bluuebunny/crossref_metadata_2025_split huggingface dataset:
SU‐F‐T‐238: Analyzing the Performance of MapCHECK2 and Delta4 Quality Assurance Phantoms in IMRT and VMAT Plans
Authors: Lu SH , Tsai YC , Lan HT , Wen SY , Chen LH , Kuo SH , Wang CW 
Published: July 2016

Purpose:Intensity‐modulated radiotherapy (IMRT) and volumetric modulated arc therapy (VMAT) have been widely investigated for use in radiotherapy and found to have a highly conformal dose distribution. Delta4 is a novel cylindrical phantom consisting of 1069 p‐type diodes with true treatments measured in the 3D target volume. The goal of this study was to compare the performance of a Delta4 diode array for IMRT and VMAT planning with ion chamber and MapCHECK2.Methods:Fifty‐four IMRT (n=9) and VMAT (n=45) plans were imported to Philips Pinnacle Planning System 9.2 for recalculation with a solid water phantom, MapCHECK2, and the Delta4 phantom. To evaluate the difference between the measured and calculated dose, we used MapCHECK2 and Delta4 for a dose‐map comparison and an ion chamber (PTW 31010 Semiflex 0.125 cc) for a point‐dose comparison.Results:All 54 plans met the criteria of <3% difference for the point dose (at least two points) by ion chamber. The mean difference was 0.784% with a standard deviation of 1.962%. With a criteria of 3 mm/3% in a gamma analysis, the average passing rates were 96.86%±2.19% and 98.42%±1.97% for MapCHECK2 and Delta4, respectively. The student t‐test of MapCHECK2/Delta4, ion chamber/Delta4, and ion chamber/MapCHECK2 were 0.0008, 0.2944, and 0.0002, respectively. There was no significant difference in passing rates between MapCHECK2 and Delta4 for the IMRT plan (p = 0.25). However, a higher pass rate was observed in Delta4 (98.36%) as compared to MapCHECK2 (96.64%, p < 0.0001) for the VMAT plan.Conclusion:The Pinnacle planning system can accurately calculate doses for VMAT and IMRT plans. The Delta4 shows a similar result when compared to ion chamber and MapCHECK2, and is an efficient tool for patient‐specific quality assurance, especially for rotation therapy.
SU‐F‐T‐250: What Does It Take to Correctly Assess the High Failure Modes of an Advanced Radiotherapy Procedure Such as Stereotactic Body Radiation Therapy?
Authors: Han D , Vile D , Rosu M , Palta J 
Published: July 2016

Purpose:Assess the correct implementation of risk‐based methodology of TG 100 to optimize quality management and patient safety procedures for Stereotactic Body Radiation Therapy.Methods:A detailed process map of SBRT treatment procedure was generated by a team of three physicists with varying clinical experience at our institution to assess the potential high‐risk failure modes. The probabilities of occurrence (O), severity (S) and detectability (D) for potential failure mode in each step of the process map were assigned by these individuals independently on the scale from1 to 10. The risk priority numbers (RPN) were computed and analyzed. The highest 30 potential modes from each physicist's analysis were then compared.Results:The RPN values assessed by the three physicists ranged from 30 to 300. The magnitudes of the RPN values from each physicist were different, and there was no concordance in the highest RPN values recorded by three physicists independently. The 10 highest RPN values belonged to sub steps of CT simulation, contouring and delivery in the SBRT process map. For these 10 highest RPN values, at least two physicists, irrespective of their length of experience had concordance but no general conclusions emerged.Conclusion:This study clearly shows that the risk‐based assessment of a clinical process map requires great deal of preparation, group discussions, and participation by all stakeholders. One group albeit physicists cannot effectively implement risk‐based methodology proposed by TG100. It should be a team effort in which the physicists can certainly play the leading role. This also corroborates TG100 recommendation that risk‐based assessment of clinical processes is a multidisciplinary team effort.
SU‐F‐T‐253: Volumetric Comparison Between 4D CT Amplitude and Phase Binning Mode
Authors: Yang G , Li X , Ma R , Yorke E , Mageras G , Tang X , Xiong W , Chan M , Reyngold M , Gewanter R , Wu A , Deasy J , Hunt M 
Published: July 2016

