bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐GG‐J‐181: The Role of Voxel‐Based T10 Calculations in Determining Correct Pharmacokinetic Parameters for Head and Neck Tumors
Authors: Cleland E , Brizel D , Yoo D , Dolguikh M , Muradyan N , Barboriak D , Craciunescu O
Published: July 2008

Purpose: To determine the optimal flip angle combination (oFAc) that generates voxel‐based T10 values, the median T10 for primary and nodes , and its implications on vascular permeability (PERM) and extracellular volume fraction (EVF) in HN patients treated with targeted therapy and chemoradiation. Method and Materials: To generate voxel‐based T10, a gradient echo sequence was used on a 1.5 T scanner with TR=6.44 msec and FA of 10, 15, 20, 30, 45°. For different FA combinations, the voxel‐based values were calculated using CAD Sciences® (White Plains, NY). The average of the median T10 in muscle and fat regions of interest (ROI) in 3 patients was calculated. Criteria for oFAc included minimal variation from published muscle and fat values at 1.5T, and minimum number of FA used for fitting. To determine , values from ROIs delineated by 2 users (A,B) were calculated. For 3 patients, the PERM and EVF from primary and nodes ROIs were calculated using T10 maps and . Results: The 10–45° FAc was chosen for subsequent T10 mapping as it had the greatest percentage of fitted pixels (90% for muscle, 100% for fat, % 83 for primary, 72% for nodes) and a , and , compared to reported 0.870 and 0.260 sec for muscle and fat, respectively. From14 patients, . The difference between the PERM and EVF calculated with voxel‐based T10 versus ranged from 6–81% for PERM, and 2.5–23% for EVF. Conclusion. The 10–45° FAc is fast and accurately describes the known T10 of normal tissue. Voxel‐based T10 calculations are essential for correct Tofts‐based PA in heterogeneous tumors. For HN, primary and nodes is a good estimate for T10 in the absence of T10 mapping capability.
SU‐GG‐J‐186: Towards Quality Assurance of 4D Radiotherapy Using a Deformable Lung Phantom
Authors: Serban M , Alexander A , Seuntjens J
Published: July 2008

Purpose: To develop experimental quality assurance (QA) procedures for 4D radiotherapy verification using a deformable lung phantom. Method and Materials: A deformable phantom consisting of a Lucite cylinder containing a latex balloon filled with dampened natural sponges and surrounded by water was developed for this purpose. The balloon is attached to a piston mimicking the diaphragm. Nylon wires and Lucite beads, emulating vascular and bronchial bifurcations, were glued throughout the sponges aiding deformable image registration (DIR). Four EBT Gafchromic film pieces were used to measure dose in different planes of a simulated tumour and lung tissue. 3D‐CT datasets (0.7×0.7×3 mm3) of the phantom in three static breathing states (End‐Exhale(EE); Mid‐Inhale(MI); End‐Inhale(EI)) were acquired. To evaluate film motion reproducibility, five repeat scans were obtained for each state. A four field, MLC‐shaped, 3D treatment plan was delivered on the MI breathing state of the phantom and recalculated with Monte Carlo. Results: The accuracy of DIR of the EI to EE breathing phases was 1.3(±2.4) mm and the film detector motion reproducibility better than 1 mm. Film placement, localization on CT images and film dose measurements proved accurate despite slight humidity from the dampened sponges. To address this, modifications to the material choice for emulation of lung tissue are underway. The differences between measured and MC calculated dose did not exceed and within and outside the tumour, respectively. Conclusion: Using a reproducible deformable phantom, this work aims to develop an experimental QA process for imaging, planning and delivery verification of 4D radiotherapy. The overall process of dosimeter placement, imaging and DIR, planning and dose delivery verification in the MI state of the deformable phantom was found accurate thereby opening the door to verifications of more complex planning and delivery strategies.
SU‐GG‐J‐190: Use of CBCT in SBRT Treatments, UTSW Experience
Authors: Papiez E , Timmerman R
Published: July 2008

Purpose: To present an impact of CBCT on efficiency and accuracy of SBRT treatments in case of lung and prostate tumors. Method and Materials: Patients interfraction and intrafaction setup errors have been analyzed for prostate SBRT treatments and for lung SBRT treatments. The CBCT has been utilized for this purpose. The CBCT measurements of shifts before the end of treatment have been also collected for comparisons. Results: Average interfractional shift for SBRT prostate treatments in vertical direction was −0.51cm with average deviation from mean of 0.29cm and with maximal shift of 1.3cm, in longitudinal direction these values were respectively −.01, 0.29 and 0.6cm and in lateral direction these values were 0.05, 0.22 and 0.8cm respectively. Average intrafractional shift for SBRT prostate treatments in vertical direction was −0.05cm with average deviation from mean of 0.07cm and with maximal shift of 0.2cm, in longitudinal direction these values were respectively 0.07, 0.12 and 0.5cm and in lateral direction these values were −0.08, 0.1 and 0.2cm respectively. Average interfractional shift for SBRT Lung treatments in vertical direction was −0.24cm with average deviation from mean of 0.37cm and with maximal shift of 1.1cm, in longitudinal direction these values were respectively −.06, 0.41 and 0.8cm and in lateral direction these values were −0.11, 0.34 and 0.9cm respectively. Average intrafractional shift for SBRT Lung treatments in vertical direction was −0.01cm with average deviation from mean of 0.06cm and with maximal shift of 0.2cm, in longitudinal direction these values were respectively 0.01, 0.04 and 0.3cm and in lateral direction these values were 0, 0.05 and 0.3cm respectively. Conclusion. Daily use of CBCT IGRT for patient setups indicates that daily corrections of setup errors at treatment justify reduction of margins in SBRT treatments of lung and prostate.
SU‐GG‐J‐192: Use of Optimized Oblique Anatomical Planes for Efficient and Accurate Organ and Tumor Segmentation
Authors: Low D , Abraham C , Parikh P , Mutic S , Thorstad W , Liu L , Khullar D , Apte A , Deasy J , Ju T
Published: July 2008

