMAT is time consuming. Automated linac log file analysis and recalculation of daily recorded fluence, and hence dose, distribution bring this closer. Methods: Matlab (R2014b, Mathworks) software was written to read in and analyse IMRT/VMAT trajectory log files (TrueBeam 1.5, Varian Medical Systems) overnight, and are archived on a backed-up network drive (figure). A summary report (PDF) is sent by email to the duty linac physicist. A structured summary report (PDF) for each patient is automatically updated for embedding into the R&V system (Mosaiq 2.5, Elekta AG). The report contains cross-referenced hyperlinks to ease navigation between treatment fractions. Gamma analysis can be performed on planned (DICOM RTPlan) and treated (trajectory log) fluence distributions. Trajectory log files can be converted into RTPlan files for dose distribution calculation (Eclipse, AAA10.0.28, VMS). Results: All leaf positions are within +/−0.10mm: 57% within +/−0.01mm; 89% within 0.05mm. Mean leaf position deviation is 0.02mm. Gantry angle variations lie in the range −0.1 to 0.3 degrees, mean 0.04 degrees. Fluence verification shows excellent agreement between planned and treated fluence. Agreement between planned and treated dose distribution, the derived from log files, is very good. Conclusion: Automated log file analysis is a valuable tool for the busy physicist, enabling potential treated fluence distribution errors to be quickly identified. In the near future we will correlate trajectory log analysis with routine IMRT/VMAT QA analysis. This has the potential to reduce, but not eliminate, the QA workload.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-149: Brachytherapy Patient Specific Quality Assurance for a HDR Vaginal Cylinder Case

Purpose: Commonly Ir-192 HDR treatment planning system commissioning is only based on a single absolute measurement of source activity supplemented by tabulated parameters for multiple factors without independent verification that the planned distribution corresponds to the actual delivered dose. The purpose on this work is to present a methodology using Gafchromic film with a statistically valid calibration curve that can be used to validate clinical HDR vaginal cylinder cases by comparing the calculated plan dose distribution in a plane with the corresponding measured planar dose. Methods: A vaginal cylinder plan was created with Oncentra treatment planning system. The 3D dose matrix was exported to a Varian Eclipse work station for convenient extraction of a 2D coronal dose plane corresponding to the film position. The plan was delivered with a sheet of Gafchromic EBT3 film positioned 1mm from the catheter using an Ir-192 Nucletron HDR source. The film was then digitized with an Epson 10000 XL color scanner. Film analysis is performed with MatLab imaging toolbox. A density to dose calibration curve was created using TG43 formalism for a single dwell position exposure at over 100 points for statistical accuracy. The plan and measured film dose planes were registered using a known dwell position relative to four film marks. The plan delivered 500 cGy to points 2 cm from the sources. Results: The distance to agreement of the 500 cGy isodose between the plan and film measurement laterally was 0.5 mm but can be as much as 1.5 mm superior and inferior. The difference between the computed plan dose and film measurement was calculated per pixel. The greatest errors up to 50 cGy are near the apex. Conclusion: The methodology presented will be useful to implement more comprehensive quality assurance to verify patient-specific dose distributions.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-166: Characterization of Efficiency and Plan Quality for the FFF Beams On Various Anatomical Sites

Purpose: To characterize efficiency and plan quality for the FFF beams for various sites. Methods: 5 brain, Head and Neck, prostate, lung and liver cancer patients IMRT plans (25 total) were generated on either Prowess 4.6 or Eclipse 13.5 using the same dose constraints for each treatment site. Step and shoot with static gantry IMRT was used for treatment delivery. PTV coverage, critical structure doses, MUs, number of segments and beam on times were compared. Results: The average PTV size was 29.0, 34.9, 89.2, 257.6, 289.2 cm3 for liver, lung, prostate, head and neck and brain respectively.All plans were normalized such that 95% of the PTV volume would receive at least 95% of prescribed dose. All doses to the critical structures for both the FFF and flat beam met the targeted dose constraints.For plans with field sizes < 10 cm, the number of segments and MUs required to achieve the same plan quality were similar. For these small field sizes with large dose per fraction, an increase in efficiency up to 58.8% is seen.Plans with field sizes > 10 cm, required 10% – 20% more segments and MUs for the FFF beam to achieve the same plan quality as the flat beam. Despite this, for fraction sizes less than 2.5 Gy the FFF beam is still approximately 13.9% more efficient in terms of delivery time. Conclusion: For the various treatment sites studied here, plans generated with the FFF beam were dosimetrically similar to those generated with a flattened beam. Despite the greater number of MUs and segments required to achieve the same plan quality as the flat beam for some plans, the FFF beam is still more efficient compared to the flat beam.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-211: Comparison of Seven New TrueBeam Linacs with Enhanced Beam Data Conformance Using a Beam Comparison Software Tool

