Monte Carlo Dose Calculation Engine Research Articles

Development and verification of an electron Monte Carlo engine for applications in intraoperative radiation therapy.

In preparation of future clinical trials employing the Mobetron electron linear accelerator to deliver FLASH Intraoperative Radiation Therapy (IORT), the development of a Monte Carlo (MC)-based framework for dose calculation was required. To extend and validate the in-house developed fast MC dose engine MonteRay (MR) for future clinical applications in IORT. MR is a CPU MC dose calculation engine written in C++ that is capable of simulating therapeutic proton, helium, and carbon ion beams. In this work, development steps are taken to include electrons and photons in MR are presented. To assess MRs accuracy, MR generated simulation results were compared against FLUKA predictions in water, in presence of heterogeneities as well as in an anthropomorphic phantom. Additionally, dosimetric data has been acquired to evaluate MRs accuracy in predicting dose-distributions generated by the Mobetron accelerator. Runtimes of MR were evaluated against those of the general-purpose MC code FLUKA on standard benchmark problems. MR generated dose distributions for electron beams incident on a water phantom match corresponding FLUKA calculated distributions within 2.3% with range values matching within 0.01mm. In terms of dosimetric validation, differences between MR calculated and measured dose values were below 3% for almost all investigated positions within the water phantom. Gamma passing rate (1%/1mm) for the scenarios with inhomogeneities and gamma passing rate (3%/2mm) with the anthropomorphic phantom, were>99.8% and 99.4%, respectively. The average dose differences between MR (FLUKA) and the measurements was 1.26% (1.09%). Deviations between MR and FLUKA were well within 1.5% for all investigated depths and 0.6% on average. In terms of runtime, MR achieved a speedup against reference FLUKA simulations of about 13 for 10 MeV electrons. Validations against general purpose MC code FLUKA predictions and experimental dosimetric data have proven the validity of the physical models implemented in MR for IORT applications. Extending the work presented here, MR will be interfaced with external biophysical models to allow accurate FLASH biological dose predictions in IORT.

RapidBrachyTG43: A Geant4-based TG-43 parameter and dose calculation module for brachytherapy dosimetry.

The AAPM TG-43U1 formalism remains the clinical standard for dosimetry of low- and high-energy -emitting brachytherapy sources. TG-43U1 and related reports provide consensus datasets of TG-43 parameters derived from various published measured data and Monte Carlo simulations. These data are used to perform standardized and fast dose calculations for brachytherapy treatmentplanning. Monte Carlo TG-43 dosimetry parameters are commonly derived to characterize novel brachytherapy sources. RapidBrachyTG43 is a module of RapidBrachyMCTPS, a Monte Carlo-based treatment planning system, designed to automate this process, requiring minimal user input to prepare Geant4-based Monte Carlo simulations for a source. RapidBrachyTG43 may also perform a TG-43 dose to water-in-water calculation for a plan, substantially accelerating the same calculation performed using RapidBrachyMCTPS's Monte Carlo dose calculationengine. TG-43 parameters , , , and were calculated using three commercial source models, one each of I, Ir, and Co, and were benchmarked to published data. TG-43 dose to water was calculated for a clinical breast brachytherapy plan and was compared to a Monte Carlo dose calculation with all patient tissues, air, and catheters set towater. TG-43 parameters for the three simulated sources agreed with benchmark datasets within tolerances specified by the High Energy Brachytherapy Dosimetry working group. A gamma index comparison between the TG-43 and Monte Carlo dose-to-water calculations with a dose difference and difference to agreement criterion of 1%/1 mm yielded a 98.9% pass rate, with all relevant dose volume histogram metrics for the plan agreeing within 1%. Performing a TG-43-based dose calculation provided an acceleration of dose-to-water calculation by a factor of165. Determination of TG-43 parameter data for novel brachytherapy sources may now be facilitated by RapidBrachyMCTPS. These parameter datasets and existing consensus or published datasets may also be used to determine the TG-43 dose for a plan inRapidBrachyMCTPS.

Development and validation of MonteRay, a fast Monte Carlo dose engine for carbon ion beam radiotherapy.