Purpose: To improve the efficiency and accuracy of tumor and normal organ segmentation by using optimized anatomical planes. Method and Materials: Contouring of tumors and normal organs is typically conducted using transverse computed tomography (CT) planes. This is due to the historical relationship between diagnostic radiology and radiation oncology, as well as the relatively poor longitudinal spatial resolution of CT relative to the transverse plane. We hypothesize that the accuracy and efficiency of segmentation will be improved if the contouring planes are aligned to anatomical landmarks and planes, similar to the methods used in surgery. This advance is made possible by the state‐of‐the art in CT systems that provide high spatial‐resolution images that do not bias the resolution in favor of the transverse plane. This program has three phases: 1) Design an algorithm that generates contour surfaces from nonparallel obliquely oriented contours. 2) Select oblique planes corresponding to surgical exposure techniques and evaluate the improved efficiency of segmentation using a custom‐generated organ surface library. 3) Develop a contouring toolset that includes tools to aid in navigating the CT dataset in 3 dimensions. Results: Phase 1 has been completed. Phase 2 is underway, with data from parotid segmentation showing progress for selecting anatomical planes similar to a superficial parotidectomy. Toolsets are being developed for phase 3, including methods for aligning the contouring plane with the anatomical reference landmarks as used in surgery. Conclusion: This process promises to provide a more efficient and effective method for manually segmenting structures based on the hypothesis that aligning the contouring planes to anatomical landmarks and structures will provide a more accurate segmentation process, and allow radiation therapy to be delivered with similar anatomical precision as surgical therapy. We anticipate this will be especially true for nodal target volumes.
SU‐GG‐J‐197: Video‐Coaching as Biofeedback‐Tool to Improve Gated Treatments: 2 Years Clinical Experience
Authors: Cossmann P , Stuessi A , von Briel C
Published: July 2008

Purpose: Gated treatments using the Varian RPM—gating™ System include in a standard configuration a coaching tool based on voice commands (“breathe‐in”/“breathe‐out”) called audio‐coaching. As this configuration does not include feedback information like amplitude and breathing period, there are limitations concerning respiration depth and breathing pattern. The aim of this study was to evaluate the impact of video‐coaching as biofeedback to achieve more regular breathing and — as a consequence — quality improvements of the 4D‐CT scans as well as duty cycle enhancements. Method and Materials: Varian RPM‐gating system is used for acquisition of the CT‐Scan (4D‐CT) as well as the treatments; for the latter it manages the controlled switching of the radiation beam during a pre‐selected specific phase of the respiratory cycle. 80 patients with gated treatments have been analyzed, whereas 40 were only audio‐coached and 40 audio‐coached with video‐feedback. We evaluated periodicity and amplitude changes as well as compliance with regard to the theoretically calculated duty cycle and determined the dependency of the parameters on the coaching type. Results: For the CT acquisitions several changes has been observed, i.e. fluctuations of the inspiration maxima are significantly smaller (p=0.005) and the breathing curves are smoother. The compliance during the treatment course was significantly increased: almost all video‐coached patients reached in average their theoretical duty cycle, whereas 60% of the patients with audio‐coaching only had more than 25% longer treatment times due to inappropriate amplitudes (p=0.001). Conclusion: Video‐coaching is suitable to significantly improve the quality of 4D scans and allows optimizing the treatment time due to better compliance. We also implemented this feedback technology combined with voluntary end‐inspiration breath hold technique thus allowing the patient to control the treatment themselves in a direct way. These results indicate that this approach could suit the individual patient need in a better way.
SU‐GG‐P‐01: Design and Implementation of Medical Physics Criteria For Performance Excellence Based On The Baldridge National Quality Program
Authors: Sternick E , Cardarelli G , Corrao A , Curran B , Garcia‐Cobian J , Hiatt J , Jang S
Published: July 2008

Purpose: To apply the techniques recommended by the Baldridge National Quality Program (BNQP) in the evaluation and sustainable improvement of medical physics management and operations. Method and Materials: The BNQP, administered by the National Institute of Standards and Technology (NIST), has developed a comprehensive set of Criteria designed to enhance the performance of U.S. organizations in a broad range of industries, including healthcare. We have customized these Criteria to have relevance for a medical physics practice in an academic radiation oncology department. The Medical Physics Criteria for Performance Excellence consist of seven categories: Leadership, Strategic Planning; Focus on Patients, Other Customers and Markets; Measurement, Analysis and Knowledge Management; Workforce Focus; Process Management; and Results. Results: A team‐based, self‐assessment approach is used for evaluation. The quantitative analysis focuses on both process and results, generating a profile of strengths and opportunities for improvement relative to outcome oriented requirements. This methodology provides for a structured examination of internal operations and trends as well as a way to benchmark with other medical physics groups. Conclusion: The Medical Physics Criteria can facilitate the enhancement of organizational performance in an increasingly complex and competitive healthcare environment by helping medical physicists align resources with approaches; improve communication, productivity and effectiveness; and achieve strategic goals.
SU‐GG‐T‐128: Rapid Dose Calculation for Dose Per MU Verification of IMRT Fields
Authors: Zhu T , Karunamuni R , Finlay J , Bjarngard B
Published: July 2008