Purpose:Motion artifact in 4DCT images can affect radiation treatment quality. To identify the most robust and accurate binning method, we compare the volume difference between targets delineated on amplitude and phase binned 4DCT scans.Methods:Varian RPM system and CT scanner were used to acquire 4DCTs of a Quasar phantom with embedded cubic and spherical objects having superior‐inferior motion. Eight patients’ respiration waveforms were used to drive the phantom. The 4DCT scan was reconstructed into 10 phase and 10 amplitude bins (2 mm slices). A scan of the static phantom was also acquired. For each waveform, sphere and cube volumes were generated automatically on each phase using HU thresholding. Phase (amplitude) ITVs were the union of object volumes over all phase (amplitude) binned images. The sphere and cube volumes measured in the static phantom scan were Vsphere=4.19cc and Vcube=27.0cc. Volume difference (VD) and dice similarity coefficient (DSC) of the ITVs, and mean volume error (MVE) defined as the average target volume percentage difference between each phase image and the static image, were used to evaluate the performance of amplitude and phase binning.Results:Averaged over the eight breathing traces, the VD and DSC of the internal target volume (ITV) between amplitude and phase binning were 3.4%±3.2% (mean ± std) and 95.9%±2.1% for sphere; 2.1%±3.3% and 98.0% ±1.5% for cube, respectively.For all waveforms, the average sphere MVE of amplitude and phase binning was 6.5% ± 5.0% and 8.2%±6.3%, respectively; and the average cube MVE of amplitude and phase binning was 5.7%±3.5%and 12.9%±8.9%, respectively.Conclusion:ITV volume and spatial overlap as assessed by VD and DSC are similar between amplitude and phase binning. Compared to phase binning, amplitude binning results in lower MVE suggesting it is less susceptible to motion artifact.
SU‐F‐T‐270: A Technique for Modeling a Diode Array Into the TPS for Lung SBRT Patient Specific QA
Authors: Curley C , Ouhib Z , Leventouri T 
Published: July 2016

Purpose:To accurately match the treatment planning system (TPS) with the measurement environment, where quality assurance (QA) devices are used to collect data, for lung Stereotactic Body Radiation Therapy (SBRT) patient specific QA. Incorporation of heterogeneities is also studied.Methods:Dual energy computerized tomography (DECT) and single energy computerized tomography (SECT) were used to model phantoms incorporating a 2‐D diode array into the TPS. A water‐equivalent and a heterogeneous phantom (simulating the thoracic region of a patient) were studied. Monte Carlo and pencil beam planar dose distributions were compared to measured distributions. Composite and individual fields were analyzed for normally incident and planned gantry angle deliveries. γ‐ analysis was used with criteria 3% 3mm, 2% 2mm, and 1% 1mm.Results:The Monte Carlo calculations for the DECT resulted in improved agreements with the diode array for 46.4% of the fields at 3% 3mm, 85.7% at 2% 2mm, and 92.9% at 1% 1mm.For the SECT, the Monte Carlo calculations gave no agreement for the same γ‐analysis criteria. Pencil beam calculations resulted in lower agreements with the diode array in the TPS. The DECT showed improvements for 14.3% of the fields at 3% 3mm and 2% 2mm, and 28.6% at 1% 1mm.In SECT comparisons, 7.1% of the fields at 3% 3mm, 10.7% at 2% 2mm, and 17.9% at 1% 1mm showed improved agreements with the diode array.Conclusion:This study demonstrates that modeling the diode array in the TPS is viable using DECT with Monte Carlo for patient specific lung SBRT QA. As recommended by task groups (e.g. TG 65, TG 101, TG 244) of the American Association of Physicists in Medicine (AAPM), pencil beam algorithms should be avoided in the presence of heterogeneous materials, including a diode array.
SU‐F‐T‐272: Patient Specific Quality Assurance of Prostate VMAT Plans with Portal Dosimetry
Authors: Darko J , Kiciak A , Badu S , Grigorov G , Fleck A , Osei E 
Published: July 2016