Monte Carlo (MC) simulations are considered the gold-standard for accuracy in radiotherapy dose calculation; so far however, no commercial treatment planning system (TPS) provides a fast MC for supporting clinical practice in carbon ion therapy. To extend and validate the in-house developed fast MC dose engine MonteRay for carbon ion therapy, including physical and biological dose calculation. MonteRay is a CPU MC dose calculation engine written in C++ that is capable of simulating therapeutic proton, helium and carbon ion beams. In this work, development steps taken to include carbon ions in MonteRay are presented. Dose distributions computed with MonteRay are evaluated using a comprehensive validation dataset, including various measurements (pristine Bragg peaks, spread out Bragg peaks in water and behind an anthropomorphic phantom) and simulations of a patient plan. The latter includes both physical and biological dose comparisons. Runtimes of MonteRay were evaluated against those of FLUKA MC on a standard benchmark problem. Dosimetric comparisons between MonteRay and measurements demonstrated good agreement. In terms of pristine Bragg peaks, mean errors between simulated and measured integral depth dose distributions were between -2.3% and +2.7%. Comparing SOBPs at 5, 12.5 and 20cm depth, mean absolute relative dose differences were 0.9%, 0.7% and 1.6% respectively. Comparison against measurements behind an anthropomorphic head phantom revealed mean absolute dose differences of with global 3%/3mm 3D-γ passing rates of 99.3%, comparable to those previously reached with FLUKA (98.9%). Comparisons against dose predictions computed with the clinical treatment planning tool RayStation 11B for a meningioma patient plan revealed excellent local 1%/1mm 3D-γ passing rates of 98% for physical and 94% for biological dose. In terms of runtime, MonteRay achieved speedups against reference FLUKA simulations ranging from 14× to 72×, depending on the beam's energy and the step size chosen. Validations against clinical dosimetric measurements in homogeneous and heterogeneous scenarios and clinical TPS calculations have proven the validity of the physical models implemented in MonteRay. To conclude, MonteRay is viable as a fast secondary MC engine for supporting clinical practice in proton, helium and carbon ion radiotherapy.

Development and benchmarking of the first fast Monte Carlo engine for helium ion beam dose calculation: MonteRay.

Monte Carlo (MC) simulations are considered the gold-standard for accuracy in radiotherapy dose calculation; however, general purpose MC engines are computationally demanding and require long runtimes. For this reason, several groups have recently developed fast MC systems dedicated mainly to photon and proton external beam therapy, affording both speed and accuracy. To support research and clinical activities at the Heidelberg Ion-beam Therapy Center (HIT) with actively scanned helium ion beams, this work presents MonteRay, the first fast MC dose calculation engine for helium ion therapy. MonteRay is a CPU MC dose calculation engine written in C++, capable of simulating therapeutic proton and helium ion beams. In this work, development steps taken to include helium ion beams in MonteRay are presented. A detailed description of the newly implemented physics models for helium ions, for example, for multiple coulomb scattering and inelastic nuclear interactions, is provided. MonteRay dose computations of helium ion beams are evaluated using a comprehensive validation dataset, including measurements of spread-out Bragg peaks (SOBPs) with varying penetration depths/field sizes, measurements with an anthropomorphic phantom and FLUKA simulations of a patient plan. Improvement in computational speed is demonstrated in comparison against reference FLUKA simulations. Dosimetric comparisons between MonteRay and measurements demonstrated good agreement. Comparing SOBPs at 5, 12.5, and 20cm depth, mean absolute percent dose differences were 0.7%, 0.7%, and 1.4%, respectively. Comparison against measurements behind an anthropomorphic head phantom revealed mean absolute dose differences of about 1.2% (FLUKA: 1.5%) with per voxel errors ranging from -4.5% to 4.1% (FLUKA: -6% to 3%). Computed global 3%/3mm 3D-gamma passing rates of ∼99% were achieved, exceeding those previously reported for an analytical dose engine. Comparisons against FLUKA simulations for a patient plan revealed local 2%/2mm 3D-gamma passing rates of 98%. Compared to FLUKA in voxelized geometries, MonteRay saw run-time reductions ranging from 20× to 60×, depending on the beam's energy. MonteRay, the first fast MC engine dedicated to helium ion therapy, has been successfully developed with a focus on both speed and accuracy. Validations against dosimetric measurements in homogeneous and heterogeneous scenarios and FLUKA MC calculations have proven the validity of the physical models implemented. Timing comparisons have shown significant speedups between 20 and 60 when compared to FLUKA, making MonteRay viable for clinical routine. MonteRay will support research and clinical practice at HIT, for example, TPS development, validation and treatment design for upcoming clinical trials for raster-scanned helium ion therapy.

TOPAS Monte Carlo simulation for a scanning proton therapy system in SPHIC

PurposeThis study aims to use TOPAS Monte Carlo (MC) code to model the beamline of a scanned proton therapy system in Shanghai Proton and Heavy Ion Center (SPHIC). This tool can be useful for treatment plan quality assurance. Methods and materialsIn-air lateral profiles of single proton spots at five positions along the Z-axis were measured, which can then be used to calculate the angular variance, spatial angular covariance, and spatial variance at the beam exit position. The mean energy and energy spread of the primary incident beam for 15 energies were tuned by comparing with measured relative integrated depth dose at the central axis. Three spread-out Bragg peak plans in homogeneous water cubes and one plan with a half anthropomorphic head phantom were created to verify the accuracy of the model. In addition, the comparison was also performed to RayStation TPS with an MC dose calculation engine for the plans. ResultsThe average difference of spot sizes was 1.3% for all five energies. For all 15 energies, the average range (D90) difference was 0.04 mm, the mean distal-fall-off (DDF) difference was 0.04 mm, and the mean full width at half maximum (FWHM) difference was 0.10 mm. For the three homogeneous cube plans, a maximum difference of 0.2 mm for the D90 was observed, and the absolute differences in the lateral penumbras for each plan all agreed within 1 mm. For the plan on the anthropomorphic half head phantom, the mean dose deviation is less than 1.2% compared to measurements. ConclusionWe successfully developed an MC model for the proton scanning system used in SPHIC, which can be helpful for dose verification of the Treatment Planning System (TPS) and quality assurance in the future.