Purpose: We have developed a fast algorithm to calculate patient specific 2D distribution of absolute dose per MU (D/MU) for megavoltage photon beams. Method and Materials: To calculate D/MU correctly, one has to perform the scatter‐integration with proper weights to account for the primary fluence distribution. In our PC‐based MU‐calculation program, the ratio of scatter‐to‐primary dose, Ds/Dp, for a 2‐D non‐uniform field is calculated as:
urn:x-wiley:00942405:media:mp1880:mp1880-math-0001 with and is the 2D intensity profile within the IMRT field, pi is 1 inside field and 0 outside field collimation for segment field i of the IMRT field. This convolution is calculated using a Fast Fourier Transform. The parameters a, w, and d0 characterize the phantom scatter properties and can be determined from measured PDD. Results: SPR can be calculated on an Intel Pentium 2.8GHz PC for 0.5‐cm grid size in less than 0.1 second for a 80×80 grid covering 40 × 40 cm2. For IMRT patients examined, the standard deviation of all comparisons is 1.5±3.9%. Conclusion: This algorithm is ideally suitable for calculating patient‐specific MU for quality assurance of patient specific IMRT fields for photon beams. The major attraction is the fast speed, which allows potential real‐time applications.
SU‐GG‐T‐131: Comparison of Mapcheck and EDR2 Film for IMRT QA
Authors: Takele T , Lamba M , Elson H
Published: July 2008

Purpose: To evaluate and compare the results of IMRT QA measurements taken using MapCheck and EDR2 film on a 6MV linac (21‐EX). Method and Materials: 10 Head & Neck IMRT treatment plans (ADAC Pinnacle) were evaluated. The treatment beams were placed on a QA phantom and a coronal dose distribution at 5cm depth was selected. This selected dose distribution was used as a reference to compare with identical dose profile measurements taken using EDR2 film and MapCheck. Three dose distribution comparisons were performed: between treatment plan & film, between treatment plan & MapCheck, and between MapCheck & film. The percentage of pixels with gamma ⩽1 was used to evaluate film results and the percentage of passed data points was used to evaluate MapCheck results. 5% dose/3 mm distance‐to agreement and 3% dose/2 mm distance‐to‐agreement tolerance conditions were used. A similar procedure was followed using EDR2 film with actual patient treatment beams angles. The mean percentage of points passing for all beams within a plan was calculated. Results: For EDR2 film vs. plan analysis, the mean pass rate is 99.8 % for (5%, 3mm) tolerance and 94.8% for (3%, 2 mm) tolerance condition. For MapCheck vs. plan: 99.9% for (5%, 3mm) tolerance and 96.5% for (3%, 2 mm) tolerance. MapCheck vs. film: 99.9% for (5%, 3mm) tolerance and 97.7% for (3%, 2 mm) tolerance. For actual gantry angle of treatment EDR2 film vs. plan: 93.3% with (5%, 3mm) tolerance and 78.2% for (3%, 2 mm) tolerance. Conclusion: IMRT QA performed using EDR2 film & MapCheck show similar results. IMRT QA performed using EDR2 film for non‐zero gantry angles result in up to a 12% increase in failing pixels relative to QA performed with all beams at 0 gantry.
SU‐GG‐T‐134: Dosimetric Verification of Dose Calculation Algorithms for IMRT Treatment Plan
Authors: Lah J , Hong J , Lee J , Chung J , Cheong K , Suh T
Published: July 2008

Purpose: The purpose of this study was to determine the accuracy of dose calculation in penumbra region from two different commercial IMRT treatment planning systems (TPS). The accuracy of IMRT calculations with a convolution/superposition and a pencil‐beam algorithm was tested using commission data with the modified values from Gaussian fitting approaches the real doses to correct for the spatial response of finite‐sized ionization chamber against measurement. Method and Materials: The IMRT head and neck phantom used in this study was housed in a custom‐designed package for efficient evaluation of the measured doses with different materials and various detectors. The Varian 21EX linear accelerator with 6 MV beam was used. The Pinnacle and the Ecilpse TPSs were calculated based on commissioning data that included beam profiles collected with a 0.125 cm3 ionization chamber. We have modified the commissioning data by a Gaussian function of an ionization chamber kernel to the real profile. Dose measurements made by ionization chamber, and glass dosimeter positioned within the phantom's target insert were compared with the calculated doses. Results: The differences for these algorithm results in average PTV doses were within 1.0%. Ionization chamber results showed approximately 1.7% better agreement than the glass dosimeters and the differences between measured and calculated doses were more than 3.0% for both algorithms. However, calculations using these algorithms after it were re‐commissioned from Gaussian fitting gave better agreement with measurements of IMRT field. A main reason of these results was attributed to detector size effects in the commissioning data. Conclusion: These results show that accurately measuring the penumbra region improves the accuracy of the dose calculations predicted by the TPS and thus is important to choose an appreciate detector.
SU‐GG‐T‐138: Dosimetric Characteristics of 2D Ion Chamber Array Matrix for Verification Radiotherapy Treatments
Authors: Sathiyan S , Ravikumar M , Supe S
Published: July 2008

