Independent Dose Calculation Software Research Articles

Generation, validation, and benchmarking of a commercial independent Monte Carlo calculation beam model for multi-target SRS

BackgroundDosimetric validation of single isocenter multi-target radiosurgery plans is difficult due to conditions of electronic disequilibrium and the simultaneous irradiation of multiple off-axis lesions dispersed throughout the volume. Here we report the benchmarking of a customizable Monte Carlo secondary dose calculation algorithm specific for multi-target radiosurgery which future users may use to guide their commissioning and clinical implementation. PurposeTo report the generation, validation, and clinical benchmarking of a volumetric Monte Carlo (MC) dose calculation beam model for single isocenter radiosurgery of intracranial multi-focal disease. MethodsThe beam model was prepared within SciMoCa (ScientificRT, Munich Germany), a commercial independent dose calculation software, with the aim of broad availability via the commercial software for use with single isocenter radiosurgery. The process included (1) definition & acquisition of measurement data required for beam modeling, (2) tuning model parameters to match measurements, (3) validation of the beam model via independent measurements and end-to-end testing, and finally, (4) clinical benchmarking and validation of beam model utility in a patient specific QA setting. We utilized a 6X Flattening-Filter-Free photon beam from a TrueBeam STX linear accelerator (Siemens Healthineers, Munich Germany). ResultsIn addition to the measured data required for standard IMRT/VMAT (depth dose, central axis profiles & output factors, leaf gap), beam modeling and validation for single-isocenter SRS required central axis and off axis (5 cm & 9 cm) small field output factors and comparison between measurement and simulation of backscatter with aperture for jaw much greater than MLCs. Validation end-to-end measurements included SRS MapCHECK in StereoPHAN geometry (2%/1 mm Gamma = 99.2% ± 2.2%), and OSL & scintillator measurements in anthropomorphic STEEV phantom (6 targets, volume = 0.1–4.1cc, distance from isocenter = 1.2–7.9 cm) for which mean difference was −1.9% ± 2.2%. For 10 patient cases, MC for individual PTVs was −0.8% ± 1.5%, −1.3% ± 1.7%, and −0.5% ± 1.8% for mean dose, D95%, and D1%, respectively. This corresponded to custom passing rates action limits per AAPM TG-218 guidelines of ±5.2%, ±6.4%, and ±6.3%, respectively. ConclusionsThe beam modeling, validation, and clinical action criteria outlined here serves as a benchmark for future users of the customized beam model within SciMoCa for single isocenter radiosurgery of multi-focal disease.

Elekta Unity MR-linac commissioning: mechanical and dosimetry tests

Abstract We report the commissioning results of Elekta Unity for the dosimetric performance and mechanical quality assurance (QA), and propose additional commissioning procedures. Mechanical tests included multi-leaf collimator (MLC) positional accuracy, radiation isocenter diameter at the center and off-center position, and coincidence between the magnetic resonance (MR) image center and radiation isocenter. Comparisons between the measurements and calculations of the simple irradiated field, intensity modulated radiation therapy (IMRT) commissioning, MLC output factor ratio, validation of independent dose calculation software and end-to-end testing were performed to evaluate dosimetric performance. The average values of the MLC positional accuracy for film- and imaging device-based analysis were −0.1 and 0.3 mm, respectively. The measured radiation isocenter size was 0.41 mm, and the off-center results were within 1 mm. The coincidence was −0.21, −1.19 and 0.49 mm along the x-, y- and z-axes, respectively. The calculated percent depth doses (PDD) and profiles agreed with the measurements. The results of independent dose calculation were within the action level recommended by American Associations of Physicist in Medicine. The gamma passing rate (GPR) for IMRT commissioning was 98.6 ± 0.9%, and end-to-end testing of adapted plans showed agreement within 2% between the measurement and calculation. We reported the results of mechanical and dosimetric performances of Elekta Unity, and proposed novel commissioning procedures. Our results should provide knowledge to the physics community for enhancing the QA programs.

