Commercial QA Research Articles

PO-1704 Commissioning and implementation of the commercial daily QA tool in proton pencil beam scanning

PO-1704 Commissioning and implementation of the commercial daily QA tool in proton pencil beam scanning

An electronic portal image device (EPID)-based multiplatform rapid daily LINAC QA tool.

PurposeTo develop an efficient and economic daily quality research tool (DQRT) for daily check of multiplatform linear accelerators (LINACs) with flattening filter (FF) and flattening filter‐free (FFF) photon beams by using an Electronic Portal Image Device (EPID).Materials and MethodsAfter EPID calibration, the monitored parameters were analyzed from a 10 cm × 10 cm open and 60° wedge portal images measured by the EPID with 100 MU exposure. Next, the repeatability of the EPID position accuracy, long‐term stability, and linearity between image gray value and exposure were verified. Output and beam quality stability of the 6‐MV FF and FFF beams measured by DQRT with the introduced setup errors of EPID were also surveyed. Besides, some test results obtained by DQRT were compared with those measured by FC65‐G and Matrixx. At last, the tool was evaluated on three LINACs (Synergy, VersaHD, TrueBeam) for 2 months with two popular commercial QA tools as references.ResultsThere are no differences between repeatability tests for all monitored parameters. Image grayscale values obtained by EPID and exposure show good linearity. Either 6 MV FF or FFF photon beam shows minimal impact to the results. The differences between FC65‐G, Matrixx and DQRT results are negligible. Monitor results of the two commercial tools are consistent with the DQRT results collected during the 2‐month period.ConclusionWith a shorter time and procedure, the DQRT is useful to daily QA works of LINACs, producing a QA result quality similarly to or more better than the traditional tools and giving richer contents to the QA results. For hospitals with limited QA time window available or lack of funding to purchase commercial QA tools, the proposed DQRT can provide an alternative and economic approach to accomplish the task of daily QA for LINACs.

SU‐F‐T‐236: Comparison of Two IMRT/VMAT QA Systems Using Gamma Index Analysis

Purpose:The goal of this study is to assess differences in the Gamma index pass rates when using two commercial QA systems and provide optimum Gamma index parameters for pre‐treatment patient specific QA.Methods:Twenty‐two VMAT cases that consisted of prostate, lung, head and neck, spine, brain and pancreas, were included in this study. The verification plans have been calculated using AcurosXB(V11) algorithm for different dose grids (1.5mm, 2.5mm, 3mm). The measurements were performed on TrueBeam(Varian) accelerator using both EPID(S1000) portal imager and ArcCheck(SunNuclearCorp) devices. Gamma index criteria variation of 3%/3mm, 2%/3mm, 2%/2mm and threshold (TH) doses of 5% to 50% were used in analysis.Results:The differences in Gamma pass rates between two devices are not statistically significant for 3%/3mm, yielding pass rate higher than 95%. Increase of lower dose TH showed reduced pass rates for both devices. ArcCheck's more pronounced effect can be attributed to higher contribution of lower dose region spread. As expected, tightening criteria to 2%/2mm (TH: 10%) decreased Gamma pass rates below 95%. Higher EPID (92%) pass rates compared to ArcCheck (86%) probably due to better spatial resolution. Portal Dosimetry results showed lower Gamma pass rates for composite plans compared to individual field pass rates. This may be due to the expansion in the analyzed region which includes pixels not included in the separate field analysis. Decreasing dose grid size from 2.5mm to 1.5mm did not show statistically significant (p<0.05) differences in Gamma pass rates for both QA devices.Conclusion:Overall, both system measurements agree well with calculated dose when using gamma index criteria of 3%/3mm for a variety of VMAT cases. Variability between two systems increases using different dose GRID, TH and tighter gamma criteria and must be carefully assessed prior to clinical use.