Purpose: To study the dosimetric characteristics of 2D ion chamber array matrix for verification of Radiotherapy treatment plans. Method and Materials: The ionization chamber array consists of 1020 single air‐vented plane‐parallel plate ion chambers arranged in 32 × 32 matrix. Each chamber is of 4.5 mm diameter, 5 mm height and 0.08 cc of sensitive volume. The measurements were performed in Clinac DHX linear accelerator with 6 MV and 18 MV photons in a solid water phantom. The absolute dose and output factors were estimated for 6 and 18 MV photons using matrix device. The detector reproducibility, dose linearity and dose rate effect was studied. The performance of 2D array, in measuring clinical dose maps, was also investigated. Dose profiles of physical and enhanced dynamic wedge fields were analyzed. Furthermore, various IMRT fluence patterns generated from treatment planning system (TPS) were measured and compared. Results: The matrix device gives the absolute dose values based on estimated calibration factor. The reproducibility of measurements was good and the output and the output factor values were in good agreement with the standard ion chamber measurements. The system response was found to be linear in the dose range of 2–500 cGy and the response of the detector was found to be independent of dose rate. The 2D verification of intensity map at different depths for physical and enhanced dynamic wedges were in good agreement. The calculated and measured IMRT fluence patterns were found to be in good agreement (γ ⩽1:96 %, criteria 3 % &3 mm). Conclusion: On the basis of broad range of tests performed in this study, we conclude that the 2D array matrix is dosimetrically accurate and it can be a useful device for QA and verification of clinical radiotherapy beams.
SU‐GG‐T‐140: Evaluation of IMRT Plans From Three Treatment Planning Systems Based On Independent Monte Carlo Dose Calculation
Authors: Chi Z , Li J , Jin L , Fan J , Lin T , Xu Q , Ma C
Published: July 2008

Purpose: This work employs the Monte Carlo method to recompute the IMRT dose distributions from three TPS to provide a platform for independent comparison and evaluation of the plan quality in terms of target conformity and delivery efficiency. Method and Materials: Three prostate cases were planned with Corvus, Xio and Eclipse TPS using appropriate optimization parameters and dose constraints. The plans were recalculated by Monte Carlo using leaf sequences and MUs for individual plans. Dose‐volume histograms and isodose distributions were compared. Other quantities such as Dmin (the minimum dose received by 99% of CTV/PTV), Dmax (the maximum dose received by 1% of CTV/PTV), the volume of rectum and bladder receiving 65 and 40Gy (V65, V40), and the volume of femur receiving 50Gy (V50) were evaluated. Results: Special care must be taken to reproduce the dose distributions from different TPS due to their implementation of effective leaf positions. This may introduce up to a few percent differences in the absolute dose between treatment plans. The Monte Carlo results agreed with the dose distributions from all the TPS to within 5%/5mm. Both XiO and Eclipse plans show less target dose heterogeneity (smaller Dmax) and lower V65 and V40 for the rectum and bladder than the Corvus plans. The PTV Dmin is about 2Gy lower for XiO plans than Corvus and Eclipse plans while the XiO and Eclipse plans have slightly higher V50 for the femur than the Corvus plans. The Eclipse and XiO plans require significantly less MUs to deliver than the Corvus plans. Conclusion: We have tested an independent Monte Carlo dose calculation system for dose reconstruction and plan evaluation. This system provides a platform for the fair comparison and evaluation of treatment plans to facilitate clinical decision making in selecting TPS and beam delivery systems for particular treatment sites.
SU‐GG‐T‐141: The Statistical Analysis of Patient Specific DQA Plans of IMRT
Authors: Chung J , Park J , Park Y , Kim H , Choi C , Kim J , Kim I , Kim I , Wu H , Chie E , Suh T , Ye S
Published: July 2008

Purpose: By analyzing measured results of patient specific DQA (dosimetry quality assurance) plans of IMRT, we identified several factors that affected the discrepancy between calculated and measured doses. Method and Materials: From July 2006 to February 2008, patient specific DQA for 150 IMRT patients of H&N cancer, abdominal and prostate cancer, and brain tumor was performed by using a home‐made cylindrical phantom. A verification point was selected in the region of uniform and high dose. A diode array was used to compare individual fluence maps in a γ‐index method. Results and Discussion: The average difference between calculated and measured doses was −1.54±1.35% for H&N cancer, 0.13±1.05% for abdominal and prostate cancer, and −0.70±1.34% for brain tumor. The maximum difference was −3.4% for H&N cancer, −3.4% for brain tumor, and −2.6% for abdominal cancer. Planed and measured fluence maps were in agreement of 95.8±7.4% with the γ‐index criteria of ±3 mm and ±3%. The number of PTVs, the number of split fields, and the degree of modulation showed strong correlations with the discrepancy. Most of DQA plans (94%) agreed with measured doses within the tolerance level of ±3%. However, we found systematic underdosage of highly modulated H&N plans while dose differences of all other cancer patients followed the Gaussian distribution. Conclusion: We recommend that highly modulated plans out of the tolerance level should be avoid even though they can be generated by RTP. We suggest that dosimetric corrections for IMRT plans over the tolerance level could be achievable only with an established IMRT QA protocol.
SU‐GG‐T‐143: Comparisons of a Monte Carlo IMRT Plan Recalculation Results with the Pinnacle Treatment Planning System
Authors: Cui J , Davidson S , Willcut V , El Naqa I , Followill D , Deasy J
Published: July 2008

