bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐376: Report on Use of a Methodology for Commissioning and Quality Assurance of a VMAT System
Authors: Mayo C , Fong de los Santos L , Kruse J , Blackwell C , McLemore L , Pafundi D , Stoker J , Herman M
Published: June 2012

Introduction: Results of use of methodology for VMAT commissioning and quality assurance, utilizing both control point tests and dosimetric measurements are presented. Methods: A generalizable, phantom measurement approach is used to characterize the accuracy of the measurement system. Correction for angular response of the measurement system and inclusion of couch structures are used to characterize the full range gantry angles desirable for clinical plans. A dose based comprehensive daily QA measurement approach is defined. Results: Agreement in the static vs. VMAT picket fence control point test was better than 0.5 mm. Control point tests varying gantry rotation speed, leaf speed and dose rate, demonstrated agreement with predicted values better than 1%. Angular dependence of the MatriXX array, varied over a range of 0.94 –1.06, with respect to the calibration condition. Phantom measurements demonstrated central axis dose accuracy for un‐modulated four field box plans was =2.5 % vs. 1% with and without angular correction respectively with better results for VMAT (0.4%) vs. IMRT (1.6%) plans. Daily QA results demonstrated average agreement of all three chambers within 0.4% over 9 month period with no false positives at a 3% threshold. Conclusions: The methodology described is simple in design and characterizes both the inherit limitations of the measurement system as well at the dose based measurements that may be directly related to patient plan QA.
SU‐E‐T‐378: Dosimetry Comparison of VMAT and Tomotherapy Plans with Dose Painting in Brain Metastases
Authors: Yang C , Sheth N , Chen Y
Published: June 2012

Purpose: To compare dosimetric results of VMAT and Tomotherapy dose painting techniques with hippocampus sparing in brain metastases. Methods: A patient with multiple brain metastases was entered into this dosimetry study. Pinnacle VMAT SmartArc™ plan was executed in version 9.2 while setting the same dose constraints in Tomotherapy planning version 4.04. The clinical goal is to perform simultaneous in‐field boost (SIB) with whole brain for 32.5 Gy while delivery extra dose per fraction to the brain metastatic sites to 63 Gy. The mean dose to each of the hippocampus was prescribed to less than 6 Gy. Dosimetric analysis was performed on the 3DVH modules by Sun Nuclear Corp™. The ArcCheck™ platform was also utilized to measure the 3%/3mm gamma passing rate. Results: Clinical planning criteria for GTV coverage were all satisfied, while Tomotherapy presents better hippocampus sparing compared both to the VMAT technique (mean: 5.29/10.05 Gy on left and 5.18/9.90 Gy on right, max:7.19/17.82 Gy on left and 7.58/20.79 Gy on right). Tomotherapy has inferior chiasm sparing with mean 32.26 Gy compared to VMAT planning 29.16 Gy. However, the dose uniformity of Tomotherapy has proven to be superior in all lesions with average mean dose 63.63 Gy with respect to 64.33 Gy; max dose of 102.2% on Tomotherapy and 105.3% on VMAT planning. ArcCheck passing rate for Tomotherapy is 98.9% with 3%/3mm gamma settings. Conclusions: Tomotherapy planning is considered a gold standard for arc‐based treatment. From the planning comparison, with VMAT delivery, achieving 6Gy dose sparing to the hippocampus presents great challenge compared to the Tomotherapy planning and delivery. One major reason is that the VMAT MLC speed cannot generate enough fluence patterns to produce the extremely high dose gradient. ArcCheck measurements for VMAT and Tomotherapy represented errors induced from the combination of TPS dose calculation algorithm and beam‐delivery inaccuracy.
SU‐E‐T‐382: An Analysis of VMAT Monthly Quality Assurance
Authors: Stenbeck J , Oves S , Gebreamlak W , Alkhatib H
Published: June 2012

Purpose: The purpose of this study is to quantify the change in monthly VMAT quality assurance (QA) and determine the tests to maintain consistent delivery with a baseline. Methods: VMAT monthly QA has been performed for over 14 months on two Elekta Synergy LINACs. A baseline was established at acceptance and the monthly QA results were compared to those initial values. Films were used to test the dependence on varying dose rate, gantry speed, rotational direction, and MLC speed. These parameters were tested independently and then together in a test called the synchronicity test. Ion chamber readings test a DMLC field with a varying dose rate and MLC speed. Introducing intentional errors into the tested fields allowed the detectable limits of the QA to be determined. Results: The monthly QA has consistently matched the baseline within a 3% dose limit on film. Analyzing the synchronicity film with a gamma test using a 5%/0.5mm tolerance showed a monthly pass rate of over 99%. The DMLC test has been identical for the entire course of VMAT QA. Furthermore, intentional changes in the MLC speed were noticed on the synchronicity test in the form of a smaller gamma pass rate as the MLC error was increased. Conclusions: There is a monthly agreement with all films testing individual parameters, ion chamber DMLC readings, as well as agreement with the synchronicity test. This collection of data has lead to the conclusion that only the synchronicity test and DMLC readings need to be performed on a monthly basis. If those tests fail, then individual parameters need to be tested to determine the singular cause of the error. Having a single test used as a red flag increases the efficiency of the monthly QA and is being implemented with an EPID to eliminate the use of film.
SU‐E‐T‐386: Gamma Analysis of Normalized and Un‐Normalized Dose Distributions
Authors: Stojadinovic S , Luo O , Bao Q , Pompos A , Gu X , Solberg T
Published: June 2012