Co-60 MR Guided Adaptive Radiation Treatment Improves Target Coverage and Organs-At-Risk Sparing: Dosimetric Analysis of 1185 Adaptive Fractions and 5 Years’ Experience

Early data indicate MRI guided online adaptive radiotherapy (MRGRT) spares organs-at-risk (OARs) when inter-fractional motion of tumor targets and critical GI organs is significant. However, these studies were limited in patient numbers. This study systematically assesses all previously adapted treatment fractions of the MR imaging system Co-60 machine at the authors’ institution. The dosimetry metrics on patients’ treatment day anatomy between the adapted plans vs the un-adapted plans are compared. The aims are to determine the reasons (and corresponding rates) necessitating plan adaptations and quantifying improvement in target coverage. All abdominal cancer patients (N = 137) previously treated with MRGRT on the VR Co-60 machine from 2015 to 2019 are included. Treatment sites were pancreas (98), adrenal (11) and not otherwise specified abdomen (28). A total 961 (81.1%) out of 1185 fractions were adapted. Plan adaptation conditions were 1) the target was edited, or 2) any critical OAR constraints were violated, or 3) target coverage was significantly worse (V95%Rx reduction >10% for PTV-PRV) than the one achieved with the previous plan. For each adapted fraction, dose was calculated using a Monte Carlo dose calculation engine previously developed by authors for both 1) the plan before adaptation and 2) the adapted new plan. A suite of computer algorithm programs were developed to 1) process the treatment plan data files exported from TPS, 2) recognize the case-specific target structure and critical OARs, 3) compute treatment-day DVH metrics (V95%Rx and D95% for the targets, and V>constraint for OARs) on the calculated dose volumes, and 4) analyze the results arithmetically and statistically. Data of 961 adapted treatment fractions were processed and analyzed. The analysis shows that 1) critical OARs were edited for 100% cases, 2) tumor targets were edited for 90 (9.4%) cases, 3) critical OAR constraints were violated for 870 (90.5%) cases by the un-adapted plans, 4) plan optimization objectives were edited for 33 (3.4%) cases and 5) all critical OAR constraints were met in all (100%) adapted plans, 6) target coverages were improved for 888 (92.4%) cases with the adapted plans compared to un-adapted plans that were normalized to meet OAR constraints. After more than 5 years and 1100 fractions of experience, results continue to confirm that adapted plans provided significantly better target coverage while preventing violation of critical OAR constraints. Future work is necessary to establish the clinical significance of these data and validate these findings in the VR MRI Linac.

A novel minimally invasive dynamic-shield, intensity-modulated brachytherapy system for the treatment of cervical cancer.

To present a novel, MRI-compatible dynamicshield intensity modulated brachytherapy (IMBT) applicator and delivery system using 192 Ir, 75 Se, and 169 Yb radioisotopes for the treatment of locally advanced cervical cancer. Needle-free IMBT is a promising technique for improving target coverage and organs at risk (OAR) sparing. The IMBT delivery system dynamically controls the rotation of a novel tungsten shield placed inside an MRI-compatible, 6-mm wide intrauterine tandem. Using 36 cervical cancer cases, conventional intracavitary brachytherapy (IC-BT) and intracavitary/interstitial brachytherapy (IC/IS-BT) (10Ci 192 Ir) plans were compared to IMBT (10Ci 192 Ir; 11.5Ci 75 Se; 44Ci 169 Yb). All plans were generated using the Geant4-based Monte Carlo dose calculation engine, RapidBrachyMC. Treatment plans were optimized then normalized to the same high-risk clinical target volume (HR-CTV) D90 and the D2cc for bladder, rectum, and sigmoid in the research brachytherapy planning system, RapidBrachyMCTPS. Plans were renormalized until either of the three OAR reached dose limits to calculate the maximum achievable HR-CTV D90 and D98 . Compared to IC-BT, IMBT with either of the three radionuclides significantly improves the HR-CTV D90 and D98 by up to 5.2%±0.3% (P<0.001) and 6.7%±0.5% (P<0.001), respectively, with the largest dosimetric enhancement when using 169 Yb followed by 75 Se and then 192 Ir. Similarly, D2cc for all OAR improved with IMBT by up to 7.7%±0.6% (P<0.001). For IC/IS-BT cases, needle-free IMBT achieved clinically acceptable plans with 169 Yb-based IMBT further improving HR-CTV D98 by 1.5%±0.2% (P=0.034) and decreasing sigmoid D2cc by 1.9%±0.4% (P=0.048). Delivery times for IMBT are increased by a factor of 1.7, 3.3, and 2.3 for 192 Ir, 75 Se, and 169 Yb, respectively, relative to conventional 192 Ir BT. Dynamic shield IMBT provides a promising alternative to conventional IC- and IC/IS-BT techniques with significant dosimetric enhancements and even greater improvements with intermediate energy radionuclides. The ability to deliver a highly conformal, OAR-sparing dose without IS needles provides a simplified method for improving the therapeutic ratio less invasively and in a less resource intensive manner.

