bluuebunny/crossref_metadata_2025 huggingface dataset:
SU‐E‐T‐10: Streamlining and Automating Dosimetric Analysis for Treatment Planning System and Linac QA
Authors: Ozturk N , Smith B , Ahn K , Aydogan B
Published: July 2013

Purpose: To streamline and automate analysis of dosimetry checks for treatment planning system (TPS) commissioning, and TPS and linac QA, through scripts. Methods: A dosimetric analysis tool was developed using scripts written in Python language. A “standard” dosimetry dataset, ideally data measured for commissioning and/or verification of linac and TPS using a water scanning system, is generated and structured into an Excel spreadsheet. Annual dosimetry measurements, made with water a scanning system, are converted to the same format; measurements with a 2D ion chamber array (Matrixx) are kept in their original format in a separate folder. Plans for the same setup geometries are generated, or existing plans recalculated, and associated 3D dose files are exported in DICOM format into proper folders. Python scripts cycle through the planned DICOM dose files, match the information (beam energy, field size, SSD, depth) in the DICOM header with the data in the Excel files, or in the Matrixx data files, extract relevant dosimetric data from the 3D dose files (PDDs, profiles, output factors), compare to measurement using an in‐house developed gamma analysis routine and display the results in a pdf file (profiles, PDDs, planar dose distributions) or tabulate in an Excel sheet (output factors, absolute doses for reference geometries, wedge factors). For points failing the gamma analysis default passing criteria, an optimization is done to iteratively find at which tolerance levels these points pass for further evaluation. Results: Using our dosimetric analysis software, a test analysis of planned and measured dosimetric data for TPS commissioning of photon and electron beams was completed in about half hour, once data were converted into the proper format. Conclusion: Scripts written in Python facilitate more comprehensive analysis of dosimetric data for TPS and linac commissioning/QA. Streamlining the data analysis through scripts increases efficiency by reducing repetitive manual tasks.
SU‐E‐T‐12: Clinical Implementation of the Dedicated Program for MU Calculation in Proton Beam Therapy
Authors: Hayashi N , Adachi Y , Kato H
Published: July 2013

Purpose: The purpose of this study is to develop the dedicated in‐house program for calculation of the monitor unit (MU) of proton therapy beam and to verify the feasibility of its clinical implementation in proton beam therapy with a combination of range modulation wheel (RMW).Materials and Methods: The MU calculation for the proton beam was suggested by Dr.Sahoo in 2008 and given by the formalism using the multiplication of several factors with regard to the structure of the proton beam system. Following his theory, we implemented eight factors into the formalism for MU calculation as follows: Relative output factor (ROF), Spread‐out Bragg peak factor (SOBPF), Range shifter factor (RSF), SOBP off‐center factor (SOBPOCF), Off‐center ratio (OCR), Field size factor (FSF), Inverse square factor (ISF), and Compensator and patient scatter factor (CPSF). Our program was built by Microsoft Visual Basic language. The MU could be calculated by division of the prescribed dose with (d/MU). After building the program, the calculated doses by the formalism were compared with the measured dose. Results: The (d/MU) was calculated by the multiplication using eight factors by use of our program. Once the energy and the settings were input to the program, these factors were estimated from the measurement data. Then MU calculation was done immediately. It was simply and satisfactory fast for the user to complete calculating (d/MU). As the results of the comparison between the measured and calculated doses, the discrepancies in all referential settings were within 2%. Conclusions: The in‐house program provides the fast MU calculation for proton beams. The accuracy of the dose calculation is good in the referential settings. However, further improvement is required for the complicated condition.
SU‐E‐T‐20: Validating That the Gamma Dose Distribution Comparison Defaults to the Distance‐To‐Agreement (DTA) Test in Steep Dose Gradients for Clinical Dose Distributions
Authors: Dou T , Morele D , Low D
Published: July 2013

Purpose: To test the validity of the central assumption that the gamma dose comparison test defaults to a distance‐to‐agreement (DTA) test in steep dose gradient regions of clinical dose distributions for typically employed dose difference and DTA criteria. Methods: The angle θ between the dose axis and the gamma vector was computed usingθ = tan−1(Λ), where Λ was the local dose gradient of the evaluated dose distribution. θ depended only on the ratio α between the two test criteria and its computation required only one dose distribution. While the most common test criteria were 3%/3mm (α = 1%/mm), we also evaluated 2%/3mm (α = 0.67%/mm) and 3%/2mm (α = 1.5%/mm). Clinical treatment plans were used to calculate θ using the three values of α. 50 cases of both prostate and head and neck and 27 cases for lung cancer were examined. The planning target volumes and selected critical structures were examined. The maximum values of θ were determined for these structures to determine if these maximum θ angles were close to 90 degrees for the selected a values. Results: Most examined targets and critical structures exhibited large values of θ. The exception was for some parotid glands where the doses were very low and relatively homogeneous. The fact that we found that most structures had at least some voxels with sufficiently large dose gradients to yield θ values near 90 degrees validated our hypothesis that for steep gradients, the gamma test defaulted to distance‐to‐agreement test for clinical dose gradients. Conclusion: The implicit assumption that the gamma dose comparison tool defaults to the DTA test in steep dose gradient regions was validated for prostate, had‐and‐neck, and lung cancer sites. While dose distributions from other sites have not been examined, it is likely that they too will yield similar results.
SU‐E‐T‐21: A Grid Intensity‐Based Dose Algorithm to Realize MLC Irregular and Inhomogeneous Field Modeling for Monte Carlo Clinical Application
Authors: Lin H , Cai J , Dai Y , Jing J , Pei X , Cao R , Chen C
Published: July 2013