Purpose: The gamma index method, as currently implemented in all commercial QA software, calls for selection of a normalization point to evaluate agreement between two dose distributions. The implication of this is that there is an infinite number of possible solutions! Which one to pick? A unique and more relevant solution is obtained only if no normalization point is used.Methods and Materials: The set of test cases suggested by the AAPM TG1 19 were planned using Pinnacle 8.0m and delivered on a Varian 21EX linac for 6 and 18 MV photons. The recommended point and planar dose measurements were obtained using a Pinpoint ion chamber, EDR2 film and MatriXX. The gamma index method using typical 3%, 3 mm criteria with and without a normalization point was used to assess the agreement between calculated and delivered planar dose distributions. The analysis was extended to a set of data for clinically treated patients. Results: The comparison with the TG119 benchmark data showed that all point dose and planar measurements for 6 MV were within the published range. Similar results, although without published data to compare with, were obtained for 18 MV as well. For all complex tests, the percentage of points passing the gamma criteria of 3%, 3 mm was (95.8±1.6)% and (95.6±1.0)% for 6 MV and 18 MV, respectively. Without a normalization point, however, the same gamma analysis fell to (20.7±6.7)% and (13.9±4.0)% for 6 MV and 18 MV, respectively. The clinical data set showed the same trend, with the gamma passing rate declining from (98.9±0.7)% to (33.4±13.1)%. Conclusion: The gamma index method provides a unique answer for gamma passing rate only without normalizing dose distributions to any particular point. The common gamma criteria of 3%, 3 mm, however, is a very poor metric in that case.
SU‐E‐T‐387: Validation of a New System for Patient Specific IMRT QA and Comparison with Other Commerical Systems
Authors: McKinsey R , Stathakis S , Esquivel C , Gutierrez A , Myers P , Nayebi N , Regan M , Papanikolaou N
Published: June 2012

Purpose: The focus of this project is to compare the Octavius 4D with current commercial available dose validation systems: MatriXX MultiCube and Delta4. Methods and Materials: Many challenges are faced with properly measuring Intensity Modulated Radiotherapy (IMRT). It has become common practice for clinics to use film, arrays, or multiple detectors to validate dose measurements pretreatment for static and dynamic treatments. IMRT QAs for various treatment sites were measured for patients using three different dose validation systems. All measurements were taken on a Varian CLinac 2100 C/D, SN‐757, 80 MLC with 6MV. The treatment plans evaluated were Step‐N‐Shoot. Data analysis was performed using the software provided with each dose validation system. Detailed information was gathered from each system with their perspective advantages. The latest system, Octavius 4D, allows one to calculate the Gamma Index for Coronal, Sagittal, and Transversal views for every slice included in the measurement along with the traditional data analysis provided; histograms, horizontal and vertical profiles, DTA. Results and Discussion:The Gamma Index values were observed using the MatriXX Multicube, Delta4, and Octavius 4D. The treatment plan included five fields at various gantry angles. Also the gamma index and profiles were calculated for various treatment sites. Delta 4 and the Octavius 4D appears to be quite comparable. Each device has the ability to allow one to verify segmented and composite fields, measure dose profiles and analysis using the Gamma Method. ConclusionsSimilar IMRT QA measurements will be made for more Step‐N‐Shoot cases with the addition of SmartArcs. The limitations of each system will be determined for each system using the Gamma Index as a reference while varying the Region of Interest, Threshold, and Gamma Method (local, normalization, and maximum dose), as well as the 2D‐ profiles for these cases.
SU‐E‐T‐389: Accuracy of a VMAT Planning System for Head and Neck Radiotherapy
Authors: Aldaais E , Tedeschi D , Gebreamlak W , Shieder T , Alkhatib H
Published: June 2012

Purpose: To determine the accuracy of VMAT treatment planning and delivery for patients undergoing radiotherapy in the head and neck. Method and Materials: A dosimetric study of a typical head and neck treatment plan has been carried out using Chamber, film and TLD's placed inside an anthropomorphic phantom. Lateral and AP port films were taken to verify the isocenter prior to treatment. Multiple treatments were performed to assess the reproducibility and uncertainty in the TLD measurements. Gafchromatic film was used between the phantom slices and then analyzed as an independent check on the TLD results. The two data sets, from TLDs and films, were then compared with the treatment planning system dose calculations. Results: The measured dose to the primary planning tumor volume agrees with the planning system within 2%. The comparison of the measured dose to the secondary tumor volume ranges from 3–6% and the spinal cord comparison ranges from 3–10%. Conclusion: This new Smart Arc treatment, VMAT, has great benefits to the patient in that patient motion and internal motion of the tumor is dramatically reduced. Challenges arise in predicting the dose near heterogeneities between the treatment planning system and actual measurement.
SU‐E‐T‐402: Coordinate Transformation after Stereotactic Frame Reapplication in Gamma Knife Radiosurgery
Authors: Park J , Han J , Kim C , Oh C , Suh T , Kim D , Chung H
Published: June 2012