Purpose: To develop an independent software tool to assist in commissioning linacs with enhanced beam conformance, as well as perform ongoing QA for dosimetrically equivalent linacs. Methods: Linac manufacturers offer enhanced beam conformance as an option to allow for clinics to complete commissioning efficiently, as well as implement dosimetrically equivalent linacs. The specification for enhanced conformance includes PDD as well as profiles within 80% FWHM. Recently, we commissioned seven Varian TrueBeam linacs with enhanced beam conformance. We developed a software tool in Visual Basic to allow us to load the reference beam data and compare our beam data during commissioning to evaluate enhanced beam conformance. This tool also allowed us to upload our beam data used for commissioning our dosimetrically equivalent beam models to compare and tweak each of our linac beams to match our modelled data in Varian’s Eclipse TPS. This tool will also be used during annual QA of the linacs to compare our beam data to our baseline data, as required by TG-142. Results: Our software tool was used to check beam conformance for seven TrueBeam linacs that we commissioned in the past six months. Using our tool we found that the factory conformed linacs showed up to 3.82% difference in their beam profile data upon installation. Using our beam comparison tool, we were able to adjust the energy and profiles of our beams to accomplish a better than 1.00% point by point data conformance. Conclusion: The availability of quantitative comparison tools is essential to accept and commission linacs with enhanced beam conformance, as well as to beam match multiple linacs. We further intend to use the same tool to ensure our beam data conforms to the commissioning beam data during our annual QA in keeping with the requirements of TG-142.

43 PARTICLE ACCELERATORS↗
DOE OSTI2015

SU-E-T-215: Comparison of VMAT-SABR Treatment Plans with Flattened Filter (FF) Beam and Flattening Filter-Free (FFF) Beam for Localized Prostate Cancer

Purpose: The purpose of this study is to access VMAT-SABR plan using flattening filter (FF) and flattening filter-free (FFF) beam, and compare the verification results for all pretreatment plans. Methods: SABR plans for 20 prostate patients were optimized in the Eclipse treatment planning system. A prescription dose was 42.7 Gy/7 fractions. Four SABR plans for each patient were calculated using Acuros XB algorithm with both FF and FFF beams of 6- and 10-MV. The dose-volume histograms (DVH) and technical parameters were recorded and compared. A pretreatment verification was performed and the gamma analysis was used to quantify the agreement between calculations and measurements. Results: For each patient, the DVHs are closely similar for plans of four different beams. There are small differences showed in dose distributions and corresponding DVHs when comparing the each plan related to the same patient. Sparing on bladder and rectum was slightly better on plans with 10-MV FF and FFF than with 6-MV FF and FFF, but this difference was negligible. However, there was no significance in the other OARs. The mean agreement of 3%/3mm criteria was higher than 97% in all plans. The mean MUs and deliver time employed was 1701±101 and 3.02±0.17 min for 6-MV FF, 1870±116 and 1.69±0.08 min for 6-MV FFF, 1471±86 and 2.68±0.14 min for 10-MV FF, and 1619±101 and 0.98±0.04 min for 10-MV FFF, respectively. Conclusion: Dose distributions on prostate SABR plans using FFF beams were similar to those generated by FF beams. However, the use of FFF beam offers a clear benefit in delivery time when compared to FF beam. Verification of pretreatment also represented the acceptable and comparable results in all plans using FF beam as well as FFF beam. Therefore, this study suggests that the use of FFF beam is feasible and efficient technique for prostate SABR.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-217: Comprehensive Dosimetric Evaluation On 3D-CRT, IMRT and Non-Coplanar Arc Treatment for Prone Accelerated Partial Breast Irradiation (APBI)