Purpose: A grid intensity‐based dose algorithm to realize MLC irregular‐inhomogeneous field modeling is presented for Monte Carlo clinical application in ARTS (Accurate Radiotherapy System). Methods: Linac modeling actually is a multi‐parameter optimization process, and especially depends on the composition and structure detail provided by venders. Maybe a real accelerator use could be substituted by an irregular‐inhomogeneous photon surface source with a compensatory contaminative electron source. MLC intensity map is regarded as many grid gather. The source photon is randomly sampled until its original grid intensity more than zero. The source particle weight is just equal to the grid intensity. The transmission direction of the source particle is decided by SID and MLC position just like a point source irradiation. The measurement data of a set of regular fields are used to commission a XH600D 6MV Linac. The 10cm*10cm field PDD is used to affirm the photon energy spectrum. Their half OARs at iso‐center surface of multiple regular fields are projected to MLC underside and fitted by Boltzmann function. A set of fitting coefficients are deduced. Their OAR differences before 1.5 cm depth are used to deduce the contaminative electron source. The MLC irregular‐inhomogeneous field is divided into several semi‐regular sub‐fields, whose side intensities and sub‐field width are confirmed by the corresponding field coefficients. This algorithm is implemented by adapting the open Monte Carlo code DPM. Results: This algorithm has been benchmarked with experiment data for regular fields. Basically the difference is under 2%/2mm. The rotational irregular‐inhomogeneous multi‐fields also are modeled. Conclusion: A grid intensity‐based dose algorithm is presented, which need not know the composition and structure inside a real Linac. This algorithm can simulate the irregular‐inhomogeneous field formed by MLC, and is promising for Monte Carlo clinical application.
SU‐E‐T‐22: RayStation Clinical MLC Modeling and Commissioning
Authors: Allen C , Pavord D , Sansourekidou P , Sutton M
Published: July 2013

Purpose: To accurately model the MLC in RayStation v3.0.0.251 and achieve acceptable clinical results. Methods: MLC parameters including transmission, leaf tip width and tongue and groove effect were investigated using previously published tests. Transmission and leaf‐tip geometry were assessed with a 2cm × 10cm MLC defined strip test on CAX and +/− 10 cm off axis with 16× 20 jaws, and a step‐wedge (Cadman, et al) irradiating 10 adjacent 1cm × 10cm MLC segments with step and shoot IMRT, while increasing the MU per segment by a fixed value. Conformal MLC shapes included the C‐shape and Squiggle (TG‐53), cross (Xiao, et al) and slanted rectangle (Phillips, et al). RayStation dose calculations were compared to EBT3 film and PTW Octavius detector 729 ion chamber array measurements. Analysis software included FilmQA™ and PTW Verisoft v5.1. All tests were performed on a Varian Trilogy.Additionally, six patient plans were created and IMRT QA was performed as clinical cases. Both split and non‐split field IMRT QA was tested. Patient disease sites included pelvis, prostate, head and neck, and lung. A passing criteria of 2%,2mm was applied. Results: After numerous iterations, the following was determined for both 6MV and 18MV: 0.017 tranmission, 0.05 cm tongue and groove, and 0.200 cm leaf tip width.IMRT analysis for a total 66 fields resulted in a 98.5% (97.2% split, 100% split) overall passing with the 2%,2mm criteria. Conclusion: The MLC model in RayStation v3.0.0.251 is clinically acceptable for patient treatment.
SU‐E‐T‐24: A New Method Correcting the Parabola Effect of Flat‐Bed Scanners Used in Radiochromic Film Dosimetry
Authors: Poppinga D , Schoenfeld A , Blanck O , Harder D , Poppe B
Published: July 2013

Purpose: In flatbed scanners used to digitize radiochromic films, a system of mirrors provides a reduced optical image of the scanned film in the entrance plane of a small CCD array. In this optical system, artifacts of the optical density arise from anisotropic scattering and polarization of the scanner light. We quantified this perturbation effect and eliminated it by a software correction. Methods: In order to measure the nonuniformity of an Epson 10000XL scanner and an Epson V700 scanner, seven EBT3 films of 4x4 cm2, exposed to doses ranging from 0 to 3 Gy were scanned at different positions × on the axis parallel to the light source. An area of interest of 30×30 pixels at the center of each film was chosen for analysis. The corresponding red channel pixel values were averaged and converted to optical density OD. These optical density values were then fitted by a parabolic function OD(×), which fully characterizes the nonuniformity of the scanner. The correction algorithm transforms the OD value measured at position × into the corrected OD value, i.e. the value that would be measured at the apex position. The calibration films are scanned at the apex position and the calibration curve is related to the apex OD value. Results: To test the correction algorithm a 20× 20 cm2 6 MV photon field was measured by film and ionization chamber and the dose difference after correction was less than 2%. This Result can be achieved all over the scanner bed, so it is possible to correct wide dose distributions measured by radiochromic films. Conclusion: This new parabola correction algorithm reduces the scanner artifacts over the whole width of the scanner bed and presents an alternative approach or an extension to the three‐channel analysis [Micke et al Med Phys 38, 2012].
SU‐E‐T‐33: A Comparative Study of Commissioning Data of Two TrueBeam LINACs with TrueBeam Representative Beam Data
Authors: Lim S , Tang G , LoSasso T
Published: July 2013