Purpose: In Gamma Knife (GK) radiosurgery, the occurrence of reapplying the stereotactic frame due to collision with the collimator leads to re‐ examination and re‐planning. For the treatment of vascular lesions, it is a burden not only to physicians but also to patients to get invasive angiography procedure again. To avoid undergoing second angiography examination, and reduce re‐planning time, a mathematical coordinate transformation method using the stereotactic images has been developed. Methods: The MR or CT images of a patient brain before and after frame reapplication can be correlated with each other using the Affine transformation. The transformation parameters which minimize the RMS error of the original and transformed coordinates between the images were determined using a genetic algorithm. Three CT image studies of skull phantom were used for the verification of the algorithm. Moreover, five MR image studies of patients who underwent more than one GK procedure were used for the clinical evaluation. The coordinates under the original treatment plan were converted to new coordinates using the transformation matrix, and their dosimetric outcomes were compared. Results: The RMS error in the coordinate transformation of skull phantom and clinical images was 0.3 mm and 0.6 mm, respectively. For total 9 treatment lesions of 0.2 ∼14.1 cc, 3% and 11% RMS error in the irradiation time and target coverage were found respectively. The patients with only translational movement during the frame reapplication showed similar plan conversion results with the original plan. Also, deeply‐located lesions showed a better RMS error of 3% in the conformity index than superficial lesions close to the skull. Conclusions: New treatment plans were obtained by applying the coordinate transformation to the original plans after the frame reapplication. The converted plans maintained the quality of the original plans with a little change in dose distribution arising from head rotation. This work was supported by a grant no. 04‐2011‐0320110130 from the Seoul National University Hospital Research Fund and a National Research Foundation of Korea (NRFK) grant funded by the Korean government (MEST) (Grant No. K20901000001‐09E0100‐00110).
SU‐E‐T‐416: Performance Test Comparing Three Pre‐Treatment Isocenter Localization Techniques for Single Fraction Cranial Stereotactic Radiosurgery
Authors: Mathews B , Saini J , Campbell D
Published: June 2012

Purpose: To develop a performance test comparing three pre‐treatment isocenter localization techniques when using head‐frame vs. immobilization mask for cranial Stereotactic Radiosurgery (SRS). This study will compare pre‐treatment positioning techniques using laser alignment vs x‐ray verification using ExacTrac or On Board Imaging. Methods: A RANDO anthropomorphic head phantom was fitted with an in‐house polystyrene insert to allow EDR2 film measurements in two orthogonal planes. A pin hole was pricked on each film to serve as a target during treatment planning. for each trial (three total), a CT scan was acquired of the phantom equipped with either an immobilization mask or invasive head frame. Treatment planning employed iPlan Image v4.1 and iPlan Dose v4.1.1. Positioning of the phantom equipped with the head‐frame was performed by aligning vault lasers to coincide with cross‐hair labels on a target positioner box. Setups utilizing an immobilization mask were verified by x‐ray verification using ExacTrac and On Board Imaging, and if alignment were not within tolerance, then shifts were made using a 6D robotic couch. Gantry star‐shot irradiation was performed using a 5mm cone to evaluate the differences between radiation isocenter and the target. The mean and standard deviations were calculated for differences in the x‐, y‐, and z‐coordinate axes. Results: Positional accuracy using ExacTrac for mask based SRS resulted in 1.10±0.86, 0.67±0.83, and 0.59±0.48mm for cross plane, inline, and vertical measurements, respectively. Differences for frame based SRS were 0.93±0.43, 0.76±0.18, and 0.34±0.12mm for cross plane, inline, and vertical measurements, respectively. Results for mask based SRS using OBI will soon follow. Conclusions: Although the frame‐based SRS techniquegenerated smaller standard deviations, the mean difference from target to radiation isocenter for both techniques fall within the statistical uncertainty of one another. Planning margins must take into account target size when treating small lesions for both techniques. Project funded by CARTI.
SU‐E‐T‐421: 6MV Radiation Small Field Dose: Off Axis and Penumbra Effects, a Study with Radiochromic Film
Authors: Baek J , Beachey DJ
Published: June 2012

Purpose: To accurately determine relative dose factor scaling, tissue depth relation, and penumbra details of small 6MV radiation fields with an emphasis on far‐off‐central‐axis fields for various MLC designs ‐subject matter important in the context of SRS, FSRT, SBRT, and IMRT. Methods: Radiochromic film designed for quantitative dosimetry, EBT3™ film (Ashland Inc.) can be reliably used as a relative dosimeter to within 1% accuracy if one controls for both film and flatbed scanner variation. This enabled a study of the fine detail of small radiation fields and the impact upon these small dose profiles by different MLC designs both on central axis and off. In particular, the impact of leaf‐end penumbra from bifocal MLC Optifocus (Siemens) and Synergy Beam Modulator (Elekta) is examined.EBT3 films were placed at 100cm SAD in solid water phantom and irradiated to 200 MU at various depths 1.5cm – 20cm and for various off‐axis locations. The films were analysed to give the detailed dosimetric profile of each small field and relate them to both a standard reference field (10 × 10)cm2 and to a broadfield flatness/symmetry irradiation (20 × 20)cm2. Films were scanned at ∼20 hours post irradiation on an Epson 2000 flatbed scanner and analysed using FilmQAPro and in‐house methods. Results: As small field size decreases, the field center falls within the penumbra of each MLC edge for megavoltage photon energies. The penumbral effects cause the conventional dosimetric quantity SP to sharply depart from the smooth fieldsize dependence for larger conventional fields. Conclusions: Careful characterization of small field dose and leaf end modeling within a TPS is crucial in both predicting accurate small field dosimetry and off‐axis dosimetry.
SU‐E‐T‐422: Lung SBRT Using Cyberknife: Technique and Treatment Outcome
Authors: Biswas T , Holland B , Rosenman J , Podder T
Published: June 2012