Evaluation of RBE-weighted doses for various radiotherapy beams based on a microdosimetric function implemented in PHITS

University of Tsukuba is developing a new TPS for boron neutron capture therapy (BNCT) equipped with Monte Carlo dose-calculation engine based on Particle and Heavy Ion Transport code System PHITS. It is currently in the process of extending its adaptation to other radiotherapy beams. For this extension, not only physical doses but also their relative biological effectiveness (RBE) must be evaluated for various radiotherapy in the same framework. Frequent and dose probability densities of lineal energy, y, are the key quantities in the RBE estimation, and they must be precisely evaluated for various locations in a patient. In this study, the probability densities of y for a site diameter of 0.564 µm were calculated for X-ray, proton, carbon-ion, and BNCT beams with appropriate geometry settings using the microdosimetric function implemented in PHITS, and they were converted to the corresponding RBE-weighted doses using the microdosimetric kinetic model. The accuracy of the calculated data were well verified by several experimental data, indicating the adequacy of the use of PHITS and microdosimetric kinetic model in the dose-calculation engine for TPS applicable to various radiotherapy.

POD-DOSI: A dedicated dosimetry system for GammaPod commissioning and quality assurance.

GammaPod, a stereotactic partial breast irradiator allowing highly conformal radiation dose delivery, has its unique mechanical design and treatment planning system (TPS). However, the uniqueness of the system poses challenges regarding initial GammaPod system commissioning and routine quality assurance (QA). In this study, we report POD-DOSI, a dedicated dosimetry system for accurate and efficient commissioning and QA of GammaPod. The POD-DOSI system consists of two subsystems, POD-Scanner and POD-Calculator. The POD-Scanner is an automatic ion-chamber positioning system driven by two translational stepper motors for anterior-posterior, longitudinal, and lateral beam scanning. The stepper motors are controlled by a microcomputer through an in-house-developed graphical user interface, which can be remotely accessed by a laptop via wireless connection. The POD-Calculator is a commissioned GPU-based Monte Carlo dose calculation engine, which calculates dose by transporting particles from phase space constructed for GammaPod. In our institution, the POD-DOSI system was used for GammaPod TPS commissioning and dose verification. The POD-Calculator was further developed as a secondary dose calculation tool performing patient-specific plan QA before each treatment. The POD-DOSI system has been fully evaluated and tested, both mechanically and dosimetrically, and applied successfully to drive the commissioning of our GammaPod system. The POD-Scanner achieved 0.1mm accuracy in ion-chamber positioning tests. The POD-Calculator generated dose profiles matched well with water phantom measurements and TPS calculations to <0.5mm accuracy. For end-to-end test on 56 different treatment plans, in-water point dose measurements by POD-Scanner were within ±2.20% of the doses calculated by POD-Calculator (range: -2.01% to 2.20%, mean: 0.04%, std_dev: 1.10%). Correspondingly, when switching the calculation medium from water to breast tissue, the point doses calculated by the POD-Calculator were within ±1.60% of the point doses calculated by the GammaPOD TPS (range: -1.59% to 1.51%, mean: -0.02%, std_dev: 0.73%). The average three-dimensional gamma passing rate between the GammaPod TPS doses and the POD-Calculator doses was 97.10% under the 2%/1mm gamma criteria. The POD-DOSI system substantially shortened the GammaPod dosimetry commissioning time from weeks to days. The developed POD-DOSI system resolves the challenges and streamlines the process of GammaPod commissioning and QA. It improves the efficiency and accuracy for both GammaPod commissioning and routine patient-specific QA.