Purpose: To compare the commissioning water tank data of the two TrueBeam type linacs with TrueBeam Representative Beam Data. Methods: Three flattening filtered (FF), 6MV, 10MV, and 15MV, and two flattening filtered free (FFF), 6FFF and 10FFF, photon beams of one TrueBeam and one TrueBeam STX Linacs (Varian Medical Systems) are compared to the TrueBeam Representative Beam Data (TRBD) as provided by Varian. All measurements are scanned in Blue Phantom (IBA) with cc04 ion chamber at SSD 100cm at the highest dose rate available for each beam. The TRBD set is the average values of three TrueBeams at a single institution acquired by Iba cc13 ion chamber. To compare the beam quality, the PDD at d10 and d20 and the corresponding PDD 10/20 ratio at field sizes of 3×3, 10×10 and 30×30 cm2 are compared. The flatness of 10×10 and 30×30 cm2 open field profiles at depth of dmax, 10cm and 20cm are also compared. The output factors for square fields are also compared. Results: The PDD difference at both d10 and d20 between all FF and FFF beams and TRBD are within 0.6% and 0.9% respectively. The average PDD ratio difference between all beams and TRBD is within 0.5%. The flatness of all the FF and FFF beams are within 0.4% and 1.0% of TRBD respectively. The output factor differences between the two TrueBeams and RTBD for all beams and field sizes are within 0.8%. Conclusion: All the beam parameters of both the FF and FFF beams of the two Truebeams are within 1% of TRBD. Research grant from Varian Medical Systems
SU‐E‐T‐35: Extracting a Neutron Dose Using Only TLDs (Thermoluminescent Detectors)
Authors: Dy A , Shahnazi K , Klein S
Published: July 2013

Purpose: To test the use of TLDs for out‐of‐field neutron measurements and demonstrate the calibration and calculations necessary to extract a neutron dose by using TLD 600 chips, which measure photons plus neutrons, and TLD 700 chips, which measure only photons. For treatments requiring high‐energy photons or protons, secondary neutron doses may become a factor and TLDs provide many advantages in a clinical setting over conventional neutron dosimeters. Methods: A set of lithium fluoride TLDs (thermoluminescent detectors) consisting of 100, 600 and 700 series Rexon TLDs were arranged at set distances in and out of field of 6MV and 18MV photon beams from an Elekta Precise Treatment System. All TLD chips were read out using a Rexon System 310 reader and raw glow output data was exported for data analysis. Results: Examination of the integrated TLD glow curves shows an energy dependent response and a higher reading for TLD 600 chips as the distance or angle from the beam field increases for the 18MV beam. At a low neutron dose, correct integration interval must be used extracted a signal above noise. Conclusion: This work demonstrates the feasibility of neutron measurements using only TLDs as opposed to TLDs with CR39, bubble detectors, diamond detectors or WENDI detectors. TLDs are commercially available in different sensitivities and relatively cheap. We speculate that the TLD 600 chips will continue to read neutron doses at large distances to its neutron cross section. Furthermore they allow for spatial resolution and in vivo measurements. With calibration for neutron doses and photon energy ranges, a quantitative neutron dose is possible. This integration and subtraction method will be used in future investigation to directly quantify neutron doses spatially with respect to the beam and for different beam characteristics.
SU‐E‐T‐168: A Feasibility Study to Use Gamma‐Histogram Analysis in Assisting Quality Assurance Criteria for Evaluating Volumetric Modulated Arc Therapy Treatment Plans
Authors: Hisey K , Morales‐Paliza M , Ding G
Published: July 2013

Purpose: To investigate if gamma‐histogram statistical analysis can be used as criteria in establishing clinical action limits for pre‐treatment quality assurance (QA) agreement between planned and delivered dose distributions in volumetric‐modulated‐arc therapy (VMAT). Methods: Radiotherapy patient‐treatment plans were calculated using AAA dose‐calculation algorithm implemented in Varian Eclipse system (v.10). 6 and 10 MV photon beams from a Varian‐Trilogy Linac were investigated. Pre‐treatment QA dosimetry on 102 VMAT plans was performed using an electronic‐portal‐imaging device (EPID) and an ion‐chamber‐based array (MatriXX). Evaluation was done by comparing planned and measured dose distributions using gamma‐histogram analysis for plans grouped by site (head and neck, prostate, brain and lung). Different dose‐difference/distance‐to‐agreement gamma criteria from 3%/1mm to 5%/3mm were evaluated considering only dose levels higher than 10% of the maximum dose. Statistical analysis of gamma histograms included mean γ values (γmean), γ values corresponding to Δ = mean + 1.5 SD (γΔ), and areal percentages with gamma values less than 1.0, 1.5, and greater than 2.0. Average values and standard deviations for each of these five parameters were calculated per site to determine specific action limits. Results: The γmean over all analyzed plans with EPID was 0.42 +/− 0.10 for 3%/1mm and 0.29+/− 0.06 for 3%/3mm, while the corresponding average percentage of points with gamma less than 1 was 95.0% +/− 5.0 and 99.1% +/− 1.6, respectively. The results showed that parameters under the 3%/1mm and 3%/3mm criteria are plan‐site specific while the 4%/3mm and 5%/3mm criteria did not provide statistically significant differences among sites for EPID. Similar trends were observed for analysis using the MatriXX. Conclusion: Statistical analysis of γ histogram parameters is useful to perform pre‐treatment QA for VMAT plans. A specific selected criterion can be used to establish clinical action levels based on clinical acceptability and machine delivery accuracy.
SU‐E‐T‐174: Standardization of Gamma Analysis for the Evaluation of Pre‐Treatment Quality Assurance of RapidArc Plans Using 2D Array Combined with Octavius Phantom
Authors: Kumar Syam , Ajaykumar S , Bharathan R , Suja C
Published: July 2013