Purpose: At East Carolina University, we have been treating primary and secondary lung cancers with Cyberknife stereotactic body radiotherapy (CK‐ SBRT) since February 2009. Till October 2011, we have treated a total of 79 patients (83 sites). In this study, we present our experience in CK‐SBRT and clinical outcome of the treated patients. Methods: Of the 79 patients, 43 were female; age of the whole patient population ranged 33.2–89.7yrs (median=73.2yrs). Patients treated for primary lung cancer (n=57) had severe chronic obstructive pulmonary disease (COPD) and were not surgical candidates. Cyberknife robotic system with tracking techniques (Synchrony=52, XsiteLung=22, XsightSpine=5) were used. Majority of the patient (n=52) had multiple gold fiducials placed (1–6 placed; 1–4 tracked per patient) either percutaneously or bronchoscopically. CT images were used for dosimetric planning, by medical physicists, using Cyberknife MultiPlan software. Prescription doses were 25Gy‐55Gy in 3–5 fractions (mean=48.2Gy, median=50Gy); doses were prescribed mainly to 80% isodoseline (range=75–96%, mean=81.4%). PTV margin varied from 0–7mm (mean±SD=3.2±1.4mm), based on the tumor locations; breathing patterns and cancer type. Dosimetric coverage of GTV and PTV were (mean±SD): 97.8±5% and 94.7±6.9%, respectively. The treatment response was assessed using either a CT or a PET scan or both. Results: The median follow up was 13.1months (range 0.3–31.9 months). Overall response rate was 98.8% (CR=73.5%). Local failure free survival at one year was 84% for primary (n=57), 76% for recurrent (n=16) lung cancer and 100% for metastatic (n=10) tumors. The toxicity rate was low with one patient reported to have chest wall pain and one patient developed grade 3–4 radiation pneumonitis. Conclusions: In most of the cases tight PTV margins were used. Since the prescriptions were at 80% isodeose line with more than 94% PTV coverage, the treatment outcome appeared reasonable. Further study relating PTV margin, dosimetric coverage, and treatment outcome is in progress.
SU‐E‐T‐423: Dosimetric Effect of Rotation on Stereotactic Body Radiotherapy (SBRT) of the Spine
Authors: Djemil T , Angelov L , Chao S
Published: June 2012

Purpose: To study the dosimetric effects of the residual setup rotation errors in spine SBRT. Methods: We selected 25 patients with 26 lesions from an IRB approved registry. All patients were setup with Exactrac IGRT and treated with Novalis. Excatrac provided 6D shifts (3 translational, 3 rotational). The translational shifts were corrected by moving the couch. The rotational shifts >2 degrees were corrected by repositioning the patient, while smaller shifts were ignored. For each patient, we rotated the simulation CT rigidly around the CTV center by the recorded residual angles, using the MIM 4.22 software. The resulting rotated CT with all contours were imported into the TPS. The clinical plans used for treatment were mapped onto the rotated CT. Dosimetric endpoints were extracted for the rotated CTV (mean, max, D90) and the rotated cord (D0.1cc, D1cc, V10, max). These endpoints were compared to those from the clinical plan. Results: For the CTV, the average ratio of the mean doses was 1.001 (0.996–1.004), the average ratio of D90 was 1.003 (0.998–1.011), and the average ratio of the maximum doses was 1.005 (0.995–1.029). For the cord, the average ratio of DO.lcc was 1.01 (0.94–1.06), the average ratio of D1cc was 1.036 (0.92–1.23), the average max doses ratio was 1.03 (0.95–1.11), and the average V10 ratio was 1.43 (0.56–2.78). Conclusions: Rotational errors in patient setup as small as 2 degrees do have dosimetric effects in spine SBRT treatments. The use of a robotic table to eliminate translational and rotational shifts is strongly recommended. It is important to note that, eventhough, the residual rotations resulted in up to 11% variation (cord max dose) from the planned doses, none of these cases violated our clinical treatment plan acceptance criteria (tolerance of the critical organs).
SU‐E‐T‐428: Class Solution for Prostate High Dose Rate Brachytherapy with Inverse Planning Simulated Annealing
Authors: Sheth N , Mistry N , Chen Y , Yang C
Published: June 2012

Purpose: To develop and validate a class solution for inverse planning simulated annealing (IPSA) with CT based prostate high dose rate brachytherapy (HDR). Methods: Between November 2008 and November 2011, our institution treated 40 prostate cancer patients with HDR in 7 Gy fractions followed by external beam radiotherapy. The HDR treatments were planned with Nucletron Oncentra using manual graphical optimization (GO). Plans were optimized to the following clinical goals: = 95% of prostate volume received 7 Gy, < 1 cc of rectum received 5.6 Gy, < 0.1 cc of rectum received 6.3 Gy, and < 0.01 cc of urethra received 8.75 Gy. New plans were manually customized using IPSA (MC‐IPSA) for each patient to match prostate coverage by the prescription dose to within ± 1% of the GO plans while meeting the rectal and urethral dose constraints. An IPSA class solution (CS‐IPSA) was created from the mean MC‐IPSA parameters. New plans were developed for each of these 40 patients using only CS‐IPSA with no further optimization. Additionally, plans were created on an independent dataset of 30 different patients using only CS‐IPSA with no further optimization. Results: Plans were optimized in about 30 minutes using GO, MC‐IPSA took an average of 14.1 ± 6.5 minutes, and CS‐IPSA optimizationwas < 1 minute. There was no significant difference (p > 0.05) among the optimization methods for all clinical goals over the 40 CS‐IPSA source patients. There was no significant difference (p > 0.05) between the source and the independent datasets for all clinical goals when using CS‐IPSA with no further optimization. Conclusion: A prostate HDR IPSA class solution was developed and validated on a source and an independent dataset. The IPSA class solution yields plans comparable to custom manual IPSA and graphical optimization while saving considerable time.
SU‐E‐T‐430: Evaluation of Inverse Optimization in Brachytherapy for Locally Advanced Cervix Cancer
Authors: Liao Y , Dandekar V , Chu J , Turian J , Kiel K
Published: June 2012