First system for fully-automated multi-criterial treatment planning for a high-magnetic field MR-Linac applied to rectal cancer

Background and purpose: In this study we developed a workflow for fully-automated generation of deliverable IMRT plans for a 1.5 T MR-Linac (MRL) based on contoured CT scans, and we evaluated automated MRL planning for rectal cancer.Methods: The Monte Carlo dose calculation engine used in the clinical MRL TPS (Monaco, Elekta AB, Stockholm, Sweden), suited for high accuracy dose calculations in a 1.5 T magnetic field, was coupled to our in-house developed Erasmus-iCycle optimizer. Clinically deliverable plans for 23 rectal cancer patients were automatically generated in a two-step process, i.e., multi-criterial fluence map optimization with Erasmus-iCycle followed by a conversion into a deliverable IMRT plan in the clinical TPS. Automatically generated plans (AUTOplans) were compared to plans that were manually generated with the clinical TPS (MANplans).Results: With AUTOplanning large reductions in planning time and workload were obtained; 4–6 h mainly hands-on planning for MANplans vs ∼1 h of mainly computer computation time for AUTOplans. For equal target coverage, the bladder and bowel bag Dmean was reduced in the AUTOplans by 1.3 Gy (6.9%) on average with a maximum reduction of 4.5 Gy (23.8%). Dosimetric measurements at the MRL demonstrated clinically acceptable delivery accuracy for the AUTOplans.Conclusions: A system for fully automated multi-criterial planning for a 1.5 T MR-Linac was developed and tested for rectal cancer patients. Automated planning resulted in major reductions in planning workload and time, while plan quality improved. Negative impact of the high magnetic field on the dose distributions could be avoided.

Dosimetric evaluation of synthetic CT generated with GANs for MRI-only proton therapy treatment planning of brain tumors.

PurposeThe purpose of this study was to address the dosimetric accuracy of synthetic computed tomography (sCT) images of patients with brain tumor generated using a modified generative adversarial network (GAN) method, for their use in magnetic resonance imaging (MRI)‐only treatment planning for proton therapy.MethodsDose volume histogram (DVH) analysis was performed on CT and sCT images of patients with brain tumor for plans generated for intensity‐modulated proton therapy (IMPT). All plans were robustly optimized using a commercially available treatment planning system (RayStation, from RaySearch Laboratories) and standard robust parameters reported in the literature. The IMPT plan was then used to compute the dose on CT and sCT images for dosimetric comparison, using RayStation analytical (pencil beam) dose algorithm. We used a second, independent Monte Carlo dose calculation engine to recompute the dose on both CT and sCT images to ensure a proper analysis of the dosimetric accuracy of the sCT images.ResultsThe results extracted from RayStation showed excellent agreement for most DVH metrics computed on the CT and sCT for the nominal case, with a mean absolute difference below 0.5% (0.3 Gy) of the prescription dose for the clinical target volume (CTV) and below 2% (1.2 Gy) for the organs at risk (OARs) considered. This demonstrates a high dosimetric accuracy for the generated sCT images, especially in the target volume. The metrics obtained from the Monte Carlo doses mostly agreed with the values extracted from RayStation for the nominal and worst‐case scenarios (mean difference below 3%).ConclusionsThis work demonstrated the feasibility of using sCT generated with a GAN‐based deep learning method for MRI‐only treatment planning of patients with brain tumor in intensity‐modulated proton therapy.

Verification of a Monte Carlo dose calculation engine in proton minibeam radiotherapy in a passive scattering beamline for preclinical trials.

Proton minibeam radiation therapy (pMBRT) is a novel therapeutic strategy that combines the benefits of proton therapy with the remarkable normal tissue preservation observed with the use of submillimetric spatially fractionated beams. This promising technique has been implemented at the Institut Curie-Proton therapy centre (ICPO) using a first prototype of a multislit collimator. The purpose of this work was to develop a Monte Carlo-based dose calculation engine to reliably guide preclinical studies at ICPO. The whole "Y1"-passive beamline at the ICPO, including pMBRT implementation, was modelled using the Monte Carlo GATE v. 7.0 code. A clinically relevant proton energy (100 MeV) was used as starting point. Minibeam generation by means of the brass collimator used in the first experiments was modelled. A virtual source was modelled at the exit of the beamline nozzle and outcomes were compared with dosimetric measurements performed with EBT3 gafchromic films and a diamond detector in water. Dose distributions were recorded in a water phantom and in rat CT images (7-week-old male Fischer rats). The dose calculation engine was benchmarked against experimental data and was then used to assess dose distributions in CT images of a rat, resulting from different irradiation configurations used in several experiments. It reduced computational time by an order of magnitude. This allows us to speed up simulations for in vivo trials, where we obtained peak-to-valley dose ratios of 1.20 ± 0.05 and 6.1 ± 0.2 for proton minibeam irradiations targeting the tumour and crossing the rat head. Tumour eradication was observed in the 67 and 22% of the animals treated respectively. A Monte Carlo dose calculation engine for pMBRT implementation with mechanical collimation has been developed. This tool can be used to guide and interpret the results of in vivo trials. This is the first Monte Carlo dose engine for pMBRT that is being used to guide preclinical trials in a clinical proton therapy centre.