Purpose: We developed a Monte Carlo based IMRT recalculation tool and determined its parameters for Varian Clinac 2100C 6 MV and 18 MV photon beams. We report our comparisons with prostate and head and neck IMRT Pinnacle treatment plans. Method and Materials: Our source model components include: a primary photon point source, an extended extra‐focal source, and contamination electrons. One unique feature of the system is that it is fluence‐based, not a segment based calculation. A modified composite fluence map for each beam is built by summing the MLC segments and modifying for the effects of leakage, and rounded leaf edges. Model parameters are automatically determined by fitting to measurements. We re‐computed two 6 MV head & neck, and three 18 MV prostate, IMRT plans created by Pinnacle. For head & neck plans, we compared the DVHs of PTV, brainstem and parotid glands, as well as the mean dose to parotid glands. For the prostate plans, the DVHs for PTV, rectum, and bladder, as well as the D50, D98, and minimum doses for PTV are compared. Results: We found that our dose calculation system is comparable with Pinnacle for prostate IMRT plans, with small differences. For the prostate tests, the D50 for the PTV agrees within 0.7% with Pinnacle. DVHs for rectum and bladder all agree closely. The model predicts more pronounced dose inhomogeneity inside PTV in head and neck cases: the average reduction in the D98 value for the primary PTV was 5.5%. Conclusion: As expected, prostate IMRT recalculations agree well with the Pinnacle results. However, differences in head and neck results may be due to improved physics in the Monte Carlo system. The results support the use of the Monte Carlo tool as a treatment planning QA tool. Conflict of Interest: Work partially supported by grant PHS CA010953.
SU‐GG‐T‐145: Dose Response of Spectral Change of AS1000 EPID
Authors: Lin M , Lee C , Chao T , Tung C
Published: July 2008

Purpose: Amorphous silicon electronic portal imaging devices have been used as 2D dosimeters due to its excellent dose linearity response. However, dose response (cGy/signal) may be spectra‐dependent when patients are in the beam. The aim of this study was to evaluate the dosimetric sensitivity of a Varian aS1000 EPID to spectral change caused by the presence of a patient and give conclusive recommendation for clinical applications. Method and Materials: The signal‐to‐absolute‐dose response curves of the EPID were established for 0 to 40 cm thick of solid water phantoms on couch. The thickness can well cover the water equivalent thicknesses of most patients from head (11 to 19 cm) to pelvis (AP 15 to 25 cm, lateral 26 to 37 cm). Monte Carlo simulation (BEAMnrc 2006) was used to evaluate spectral variation at the EPID plane. Results: The results show that spectra at the EPID plane change dramatically for phantom thickness from 0 to 5 cm, and become more stable with further increased phantom thickness. Direct measurements have shown that large discrepancy up to 9.6% can be found for dose response within phantom thickness between 0 and 30 cm. It was also shown that the max variation between 10 to 40 cm which cover thicknesses of head and pelvis, 10 to 20 cm which cover thicknesses of head, 15 to 40 cm which cover thicknesses of pelvis, were 2.7%, 1.3%, 1.1% respectively. Conclusion: We thus concluded that for clinical absolute dose measurements, opened field dosimetry (without patient in the beam) and transit dosimetry should have identical dose response curves. From the different variations of dose response among 10 to 40 cm, 10 to 20 cm, and 15 to 40 cm, we suggest that for transit dosimetry, head and pelvis should have its own one dose response curve.
SU‐GG‐T‐148: Quantification of IMRT Patient Dose Deviations Due to Daily MLC‐Leaf Positional Variations
Authors: Dogan N , Saleh H , Fatyga M , Bartee C , Siebers J
Published: July 2008

Purpose: To develop a tool utilizing MLC‐log files and Monte Carlo (MC) dose recalculation that will allow cumulative deviations of IMRT patient plans to be assessed over the treatment course by taking into account the possible inaccuracy in the IMRT delivery. Method and Materials: Prostate, head and neck and lung IMRT patients were selected. The delivered MLC positions during the IMRT delivery were recorded in the form of MLC‐log files which were converted to MLC leaf‐sequence files. These files were then transferred back to the TPS and were attached to the original planned IMRT fields to regenerate the delivered dose distribution. Delivered fractional dose to each patient was then re‐produced using MC calculation. The recalculated fractional doses calculated via MC, which utilized the delivered MLC leaf‐sequences, were then combined to produce correct cumulative dose distribution received by the patient during treatment. Both delivered fractional and cumulative dose distributions and corresponding Dose‐Volume statistics were then compared with the ones obtained from the original IMRT plan. Results: For H&N IMRT case, the fractional changes in delivered dose‐volume indices were <1%. The changes in critical structure doses were negligible. For lung IMRT case, the differences in all dose‐volume parameters with MC re‐calculation using the delivered MLC‐sequences and the original planned MC dose calculation were less than 1.1% for PTV and all critical structures, except for the esophagus where differences in D30 were 2.4%. The similar results have been obtained for the prostate case in the study. Conclusion: The utilization of Monte Carlo for the recalculation of actual fractional doses delivered to the patients using the delivered MLC leaf sequence files for each IMRT field provides a powerful tool for offline QA of IMRT patients and can also be utilized for the verification of adaptive radiotherapy.