Purpose: Brachytherapy is a vital part of treating locally advanced cervix cancer. Point‐based 2D treatment planning is conventionally used. New CT/MRI‐compatible applicators for HDR brachytherapy make 3D conformal planning possible. GEC‐ESTRO endorsed the EMBRACE (intErnational study on MRI‐guided BRachytherapy in locally Advanced CErvical cancer) protocol which recommends standard‐plan‐based manual optimization over inverse optimization due to the concern of the uncertainty of high dose in targets and adjacent normal tissue. This study investigated the feasibility of inverse optimization planning. Methods: Eight cervix cases using tandem/ring applicators +/− parametrial needles were evaluated. Both manually and inversely optimized 3D conformal plans using Oncentra® Brachy were generated for each case following EMBRACE guidelines. Planning time and DVH parameters including D90 and V100% for HR‐CTV, D90 for IR‐CTV, D2cc for normal structures (bladder, rectum, sigmoid colon, and small bowel) were compared. Dose was reported in total EQD2 dose, assuming 45Gy in 25 fractions external beam and 28Gy in 4 fractions HDR treatment. Prescription dose (PD) and PD×2 isodose volumes and V100% and V200% for normal tissue (excluding all contoured OARs) were compared to evaluate the high dose volumes. Results: The average planning time was reduced by 55% with inverse planning. Target coverage between inverse and manual plans differed by <2% for HR‐CTV (D90 and V100) and IR‐CTV (D90). Inverse planning reduced the D2cc for normal structures by 4.2%–5.7% and the V100% and V200% for normal tissue by 31% and 40%, respectively. For 7 of the 8 cases, small bowel was observed near the target and received significant dose with either approach. Conclusions: In this study, inverse planning improved DVH parameters over manual planning, with less planning time. Reporting normal tissue dose should alleviate the concern of undetected high dose regions. Even though small bowel is not often considered in traditional planning, dose should be reported.
SU‐E‐T‐431: Investigation of BrachyVision™ Acuros™ Using Varian Surface Applicators
Authors: Simiele S , Fulkerson R , Micka J , DeWerd L
Published: June 2012

Purpose: Conical brachytherapy surface applicators with diameters ranging from 10 mm to 45 mm have been developed by Varian Medical Systems, Inc. These applicators are designed to be used with the GammaMedplus iX and VariSource iX high‐dose rate Ir‐192 afterloaders, allowing for conformal dose delivery for the treatment of surface lesions. Treatment plans for these applicators are created in BrachyVision Acuros. Few studies have been completed with Acuros in clinical situations. The purpose of this work is to perform a comparison of the Acuros‐calculated dose distributions with those calculated using Monte Carlo and measured with various detectors. Methods: Surface applicator treatment plans for each source/applicator combination were created using Acuros and a virtual water phantom. Simulations to characterize the dose distributions were completed using MCNP5 based on specifications provided by the manufacturer. A collision kerma tally was used to determine the dose distributions at the surface and at depth in water. Experimental verification of the depth‐dose and surface dose distributions was completed using an ionization chamber, and TLDs and film, respectively. Acuros‐calculated depth‐dose and isodose values were compared to the Monte Carlo and experimental values. Results: Assessment of the surface dose distributions shows a peak at the center of the applicator with rapid fall off to the edges. The TPS‐calculatedpercentage depth‐dose curves were within 3.7% of the MC and 5.8% of the measured for the 30 mm applicator and were within 4.4% of the MC and measured for the 35 mm applicator. Conclusions: BrachyVision Acuros is capable of calculating the depth‐dose and surface dose distributions for the simple water phantom case with surface applicators. Investigation of additional treatment geometries and applicators is ongoing. Conflict ofInterest: Varian Medical Systems, Inc. provided financial support, software, sources, and applicators. Varian Medical Systems, Inc. provided financial support, software, sources, and applicators.
SU‐E‐T‐433: Pear‐Shaped Based Dose Optimization for HDR Intracavitary Brachytherapy for Cervical Cancer Patients with Small Uterus
Authors: Shen S , Kim R , Duan J , Wu X , Popple R , Cardan R , Brezovich I
Published: June 2012

Purpose: Currently, CT has been widely used for HDR planning as MRI is not widely available for tumor imaging. Conventional pear‐shaped isodose distribution may not be discarded completely because of possible microscopic diseases into parametrium/uterus. For patients with small uterus, organs at risk (OARs) can fall inside 100% conventional pear‐shaped isodose‐line. This study compares two pear‐shaped based dose optimization methods for OARs sparing. Methods: Seven cervical cancer patients with small uterus were evaluated using 2 methods. For Method A, with conventional dwell‐time loading, point A lateral distance was reduced until all OARs' D2cc were within the dose limits. For Method B, a reference target volume was generated using conventional pear‐shaped 100% isodose‐ surface. While isodose‐line near the point A was adjusted for OARs sparing, isodose‐line surrounding ovoids were optimized to match the reference target volume. For equivalent OAR sparing, 100% isodose‐line width (lateral dimension) at 1 cm inferior to point A (−1 cm) and at across centers of ovoids (ovoid) were compared between the 2 methods. Results: OARs fall inside conventional 100% isodose‐line in all cases. Median position of hot spots was 0.2 cm (range −;1.2 to 2.9 cm) superior to point A. Using Method A, point A lateral distance was adjusted to 1.4–1.7 cm for OARs sparing. Median width of 100% isodose‐line was 5.82 cm at ovoid level, and 4.50 cm at −1 cm level. At ovoid level, median width of 100% isodose‐line was reduced by 9(8–13)% for Method A, and was unchanged for Method B. At −1 cm level, median width of 100% isodose‐line was reduced by 19(2– 33)% for Method A, and 11(0–15)% for Method B. Conclusions: for patients with small uterus, OARs are often fall inside 100% pear‐s haped isodose‐line near point A level. OARs can be spared without dramatically compromise treatment volume coverage around cervix using Method B.
SU‐E‐T‐435: Automatic Monte Carlo Dose Calculations of Proton Treatment Plans
Authors: Titt U , Mirkovic D , Liu A , Mohan R
Published: June 2012