Evaluation of the RayStation electron Monte Carlo dose calculation algorithm

The aim of this work was to evaluate the accuracy of the RayStation treatment planning system electron Monte Carlo algorithm against measured data for a range of clinically relevant scenarios. This was done by comparing measured percentage depth dose data (PDD) in water, profiles at oblique incidence and with heterogeneities in the beam path, and output factor data and that generated using the RayStation treatment planning system Monte Carlo VMC++ based calculation algorithm. While electron treatments are widely employed in the radiotherapy setting accurate modelling is challenging (TPS) in the presence of patient being both heterogeneous and nonrectangular. Watertank-based measurements were made on a Varian TrueBeam linear accelerator covering electron beam energies 6 to 18 MeV. These included both normal and oblique incidence, heterogeneous geometries, and irregular shaped cut-outs. The measured geometries were replicated in RayStation and the Monte Carlo dose calculation engine used to generate dosimetric data for comparison against measurement in what were considered clinically relevant settings. Water-based PDDs and profile comparisons showed excellent agreement for all electron beam energies. Profiles measured with oblique beam incidence demonstrated acceptable agreement to the treatment planning system calculations although the correspondence worsened as the angle increased with the planning system overestimating the dose in the shoulder region. Profile measurements under inhomogeneities were generally good. The planning system had a tendency to overestimate dose under the heterogeneity and also demonstrated a broader penumbra than measurement. Of the 170 different output factors calculated in RayStation over the range of electron energies commissioned, 141 were within ± 3% of measured values and 164 within ± 5%. Four of the 6 comparisons beyond 5% were at 18 MeV and all had a cut-out edge within 3 cm of the beam central axis/measurement point. The RayStation implementation of a VMC++ electron Monte Carlo dose calculation algorithm shows good agreement with measured data for a range of scenarios studied and represented sufficient accuracy for clinical use.

Benchmarking Monte-Carlo dose calculation for MLC CyberKnife treatments

BackgroundVendor-independent Monte Carlo (MC) dose calculation (IDC) for patient-specific quality assurance of multi-leaf collimator (MLC) based CyberKnife treatments is used to benchmark and validate the commercial MC dose calculation engine for MLC based treatments built into the CyberKnife treatment planning system (Precision MC).MethodsThe benchmark included dose profiles in water in 15 mm depth and depth dose curves of rectangular MLC shaped fields ranging from 7.6 mm × 7.7 mm to 115.0 mm × 100.1 mm, which were compared between IDC, Precision MC and measurements in terms of dose difference and distance to agreement. Dose distributions of three phantom cases and seven clinical lung cases were calculated using both IDC and Precision MC. The lung PTVs ranged from 14 cm3 to 93 cm3. Quantitative comparison of these dose distributions was performed using dose-volume parameters and 3D gamma analysis with 2% global dose difference and 1 mm distance criteria and a global 10% dose threshold. Time to calculate dose distributions was recorded and efficiency was assessed.ResultsAbsolute dose profiles in 15 mm depth in water showed agreement between Precision MC and IDC within 3.1% or 1 mm. Depth dose curves agreed within 2.3% / 1 mm. For the phantom and clinical lung cases, mean PTV doses differed from − 1.0 to + 2.3% between IDC and Precision MC and gamma passing rates were > =98.1% for all multiple beam treatment plans. For the lung cases, lung V20 agreed within ±1.5%. Calculation times ranged from 2.2 min (for 39 cm3 PTV at 1.0 × 1.0 × 2.5 mm3 native CT resolution) to 8.1 min (93 cm3 at 1.1 × 1.1 × 1.0 mm3), at 2% uncertainty for Precision MC for the 7 examined lung cases and 4–6 h for IDC, which, however, is not optimized for efficiency but used as a gold standard for accuracy.ConclusionsBoth accuracy and efficiency of Precision MC in the context of MLC based planning for the CyberKnife M6 system were benchmarked against MC based IDC framework. Precision MC is used in clinical practice at our institute.

A Treatment Planning System for Intensity-Modulated Small Animal Radiotherapy Realized Using an Existing Movable Rectangular Collimator