This work supported by NIH grant P01CA11602.
SU‐GG‐T‐151: On the Sensitivity of Patient‐Specific IMRT QA to MLC Position Errors
Authors: Yan G , Simon T , Peng L , Fox C , Liu C , Li J
Published: July 2008

Purpose: to assess the ability of patient‐specific IMRT QA procedure using planar dose comparison in detecting MLC positioning errors. Method and Materials: Eight IMRT plans (total of 53 fields) previously used for patient treatment with 6 MV photon beams from Varian Trilogy were randomly selected. Treatment plans were generated with a commercial planning system (Pinnacle3). Random errors (±2 mm) and systematic errors (±1 mm and ±2 mm) of MLC positioning were introduced into each plan. Planar dose distribution, calculated for each field with and without MLC positioning errors, was compared to measured dose distribution using a 2‐dimensional diode array (MapCHECK™). The agreement was analyzed using absolute DTA comparison as well as γ analysis with 2%/2mm and 3%/3mm criteria. The decrease in average passing rates was used to assess the sensitivity of patient‐specific IMRT QA procedure to MLC positioning errors. Results: Decrease in average passing rates with absolute DTA comparison and γ analysis showed similar trends with the introduction of MLC positioning errors. With 3%/3mm, only slight decrease (∼2%) was observed with random errors and ±1 mm systematic errors. Though ∼7% drop was noticed with ±2 mm systematic errors, the average passing rates were all above the error detection threshold (90%). When using 2%/2mm, average passing rates with systematic errors dropped below the threshold, with ∼5% and ∼15% decrease for ±1 mm and ±2 mm errors respectively. The average passing rates with random errors were still above the threshold. Conclusion: Our study indicates that IMRT QA procedure using either DTA criteria or γ index is not sensitive to MLC positioning errors up to 2 mm when using 3%/3mm criteria. When using 2%/2mm, only systematic errors of ±2 mm could be detected. Patient‐specific IMRT QA should be combined with a periodic MLC positioning check in order to guarantee the accuracy of IMRT delivery.
SU‐GG‐T‐154: Use of I'mRT MatriXX for Routine Dynamic MLC QA and IMRT Dose Verification
Authors: Bhardwaj Anup , Sharma SC , Patel FD , Ghoshal S , Oinam AS , Kapoor R , Kumar R , Goswami P
Published: July 2008

Purpose: To investigate the utility of 2D ion chamber array, I'mRT MatriXX™ (Scanditronix Wellhofer, Sweden) for dynamic MLC QA and IMRT dose verification. Method and Materials: The MLC QA test patterns designed for millennium 80 multileaf collimator were chair, x—wedge, pyramid, peak, open swipe field, garden fence and picket fence. For IMRT verification, five prostate cancer patients were planned using dynamic IMRT technique on Eclipse treatment planning system using 6 MV photons. The MLC QA test patterns and IMRT plans were executed on 2D ion chamber array, I'mRT MartiXX (24×24 cm2 active area, 1020 ventilated ion chambers) with equivalent 5 cm solid water buildup, keeping SSD 95. Planned and delivered dose delivery was compared using Gamma analysis (Δ dose 3% and Δ distance 3mm). Results: Dose response of MatriXX was linear in 0.2–10 Gy. Dose rate dependence was with in 0.15% in range of 1–6 Gy/min. Dynamic MLC QA tests such as chair, x‐wedge, pyramid, and open swipe field were successfully verified and passed the gamma analysis criterion with more than 95% pixels in defined field size. But because of less spatial resolution (7.62 mm), matrix was not able to recognize garden fence, picket fence, and 2.5 mm pattern in peak test. Mean and SD of difference between TPS calculated and measured CAX doses were 1.27% and 1.06 respectively for IMRT plans. Mean and SD of gamma analysis were 94.85% and 2.16 respectively. Dose differences were more than 3% along y direction in penumbra region because dose distribution can not be faithfully reflected by linear interpolation in high dose gradient region by MatriXX. Other than penumbra region, all pixels successfully passed the gamma analysis criterion. Conclusion: I'mRT MatriXX can be used for routine MLC and pretreatment IMRT QA. But care should be taken while taking measurements in penumbra region.
SU‐GG‐T‐155: Quality Assurance for IMRT in Belgium: Verification of the Integral Delivered Dose with Alanine‐ESR Dosimetry
Authors: Schaeken B , Van den Weyngaert D , Janssens H , Verellen D
Published: July 2008

Purpose: To face IMRT treatments with confidence, a federal QA program is set up in Belgium to verify the integral delivered dose for the routine technique as it is applied in the individual centers. The measured dose is compared to the TPS calculated dose as stated by the participant. Method and Materials: The integral IMRT‐delivered dose is measured at 3 locations within a phantom: at the center of two CTV's and at the center of one OAR in between. Dose is measured with alanine detectors which are read out in a desk top ESR‐spectrometer. Alanine dosimetry shows a linear variation with dose, no energy dependence nor fading. Dose is measured as the intensity of the central line in the powder absorption spectrum of alanine. The alanine pellets are calibrated in terms of “dose to water” between 1 Gy and 50 Gy by irradiation in a Co‐60 beam against water The participants are asked to pass the phantom through their routine process in order to perform a “end‐to‐end‐test”: acquiring CT scans for imaging, defining 2 cylindrical CTV's and one OAR as well to outline the detector volume. Complete freedom is given to the local staff in making a treatment plan: number of beams, optimization criteria, constraints, irradiation mode…). The only restriction is to deliver 10 Gy at the two CTV's and 3 Gy to the OAR. Finally the phantom is placed and lined up on the treatment couch using the routine procedure and irradiated. Results: up to now 6 centers are visited for which 10 tests with different IMRT techniques were performed: Tomotherapy(5), Segmented MLC(4), Dynamic MLC(1). The mean value of the ratio between stated and measured dose for CTV1 is 0.989 (sd=0.024); for CTV2 0.992 (sd=0.019); and 0.958 (sd=0.092) for OAR.
SU‐GG‐T‐163: Discrepancy of IMRT Dose Delivery Due to Dynamic MLC Gravity Effect
Authors: Lee J , Hong S , Choi K , Chung J , Lee D , Suh T
Published: July 2008