Purpose: Providing a user friendly automated Monte Carlo dose computation system for proton treatments using passively scattered and intensity modulated proton therapy plans, developed at the proton therapy facility of the M.D. Anderson Cancer Center. Methods: In house software was developed to automatically extract patient CT images, as well as the setup geometry and proton beam parameters from DICOM files, to create a Monte Carlo (MCNPX) model simulating the beam line arrangements of the various beams used in any given proton treatment plan. A graphical user interface provides an easy and intuitive workspace. A library of phase space files provides source proton beams with the desired modulation width and range in water. Energy deposition is scored in the voxelized CT volume, converted to dose and compared to results of analytical dose computations. Results: : Monte Carlo models of patient specific beam line equipment, such as the brass collimator and the range compensator, as well as avoxelized model of the patient, are automatically created and implemented into the model of the simulated beam. Simulation of proton beams result in energy deposition distributions in a volume of interest defined by the user during program start. Conclusions: Current efforts focus on production ofthe phase space library and final debugging of the program flow. It is expected that a prototype version of the system will be functional in summer 2012.
SU‐E‐T‐443: The Dosmetic Difference of RapidArc Plans in Radiotherapy of Multiple Hepatic Malignancy Applying 6MV and 15MV X‐Ray
Authors: Gong G , Yin Y , Liu T
Published: June 2012

Purpose: To investigate the dosmetric difference in the application of RapidArc using 6MV X and 15MVX X‐ray for radiotherapy of multiple hepatic malignancy. Methods: 12 cases with multiple hepatic tumors (primary 5 cases or secondary 7 cases) were selected. All patients underwent the three dimensional CT simulation in free breathing. For each patient, RapidArc plans with single or two 358° arcs using 6MV X or 15MVX‐ray were designed respectively, the prescription dose was 2Gy/Fractionx25 Fractions. The dosimetric differences were compared among RapidArc plans. Results: All of RapidArc plans can meet the clinical requirement. There were no significant difference were found in the conformity index (CI), homogeneity index (HI), the maximum dose and the minimum dose of PTV among RapidArc plans(P>0.05), and all the CI can get to 0.91 and HI can get to 0.88. In the RapidArc plans with two 358° arcs, the V5,V10,V15 of normal liver were higher than with single arc, while V20, V25, V30, V35, V40 were lower than with single arc. The radiation dose of normal liver, stomach, duodenum and spinal cord differed no significantly among different plans(P>0.05). The monitor units of RapidArc plans using 6MV X‐ ray increased 12% compared to 15MV averagely. Conclusions: The 6MV X‐ray would be selected chiefly in the radiotherapy of multiple haptic tumor using RapidArc with single or two whole arcs.
SU‐E‐T‐444: 4D‐CT and Active Breathing Coordinator Play Similar Role in Sparing Normal Liver Tissue in the Radiotherapy of Hepatocellular Carcinoma
Authors: Gong G , Yin Y , Liu T
Published: June 2012

Purpose: To investigate the difference in sparing normal liver tissue between 4D‐CT and active breathing coordinator (ABC) in the radiotherapy of Hepatocellular carcinoma(HCC) applying RapidArc. Methods: Ten patients with HCC underwent 3D‐CT at end inspiration hold(EIH) associated with active breathing coordinator(ABC),and 4D‐CT scan. The 4D‐CT images were sorted in to 10 serious CT images according respiratory phase. Gross tumor volumes(GTVs) were manually contoured on different CT images. The individual internal gross target volume(IGTV) was obtained from 10 GTVs of 4D‐CT images. Plan target volumes (PTVs) were obtained based on IGTV and GTVEIH. PTV1 was obtained from IGTV plus 5 mm margins isotropically, and PTV2 was obtained from GTVEIH using 8 mm margins isotropically. RapidArc plans were designed on PTV1 and PTV2, for PTV1 RapidArc plans with one single whole arc were applied and for PTV2 three 135°arcs, and name RapidArc1 and RapidArc2. Dosimetric differences were compared. Results: There were no significant difference in conformity index (0.93±0.05 Vs 0.93±0.03), homogeneity index(1.08±0.01 Vs 1.08±0.01), the Dl%(54.44±0.36 Gy Vs54.68±0.47 Gy) and D99%(49.18±0.48Gy Vs 49.00±0.34 Gy) between RapidArc1 and RapidArc2(P>0.05). There were no significant differences in the mean dose(8.23±1.5Gy Vs 7.63±3.00Gy),V5(46.64±19.31Vs43.29±19.94), V10(28.73±11.54 Vs 28.23±12.37), V15(17.87±6.61 Vs 18.20±7.55), V20(11.62±4.39 Vs 11.83±4.58), V25(7.71±2.91Vs 7.58±2.79),V30(5.14±2.01Vs5.05±1.79), 35(3.41±1.35Vs 3.35±1.21) and V40(2.12±0.86Vs2.06±0.75) between RapidArc1 and RapidArc2 (P>0.05). Conclusions: The RapidArc plans with three 135°arcs associated could achieve similar dose delivery as the plans with single whole arc, and 4D‐CT and ABC could play similar role in sparing normal liver tissue assuring the accuracy of target volume in radiotherapy of HCC.
SU‐E‐T‐447: Evaluation of the Anisotropic Analytical Algorithm (AAA) Heterogeneity Correction Dose Calculation in Flattened and Flattening‐ Filter‐Free (FFF) Beams for High Energy X‐Ray Beams Using the Radiological Physics Center (RPC) Lung Phantom
Authors: Repchak R , Molineu A , Popple R , Kry S , Howell R , Followill D
Published: June 2012