Purpose: To evaluate and standardize gamma analysis for different RapidArc plans. Methods: 45 different RapidArc plans were selected for the analysis study. Verification plan was created for each treatment plans in Eclipse 10.0 TPS using the AAA algorithm. Gamma analysis Pre‐treatment quality assurance was done using 2D array combined with Octavius phantom. Analysis was done separately for head and neck, thorax and abdomen case using different dose difference (DD) and distance to agreement (DTA) passing criteria. Results: The standard gamma passing criteria (3mm, 3%) shows a good pass percentage for all the sites with an average passing percentage of 95.49 (SD ± 3.75), 97.82 (SD ± 1.95) and 97.89 (SD ± 2.43) with head and neck, thorax and abdomen cases respectively. But when comparing head and neck and thorax cases, there is a significant difference between 1% DD and 3% DD for thorax cases. Also there is a significant difference between 1% DD and 3% DD with thoracic cases when compared to head and neck and abdomen cases. P‐Value of 0.009 (for 1mm, 1% gamma), 0.003 (for 2mm, 1% gamma), 0.010 (for 3mm, 1% gamma) was observed when analysis was done comparing head and neck with thorax cases. Also significant changes were noted when comparing thorax cases with abdomen with P‐Value of 0.001 (for 1mm, 1% gamma), 0.003 (for 2mm, 1% gamma), and 0.047 (for 3mm, 1% gamma). Same conditions were observed when comparison done for thorax and abdomen cases, with a significance difference with thorax cases. Conclusion: It is recommended to standardize the gamma passing criteria for specific site rather than going for the standard (3mm DTA, 3% DD) criteria. Also it is suggested to choose lower DD passing criteria to know the mismatch areas in the fluence when ever analysis done with thoracic cases.
SU‐E‐T‐181: Commissioning of COMPASS System for Flattening Filter Free Beams Patient Specific Quality Assurance
Authors: Perez‐Rozos A
Published: July 2013

Purpose: To validate and implementate the COMPASS and MatriXX Evolution systems (Iba dosimetry) for specific patient quality assurance using flattening filter free beams from a TruebeamSTx (Varian Medical Systems) linear accelerator. Methods: We use MatriXX Evolution 2D array mounted on isocenter using a gantry holder combined with angle sensor. 6MV FFF beams are modeled and verified into Pinnacle v9.2 (Philips) and Compass software. Matrixx dose rate response was assesed for dose rates from 4 Gy/min to 14 Gy/min. We begin the commissioning process comparing measurements and calculation of simple fields, and then we choose several SBRT cases comparing TPS doses and Compass calculated and reconstructed doses using as quality index the number of points with gamma index <1 inside 50% isodose. Verification include comparison of MatriXX measured fluences with Compass predicted fluences. Results: Compass modelling of FFF beams is accurate within 0.5%, same accuracy than conventional beams. Matrixx shows dose rate dependence below 0.2%. Comparison between Compass and TPS shows an agreement of 96% (points with gamma index <1), with no essential different between reconstructed and calculated measurements. Compass predicted fluences agree with matrixx measurements, with differences between +−2% inside beam and with higher diferences in penumbra region (some chambers with 10% differences) Conclusion: Compass was commissioned and validated for use with flattening filter free beams. Low dose rate dependence of Matrixx detector allows for measurements of IMRT or VMAT plans with high dose rate modulation. Compass calculated dose is as accurate as reconstructed dose, but last one allows for verification of machine delivery together with TPS verification.
SU‐E‐T‐185: Time‐Dependent Calibration Correction for EBT Film Dosimetry
Authors: Chen D , Kim J , Gordon J , Chetty I
Published: July 2013

Purpose: The aim of this study is to simplify EBT film‐based dosimetry calibration. In addition, two different approaches are proposed for film and scanner non‐uniformity reduction. Methods: EBT films, EBT3 and EBT2 were exposed under a calibration plan using 6X flattening‐filter‐free (FFF) photon beams. In method 1, pre‐irradiation scans were carried out and subtracted from post‐irradiation scans to calculate net‐optical density (net OD), removing non‐uniformity from both scanner and film. In method 2, two unexposed films were independently scanned for each irradiated film scan and subtracted from post‐irradiation scans. Calibration curves were then generated using the calibration plan dose and the film net OD values. Finally, a set of time‐dependent correction factors were derived from the calibration curves. The per‐batch average correction factors were applied in order to test the feasibility of using a per‐batch generic calibration curve. All converted film doses were verified against the planned dose. The scanner light effect on the film dose was estimated by measuring the changes in mean pixel value. Results: Up to 7% pixel value change was noted four days after exposure. A correction was necessary if a generic calibration curve was utilized. The method to remove non‐uniformity using the pre‐exposure film (method 1) was more stable than using two unexposed films (method 2). The batch average correction factors reduced calibration curve differences to less than 0.6%. The dose effect from each scan was minimal (∼0.1 cGy). Conclusion: It is feasible to use one generic calibration curve per film batch with a time‐dependent correction factor table without compromising overall EBT film dosimetry accuracy. This method may alleviate the current practice of the typical labor intensive film‐based dosimetry for patient specific QA as well as physics commissioning tasks.
SU‐E‐T‐187: The Value of Rapid Reviews
Authors: Lowenstein J , Roll J , Hollan A , Nguyen H , Followill D
Published: July 2013