Purpose: The aim of the present study was to investigate the MLC gravity effect on IMRT dose dynamic delivery at different gantry angles. Method and Materials: To investigate the DMLC gravity effect on IMRT dose fluence, 2D ion‐chamber matrix (MatriXX) was mounted to Varian 21EX Linac. One individual IMRT dynamic segments were applied by MSS and SW for 6 MV photon beam at five different gantry angles, which were 0° (neutral gravity), 45° (semi‐along gravity), 90° (vertical‐along gravity), 315° (semi‐against gravity) and 270° (against gravity). To test the correlation of leaf speed and gravity, the half MUs for planned dose were delivered for a relative comparison. Strict γ‐index (dose difference: 2%, distance to agreement: 2 mm) histogram was used for a quantitative analysis of the discrepancy. The dose distribution by MSS under neutral gravity (gantry 0°) with 137 MUs at prescribed dose (45 cGy) point was used as a reference to compare other results. Results: The γ‐index histograms showed the increased tendency of the dose discrepancy toward the gravity‐along direction rather than against directions. The acceptable proportional ranges below 1 of γ‐index were 96.2–99.6% (mean: 97.6%), 92.6–93.5% (mean: 93.0%), 90.4–92.6% (mean: 91.3%), 94.6–98.0% (mean: 96.4%), 92.9–96.8% (mean: 95.0%) for neutral, semi‐along, vertical‐along, semi‐against, and vertical‐against gravity of MLC positions respectively. It was observed that MSS deliveries were more stable than SW data (unacceptable γ‐index range 1.0–2.0: mean 3.6% for MSS, 5.4% for SW). For dose measurement on the prescribed dose point, all measurements showed a good agreement within 1%. Conclusion: Our experiment conclusively reveals that the DMLC gravity definitely affects IMRT dose distribution. The effect may impact more severe in gravity along direction and SW, while leaf speed does not influence so much. Conflict of Interest: This work was supported by a grant of Seoul R&BD Program (10550).
SU‐GG‐T‐165: Multiple MLC Carriage Groups and Single Point IMRT QA Measurements
Authors: Ferenci MS , Beatty RE , Saw CB
Published: July 2008

Purpose: To investigate the discrepancy between reported and measured doses of individual subfields in multiple MLC carriage groups for IMRT QA using the Varian system. Method and Materials: The Varian leaf motion controller splits large fields into multiple MLC carriage groups for dynamic delivery. This process is handled automatically by the treatment planning system at time of transfer to the R&V system without requiring dose recalculation. As such, the reported point doses can be different from measured point doses for the individual subfields. Fifty IMRT fields that were split into two or more subfields were examined. The large fields were calculated and delivered on an IMRT verification phantom. To further investigate the point dose contribution from individual subfields, the fields created by the export process were recalculated. The reported and measured point doses were compared for each subfield individually and for the original large‐field as a whole. Results: Comparisons of the reported point doses and measured point doses for the original large‐field as a whole are typically within a few percent. However, the reported point doses for the individual subfields are inconsistent with the measured point dose for the original plan. In some instances, this difference can be orders of magnitude. Point dose contributions from the subfields as reported in the recalculated plans are more intuitive and consistent with the measured point doses. Conclusion: The reported dose of large‐fields with multiple MLC carriage groups as a whole is understood and in acceptable agreement with measurements. However, the origin of the reported point dose contribution of each individual subfield in the original plan is unclear and may not be correct. The use of this dose in comparison with measurements is not recommended without recalculation.
SU‐GG‐T‐167: The Effect of Leaf Transmission On IMRT QA in a MiniMLC Linear Accelerator
Authors: Misic V , Doemer A , Harrison A , Fallon K , Yu Y , Xiao Y
Published: July 2008

Purpose: Commissioning treatment planning systems for IMRT require more tests and verification of the beam model than those required for 3D conformal techniques. This study presents the dependence of IMRT QA pass/fail rate on the modeling of MLC leaf transmission in a MiniMLC linear accelerator. This particular modeling parameter doesn't affect the tests for 3D conformal situations per commissioning guideline. The results of both film QA and Mapcheck analysis will be presented. Method and Materials: Elekta Synergy S linac equipped with Beam Modulator collimating head was used (4mm leaves, no movable backup diaphragms) Beams were modeled in CMS XIO following the guidelines of TG53. IMRT plans were calculated for a phantom target (mock prostate) and the accuracy of the dose delivery was measured using both film and Mapcheck Gamma analysis. Then, the beam model in XIO planning system was replaced by the model with substantially lower MLC transmission factors, the plans were re‐optimized, and re‐delivered. Results: Original beam fitting (following linac commissioning) was internally verified by at least two independent measurements and checked against standard datasets (average passing rate of 97.8%). However, in our test plans, these fits showed relatively poor agreement between planned and delivered treatment as verified by both film and Mapcheck‐based dosimetry. Average passing rate using film dosimetry was 88% and using Mapcheck it was 71%. After beam re‐fitting using the decreased MLC Transmission factor, the agreement between planned and delivered dose increased to 98% and 87%, respectively. Conclusion: Commissioning of treatment planning systems for IMRT should include measurement verifications for IMRT plans of relatively complex modulation, in addition to standard tests from guidelines for 3D conformal planning.
SU‐GG‐T‐170: Using a 3D Diode Array System to Perform Routine IMRT Machine QA
Authors: Penn S Tafon , Xue T
Published: July 2008