TU-E-BRB-00: Deformable Image Registration: Is It Right for Your Clinic

Deformable image registration (DIR) is developing rapidly and is poised to substantially improve dose fusion accuracy for adaptive and retreatment planning and motion management and PET fusion to enhance contour delineation for treatment planning. However, DIR dose warping accuracy is difficult to quantify, in general, and particularly difficult to do so on a patient-specific basis. As clinical DIR options become more widely available, there is an increased need to understand the implications of incorporating DIR into clinical workflow. Several groups have assessed DIR accuracy in clinically relevant scenarios, but no comprehensive review material is yet available. This session will also discuss aspects of the AAPM Task Group 132 on the Use of Image Registration and Data Fusion Algorithms and Techniques in Radiotherapy Treatment Planning official report, which provides recommendations for DIR clinical use. We will summarize and compare various commercial DIR software options, outline successful clinical techniques, show specific examples with discussion of appropriate and inappropriate applications of DIR, discuss the clinical implications of DIR, provide an overview of current DIR error analysis research, review QA options and research phantom development and present TG-132 recommendations. Learning Objectives: 1. Compare/contrast commercial DIR software and QA options 2. Overview clinical DIR workflow for retreatment 3. To understand uncertainties introduced by DIR 4. Review TG-132 proposed recommendations

SU‐E‐T‐690: Sensitivity Analysis to Machine Error: Comparisons of VMAT QA Systems

Purpose:In VMAT delivery, the gantry angles, dose rate and the MLC positions are all modulated. It is therefore necessary to perform pre‐treatment QA to detect any possible errors either in the plan or machine delivery system. Previously we developed a QA technique for VMAT using EPID in cine mode on a TrueBeam LINAC. The purpose of this study is to compare the technique with commercially available VMAT QA systems on the sensitivity to machine error.Methods:In our technique, the VMAT plan was delivered with EPID acquiring cine images simultaneously. The measured portal dose (PD) is derived from the acquired images. The predicted PD is calculated using the control point information in the plan and the delivery information in the EPID images. 3D γ analysis with the 3rd axis being gantry angle is performed between predicted and measured PD. The commercial VMAT QA system was Delta‐4 system from ScandiDose. The QA of the original plan is the reference. Several types of machine errors were simulated and evaluated: gantry angle, MLC position, and output. The original plan is modified by introducing intentional errors of various magnitudes. The modified plan is delivered and the measured PD is compared with the original predicted PD to determine the sensitivity to machine errors.Results:For the reference, in Delta‐4, the γ passrate is 99.6% for 3%/3mm criteria, and our technique has γ passrate of 98.5% for 3%/3mm/2° criteria. When errors are introduced, the passrate decreases. The sensitivity of Deltat4 (EPID) to gantry angle, MLC, and output are 1.4%/° (2.8%/°), 22%/mm(6%/mm), and 0%/% (0.1%/%), respectively. Similar results were observed under different criteria.Conclusion:Compared with Delta‐4 system, the EPID technique is more sensitive to gantry angle error, but less sensitive to MLC positioning error. Delta‐4 system is insensitive to the machine output error.This work was partially supported by the National Natural Science Foundation of China (61171005) and the China Scholarship Council (CSC).

SU‐E‐T‐38: A Head to Head Comparison of Two Commercial Phantoms Used for SRS QA

Purpose:To compare and contrast two commercial SRS QA phantoms.Methods:Both phantoms were evaluated in terms of their ease of setup as well as the time required to switch inserts for different tests. They were both used to evaluate the coincidence of the radiation and laser isocenters of a linear accelerator. End‐to‐end dosimetric tests were also performed using both ion chambers and films along two planes through the center of the phantoms. Since one phantom allows for multiple ion chamber orientations, a test was also performed to determine the effect of having the chamber oriented along the radiation beam axis’.Results:Changing inserts took 2 minutes on average for one phantom compared to 5 minutes for the other. The laser/radiation isocenter coincidence as determined from each phantom showed a maximum difference of 0.2mm. Ion chamber results were within 0.5% of the expected values when the chamber was perpendicular to the beams but measured a 3% underdose when the chamber was along the beam direction. Gamma (2%,2mm) pass rates of corresponding films were within 1% between phantoms.Conclusion:The results of the corresponding tests run on both phantoms were comparable, showing that the phantoms were equivalent for the subset of SRS QA tests run here. However, the under dose observed when the chamber was parallel to the beam direction suggests that this configuration should be avoided.