PO-1537 Evaluation of an independent dose calculation software based on AAPM Task Group 219

PO-1537 Evaluation of an independent dose calculation software based on AAPM Task Group 219

Implementation of TomoEDGE in the independent dose calculator CheckTomo

PurposeCheckTomo is an independent dose calculation software for tomotherapy. Recently, Accuray (Accuray Inc., Sunnyvale, CA, USA) released an upgrade of its tomotherapy treatment device, called TomoEDGE Dynamic Jaws, which improves the quality of treatment plans by enhancing the dose delivery with the help of jaws motion. This study describes the upgrade of CheckTomo to that new feature.MethodsTo account for the varying width and off‐axis shift of dynamic jaws fields, the calculation engine of CheckTomo multiplies the treatment field profile by a penumbral filter and shifts the dose calculation grid. Penumbral filters were obtained by dividing the edge field profiles by that of the corresponding nominal field. They were sampled at widths 1.0, 1.8, and 2.5 cm at isocenter in the edges of the 2.5 and 5 cm treatment field.ResultsThe upgrade of CheckTomo was tested on 30 patient treatments planned with dynamic jaws. The gamma pass rate averaged over 10 abdomen plans was 95.9%, with tolerances of 3 mm/3%. For 10 head and neck plans, the mean pass rate was 95.9% for tolerances of 4 mm/4%. Finally, misplacement and overdosage errors were simulated. In each tested cases, the 2 mm/3% gamma pass rate fell below 95% when a 4 mm shift or 3% dose difference was applied.ConclusionsThese results are equivalent to what CheckTomo achieves in static jaws cases. So, in terms of dose calculation accuracy and errors detection, the upgraded version of CheckTomo is as reliable for dynamic jaws plans as the former release was for static cases.

SU‐E‐T‐32: A Feasibility Study of Independent Dose Verification for IMAT

Purpose:To assess the feasibility of the independent dose verification (Indp) for intensity modulated arc therapy (IMAT).Methods:An independent dose calculation software program (Simple MU Analysis, Triangle Products, JP) was used in this study, which can compute the radiological path length from the surface to the reference point for each control point using patient's CT image dataset and the MLC aperture shape was simultaneously modeled in reference to the information of MLC from DICOM‐RT plan. Dose calculation was performed using a modified Clarkson method considering MLC transmission and dosimetric leaf gap. In this study, a retrospective analysis was conducted in which IMAT plans from 120 patients of the two sites (prostate / head and neck) from four institutes were retrospectively analyzed to compare the Indp to the TPS using patient CT images. In addition, an ion‐chamber measurement was performed to verify the accuracy of the TPS and the Indp in water‐equivalent phantom.Results:The agreements between the Indp and the TPS (mean±1SD) were −0.8±2.4% and −1.3±3.8% for the regions of prostate and head and neck, respectively. The measurement comparison showed similar results (−0.8±1.6% and 0.1±4.6% for prostate and head and neck). The variation was larger in the head and neck because the number of the segments was increased that the reference point was under the MLC and the modified Clarkson method cannot consider the smooth falloff of the leaf penumbra.Conclusion:The independent verification program would be practical and effective for secondary check for IMAT with the sufficient accuracy in the measurement and CT‐based calculation. The accuracy would be improved if considering the falloff of the leaf penumbra.

EP-1425: Frameless linac based radiosurgery of arteriovenous malformations: geometrical accuracy

(calculated vs. measured) within ±2%. For that tuning task, isocenter dose measurements in a polystyrene phantom were compared to the calculated ones for five IMRS stereotactic plans. Three correction values to the factory DLG value were analyzed: 0.0, -0.25 and -0.5 mm. Accuracy of the M3D software to reproduce the penumbra of stereotactic fields was investigated by comparing the profiles measured in water with the calculated ones for a 1x1 cm MLC-collimated field size. Twelve cranial IMRS plans calculated using the Eclipse were retrospectively recalculated using the Mobius3D software (version 1.3). The same monitor units and calculation voxel sizes (1 mm) were used for both systems. The aperture (complete irradiation area outline) of the modulated beams ranged from 0.9 to 4.4 cm . Differences between both algorithms were evaluated using the 3D gamma tool available in the M3D system. Gamma passing rates for the target and organs at risks (OARs: brainstem, chiasm, optic nerves and normal brain tissue) were compared for 3%/1 mm, 3%/2 mm and 5%/1 mm criteria. Results: 1) Differences (M3D vs. measured) within 1 mm were found for the penumbras of the 1x1 cm field. 2) Dose differences of 2.7% (SD: 1.6%), 1.5% (SD: 1.9%) and 0.4% (SD: 2.0%) were found for the DLG correction values of 0.0, -0.25 and -0.5 mm, respectively. 3) Using the optimal DLG correction (-0.5 mm), the target 3D gamma passing rates were: 94% (73-94%), 97% (80-100%) and 100% (97-100%) for the 3%/1 mm, 3%/2 mm and 5%/1 mm criteria, respectively. 100% rates were obtained for all OARs regardless of the gamma criterium. Conclusions: Great agreement was obtained (within 5% and 1 mm) between IMRS plans calculated by the Eclipse and by the independent dose calculation software M3D. Our findings are restricted to small field sizes down to 1x1 cm . The M3D software may be proposed as an alternative to patientspecific QA based on measurements for IMRS plans.