Purpose: The Radiological Physics Center (RPC) performs rapid reviews for several different study groups and for a variety of disease sites including colon, breast, endometrial and cervix. Rapid Reviews have been performed for high dose rate brachytherapy studies, 3D CRT and IMRT studies. The purpose of rapid reviews is to verify that the radiation oncologist is capable of treating a patient per protocol prior to treatment commencing with the goal of reducing the number of deviations. Methods: The rapid review process requires that the institution electronically submit the protocol patient treatment plan prior to the commencement of treatment for a dosimetric and clinical review. Dependent on the protocol, the first patient or every patient submitted by a physician might require a rapid review. Rapid reviews enable the RPC to provide feedback to the physician to rectify errors prior to the start of treatment. Deviations are assessed according to defined criteria within the specific protocolResults: For three protocols, where rapid reviews were required for the first patient placed on protocol, 24%, 48% and 53% required a revision and resubmission for a re‐review due to a significant protocol deviation. For one protocol, where rapid reviews were required for all patients, 81% of the submitted patient cases required a revision and resubmission for a re‐review. Radiation Oncologists who completed the rapid review process received no major deviations on subsequent patient's placed on protocol. Conclusion: Rapid reviews serve the purpose of reducing the number of protocol deviations by providing feedback to Radiation Oncologists on how to better comply with the requirements of the protocol prior to commencing treatment of a patient on the study.This work was supported by PHS grants CA10953 and CA081647 awarded by NCI, DHHS. This work was supported by PHS grants CA10953 and CA081647 awarded by NCI, DHHS.
SU‐E‐T‐190: Manufacturing Accuracy of Range Compensators — Analysis of Over 12,000 Milling Points
Authors: Ramirez E , Rains M , Rana S , Zheng Y
Published: July 2013

Purpose: Range compensators are used in both passive and active uniform scanning proton beams to conform proton dose to the target's distal boundary. The manufacturing accuracy of compensators has a direct effect on range uncertainty in proton beams. The purpose of the study is to investigate the thickness difference between manufactured and planned compensators and its effect on range uncertainty. Methods: We used a range compensator QA table with 2‐D motors and overhead 1D laser measurement tool to measure the compensator thickness. The QA device allows automatic multiple milling point measurements with minimal man‐hours, with export of QA results to a tabulated file for ease of data analysis. We recorded the QA results of over 12,000 points across over 500 different blue wax compensators and analyzed the thickness deviation from treatment planning with a histogram plot. Results: The average measured compensator thickness is about 0.03 mm less than the expected according to the treatment plans. The standard deviation is about 0.17 mm. Causes for thickness deviation of larger than 0.5 mm were investigated. The corresponding water equivalent range uncertainty of a compensator is similar to the physical thickness deviation because the blue wax has a relative stopping power ratio of 0.97. Some large deviations due to human errors were analyzed separately. Conclusion: The range uncertainty through the range compensator is dependent on the accuracy of the milling device and also the relative stopping power of the compensator material. It is recommended to use material with stopping power close to water for compensators to mitigate the errors in milling yet also to reduce the bulkiness of the compensator. The range uncertainty due to compensator thickness inaccuracy is estimated to be about 0.3 mm (2 sigma) in our clinic.
SU‐E‐T‐193: A Custom Web Application for a GPU‐Based Monte Carlo IMRT/VMAT QA Tool
Authors: Folkerts M , Graves Y , Gautier Q , Kim G , Jia X , Jiang S
Published: July 2013

Purpose: To develop a user friendly web application for a GPU‐based Monte Carlo (MC) 3D dosimetry quality assurance (QA) tool which runs in modern web browsers and interacts remotely with specialized hardware/software resources. Methods: We developed a new QA web application based on existing technologies (HTML5, Python, and Django) to interface with a command line‐based MC QA tool. It eliminates the need for users of this cutting‐edge GPU software to purchase expensive/specialized hardware and use a command‐line based environment. The Results is a web app with a user‐friendly interface enabling control of GPU accelerated software for MC‐based QA. Users upload zipped DICOM RP, CT, and RD data and set the expected statistic uncertainty for the MC dose calculation. After the files are uploaded, the remote software is automatically launched to generate intermediate data necessary for the GPU‐based MC dose calculation. The MC dose calculation is then executed on the remote GPU server and the resultant dose and original plan dose (from uploaded RD file) are displayed in the web GUI for the user to review. A 3D gamma index map and DVH curves are also displayed to the user. Finally, a PDF QA report that summarizes the results can be downloaded. Results: We successfully developed a web app for a GPU‐based QA tool that consists of fluence map generation, CT image processing, GPU based MC dose calculation, gamma index calculation, and DVH calculation. The Results is an IMRT and VMAT QA tool that conducts an independent dose calculation for a given treatment plan. The computation time from data uploading to viewing results and downloading report is less than 2 min. Conclusion: We developed a GPU‐based MC QA tool with a user‐friendly web‐based interface. The high efficiency and accessibility greatly facilitate IMRT and VMAT QA.
SU‐E‐T‐198: Dosimetric Effect of Multi‐Leaf Collimator Transmission On Intensity‐Modulated Radiation Therapy
Authors: Yang R , Wang J
Published: July 2013