TU-E-BRB-01: Overview of DIR Advantages/Challenges and Workflow

Deformable image registration (DIR) is developing rapidly and is poised to substantially improve dose fusion accuracy for adaptive and retreatment planning and motion management and PET fusion to enhance contour delineation for treatment planning. However, DIR dose warping accuracy is difficult to quantify, in general, and particularly difficult to do so on a patient-specific basis. As clinical DIR options become more widely available, there is an increased need to understand the implications of incorporating DIR into clinical workflow. Several groups have assessed DIR accuracy in clinically relevant scenarios, but no comprehensive review material is yet available. This session will also discuss aspects of the AAPM Task Group 132 on the Use of Image Registration and Data Fusion Algorithms and Techniques in Radiotherapy Treatment Planning official report, which provides recommendations for DIR clinical use. We will summarize and compare various commercial DIR software options, outline successful clinical techniques, show specific examples with discussion of appropriate and inappropriate applications of DIR, discuss the clinical implications of DIR, provide an overview of current DIR error analysis research, review QA options and research phantom development and present TG-132 recommendations. Learning Objectives: 1. Compare/contrast commercial DIR software and QA options 2. Overview clinical DIR workflow for retreatment 3. To understand uncertainties introduced by DIR 4. Review TG-132 proposed recommendations

TU-E-BRB-02: DIR QA Options and Research Development

Deformable image registration (DIR) is developing rapidly and is poised to substantially improve dose fusion accuracy for adaptive and retreatment planning and motion management and PET fusion to enhance contour delineation for treatment planning. However, DIR dose warping accuracy is difficult to quantify, in general, and particularly difficult to do so on a patient-specific basis. As clinical DIR options become more widely available, there is an increased need to understand the implications of incorporating DIR into clinical workflow. Several groups have assessed DIR accuracy in clinically relevant scenarios, but no comprehensive review material is yet available. This session will also discuss aspects of the AAPM Task Group 132 on the Use of Image Registration and Data Fusion Algorithms and Techniques in Radiotherapy Treatment Planning official report, which provides recommendations for DIR clinical use. We will summarize and compare various commercial DIR software options, outline successful clinical techniques, show specific examples with discussion of appropriate and inappropriate applications of DIR, discuss the clinical implications of DIR, provide an overview of current DIR error analysis research, review QA options and research phantom development and present TG-132 recommendations. Learning Objectives: 1. Compare/contrast commercial DIR software and QA options 2. Overview clinical DIR workflow for retreatment 3. To understand uncertainties introduced by DIR 4. Review TG-132 proposed recommendations

TU-E-BRB-03: Overview of Proposed TG-132 Recommendations

Deformable image registration (DIR) is developing rapidly and is poised to substantially improve dose fusion accuracy for adaptive and retreatment planning and motion management and PET fusion to enhance contour delineation for treatment planning. However, DIR dose warping accuracy is difficult to quantify, in general, and particularly difficult to do so on a patient-specific basis. As clinical DIR options become more widely available, there is an increased need to understand the implications of incorporating DIR into clinical workflow. Several groups have assessed DIR accuracy in clinically relevant scenarios, but no comprehensive review material is yet available. This session will also discuss aspects of the AAPM Task Group 132 on the Use of Image Registration and Data Fusion Algorithms and Techniques in Radiotherapy Treatment Planning official report, which provides recommendations for DIR clinical use. We will summarize and compare various commercial DIR software options, outline successful clinical techniques, show specific examples with discussion of appropriate and inappropriate applications of DIR, discuss the clinical implications of DIR, provide an overview of current DIR error analysis research, review QA options and research phantom development and present TG-132 recommendations. Learning Objectives: 1.Compare/contrast commercial DIR software and QA options 2.Overview clinical DIR workflow for retreatment 3.To understand uncertainties introduced by DIR 4.Review TG-132 proposed recommendations

SU‐E‐T‐62: A Preliminary Experience of Using EPID Transit Dosimetry for Monitoring Daily Dose Variations in Radiation Treatment Delivery