Purpose:To evaluate the effectiveness of using the Portal Dosimetry (PD) method for patient specific quality assurance of prostate VMAT plans.Methods:As per institutional protocol all VMAT plans were measured using the Varian Portal Dosimetry (PD) method. A gamma evaluation criterion of 3%‐3mm with a minimum area gamma pass rate (gamma <1) of 95% is used clinically for all plans. We retrospectively evaluated the portal dosimetry results for 170 prostate patients treated with VMAT technique. Three sets of criterions were adopted for re‐evaluating the measurements; 3%‐3mm, 2%‐2mm and 1%‐1mm. For all criterions two areas, Field+1cm and MLC‐CIAO were analysed.To ascertain the effectiveness of the portal dosimetry technique in determining the delivery accuracy of prostate VMAT plans, 10 patients previously measured with portal dosimetry, were randomly selected and their measurements repeated using the ArcCHECK method. The same criterion used in the analysis of PD was used for the ArcCHECK measurements.Results:All patient plans reviewed met the institutional criteria for Area Gamma pass rate. Overall, the gamma pass rate (gamma <1) decreases for 3%‐3mm, 2%‐2mm and 1%‐1mm criterion. For each criterion the pass rate was significantly reduced when the MLC‐CIAO was used instead of FIELD+1cm. There was noticeable change in sensitivity for MLC‐CIAO with 2%‐2mm criteria and much more significant reduction at 1%‐1mm. Comparable results were obtained for the ArcCHECK measurements. Although differences were observed between the clockwise verses the counter clockwise plans in both the PD and ArcCHECK measurements, this was not deemed to be statistically significant.Conclusion:This work demonstrates that Portal Dosimetry technique can be effectively used for quality assurance of VMAT plans. Results obtained show similar sensitivity compared to ArcCheck. To reveal certain delivery inaccuracies, the use of a combination of criterions may provide an effective way in improving the overall sensitivity of PD.Funding provided in part by the Prostate Ride for Dad, Kitchener‐Waterloo, Canada.
SU‐F‐T‐273: Using a Diode Array to Explore the Weakness of TPS DoseCalculation Algorithm for VMAT and Sliding Window Techniques
Authors: Park J , Lu B , Yan G , Park J , Li F , Li J , Liu C 
Published: July 2016

Purpose:To identify the weakness of dose calculation algorithm in a treatment planning system for volumetric modulated arc therapy (VMAT) and sliding window (SW) techniques using a two‐dimensional diode array.Methods:The VMAT quality assurance(QA) was implemented with a diode array using multiple partial arcs that divided from a VMAT plan; each partial arc has the same segments and the original monitor units. Arc angles were less than ± 30°. Multiple arcs delivered through consecutive and repetitive gantry operating clockwise and counterclockwise. The source‐toaxis distance setup with the effective depths of 10 and 20 cm were used for a diode array. To figure out dose errors caused in delivery of VMAT fields, the numerous fields having the same segments with the VMAT field irradiated using different delivery techniques of static and step‐and‐shoot. The dose distributions of the SW technique were evaluated by creating split fields having fine moving steps of multi‐leaf collimator leaves. Calculated doses using the adaptive convolution algorithm were analyzed with measured ones with distance‐to‐agreement and dose difference of 3 mm and 3%..Results:While the beam delivery through static and step‐and‐shoot techniques showed the passing rate of 97 ± 2%, partial arc delivery of the VMAT fields brought out passing rate of 85%. However, when leaf motion was restricted less than 4.6 mm/°, passing rate was improved up to 95 ± 2%. Similar passing rate were obtained for both 10 and 20 cm effective depth setup. The calculated doses using the SW technique showed the dose difference over 7% at the final arrival point of moving leaves.Conclusion:Error components in dynamic delivery of modulated beams were distinguished by using the suggested QA method. This partial arc method can be used for routine VMAT QA. Improved SW calculation algorithm is required to provide accurate estimated doses.
SU‐F‐T‐276: Source Modeling and VMAT Quality Assurance Referring to the TrueBeam Representative Beam Data for Eclipse
Authors: Wu Q 
Published: July 2016