TH‐E‐BRE‐05: Analysis of Dosimetric Characteristics in Two Leaf Motion Calculator Algorithms for Sliding Window IMRT

Purpose:The Smart leaf motion calculator (SLMC) in Eclipse treatment planning system is an advanced fluence delivery modeling algorithm as it takes into account fine MLC features including inter‐leaf leakage, rounded leaf tips, non‐uniform leaf thickness, and the spindle cavity etc. In this study, SLMC and traditional Varian LMC (VLMC) algorithms were investigated, for the first time, in dosimetric characteristics and delivery accuracy of sliding window (SW) IMRT.Methods:The SW IMRT plans of 51 cancer cases were included to evaluate dosimetric characteristics and dose delivery accuracy from leaf motion calculated by SLMC and VLMC, respectively. All plans were delivered using a Varian TrueBeam Linac. The DVH and MUs of the plans were analyzed. Three patient specific QA tools – independent dose calculation software IMSure, Delta4 phantom, and EPID portal dosimetry were also used to measure the delivered dose distribution.Results:Significant differences in the MUs were observed between the two LMCs (p≤0.001).Gamma analysis shows an excellent agreement between the planned dose distribution calculated by both LMC algorithms and delivered dose distribution measured by three QA tools in all plans at 3%/3 mm, leading to a mean pass rate exceeding 97%. The mean fraction of pixels with gamma < 1 of SLMC is slightly lower than that of VLMC in the IMSure and Delta4 results, but higher in portal dosimetry (the highest spatial resolution), especially in complex cases such as nasopharynx.Conclusion:The study suggests that the two LMCs generates the similar target coverage and sparing patterns of critical structures. However, SLMC is modestly more accurate than VLMC in modeling advanced MLC features, which may lead to a more accurate dose delivery in SW IMRT. Current clinical QA tools might not be specific enough to differentiate the dosimetric discrepancies at the millimeter level calculated by these two LMC algorithms.NIH/NIGMS grant U54 GM104944, Lincy Endowed Assistant Professorship

Results of 1 year of clinical experience with independent dose calculation software for VMAT fields.

It is widely accepted that a redundant independent dose calculation (RIDC) must be included in any treatment planning verification procedure. Specifically, volumetric modulated arc therapy (VMAT) technique implies a comprehensive quality assurance (QA) program in which RIDC should be included. In this paper, the results obtained in 1 year of clinical experience are presented. Eclipse from Varian is the treatment planning system (TPS), here in use. RIDC were performed with the commercial software; Diamond® (PTW) which is capable of calculating VMAT fields. Once the plan is clinically accepted, it is exported via Digital Imaging and Communications in Medicine (DICOM) to RIDC, together with the body contour, and then a point dose calculation is performed, usually at the isocenter. A total of 459 plans were evaluated. The total average deviation was -0.3 ± 1.8% (one standard deviation (1SD)). For higher clearance the plans were grouped by location in: Prostate, pelvis, abdomen, chest, head and neck, brain, stereotactic radiosurgery, lung stereotactic body radiation therapy, and miscellaneous. The highest absolute deviation was -0.8 ± 1.5% corresponding to the prostate. A linear fit between doses calculated by RIDC and by TPS produced a correlation coefficient of 0.9991 and a slope of 1.0023. These results are very close to those obtained in the validation process. This agreement led us to consider this RIDC software as a valuable tool for QA in VMAT plans.