Purpose:To investigate the use of EPID transit dosimetry for monitoring daily dose variations in radiation treatment delivery.Methods:A patient with head and neck cancer treated using nine field IMRT beams was used in this study. The prescription was 45 Gy in 25 fractions. A KV CBCT was acquired before each treatment on a Varian NTX linear accelerator. Integrated images using MV EPID were acquired for each treatment beam. Planning CT images, treatment plan, and daily integrated images were imported into a commercial QA software Dosimetry Check (v4r4 Math Resolutions, LLC, Columbia, MD) to calculate 3D dose of the day assuming 25 fractions treatment. Planning CT images were deformed and registered to each daily CBCT using Varian SmartAdapt (v11.MR2). ROIs were then propagated from planning CT to daily CBCT. The correlation between maximum, average dose of ROIs and ROI volume, center of mass shift, Dice Similarity Coefficient (DSC) were investigated.Results:Not all parameters investigated showed strong correlations. For PTV and CTV, the average dose has inverse correlation with their volume change (correlation coefficient −0.52, −0.50, respectively) and DSC (−0.59, −0.59, respectively). The average dose of right parotid has correlation with its volume change (0.56). The maximum dose of spinal cord has correlation with the center of mass superior‐inferior shift (0.52) and inverse correlation with the center of mass anterior‐posterior shift (−0.73).Conclusion:Transit dosimetry using EPID images collected during treatment delivery offers great potential to monitor daily dose variations due to patient anatomy change, motion, and setup errors in radiation treatment delivery. It can provide a patient‐specific QA tool valuable for adaptive radiation therapy. Further work is needed to validate the technique.

EP-1563: Sensitivity of various commercial QA systems to MLC errors and correlation between gamma analysis results and DVH

EP-1563: Sensitivity of various commercial QA systems to MLC errors and correlation between gamma analysis results and DVH

SU‐E‐T‐514: Simultaneously Determination of Radiation Isocentricity of Gantry, Collimator and Couch Using a Commercial Three‐Dimensional Dosimetry QA Apparatus

Purpose:Radiation isocentricity is an important benchmark for a LINAC and is typically determined by 3 separate film star‐shots. We developed a technique to simultaneously determine the radiation isocenter of gantry, collimator and couch with a commercial 3D QA apparatus.Methods:The ArcCHECK from SunNuclear was used on two LINACs. It was aligned with room lasers. For gantry rotation, collimator and couch were set to zero and gantry was placed to 0, 49, 213 and 311 degrees. Similarly, a set of collimator/couch angles were chosen with the other two axes at neutral positions. The measured dose matrices were analyzed by an in‐house MATLAB program. For each shot, the central axis was determined by computing the FWHM of the diode arrays. The largest inscribed circle from these central axis lines was used to determine isocenter: the radius as the benchmark of isocentricity and the coordinates of the center as the discrepancy of radiation isocenter to the origin defined by lasers. To validate the method, the couch was shifted by ~5 mm in all three directions and measurements were repeated.Results:The radius of the largest inscribed circle for gantry, collimator and couch are (0.3, 0.5, 0.2) mm for one LINAC and (0.2, 0.3, 0.1) mm for the other, in agreement with the film star‐shots at annual QA. The discrepancies of radiation isocenter are generally within 1 mm, except gantry rotation on one LINAC due to the drift of foot laser. The differences in positions detected are consistent with the intentional predefined shift.Conclusion:We have demonstrated a technique for the simultaneous measurement of gantry, collimator, and couch isocentricity with a set of carefully chosen irradiation parameters based on the specific construction geometry of the 3D detector ArcCheck. This can replace the standard film star‐shots. The future work includes improving operation efficiency.