Purpose: To investigate the dosimetric effect of multi‐leaf collimator (MLC) transmission on Intensity‐modulated radiation therapy. Methods: MLC transmission through the leaves and rounded ends were measured with ion chamber for Varian Trilogy linear accelerator with the energy of 6 MV and 10 MV. The intraleaf and interleaf transmission were also measured with the electronic portal imaging device of aS1000. 10 cancer patients treated with intensity‐modulated radiation therapy were used to evaluate the MLC parameters modeling in the Eclipse treatment planning system. Results: The average transmissions of Millennium MLC were 1.6% and 1.8% for 6 MV and 10 MV X‐rays. The transmission increased with the field size and depth of measurement. The transmissions at off axis position were a little lower than those on the central axis. The intraleaf transmissions measured with aS1000 were 0.8%–1.2% and 1.1%–1.6%, the interleaf transmission were 1.3%–1.9% and 1.6%–2.5% for 6 MV and 10 MV X‐rays respectively. Modeling with the measured MLC parameters, the Eclipse treatment planning system could calculate the dose distribution accurately. The gamma index pass rate at 3%3 mm was above 95%, except for two patients with nasopharyngeal cancer with the pass rate of 93.6% and 94.5%. Conclusion: The transmissions through the MLC leaves and the leaf ends contribute to the dose throughout the target significantly for IMRT. MLC transmission varied with the field size, depth of measurement and off axis position. This work was supported within the grant project: National Natural Science Foundation of China (No. 81071237).
SU‐E‐T‐200: Impact of Detector Element‐Specific Angular Correction Factors for the MaxtriXX Ion Chamber Array for Patient‐Specific Dose Validation
Authors: Casares O , Kim S , Armas J , Papanikolaou N , Gutierrez A
Published: July 2013

Purpose: The purpose of the study was to create detector element‐specific angular correction factors (DESACF) for each detector element of the MatriXX planar ion chamber array and compare them to the default ACF provided by the vendor. Additionally, the impact of these correction factors on the Gamma Index (GI) was quantified. Methods: The ACF for each detector was determined using the MatriXX manual guidelines. By doing so, the ACF of a specific ion chamber element is determined by the ratio of the calculated dose to the MatriXX measured dose as a function of gantry angle. Dose calculations were performed in Pinnacle TPS (Ver. 9.2) using 6 and 10MV energies. Open field beams were calculated every 5° (0° to 180°) with a 1° sampling (85° – 95°). With this, a DESACF table was created. To evaluate the impact of the DESACF on patient‐specific dose validations, eleven (n=1 1) previously irradiated patient‐specific dose validations using 6MV VMAT beams were re‐analyzed. GI values were recorded using the criteria: 3%/3mm, 2%/2mm, 1%/1mm. Results: The DESACFs for 6MV were found to be different than the default ACF by up to 7% for given angles, significant differences existed for angles (85° to 95°). For 10MV, differences (5%) existed when DESACFs were created using solely the mean CF values of a 10×10cm2 ROI versus a 21×21cm2. Differences between the mean patient GI values using the DESACF and default ACF for 3%/3mm, 2%/2mm, & 1%/1mm were 0.6 (p>0.01), 2.3 (p=0.02), & 0.1% (p>0.01), respectively. Statistically significant differences might be noted with a larger sample, especially at 2%/2mm. Conclusion: Large differences in the default ACF and DESACF were noted for 6MV. For 10MV, the DESACF showed dependence on ROI size to derive mean CF value. For evaluated cases, no significant difference was noted in the GI due to DESACF.
SU‐E‐T‐203: Patient Specific IMRT QA Analysis Comparison of Four Commercially Available Systems
Authors: Briceno J , McKinsey R , Esquivel C , Mavroidis P , Papanikolaou N , Stathakis S
Published: July 2013

Purpose: IMRT patient specific QA is often used across institutions to provide a quantitative measure of the accuracy by which a treatment plan is delivered. The aim of this project is to evaluate the performance of four commercially available devices while varying the acceptance criteria of dose difference and distance to agreement (DTA). Methods: Ten VMAT and 10 static field IMRT plans were evaluated. All the plans were optimized using the Pinnacle v9.2. Measurements were performed on a Varian 2100CD linac equipped with millennium 80MLC. The gamma index was chosen as the primary metric for the evaluation of the agreement between the planned and measured dose distributions. The gamma index was calculated for each plan using 10% and 20% dose thresholds, 3%/3mm, 2%/2mm. The analysis was performed for the composite plans as well as field‐by‐field using the software provided with each IMRT QA systemResults: Octavius II showed higher passing gammas for 3%3mm and 2%2mm compared to the other detectors in all the IMRT field‐by‐field comparison. In the IMRT true composite plans, the gamma index values (3%/3mm) were: 89.5, 87.3, 89.2, 88.8 for Delta4, IBA Matrixx, Octavius4D and PTW Octavius II, respectively. For the same IMRT plans with the beams delivered with the gantry in the upright position, the gamma indices were 89.5, 98.4, 94.0, 100. For the VMAT plans, the gamma index values were 93.7, 95.0, 91.2, and 97.5. The gamma index values from the evaluation of the VMAT plan using a dose threshold of 20% were 91.8, 95.1, 88.6, and 97.3, respectively. Conclusion: The detectors response is very similar for the three treatment techniques examined. Stricter gamma index criteria reduced the passing rate of the plans by about 20%. The differences between the detectors did not show any trend depending on method, site, or mode of delivery.
SU‐E‐T‐206: IMRT/VMAT Quality Assurance Using Portal Dosimetry
Authors: Pan X , Ochran T , Bradley W
Published: July 2013