Precise small animal radiotherapy is of paramount importance for the advancement of human radiotherapy. Using collimators of fixed sizes and shapes, current standard small animal irradiator cannot cover the tumor, while sparing organs at risk (OARs) to a satisfactory degree. However, current irradiators typically have a movable rectangular collimator. The purpose of this study is to realize intensity modulated radiotherapy (IMRT) for small animal irradiation using the movable rectangular collimator. We report our progress on the development of a treatment planning system and evaluation of the performance. The small animal IMRT treatment planning is formulated as a direct aperture optimization problem with the constraint of using only rectangular aperture shapes. We compute the dose deposition matrix using our in-house developed fast GPU-based Monte Carlo dose calculation engine. Solve the optimization problem consists of two sequential steps. The first step uses a column generation algorithm to determine a series of rectangular apertures and corresponding optimal beam-on time. The second step determines the most efficient aperture order at each beam angle to deliver the generated apertures. As such, we generate a graph with vertices being the apertures and links being transition time between apertures. The optimal order is obtained by finding the shortest-path traversing the graph. We evaluate the developed treatment planning system on a simulated water phantom case with a C-shaped target around a cylindrical OAR and a real mouse case with a lung tumor. We compare the plan quality and delivery efficiency of IMRT plans with those plans generated using cone-shaped collimators that have the smallest sizes to cover the tumor as seen from each beam’s eye view. In both cases, when IMRT plan and cone-based plan are normalized to the same target coverage, OARs are spared much more effectively in IMRT plans. Average dose can be reduced for OAR in water phantom case and lung in real mouse case by 25.3% and 13.9%, respectively. Max doses for OARs in IMRT plan and cone-based plan are almost the same for both cases. The beam-on time of IMRT plan for the mouse case is ∼80 s, approximately doubling that of cone-based plan because of reduced beam output under the apertures. The IMRT plan requires additional 6.9 s of collimator motion time. We have developed a treatment planning system to achieve IMRT for small animal irradiation using a movable rectangular collimator typically available on a current irradiator. The IMRT plan quality surpasses that of the cone-based plan. Treatment delivery time is prolonged mainly due to reduced beam output.Abstract 3824; Table 1CasePlanCTV quantityOARs quantityTreatment time (s)Normalized to prescription doseBeam-onCollimator motionD95D5DmeanDmaxWater phantomIMRT1.01.0390.7691.041----Cone-based1.01.0241.0291.047----Real mouseIMRT1.01.2380.174 (lung)1.242 (heart)82.206.9Cone-based1.01.2240.202 (lung)1.239 (heart)40.730.0 Open table in a new tab

Highly efficient and sensitive patient-specific quality assurance for spot-scanned proton therapy.

The purpose of this work was to develop an end-to-end patient-specific quality assurance (QA) technique for spot-scanned proton therapy that is more sensitive and efficient than traditional approaches. The patient-specific methodology relies on independently verifying the accuracy of the delivered proton fluence and the dose calculation in the heterogeneous patient volume. A Monte Carlo dose calculation engine, which was developed in-house, recalculates a planned dose distribution on the patient CT data set to verify the dose distribution represented by the treatment planning system. The plan is then delivered in a pre-treatment setting and logs of spot position and dose monitors, which are integrated into the treatment nozzle, are recorded. A computational routine compares the delivery log to the DICOM spot map used by the Monte Carlo calculation to ensure that the delivered parameters at the machine match the calculated plan. Measurements of dose planes using independent detector arrays, which historically are the standard approach to patient-specific QA, are not performed for every patient. The nozzle-integrated detectors are rigorously validated using independent detectors in regular QA intervals. The measured data are compared to the expected delivery patterns. The dose monitor reading deviations are reported in a histogram, while the spot position discrepancies are plotted vs. spot number to facilitate independent analysis of both random and systematic deviations. Action thresholds are linked to accuracy of the commissioned delivery system. Even when plan delivery is acceptable, the Monte Carlo second check system has identified dose calculation issues which would not have been illuminated using traditional, phantom-based measurement techniques. The efficiency and sensitivity of our patient-specific QA program has been improved by implementing a procedure which independently verifies patient dose calculation accuracy and plan delivery fidelity. Such an approach to QA requires holistic integration and maintenance of patient-specific and patient-independent QA.

RapidBrachyMCTPS: a Monte Carlo-based treatment planning system for brachytherapy applications

Despite being considered the gold standard for brachytherapy dosimetry, Monte Carlo (MC) has yet to be implemented into a software for brachytherapy treatment planning. The purpose of this work is to present RapidBrachyMCTPS, a novel treatment planning system (TPS) for brachytherapy applications equipped with a graphical user interface (GUI), optimization tools and a Geant4-based MC dose calculation engine, RapidBrachyMC. Brachytherapy sources and applicators were implemented in RapidBrachyMC and made available to the user via a source and applicator library in the GUI. To benchmark RapidBrachyMC, TG-43 parameters were calculated for the microSelectron v2 (192Ir) and SelectSeed (125I) source models and were compared against previously validated MC brachytherapy codes. The performance of RapidBrachyMC was evaluated for a prostate high dose rate case. To assess the accuracy of RapidBrachyMC in a heterogeneous setup, dose distributions with a cylindrical shielded/unshielded applicator were validated against film measurements in a Solid WaterTM phantom. TG-43 parameters calculated using RapidBrachyMC generally agreed within 1%–2% of the results obtained in previously published work. For the prostate case, clinical dosimetric indices showed general agreement with Oncentra TPS within 1%. Simulation times were on the order of minutes on a single core to achieve uncertainties below 2% in voxels within the prostate. The calculation time was decreased further using the multithreading features of Geant4. In the comparison between MC-calculated and film-measured dose distributions, at least 95% of points passed the 3%/3 mm gamma index criteria in all but one case. RapidBrachyMCTPS can be used as a post-implant dosimetry toolkit, as well as for MC-based brachytherapy treatment planning. This software is especially well suited for the development of new source and applicator models.

DEVELOPMENT OF A MULTIMODAL MONTE CARLO BASED TREATMENT PLANNING SYSTEM.