Purpose:To study quality assurance (QA) of volumetric modulated arc therapy (VMAT) after the 6MV and 10MV photon beam source modeling, referring to the Varian TrueBeam representative beam data for Eclipse.Methods:The source model needs specific measured beam data, such as PDDs and profiles, diagonal profile, output factors (OFs), and MLC transmission factor (TF) and dosimetric leaf gap (DLG), et al. We downloaded the representative data from myVarian website, which includes TrueBeam 4MV‐15MV photon beam data and 6MeV‐22MeV electron beam data in w2CAD file format for use with Eclipse and in Excel spreadsheet format for use in data comparison. The beam data in W2CAD format can be imported into the Eclipse system and calibrated for use, as appropriate. We used PTW MP3 water tank to measure the beam data in some typical field sizes, and compared the measured data with the representative data. We found that the PDDs, profiles and OFs are similar. However according to some papers and our measurements, we decided that our MLC TF and DLG are 1.58 and 1.33 (6MV), 1.79 and 1.57 (10MV), respectively. After we had configured the anisotropic analytical algorithm (AAA) with the representative data in Eclipse, we also have done dosimetric verification for 88 VMAT plans.Results:The end‐to‐end test procedures of VMAT were performed for 6MV and 10MV energy modes. The NE Farmer ion chamber mean measurements showed 1.2% (6MV, 38 cases) and 1.2% (10MV, 50 cases) between measurement and calculation; the Sun Nuclear ArcCheck mean measurements demonstrated gamma pass rates are as followings: 98.9%, 93.2%, 61.0% for 6MV, and 98.9%, 91.9%, 59.5% for 10MV, using 3%/3mm, 2%/2mm, 1%/1mm, 10% threshold criteria, respectively.Conclusion:The representative data is applicable to our TrueBeam for the VMAT plan, though our MLC factors are a little different, and its patientspecific QA is good.
SU‐F‐T‐278: Evaluation of Commercially Available System for Patient Specific QA Using Dose Volume Histograms
Authors: Alexandrian A , Kabat C , Roring J , Papanikolaou N , Stathakis S 
Published: July 2016

Purpose:To evaluate a commercial system for patient specific quality assurance using measurements and re‐calculated dose volume histograms.Methods:The PTW OCTAVIUS4D was used to physically measure the dose distribution from previously accepted IMRT patient plans for a variety of sites. PTW VeriSoft was used to for the IMRT QA evaluation. Patient plans, CT images, dose distribution and structures were imported in the VeriSoft. For each patient IMRT QA, the software can use the CT and structure information to calculate the dose to the patient from the measurement. The DVHs were then compared to the imported ones. The difference of the mean dose per organ was calculated for each plan and used in the comparison.Results:For treatment sites with no tissue inhomogeneities, such as pelvis, the DVHs produced by the TPS and VeriSoft showed good agreement; however, small structures such as eyes, optic nerves or brainstem did not adequately match up when comparing the DVH from the TPS to VeriSoft. For treatment sites with inhomogeneity, such as the lung, showed larger dose differences between the two methods, this is most likely due to dose calculation limitations of the PTW VeriSoft DVH algorithm.Conclusion:Overall, the DVHs produced by VeriSoft can give a physicist quick insight to the validity of the IMRT plan; however, there are limitations when plans of heterogeneous treatment sites are evaluated since the dose calculation algorithm in Verisoft cannot accurately account for it.
SU‐F‐T‐284: The Effect of Linear Accelerator Output Variation On the Quality of Patient Specific Rapid Arc Verification Plans
Authors: Sandhu G , Cao F , Szpala S , Kohli K 
Published: July 2016