Purpose: Compare the accuracy of AAA heterogeneity corrected dose calculation algorithm for high energy x‐ray beams (>10 MV) for flattened and FFF beams using RPC anthropomorphic thorax phantom. Methods: Six static beam SBRT treatment plans were created using the Varian Eclipse treatment planning system (TPS) AAA v.8.9.08 heterogeneity correction algorithm. Two flattened beam plans (6 MV and 18 MV) and four other plans (6 MV, 6 MV FFF, 10 MV FFF and 15 MV) were delivered using a Clinac 21EX and TrueBeam STx, respectively. Prescription dose/coverage, 6 Gy to 95% PTV, and constraints were the same for all plans. The phantom contained radiochromic films in the 3 major planes and TLDs in the heart, spine, and tumor. Point doses and 2D dose distributions were exported from the Eclipse TPS and compared with the measured doses. The gamma index analysis evaluation criteria of ±5% dose to agreement and 3 mm distance to agreement was used. Results: TLD to TPS tumor point dose ratios were 0.971±0.006(6MV) and 0.957±0.002(6MV), 0.995±0.005(15MV), 1.114±0.006(18MV), and 0.957±0.003(6MV FFF), 0.974±0.011(10MV FFF) for the six plans. Using ±5%/3mm gamma analysis criteria, the average passing rates for all three films were 96.3% and 95.5%, 97.4%, 66.1%, 93.7%, and 96.3% for the 6 MV, 6 MV, 15 MV, 18 MV, 6 MV FFF, and 10 MV FFF plans, respectively. Dose profiles were also evaluated. Conclusions: The current RPC credentialing criteria are: RPC/Inst. tumor dose ratio of 0.97±0.05 and 85% of the pixels in each film plane must pass a ±5%/5mm gamma index analysis. These data demonstrate that the AAA heterogeneity correction dose calculation algorithm is accurate for photon energies in 6–15 MV range for flattened and FFF beams. Heterogeneity corrected dose calculations for photon energies >15 MV were not accurate. Work supported by grants CA10953 and CA81647 (NCI, DHHS).
SU‐E‐T‐448: Switch Patients between Collimation Systems for CyberKnife Treatment Feasibility Study
Authors: Fan J , Xu Q , Wang L , Jin L , Li J , Lin T , Hayes S , Tam T , Ma C
Published: June 2012

Purpose: There are two collimation systems associated with the CyberKnife system, the fixed cone collimator and the Iris collimator. The Iris collimator is used more frequently because of its superior flexibility. However, sometimes treatments have to be canceled or postponed due to Iris collimator mechanical failures. The purpose of this study is to investigate the feasibility of switching collimation systems without replanning. Methods: We first performed Monte Carlo simulations on 10 clinical cases using the Iris collimator and the fixed cone collimator. The conformality index (CI), target volume coverage and the maximum, minimum and mean doses to the critical structures from the iris and fixed plans were compared to determine the feasibility of switching between collimator types without replanning. Results: Our results showed that the two types of collimators deliver similar dose distributions. The average target doses for the fixed plans were 1% to 6% higher than those for the Iris plans. The average CI for the fixed plans was 1.36 compared to 1.28 for the Iris plans. Thus, we adjusted the Iris sizes with a scale factor of 1.024 to achieve a better dose match with the fixed collimators. Doses for the 10 cases were then recalculated. Once this correction was made, the difference between the average target doses for the two collimator plans was reduced to less than 2% and the CIs became almost identical. Conclusions: Small target dose differences were found between plans using different collimation systems, which may be compensated for by adjusting the Iris collimator sizes to ensure similar dose distributions. The differences in the doses to the critical structures between the collimation systems were insignificant. After adjusting the Iris collimator sizes and re‐commissioning the planning system, patients can be safely switched from the Iris collimator to the fixed cone collimator without replanning.
SU‐E‐T‐451: Optimization of Normalized Prescription Isodose Selection for Stereotactic Radiation Therapy: Conventional Vs. Robotic Linac
Authors: Ding C , Solberg T , Xing L , Heinzerling J , Timmerman R
Published: June 2012

Purpose: To determine the optimal prescription isodose line that minimizes normal tissue irradiation for stereotactic radiation therapy comparing conventional linear accelerator and robotic delivery. Methods: A computer based digital torso phantom which has the capability to simulate respiratory and cardiac motion were used in this study. Spherical targets were constructed in lung and liver, with diameter of 20mm, 30mm, and 40mm. Two concentric 5mm shells, from the target surface extending 5mm radially and from 5mm to 10mm, were identified/contoured. Non‐coplanar, non‐ opposing 3D conformal beams were designed for linac planning. Variable prescription isodose lines were achieved by varying the block margin. 4D dose calculation was used for moving target and surrounding tissue. After linac planning, the CT images and contours were transferred for Cyberknife® planning. Variable prescription isodose lines were achieved by inverse planning technique. Doses of 60Gy in 3 fractions were prescribed to cover exactly 95% of target tumor with each technology. gEUD (generalized effective uniform dose) with different formulations for parallel and serial tissues was used for comparison between different plans. Results: For linac plans, the optimal prescription isodose line yielding maximum normal tissue sparing occurs between 50% and 70% for the lung tumor and 60% and 90% for liver tumor. The gEUD difference between plans with optimum and arbitrarily chosen prescription isodose line may be up to 20% of prescription dose. For Cyberknife plans, the optimal prescription isodose line is approximately 50% for tissues displaying either parallel or serial behavior. These results are similar for different tumor sizes. Conclusions: Both conventional linac and Cyberknife® delivery can provide conformal tumor coverage with normal tissue sparing. By carefully choosing the optimal prescription isodose line, the gEUD of the surrounding normal tissue can be reduced by up to 20% of prescription dose.
SU‐E‐T‐452: Impact of Abdominal Compression on the Tumor Motion in the Treatment of NSCLC Using Stereotactic Body Radiosurgery
Authors: Martin K , Gomez J , Singh A , Malhotra H
Published: June 2012