SU‐E‐T‐433: Calibration Accuracy in Mailed High‐Resolution 3D Dosimetry Service for SRS/SBRT QA

Purpose:SRS/SBRT combines hypofractionation with excellent dose distributions. However, extremely steep gradients across the target along with dose escalation, if not administered accurately, may lead to serious complications, recurrences, or even fatalities. Existing commercial QA products either lack adequate spatial resolution or the 3D aspect. By contrast, the new CrystalBall™ mailed high‐resolution 3D dosimetry service removes the above limitations while reducing the overall workload on medical physics staff. The exposed dosimeters, which change optical density in proportion to local dose, are sent back to the manufacturer (MGS Research Inc., Madison, CT) for sub‐millimeter‐resolution laser‐CT scanning and QA data analysis. QA report is returned electronically within 24 hours. The purpose of this study was to evaluate the dose calibration accuracy in this system.Methods:Two spherical CrystalBall™ polymer gel dosimeters from the same batch, 166 mm diameter, with embedded 3D image registration markers, were mounted in a special phantom designed for reproducible positioning. For full end to end testing, the optical guidance array was mounted onto the phantom and a CT was taken. Two separate Rapid Arc SRS plans were designed. Varian Medical Systems optical guidance system was used to position the phantom and the SRS treatment plans were delivered to the two spheres on Varian's Trilogy Accelerator. Exposed dosimeters were mailed back to the manufacturer for laser CT scanning and analysis.Results:For each plan, 3D gamma passing rate was 100% for 2%/2mm distance‐to‐agreement criteria above 50% isodose level. The two calibration curves, generated using volumetric dose and optical density data, showed excellent mutual agreement (max difference 2.2%, median difference 0.75%).Conclusion:The clinical utility of new CrystalBall™ mailed QA service for SRS/SBRT and high accuracy of dose calibration have been validated. The workflow associated with the use of the CrystalBall™ in clinical setting was found to be minimal.The presenting author is the founder of and has an ownership in MGS Research Inc which manufactures the CrystalBall system for 3D dosimetry.

A comparison of the gamma index analysis in various commercial IMRT/VMAT QA systems

PurposeTo investigate the variability of the global gamma index (γ) analysis in various commercial IMRT/VMAT QA systems and to assess the impact of measurement with low resolution detector arrays on γ. MaterialsFive commercial QA systems (PTW 2D-Array, Scandidos Delta4, SunNuclear ArcCHECK, Varian EPID, and Gafchromic EBT2 film) were investigated. The response of γ analysis to deliberately introduced errors in pelvis and head & neck IMRT and RapidArc™ plans was evaluated in each system. A theoretical γ was calculated in each commercial QA system software (PTW Verisoft, Delta4 software, SNC Patient, Varian Portal Dosimetry and IBA OmniPro, respectively), using treatment planning system resolution virtual measurements and compared to an independent calculation. Error-induced plans were measured on a linear accelerator and were evaluated against the error-free dose distribution calculated using Varian Eclipse™ in the relevant phantom CT scan. In all cases, global γ was used with a 20% threshold relative to a point selected in a high dose and low gradient region. The γ based on measurement was compared against the theoretical to evaluate the response of each system. ResultsThere was statistically good agreement between the predicted γ based on the virtual measurements from each software (concordance correlation coefficient, ρc>0.92) relative to the independent prediction in all cases. For the actual measured data, the agreement with the predicted γ reduces with tightening passing criteria and the variability between the different systems increases. This indicates that the detector array configuration and resolution have greater impact on the experimental calculation of γ due to under-sampling of the dose distribution, blurring effects, noise, or a combination. ConclusionsIt is important to understand the response and limitations of the gamma index analysis combined with the equipment in use. For the same pass-rate criteria, different devices and software combinations exhibit varying levels of agreement with the predicted γ analysis.

SU‐E‐J‐54: The Characterization of a 3D Real‐Time Surface System with a Single High‐Definition (HD) Camera