Purpose:The aim of the current study is to investigate the effect of machine output variation on the delivery of the RapidArc verification plans.Methods:Three verification plans were generated using Eclipse™ treatment planning system (V11.031) with plan normalization value 100.0%. These plans were delivered on the linear accelerators using ArcCHECK− device, with machine output 1.000 cGy/MU at calibration point. These planned and delivered dose distributions were used as reference plans. Additional plans were created in Eclipse− with normalization values ranging 92.80%–102% to mimic the machine output ranging 1.072cGy/MU‐0.980cGy/MU, at the calibration point. These plans were compared against the reference plans using gamma indices (3%, 3mm) and (2%, 2mm). Calculated gammas were studied for its dependence on machine output. Plans were considered passed if 90% of the points satisfy the defined gamma criteria.Results:The gamma index (3%, 3mm) was insensitive to output fluctuation within the output tolerance level (2% of calibration), and showed failures, when the machine output exceeds ≥3%. Gamma (2%, 2mm) was found to be more sensitive to the output variation compared to the gamma (3%, 3mm), and showed failures, when output exceeds ≥1.7%. The variation of the gamma indices with output variability also showed dependence upon the plan parameters (e.g. MLC movement and gantry rotation). The variation of the percentage points passing gamma criteria with output variation followed a non‐linear decrease beyond the output tolerance level.Conclusion:Data from the limited plans and output conditions showed that gamma (2%, 2mm) is more sensitive to the output fluctuations compared to Gamma (3%,3mm). Work under progress, including detail data from a large number of plans and a wide range of output conditions, may be able to conclude the quantitative dependence of gammas on machine output, and hence the effect on the quality of delivered rapid arc plans.
SU‐F‐T‐285: Evaluation of a Patient DVH‐Based IMRT QA System
Authors: Zhen H , Redler G , Chu J , Turian J 
Published: July 2016

Purpose:To evaluate the clinical performance of a patient DVH‐based QA system for prostate VMAT QA.Methods:Mobius3D(M3D) is a QA software with an independent beam model and dose engine. The MobiusFX(MFX) add‐on predicts patient dose using treatment machine log files. We commissioned the Mobius beam model in two steps. First, the stock beam model was customized using machine commissioning data, then verified against the TPS with 12 simple phantom plans and 7 clinical 3D plans. Secondly, the Dosimetric Leaf Gap(DLG) in the Mobius model was fine‐tuned for VMAT treatment based on ion chamber measurements for 6 clinical VMAT plans. Upon successful commissioning, we retrospectively performed IMRT QA for 12 VMAT plans with the Mobius system as well as the ArcCHECK‐3DVH system. Selected patient DVH values (PTV D95, D50; Bladder D2cc, Dmean; Rectum D2cc) were compared between TPS, M3D, MFX, and 3DVH.Results:During the first commissioning step, TPS and M3D calculated target Dmean for 3D plans agree within 0.7%±0.7%, with 3D gamma passing rates of 98%±2%. In the second commissioning step, the Mobius DLG was adjusted by 1.2mm from the stock value, reducing the average difference between MFX calculation and ion chamber measurement from 3.2% to 0.1%. In retrospective prostate VMAT QA, 5 of 60 MFX calculated DVH values have a deviation greater than 5% compared to TPS. One large deviation at high dose level was identified as a potential QA failure. This echoes the 3DVH QA result, which identified 2 instances of large DVH deviation on the same structure. For all DVH's evaluated, M3D and MFX show high level of agreement (0.1%±0.2%), indicating that the observed deviation is likely from beam modelling differences rather than delivery errors.Conclusion:Mobius system provides a viable solution for DVH based VMAT QA, with the capability of separating TPS and delivery errors.
SU‐F‐T‐286: Calculation‐Based Patient Specific IMRT QA Detects Potential Errors That Measurement‐Based QA Does Not
Authors: Mossahebi S , Langen K , Guerrero M , Yi B , Lu W , Kalavagunta C , Prado K , Chen S 
Published: July 2016