To establish boron neutron capture therapy (BNCT), the University of Tsukuba is developing a treatment device and peripheral devices required in BNCT, such as a treatment planning system. We are developing a new multimodal Monte Carlo based treatment planning system (developing code: Tsukuba Plan). Tsukuba Plan allows for dose estimation in proton therapy, X-ray therapy and heavy ion therapy in addition to BNCT because the system employs PHITS as the Monte Carlo dose calculation engine. Regarding BNCT, several verifications of the system are being carried out for its practical usage. The verification results demonstrate that Tsukuba Plan allows for accurate estimation of thermal neutron flux and gamma-ray dose as fundamental radiations of dosimetry in BNCT. In addition to the practical use of Tsukuba Plan in BNCT, we are investigating its application to other radiation therapies.

Abstract ID: 41 Consequences of patient heterogeneities for intermediate-energy sources in post-implant assessment of prostate brachytherapy treatment plans

Purpose Recent studies have identified and proposed gamma emitting radionuclides (75Se, 169Yb, 153Gd) with intermediate energy (50 keV Materials and methods Post implant treatment plans were simulated with a Geant4-based Monte Carlo dose calculation engine, BrachySource, coupled to a column-generation based optimizer, for a prostate brachytherapy case. The patient was treated with a brachytherapy boost with a dose of 15 Gy in a single fraction. Simulations were performed using 60Co, 192Ir, 75Se, 169Yb, and 153Gd as the active cores of the source. The plans were independently approved by two radiation oncologists. Two MC calculation protocols were performed for each radionuclide: (1) dose calculations for which patient anatomy is modelled as unit density water and (2) dose calculations for which patient anatomy is modelled with accurate chemical composition of tissues and densities are obtained using the HU values from CT scan. Results With 90% of the planning target volume (PTV) receiving over 15 Gy, plans can reduce the PTV V150 to 19.8%, 18.0%, 18.5%, 13.7% and 11.6% for 60Co, 192Ir, 75Se, 169Yb, and 153Gd, respectively, without sacrificing the urethral D10, the bladder V75 and the rectum V75. In general, dose homogeneity within the PTV increased with decreasing average photon energy. The inclusion of tissue composition and density corrections resulted in a reduction of the PTV D90 (urethral D10) by 0.0% (0.0%), 0.8% (0.7%), 1.8% (1.6%), 3.0% (4.7%) and 4.5% (4.1%) for 60Co, 192Ir, 75Se, 169Yb, and 153Gd, respectively. Conclusion Intermediate-energy sources have the potential to increase dose homogeneity within the PTV while reducing hot spots in the urethra, bladder, and rectum. This work shows the importance of accurate MC-based treatment planning engine, which can account for tissue composition and heterogeneities, for the dosimetry of intermediate-energy sources.

Abstract ID: 122 Verification of dose estimation for Monte-Carlo based treatment planning system for boron neutron capture therapy

University of Tsukuba is developing a treatment device for accelerator-based for boron neutron capture therapy (BNCT). In the project, not only the treatment device (neutron source) but also several peripheral devices requiring in BNCT treatment [1] . As part of the development, a Monte-Carlo based treatment planning system (Developing code: Tsukuba-Plan) applicable to BNCT is also being developed. Regarding Monte-Carlo dose calculation engine, the Tsukuba-Plan has employed PHITS as the multi-purpose Monte Carlo Particle and Heavy Ion Transport code System. PHITS allows to calculate behaviors for several radiations such as neutrons, photons, protons and heavy-ions [2] . Therefore the Tsukuba-Plan with PHITS enables to perform dose estimation for not only BNCT but also particle radiotherapy and X-ray therapy. A prototype of the Tsukuba plan has been completed. At present, we are carrying out several verifications for the Tsukuba-Plan. To verify dose estimation accuracy of the system, some experiments with a water phantom were simulated by using the Tsukuba-Plan, and the calculation results were compared with experimental data. In the experiments, gold foils and TLDs were set in the phantom, and then the phantom was set to in front of the beam aperture of the neutron source for BNCT device. Neutron beam was irradiated to the phantom, finally two-dimensional distributions for thermal neutron flux and gamma-ray dose in the phantom were measured. On the other hand, regarding simulation of the experiments with the Tsukuba-Plan, CT images of the water phantom were loaded to Tsukuba-Plan, and the irradiation conditions were represented. And calculations of two-dimensional distributions for both of thermal neutron flux and gamma-ray dose in the phantom were determined by using PHITS. The calculation results obtained from the Tsukuba-Plan were compared with the experimental values. The calculation values were in good agreement with the experimental values within statistical errors and experimental errors. The verification results demonstrated that Tsukuba-Plan enables to perform dose estimation for BNCT. Clinical group of University of Tsukuba plans to perform clinical trial for BNCT by using the neutron source for BNCT treatment device in the near future. Tsukuba-Plan will be applied to the clinical trials in practical use.