Purpose: Accelerated partial breast irradiation (APBI) is an effective treatment for early stage breast-cancer. Irradiation in a prone position can mitigate breast motion and spare heart and lung. In this study, a comprehensive study is performed to evaluate various treatment techniques for prone APBI treatment including: 3D-CRT, IMRT, co-planar and non-coplanar partial arcs treatment. Methods: In this treatment planning study, a left breast patient treated in prone position in our clinic was imported into Varian Eclipse TPS. Six beams tangential to chest wall were used in both 3D-CRT and IMRT plans. These six beams were coplanar in a transactional plane achieved by both gantry and couch rotation. A 60-beam IMRT plan was also created to explore the maximum benefit of co-planar IMRT. Within deliverable couch rotation range (±30°), partial arc treatment plans with one and up to ten couch positions were generated for comparison. For each plan, 30Gy in 6 fractions was prescribed to 95% PTV volume. Critical dosimetric parameters, such as conformity index, mean, maximum, and volume dose of organ at risk, are evaluated. Results: The conformity indexes (CI) are 3.53, 3.17, 2.21 and 1.08 respectively to 3D-CRT, 6-beam IMRT, 60-beam IMRT, and two-partial-arcs coplanar plans. However, arc plans increase heart dose. CI for non-coplanar arc plans decreases from 1.19 to 1.10 when increases couch positions. Maximum dose in ipsilateral lung (1.98 to 1.13 Gy), and heart (0.62 to 0.43 Gy) are steadily decreased with the increased number of non-coplanar arcs. Conclusions: The dosimetric evaluation results show that partial arc plans have improved CIs compared to conventional 3D-CRT and IMRT plans. Increasing number of partial arcs decreases lung and heart dose. The dosimetric benefit obtained from non-coplanar arcs should be considered with treatment delivery time.

60 APPLIED LIFE SCIENCES↗
DOE OSTI2015

SU-E-T-224: Considerations for the Proper Treatment of Multiple Cranial Metastases with Single Isocenter Volumetric Modulated Arc Therapy

Purpose: To investigate some limitations of single isocenter VMAT for cranial multiple met cases. Methods: A single isocenter VMAT plan (Varian, Eclipse AAA10 commissioned down to 1 cm) was designed for two 7mm diameter spherical targets in a rectangular Solid Water (Gammex) phantom. The targets were separated by a distance of 6cm and the isocenter was centered in one of the targets. The plan was delivered (Varian, Truebeam STx) three separate times with different artificial couch angle errors of 0, 0.5 and 1 degree. The coronal dose distributions were measured with calibrated EBT3 film placed at mid-phantom. EBT3 film dosimetry was also performed on the delivery of separate multiple arc vmat plans to targets below 6mm in diameter. Results: Measurements of the sup/inf dose profiles through the high dose distributions show no movement of the central axis high dose region and shifts of the high dose region intended for the off-axis target. For the 1 degree rotation error, the high dose region was shifted 1.04mm from the target. This corresponds to the shift expected from triangulation (60mmxTan(1deg)=1.047mm). Furthermore, a streak of 10% interleaf leakage dose was observed and is likely a Result of the off axis target traveling a wide path such that a long length of MLC is exposed for the whole arc. The calculated dose was about 10% to 15% low compared to that measured on film for a 5mm diameter target. Conclusion: Judicious use of additional margin for off axis targets or limits on the span of multiple mets treated with one isocenter is recommended. The magnitude of the margin should be based on the rotational errors evaluated for the positioning system and the distance of the target from the isocenter. A lower limit of lesion size that can be accurately treated with VMAT should be determined.

60 APPLIED LIFE SCIENCES↗