Purpose:Calculation‐based patient‐specific IMRT/VMAT QA, as a DICOM‐RT‐based plan verification system, has been commissioned and is currently being used at our institution. We report our investigation of IMRT/VMAT plan verification failures/warnings out of more than 1,000 plans verified over an 18‐month period.Methods:Seven patients with QA failures/warnings from our calculation‐based IMRT/VMAT QA were selected. Dose to 95% of PTV volume (D95%) and mean PTV dose with a difference of greater than 3%, a global gamma passing rate of less than 95%, and a mean dose difference to organ at risk (OAR) larger than 5% were set as the failure/warning criteria. The treatment sites of the selected patients included pelvis, leg, head and neck, brain, and breast. Measurement‐based IMRT/VMAT QA was done on each patient using MapCHECK2. Root cause analysis (RCA) was performed on all patients to investigate the IMRT/VMAT failures/warnings.Results:All seven patients’ plans passed measurement‐based IMRT/VMAT QA with a gamma passing rate of more than 95%. Our RCA of patients showed the IMRT/VMAT QA failures detected by the calculation‐based method were mainly due to inclusion of the skin in PTV, and tissue heterogeneity effects particularly at tissue‐air and tissue‐bone interfaces.Conclusion:Calculation‐based IMRT/VMAT QA can detect potential failures which cannot be detected by standard measurement‐based QA.
SU‐F‐T‐290: Modeling MLC Penumbra Within the Eclipse TPS ‐ A Major Mode of IMRT QA Failure
Authors: Grams M , Antolak J , Deisher A , Fong de los Santos L 
Published: July 2016

Purpose:To illustrate how inaccurate modeling of the MLC penumbra within the Eclipse TPS can lead to dosimetric differences and decreased IMRT QA passing rates.Methods:Gafchromic film was used to compare 6 MV measured profiles from 2×2 cm2 MLC‐defined fields to profiles calculated by the Eclipse TPS (v13.6) under two different scenarios. The first scenario involved calculations using the original MLC opening (original Eclipse). In the second, we selectively broadened the penumbra by summing two appropriately weighted fields: One with 95% of MUs delivered using the original MLC opening, and a second with the remaining MUs delivered with all MLCs opened an additional 5 mm (modified Eclipse). MATLAB code was written to generate MLC patterns and MU weighting in this manner and used to calculate modified Eclipse doses for 25 different clinical IMRT and VMAT plans. Patient specific QA measurements were made with film and compared to both original and modified Eclipse calculations.Results:For the 2×2 cm2 fields, agreement was observed between measured and original Eclipse profiles everywhere except in the penumbral region 5–10 mm from the end of the MLC where doses 10–30% higher than expected were measured. Near perfect agreement throughout the entire profile was observed when comparing measurement to the modified Eclipse calculation with the broadened penumbra. For the 25 clinical treatment plans, the average 2%/0 mm gamma passing rate using the original Eclipse calculations was 82.3%, while for the modified Eclipse calculations it improved to 90.1%.Conclusion:The approximation used by the Eclipse TPS to model the rounded end of the MLC is a failure mode that could lead to poor quality and/or failing QA for IMRT and VMAT plans. Improved modeling of the penumbra in the region 5–10 mm from the end of the MLC is required to completely correct this discrepancy.