I‐125 ROPES eye plaque dosimetry: Validation of a commercial 3D ophthalmic brachytherapy treatment planning system and independent dose calculation software with GafChromic® EBT3 films

The purpose of this study was to measure the dose distributions for different Radiation Oncology Physics and Engineering Services, Australia (ROPES) type eye plaques loaded with I-125 (model 6711) seeds using GafChromic(®) EBT3 films, in order to verify the dose distributions in the Plaque Simulator™ (PS) ophthalmic 3D treatment planning system. The brachytherapy module of RADCALC(®) was used to independently check the dose distributions calculated by PS. Correction factors were derived from the measured data to be used in PS to account for the effect of the stainless steel ROPES plaque backing on the 3D dose distribution. Using GafChromic(®) EBT3 films inserted in a specially designed Solid Water™ eye ball phantom, dose distributions were measured three-dimensionally both along and perpendicular to I-125 (model 6711) loaded ROPES eye plaque's central axis (CAX) with 2 mm depth increments. Each measurement was performed in full scatter conditions both with and without the stainless steel plaque backing attached to the eye plaque, to assess its effect on the dose distributions. Results were compared to the dose distributions calculated by Plaque Simulator™ and checked independently with RADCALC(®). The EBT3 film measurements without the stainless steel backing were found to agree with PS and RADCALC(®) to within 2% and 4%, respectively, on the plaque CAX. Also, RADCALC(®) was found to agree with PS to within 2%. The CAX depth doses measured using EBT3 film with the stainless steel backing were observed to result in a 4% decrease relative to when the backing was not present. Within experimental uncertainty, the 4% decrease was found to be constant with depth and independent of plaque size. Using a constant dose correction factor of T = 0.96 in PS, where the calculated dose for the full water scattering medium is reduced by 4% in every voxel in the dose grid, the effect of the plaque backing was accurately modeled in the planning system. Off-axis profiles were also modeled in PS by taking into account the three-dimensional model of the plaque backing. The doses calculated by PS and RADCALC(®) for uniformly loaded ROPES plaques in full and uniform scattering conditions were validated by the EBT3 film measurements. The stainless steel plaque backing was observed to decrease the measured dose by 4%. Through the introduction of a scalar correction factor (0.96) in PS, the dose homogeneity effect of the stainless steel plaque backing was found to agree with the measured EBT3 film measurements.

Application of an independent dose calculation software for estimating the impact of inter-fractional setup shifts in Helical Tomotherapy treatments

The purpose of this study is to validate the capability of in-house independent point dose calculation software to be used as a second check for Helical Tomotherapy treatment plans. The software performed its calculations in homogenous conditions (using the Cheese phantom, which is a cylindrical phantom with radius 15 cm and length 18 cm) using a factor-based algorithm. Fifty patients, who were treated for pelvic (10), prostate (14), lung (10), head & neck (12) and brain (4) cancers, were used. Based on the individual patient kVCT images and the pretreatment MVCT images for each treatment fraction, the corresponding daily patient setup shifts in the IEC-X, IEC-Y, and IEC-Z directions were registered. For each patient, the registered fractional setup shifts were grouped into systematic and random shifts. The average systematic dosimetric variations showed small dose deviation for the different cancer types (1.0%–3.0%) compared to the planned dose. Of the fifty patients, only three had percent differences larger than 5%. The average random dosimetric variations showed relatively small dose deviations (0.2%–1.1%) compared to the planned dose. None of the patients had percent differences larger than 5%. By examining the individual fractions of each patient, it is observed that only in 31 out of 1358 fractions the percent differences exceeded the border of 5%. These results indicate that the overall dosimetric impact from systematic and random variations is small and that the software is a capable platform for independent point dose validation for the Helical Tomotherapy modality.