Purpose: Involuntary motion of the tumor during the treatment of NSCLC using stereotactic body radiosurgery presents its own unique challenges. In this study, we quantify the impact of abdominal compression technique to minimize tumor motion as a function of location of tumor in a patient. Methods: 25 patients (5 in each lung lobe viz. RUL, RML, RLL, LUL and LLL) were retrospectively analyzed. A 4DCT study encompassing the tumor was used on a 16 slice GE CT scanner along with Varian RPM gating system. The images were retrospectively binned in 10 phases. The motion of tumor was analyzed phase by phase in transverse, sagittal & coronal projections of the 3D image. This gave us 2 values for anterior‐posterior, superior‐inferior and lateral‐medial motions each and was averaged out. Results: Analysis of data reveals that the motion (mean ± 1SD) in the superior‐inferior direction was 1.8 ± 0.9, 4.2±2.8, 7.4±2.3, 1.5±0.8, 3.1±2.8 mm for tumors located in RUL, RML, RLL, LUL and LLL, respectively. Along the anterior‐posterior direction the respective values were 2.5 ± 1.9, 2.4 ± 1.1, 2.7 ± 1.3, 1.4 ± 0.2 and 1.8 ± 1 mm. Similarly, along the lateral direction, the respective values were 2.1 ± 1.1, 1.9 ± 1.1, 1.6 ± 1.3, 1.1 ± 0.3 and 1.8 ± 0.7 mm. When the data was analyzed removing the location of the tumor in the thorax, the median displacement along the superior‐inferior, anterior‐posterior, lateral direction was 2.3, 1.6 and 1.5 mm, respectively while the respective maximum value were 9.2, 5 & 3.8 mm. Conclusions: The use of abdominal compression provides a simple inexpensive yet easily tolerable device to control the motion of the tumor in the management of NSCLC for SBRT treatments. This will allows the treatment of the tumor without resorting to complex and time consuming gated treatments.
SU‐E‐T‐455: Novel Planning Techniques for Lung SBRT
Authors: Caroprese B , Desai P , McKellar H
Published: June 2012

Purpose: Two new planning techniques in lung SBRT are presented. The first technique involves a differential dosing strategy for patients with compromised pulmonary function. The second technique compares supine vs prone setup for extreme posterior lesions. CyberKnife™(CK) prone setup is complicated due to patient discomfort from longer treatment times and the inability to track without fiducials. Methods: CK(G.3) Multiplan™(V3.5). Synchrony™, XSight™ Lung Tracking Systems. Our lung SBRT patients are tracked using fiducials with Synchrony or without fiducials with XSight using a 60 Gy in three fractions scheme. If the ray‐tracing optimized plan results in V15Gy greater than 10% we employ the differential dosing technique. A new PTV is created to encompass the 54 Gy isodose surface. A more conformal plan with a dose constraint of 60Gy to CTV and 54Gy to PTV is created appreciably lowering the V15Gy. Alternatively a 54Gy PTV can be created from measured respiration excursions. For the prone/supine comparison, plans were generated for both positions then evaluated. Results: Patients planned with the differential dose technique have a good tumor response as evidenced by a follow‐up PET. Although prone setup is preferred for extremely posterior tumors, a dosimetrically comparable supine plan can be created to replicate the prone plan. The supine low dose spillage was only slightly greater than in the prone case. Conclusions: We conclude that the 54Gy/60Gy dosed patients have almost the same tumor response as the standard 60 Gy treatment. A dosimetrically similar supine plan obviates the need for a prone delivery.
SU‐E‐T‐456: Potential Optimization of Stereotactic Body Radation Therapy (SBRT) from a Simple Field Timing Rearrangement
Authors: Schmitt J , Warren G , Wang I
Published: June 2012

Purpose: Stereotactic Body Radiation Therapy (SBRT) is a radiotherapy technique which uses high dose fractions with multiple coplanar and non‐ coplanar beams. Treatments are typically protracted with more fields than conventional radiation treatment schemes. The timing of field delivery may have an impact on the radiobiological results for SBRT. Methods: In a cohort of eight SBRT patient treatments, the protraction factor (G‐value), LPL, and LQL models were used to optimize field arrangements. An actual field timing delivered in the clinic (C) was included for comparison. The LPL model was used to quantify the difference in survival fractions (SF). Published data from three cell lines for non‐small cell lung cancers: H460, H660, and H157 was used to acquire the model parameters. The results were displayed as (C:O)̂N or (V:O)̂N, where C, V, and O were the SF for the clinical (C), least favorable (V), and optimal (O) field timings respectively. N represents the number of fractions for the SBRT protocol. Results: Results from all three models indicate that the optimal field order occurs when the fields are arranged in a triangle like pattern, where the highest dose fields are positioned centrally. Minimization of cell kill was achieved with a V‐shaped orientation, although these results were not as conclusive. Results of the SF ratios demonstrated that regardless the cell type and model the triangle shape had lower cell survival fractions compared to both the C and the V arrangement. For example, the H460, with repair half‐time = 1.50 h, an average ratio of (C:O)̂3 = 5.8, suggesting the triangle pattern is approximately 6 times more effective than the clinical plan, after 3 fractions. Conclusions: Rearranging field timing for a SBRT treatment so that maximal dose is deposited in the central fields of treatment may optimize cell kill and potentially affect overall treatment outcome.