Purpose: The purpose of this work is to investigate the application of an amorphous silicon electronic portal imaging device (EPID) in IMRT/VMAT QA as a replacement for conventional IMRT/RapidArc QA tools. Methods: 20 IMRT/RapidArc treatment plans for treatment site of head and neck, breast, lung, abdomen, and pelvis were selected randomly for the study. Verification plans on ArcCheck phantom (Sun Nuclear Inc.) (ArcCheck Verification Plan, AC_Veri_Plan) and for portal dose prediction (PD_Veri_Plan) were generated in Eclipse treatment planning system, and delivered in ArcCheck phantom measurement and portal dosimetry for each treatment plan, respectively. For AC_Veri_Plan, absolute dose was measured by ion chamber inserted in ArcCheck phantom and relative dose is evaluated by the gamma method (criterion %3/3mm) using SNC dosimetry software. For PD_Veri_Plan, absolute intensity was measured in an area of 1cmx1cm and relative dose by the gamma method in portal dosimetry. The results of absolute and relative dose difference using both of phantom measurements and portal dosimetry were compared. Results: For 20 AC_Veri_Plans, variation between the measured and calculated absolute dose is within 3% {range ‐ 2.29% to 2.34%, average 0.46%}. The percentage of gamma<1 is above 90% {range 93.9% to 100%, average 98.85%}. For 20 PD_Veri_Plans, variation between measured and calculated intensity is within 4% {range −2.47% to 3.34%, average 1.26%}. The percentage of gamma<1 is also above 90% {range 95.9% to 100%, average 99.61%}. All of AC_Veri_Plans and PD_Veri_Plans pass the QA, although the variation of absolute intensity on average in PD_Veri_Plans has about 0.8% higher than that of AC_Veri_Plans. The tolerance is 5% for the absolute dose variation and 90% of gamma<1 for the relative dose. Conclusion:Phantom measurement for IMRT/VMAT QA is a time‐consuming task. Portal dosimetry can be used as a rapid and convenient plan verification tool for IMRT/VMAT.
SU‐E‐T‐208: Automated Routine 3D Secondary Patient Dose Calculation Prior to and During Fractionated Treatment
Authors: Schillemans W , Seppenwoolde Y , Akhiat H , Doorn X , Kanis B , Linton N , Heijmen B , Dirkx M
Published: July 2013

Purpose: Development and evaluation of a fully automated secondary 3D patient dose calculation system to replace the conventional point‐based MU‐check and to ensure correct plan transfer to the record‐and‐verify system (RVS) and plan integrity during patient treatment. Methods: Basis is a fully automatic workflow in the RVS (MOSAIQ), developed in collaboration with the vendor. Treatment parameters (3DCRT/IMRT) in the RVS are converted into a DICOM RTPlan object. A dose engine (Oncentra), independent of the original TPS (XiO/Monaco), is then used to recalculate the 3D patient dose. The system is used for two scenarios. To verify the originally calculated dose and plan transfer, the secondary dose is compared to the TPS dose prior to the first fraction. In between fractions the dosimetric impact of changes in treatment parameters in the RVS, made deliberately (e.g., addition of imaging field) or accidentally (i.e., erroneous parameter change) is determined. In this scenario, the daily recalculated dose is compared to the secondary dose from the first scenario. In both scenarios a report is automatically generated and stored in the patient's chart. The physicist is notified in case of non‐negligible errors. Results: Although for the first scenario small differences are generally observed due to differences in dose calculation algorithms and inaccuracies in their commissioning, clinically relevant errors from our clinic or described in literature could easily be detected. With the second scenario even the smallest dosimetric differences are detected, since the same secondary dose engine is used. This leads to an improved understanding and overview of the impact of parameter changes in the RVS with minimal user interaction. Conclusion: The new automated 3D QA system replaces the MU‐check, checks the integrity of RVS treatment parameters on a daily basis, and quantifies the dosimetric impact of any changes. Without increasing workload, this contributes to increased patient safety.
SU‐E‐T‐212: To Evaluate Significance of Gamma Index Between the Measurement of 2D Detector Arrays and the Calculated Patient 3D Dose Distribution
Authors: Kim S , Qiu Y , Mavroidis P , Papanikolaou N , Stathakis S
Published: July 2013

Purpose: To evaluate significance of gamma index between the measurement of 2D detector arrays and the calculated patient 3D dose distribution. Methods: DMLC (Dynamic Multi‐Leaf Collimator) of IMRT (Intensity Modulated Radio Therapy) delivery information recorded in log files during delivery. The Dynalog file includes amongst other, the beam on and off status, segment dose index, and individual leaf positions. In this study, three previous treated IMRT patient plans are selected and delivered using a Varian CLINAC 600 C/D linear accelerator equipped with Millennium 120 MLC. Patient specific measurements were obtained using the PTW OCTAVIUS II system for all individual fields, while simultaneously recording the Dynalog file. Using an in‐house Matlab code, the dynalog data are converted to an adapted format of fluence map to Eclipse v8.9 treatment planning system. Using the Dynalog file based fluence maps we are able to calculate the dose for each field and the also to calculate the patient dose distribution. Comparisons of individual fields and of the patient 3D distribution were then performed and the analysis was based on gamma index passing rate for the individual fields, and DVH and dose differences for the patient dose distributions. Results: Our study confirms that the measured planar dose for individual fields has a good agreement to the calculated dose using the DMLC Dynalog file fluence maps. Filed by field analysis between detector measured and dynalog file fluence based calculations had 94.2% passing pixels using 3mm/3% criteria. Conclusion: Results show that the calculated dose based on Dynalog record is comparable to measured dose on PTW OCTAVIUS II detector. Gamma index values showed the reasonable dosimetric identity between two dose distributions.
SU‐E‐T‐213: Comparison of Two Methods for Patient Specific VMAT QA Using Portal Dosimetry and IBA MatriXX
Authors: Xu H
Published: July 2013