SU-E-T-73: Investigation of Dose Reconstruction Using the Dosimetry Check Platform for Different Anatomical Sites

Purpose: to evaluate the dependence of the anatomical site being treated when using the Dosimetry Check software for patient specific IMRTquality assurance. Methods: Seventeen step and shoot IMRT patients were used to evaluate the dependence of the treatment site on the performance of the Dosimetry Check software (Math Resolution, LLC, Maryland). The treatments were delivered using a Varian Novalis Tx with an HD 120 MLC system. Integrated images for each patient were taken with an aSi1000 EPID (Varian Medical Systems). An integrated image was taken for each individual field and imported into the Dosimetry Check software. Using the Pinnacle treatment planningsoftware, the CT scans, structure file, plan file, and dose file were exported and then imported in to the Dosimetry Check software. The software then used the imported fluence fields to calculate the absolute dose and dose volume histogram to compare with the reference data exported from the treatment planning system. Gamma analysis was used to compare the measured data with the reference data. A 3% ‐ 3mm criteria normalized to the prescription dose with a 5% dose threshold was used. Results: Some treatment site dependence was observed. Of the fivesites investigated, two showed very similar results. In the remaining sites, the liver patients showed very strong agreement between measured data and reference data while the lung and H/N patients barely met our passing criteria. Conclusions: Dosimetry Check is an independent dose calculation software that uses a pencil beam algorithm. Pencil beam algorithms are fast but are also known to over‐estimate dose in low density heterogeneities. That should be a consideration for dose reconstruction with H/N and lung patients.

WE‐C‐BRB‐02: Independent Two‐Dimensional Dose Validation for TomoTherapy

Purpose: To develop a two‐dimensional (2D) dose calculation software for helical tomotherapy with absolute dose validation capability. Methods: This in‐house software takes advantage of archived patient treatment planning documents, initial coordinates of red and green lasers, central coronal plane slice numbers of the Cheese phantom, and clinical dosimetric functions. A tomotherapy DQA plan has to be generated and archived first. The software performs an independent absolute dose check to the tomotherapy plan. The software calculates the 2D dose map of the central coronal plane of the Cheese phantom, and the 2D map is narrowed into a 3.2cm×3.1cm rectangular on the plane to save calculation duration. Doses of points on the plane are calculated with 1 mm resolution, so that a total of 992 points are calculated for each patient case. The center of the 2D square is the cross point of red lasers, which is the center of the Cheese phantom by default. The 2D dose map calculated is thereafter compared with the planned one, which is a 3D dose matrix from the DQA plan. Gamma index is then calculated with 3mm and 5% criteria. Results: The newly developed software has been tested on ten tomotherapy patients (cases of 1 pancreas, 2 brain, 1 stomach, 1 lung, 1 head & neck, 3 prostate, and 1 esophagus). The gamma distributions are all passed with a minimum ratio of 95%. Conclusions: An in‐house independent dose calculation software for helical tomotherapy has been developed to independently validates 2D doses with gamma index. Gamma in this software is calculated by comparing the 2D calculation to 3D doses, which makes the introduced method more superior than normal IMRT or tomotherapy QA. Validation of the software on more cases and more tomotherapy units is necessary.

Systematic and Random Dosimetric Impact Studies on 100 Helical Tomotherapy Cancer Cases

To assess the dosimetric consequence of inter-fractional setup shifts on helical tomotherapy plans with self-developed independent dose calculation software MU-Tomo. A 2nd dose validation software for helical TomoTherapy , called MU-Tomo, has been developed to independently validates point dose upon archived patient documents, initial coordinates and planned dose of the point of calculation, and common dosimetric functions. This work has studied a hundred helical tomotherapy patients from five different treatment sites (30 prostate, 26 head and neck, 18 lung, 17 pelvis, and 9 brain patients). The daily setup shifts were quantified and grouped into systematic (mean daily setup shift for each patient) and random shifts (shifts after corresponding systematic shifts subtraction). Both Systematic and random shifts were incorporated into MU-Tomo to evaluate the systematic and random variations of dosimetric consequences, separately. Systematic variations showed dose deviation with the largest one -10.02% compared to the planned dose and overall SD 3%. Mean random variations showed dose deviation with the largest one -5.65% compared to the planned dose and overall SD 1.9%. According to the ANOVA analyses, random dosimetric variations were found significantly different among specific patient, while systematic dosimetric variations were significantly different between head and neck and brain group and body group. No significant differences were discovered among specific patients for systematic variations, and no significant differences were observed within each of the two groups for random variations. Dosimetric consequences are not significantly correlated with treatment fraction number according to the Pearson correlation analysis. By comparing doses without any shift and with the random shift, the overall dosimetric impacts to each patient are small with the mean value -0.0053% and SD of 1.11%, and 99% of the averaged variation results were within 3.5%. For helical tomotherapy modality, the overall dosimetric impact from random variations is small; instead, systematic shifts cause more dosimetric impact.