Purpose: 3D dose verification of IMRT delivery is very time consuming. With the expectation of the increase uses of adaptive IMRT plans in the near future, more efficient way of IMRT QA is needed. We use a 3D diode array for routine IMRT machine QA, and hope it can lead to less plan specific IMRT QA. Method and Materials: Varian Eclipse, Trilogy with 6MV and 10 MV photon beams using sliding window technique IMRT are used. The 3D diode array is the Delta4 system from Scandidos. Delta4 has 1069 P type Si diodes on three wings, which are inserted to two planes in a cylindrical PMMA phantom. Four single beam plans (one open field, one wedge field for each energy) and two IMRT plans (one typical head and neck with 6MV, and one typical prostate with 10 MV) are used to irradiate the Delta4 weekly. The data of first measurement is set as reference data, subsequence measurement is compared with it by using 2D isodose display, profile comparisons, percentage dose deviation, and DTA and Gamma index. The open field measurement checks the combination of output, PDD, and flatness and symmetry. The IMRT measurement checks the combination of the above parameters plus IMRT delivery at various gantry angles. Results: Of about 10 weeks of measurements, the average percentage of diode with Gamma index (3% dose and 3 mm) 1 or less is more than 97% with standard deviation less than 2% for the prostate IMRT plan and the single beam plans. For the head and neck IMRT plan, we see more variations (the lowest one is only 78%). Conclusion: For simple IMRT plans such as prostate, this method works very well. More work has to be done for complicate IMRT plans such as Head and neck.
SU‐GG‐T‐173: Investigation of the Transmission Detectors for Daily Dose Verification and QA of IMRT Treatments
Authors: Desai P , Stathakis S , Gutiérrez A , Mavroidis P , Papanikolaou N
Published: July 2008

Purpose: To study the feasibility of using transmission type detectors for daily IMRT patient dose reconstruction and real time dose delivery verification. Method and Materials: Because of the complexity of IMRT there is a need for quality assurance for every patient. However, the daily delivered intensities may vary slightly from the planned ones. In this work we investigated the feasibility of using of transmission type detectors by using films for the verification of daily dose delivered to the patient. Films (Kodak EDR2) were placed in between 2 cm solid water after the MLC and at 100cm from the source. The optical density matrix (ODM) of the deliverable intensity maps were exported from the treatment planning system (TPS) for each beam calculated. A comparison between the ODM and the films was used to validate the TPS intensity maps. Results: The film measurements were compared to TPS predicted intensity maps. The agreement between calculated and measured intensity maps were in good agreement. The agreement was better when the intensity maps were compared against the film after the MLC. In both cases the TPS underestimated the dose/intensity at the low dose regions. The underestimation could be due to incorrect MLC leakage in the TPS machine model. By comparing the films at the two locations we observed that the low dose regions have the highest discrepancy, with the film closer to the source measuring lower dose at the low dose regions by 3 to 15%. Conclusion: Transmission detectors such as films can be used in order to compare the delivered intensity maps against the TPS predicted ones. It is feasible to have a transmission detector to record and verify the delivered ODM on daily basis and then calculate the dose delivered to the patient especially if cone beam CT is performed daily.
SU‐GG‐T‐176: Helical Tomotherapy Room Shielding: Leakage Radiation Levels and Tenth Value Layer Measurements Around Tomotherapy Machine
Authors: Goddu S , Ramirez J Garcia , Kintzel E , Mutic S , Chaudhari S , Klein E , Rangaraj D , Low D
Published: July 2008

Purpose: The objectives of this study were to measure the leakage radiation levels surrounding the tomotherapy machine and to determine the tenth value layers (TVL) for concrete. Method and Materials: A custom designed shield was fabricated with Cerrobend to shield a 1000cc spherical ionization‐chamber used in these measurements. Measurements were performed inside the treatment room at the height of the axis of rotation (AOR). Leakage measurements were performed for rotational delivery with the field size of 5×40cm2 and all the MLC leaves were closed. For TVL measurements, concrete slabs of 2.2g/cc were used. Measurements were repeated with full scattering conditions of a 30cm diameter phantom. Results and Discussion: The results indicate that our measured leakage values are 2–4 times lower than the vendor's data. This difference is attributed to the low energy scatter bouncing off the walls. The results also revealed that, for distances >3m, the leakage radiation followed the inverse square relationship within ±10%. Under full scattering conditions radiation levels are approximately 2.5–4 times higher for locations in the front of the gantry. This increase is higher along the AOR. For points that are behind the gantry and away from the AOR, measured phantom scatter component is much lower due to attenuation by the hardware of the machine. TVL measurements for the tomotherapy machine were found to be 21cm for Leakage radiation. These results are in agreement with the published literature2. When the phantom scatter is included in the measurements TVL dropped to 11cm. This is due to higher attenuation for the low energy scatter. Conclusion: Measured leakage levels around the tomotherapy unit were found to be 2–4 times lower than the values reported. The tenth value layer (TVL) for the tomotherapy beam was found to be 21cm of concrete.

This work is supported in part by Tomotherapy Inc.