Purpose: To quantitatively evaluate two Methods: portal dosimetry and MatriXX placed in a dedicated holder, for clinical VMAT patient specific QA using gamma analysis. Methods: 21 prostate VMAT double‐arc plans were generated in Eclipse. We used portal dosimetry and MatriXX to conduct plan verifications. Portal dosimetry, including the absolute dose mode, was commissioned according to Varians guide. The MatriXX was commissioned as per vendor manual. In our study, Matrixx was inserted in a dedicated holder that was mounted on a linac treatment head with 5.0cm effective depth from the surface to the detector plane. In this geometry, the MatriXX detector plane is always facing the source perpendicularly. Thus the angular corrections for MatriXX detectors were not required. Gamma index was calculated using appropriate values of dose difference and distance‐to‐agreement. The threshold value, used for excluding low dose regions, was set to 5%. In portal dosimetry, calculated dose and measured dose were auto‐aligned and gamma index was obtained in the absolute dose mode. Portal dosimetry system was calibrated weekly or as needed to ensure its optimal working conditions. Results: In the MatriXX measurement, the Bland Altman plot was used to show that, with 95% confidence level, the measured Dmax agreed with the calculated Dmax. Then the dose distributions measured from MatriXX were normalized to Dmax and IBA so±ftware was used for gamma analysis. For gamma index calculated with 3%/3mm, both portal dosimetry (98.6%±1.1%) and MatriXX (97.0%±1.1%) exhibit similar passing rates, with portal doismetry demonstrating slightly higher passing rates than MatriXX. Conclusion: This work indicates that for VMAT patient specific QA, a well calibrated portal dosimetry system can be equivalent to or better than the MatriXX system. Future endeavors may extend to the analysis of VMAT plans for other sites and exploration of the method using the MatriXX inserted in a MultiCube phantom.
SU‐E‐T‐216: A Clinical Dosimetry Analysis of Total Body Irradiation for Leukemia Patients
Authors: Filippi J , Patel A , Gupta N , Weldon M , Woollard J , Ayan A , Rong Y , Martin D , Pelloski C , Welliver M , Lu L
Published: July 2013

Purpose: Perform a retrospective dosimetry study of total body irradiation (TBI) on leukemia and bone marrow transplant patients. Methods: The in vivo dosimetry data of 129 patients treated with TBI between 2008 and 2011 were retrieved from the database and analyzed. These patients were mostly treated with the regime of a single fraction or 6 fractions with some exceptions of 8‐fraction or 2‐fraction treatments depending on the protocols that were applied. For every fraction of treatment, 10 pairs of diode dosimeters were used to monitor the doses to the mid‐line of head, neck, arms, mediastinum, left lung, right lung, umbilicus, thigh, knee, and angle for both AP and PA fields. The doses to the midline of the above body parts were considered to be the average of the AP and PA readings of each diode pair. Dose deviation from the prescribed value for each body part was studied by plotting the histogram of the frequency versus deviation and comparing this with the dose delivered to the midline of the umbilicus to where the dose was prescribed. The correlation of dose deviation to body part thickness was also studied. Results: The dose differences between measurement and prescription for all body parts are mostly less than 10%. The dose inhomogeneity on different body parts could be manually improved by using compensators but the method is cumbersome. The dose deviation in many histograms ranging from about −10% to 10% indicates some incongruity of dose distribution. This could be due to the method of using lead compensators for a manual dose adjustment which could not ideally compensate different body thicknesses everywhere. Conclusion: The conventional TBI could give uniform dose to the major body parts under the in vivo dosimetry monitoring at the level of 10%, but the treatment procedure is cumbersome and time consuming.
SU‐E‐T‐217: The Effect of Image‐Guided Isocenter Shifts On Optically‐Stimulated Luminescent in Vivo Dosimetry
Authors: Rea A , Kuruvilla A , Riegel A , Kapur A , Chou H , Jamshidi A , Potters L
Published: July 2013

Purpose: The purpose of this study was to characterize the uncertainty in dose measurements by optically‐stimulated luminescent dosimeters (OSLD) as a Results of image‐guided isocenter shifts in volumetric modulated arc therapy (VMAT) of prostate cancer patients. Methods: Daily image‐guided couch shifts were extracted from the record and verify system for 25 pre‐op prostate cancer patients (1130 fractions) with implanted fiducials and 7 post‐op prostate cancer patients (255 fractions) registered using bony anatomy. Standard deviations were calculated to quantify typical isocenter shifts in the superior‐inferior, anterior‐posterior and lateral directions. Typical shifts were applied to treatment plans for 13 pre‐op and 9 post‐op prostate cancer patients treated with VMAT and tracked with weekly OSLDs. Keeping the number of monitor units constant, the dose to the OSLD was recalculated for all 27 combinations of isocenter shifts. All shifted measurements were compared to the original location. Standard deviations of these percent difference distributions quantified the dosimeter uncertainty due to isocenter shifts for fiducial‐matched and bone‐matched image guidance. Clinical OSLD readings were compared with calculated uncertainties and correlated with actual image‐guided shifts. Results: Shifts for fiducial‐matched and bony‐landmark matched image guidance were 4 mm/5 mm/5 mm, and 3 mm/2 mm/3 mm in the superior‐inferior, anterior‐posterior, and lateral directions respectively. Standard deviations of 7.4% for prostate patients matched to the fiducial marker and 5.6% for the patients matched to bony anatomy were calculated. Clinical OSLD readings often exceeded these values and showed little correlation with actual image‐guided shifts. Conclusion: Image‐guided isocenter shifts contribute substantial uncertainty in expected dose to OSLDs that must be taken into account if the dosimeter is placed before image guidance. Additional clinical uncertainties must be investigated before appropriate tolerances can be applied to OSL dosimetry.