TH‐D‐BRB‐01: A Software Solution for Independent Dose Calculation of Helical Tomotherapy

Purpose: To translate and write helical tomotherapy treatment information into a non‐helical format such that an independent dose calculation method implementing the EGS4/MCSIM software environment is viable. Method and Materials: In‐house software was developed using the MATLAB computing platform to translate helical tomotherapy treatment sinogram files into a non‐helical format. Several steps are involved in this process. The patient .xml file is obtained through archived information to identify the procedural sinogram and several other delivery parameters. The sinogram is translated to create 51 fluence maps corresponding to the 51 discrete angles over which a complete tomotherapy rotation is divided effectively converting a helical delivery into a 51‐angle delivery. The in‐house software writes an input file referencing these 51 fluence maps that is readable within the Monte Carlo dose calculation user code EGS4/MCSIM. EGS4/MCSIM calculates dose using this translated data providing an independent dose verification method. The final step is to evaluate the EGS4/MCSIM calculations against the treatment planning system. Results: Initial MATLAB programming work has been successful in translating the helical tomotherapy sinogram files. The software is able to decode the sinogram and create the necessary input files for EGS4/MCSIM dose computation. Preliminary sample patients have shown decent agreement with initial percent differences ranging from –6.0% to 3.5% for point doses. Sampled dose profiles have shown mean percent differences within 3% for both horizontal and vertical orientations. Conclusion: This work demonstrates the potential for implementing helical delivery modalities into independent dose calculation software. This work shows that it is possible to decode a helical sinogram use known parameters to create dose maps and with those maps write an input file for EGS4/MCSIM. Ongoing work is being performed to refine the dose verification process in the EGS4/MCSIM environment utilizing input files created through the in‐house software.

Patient-specific IMRT verification using independent fluence-based dose calculation software: experimental benchmarking and initial clinical experience

Experimental methods are commonly used for patient-specific intensity-modulated radiotherapy (IMRT) verification. The purpose of this study was to investigate the accuracy and performance of independent dose calculation software (denoted as ‘MUV’ (monitor unit verification)) for patient-specific quality assurance (QA). 52 patients receiving step-and-shoot IMRT were considered. IMRT plans were recalculated by the treatment planning systems (TPS) in a dedicated QA phantom, in which an experimental 1D and 2D verification (0.3 cm3 ionization chamber; films) was performed. Additionally, an independent dose calculation was performed. The fluence-based algorithm of MUV accounts for collimator transmission, rounded leaf ends, tongue-and-groove effect, backscatter to the monitor chamber and scatter from the flattening filter. The dose calculation utilizes a pencil beam model based on a beam quality index. DICOM RT files from patient plans, exported from the TPS, were directly used as patient-specific input data in MUV. For composite IMRT plans, average deviations in the high dose region between ionization chamber measurements and point dose calculations performed with the TPS and MUV were 1.6 ± 1.2% and 0.5 ± 1.1% (1 S.D.). The dose deviations between MUV and TPS slightly depended on the distance from the isocentre position. For individual intensity-modulated beams (total 367), an average deviation of 1.1 ± 2.9% was determined between calculations performed with the TPS and with MUV, with maximum deviations up to 14%. However, absolute dose deviations were mostly less than 3 cGy. Based on the current results, we aim to apply a confidence limit of 3% (with respect to the prescribed dose) or 6 cGy for routine IMRT verification. For off-axis points at distances larger than 5 cm and for low dose regions, we consider 5% dose deviation or 10 cGy acceptable. The time needed for an independent calculation compares very favourably with the net time for an experimental approach. The physical effects modelled in the dose calculation software MUV allow accurate dose calculations in individual verification points. Independent calculations may be used to replace experimental dose verification once the IMRT programme is mature.