Purpose: To investigate a single high‐definition (HD) camera of 3D realtime surface system (AlignRT_1HD, VisionRT, Inc.) as the potential alternative to the standard configuration of the system with three charge‐coupled device (CCD) cameras (AlignRT_3C) and to evaluate the localization accuracy of AlignRT_1HD compared to AlignRT_3C. Methods: Both AlignRT_3C and AlignRT_1HD were installed in the same treatment room with Varian LINAC. A commercial daily QA phantom (DailyQA3TM, Sun Nuclear) and 5 IMRT patients with intracranial and head and neck tumors receiving non‐coplanar treatment were used to evaluate system characteristics and position‐tracking accuracies of AlignRT_1HD through comparison with the AlignRT_3C and kV‐CBCTs. Surface‐image data sets were acquired simultaneously by both systems for the evaluation of inter‐and intra‐fractional motion at daily treatment of each patient. Results: The system origin displacements agreed to within 0.5 mm/0.5°. Compared to the CBCTs without couch rotations, the mean registration errors obtained using AlignRT_1HD were approximately 0.4 mm/0.8° (for phantom displacements up to ± 3cm in 3 axes), 1.1 mm/0.8° (for inter_frational motion in patients), and 0.3 mm/0.4° (for intra_frational motionin patients) less than those obtained using the AlignRT_3C. For non‐coplanar treatments, without the surface images acquired by two side camera pods using AlignRT_1HD in this study, the accuracy of patient setup was only guaranteed up to ±10° couch angles. The average setup time using AlignRT_1HD was reduced by approximately 1 min per session. Conclusion: As judged by CBCTs, AlignRT_1HD is capable of increasing in positioning accuracy and setup efficiency for high precision treatment, with the enhancements in image resolution, frame rate and field of view using HD cameras. The standard configuration with 3‐camera‐pods of AlignRT_3HD was essential for non‐coplanar treatment and the localization accuracy with couch angle up to 90° needs to be further quantified.

SU‐E‐T‐258: Commissioning of a Commercial Treatment Planning System Verification Software Package

Purpose: A commercial software package (Mobius3d, Mobius Medical Systems) was acquired for use as an additional QA tool of our current treatment planning system (TPS). The system reads DICOM RT files generated from the TPS and performs an independent dose calculation for comparison to the TPS. This work summarizes our methods for commissioning a system such as this. Methods: Preliminary comparisons of our TPS and measured data to the QA softwares beam model were done by comparing PDDs and profiles with field sizes ranging from 4&×;4 to 40×40. Static fields and step and shoot IMRT plans were generated on a homogeneous medium for comparisons of 6x photons. For the homogeneous IMRT cases, ion chamber measurements were compared to the dose calculated in the TPS and in the verification system. Results: Analysis of PDD data showed that the average PDD error of the verification model (relative to the TPS) was 0.5% compared to our measured data which was 0.1%. The average infield profile error over all field sizes and depths of the TPS to our reference measured data set was 0.3% whereas the verification system relative to the TPS was 1.7%. Simple beam geometries between the TPS and the verification system were 0.8% difference on average. Ion chamber measurements on a homogeneous phantom differed from the TPS on average by 0.5% whereas the verification system was 2%. The results indicate an adjustment in the beam model of the verification system is needed to better match our current beam model/measured data. Conclusion: Preliminary commissioning results of a commercial QA dose algorithm were completed. Adjustment of the verification softwares beam model is necessary before further testing is done. Further analysis is needed to fully investigate this system to be used clinically as a QA tool of our current TPS. “Evaluation equipment provided by Mobius Medical Systems, LP”

SU‐E‐T‐301: A Novel Daily QA Device for Proton Therapy

We describe the design and use of a daily QA device for proton therapy. The device is designed for therapists to check the readiness of the IBA Proton Therapy System (IBA, Louvain-la-Neuve, Belgium) during morning QA. The checks include connectivity, positioning, mechanical, imaging and dosimetric parameters of the proton therapy system. The device consists of a commercial QA device, (rf-DailyQA3 -Sun Nuclear Corporation, Melbourne, FL), in conjunction with a home-made acrylic phantom and mechanical indexing jig. The indexing jig indexes the rf-DailyQA3 to treatment couch. Fiducial markers embedded in the phantom are used for checking the x-ray image and alignment accuracy of the imaging system (VeriSuite, MedCom, Darmstadt- Germany). The rf- DailyQA3 is used to check the proton beam output, range and symmetry, which are acquired during one single beam delivery of 100 monitor units. We developed in-house software to calculate the variation of beam range and symmetry, based on readings from the various ion chambers inside the rf-DailyQA3. The device has been employed to perform daily QA since June 2010 at two operational proton treatment centers and will soon be implemented at ProCure's New Jersey center. All QA tests are performed by radiation therapists and reviewed by the medical physicist on duty. Due to the simplicity of the device and the associated processing software, the QA time is less than 20 minutes per room. The measurement data collected by the device during daily QA are recorded in the OIS. The integrity of the data is validated by comparing against other independent measurements. The daily QA device has been proven to be robust, reliable and user-friendly. The performance of this system has been proven to be stable and accurate using trend analyses. Key words:proton therapy, daily QA, output, range, symmetry.

SU-E-T-152: Development of a Phantom for Commissioning and Patient Specific QA for Volumetric Modulated Arc Therapy (VMAT).

To design a cost effective phantom for commissioning tests and patient specific quality assurance in VMAT techniqueMethods: The phantom is made of PMMA with the physical density of 1.18 gm/cc. It consists of 20 numbers of 20cm diameter discs connected together in a horizontal stack, making a cylinder of length 20cm. The centers of the discs are drilled with 2.1cm hole which accommodates chamber sleeve of near 2.1cm diameter, which is made of Delrin with the physical density of 1.414gm/cc. The cylindrical geometry of the phantom is ideal for rotational therapy QA like VMAT or Rapid arc. The entire phantom is self supporting and hence no supporting bar or holders are in the path of beam geometry. The chamber sleeve itself acts as the supporting rod for these discs and it can be inserted in to the disc assembly from distance of-9cm to +10cm from the origin and hence any axial point from -9cm to +10cm with respect to isocenter can be used for point dose measurement. The other side of the chamber sleeve is filled by spacer rod for sustaining the discs in place. The films can be inserted, transversely in any XZ plane from -9cm to +10cm from the origin between the discs next to the chamber center. Simultaneous irradiation for the chamber and the film is done for VMAT plans without collapsing the gantry angles to nominal angle of zero. Evaluated the results using RIT film analysis software for gamma index of 3%, 3mm. Good agreement is found with more than 95% of pixels passing 3% 3mm criteria. The point dose verification showed less than 3% variation with TPS planned dose. Most of the commercial QA systems needs gantry to be collapsed to zero degree to perform QA for modern RT techniques. Especially for techniques like VMAT, collapsing gantry to zero will fail to validate the influence of gantry speed on dose delivery.

SU-E-T-386: Gamma Analysis of Normalized and Un-Normalized Dose Distributions.

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

Feasibility study of performing IGRT system daily QA using a commercial QA device

The purpose of this study was to investigate the feasibility of using a single QA device for comprehensive, efficient daily QA of a linear accelerator (Linac) and three image‐guided stereotactic positioning systems (IGSPSs). The Sun Nuclear Daily QA 3 (DQA3) device was used to perform daily dosimetry and mechanical accuracy tests for an Elekta Linac, as well as daily image geometric and isocenter coincidence accuracy tests for three IGSPSs: the AlignRT surface imaging system; the frameless SonArray optical tracking System (FSA) and the Elekta kV CBCT. The DQA3 can also be used for couch positioning, repositioning, and rotational tests during the monthly QA. Based on phantom imaging, the Linac coordinate system determined using AlignRT was within 0.7 mm/0.6° of that of the CBCT system. The difference is attributable to the different calibration methods that are utilized for these two systems. The laser alignment was within 0.5 mm of the isocenter location determined with the three IGSPSs. The ODI constancy was ± 0.5 mm. For gantry and table angles of 0°, the mean isocenter displacement vectors determined using the three systems were within 0.7 mm and 0.6° of one another. Isocenter rotational offsets measured with the systems were all ≤ 0.5°. For photon and electron beams tested over a period of eight months, the output was verified to remain within 2%, energy variations were within 2%, and the symmetry and flatness were within 1%. The field size and light‐radiation coincidence were within 1mm ± 1 mm. For dosimetry reproducibility, the standard deviation was within 0.2% for all tests and all energies, except for photon energy variation which was 0.6%. The total measurement time for all tasks took less than 15 minutes per QA session compared to 40 minutes with our previous procedure, which utilized an individual QA device for each IGSPS. The DQA3 can be used for accurate and efficient Linac and IGSPS daily QA. It shortens QA device setup time, eliminates errors introduced by changing phantoms to perform different tests, and streamlines the task of performing dosimetric checks.PACS number: 87.56.Fc