Monte Carlo dosimetry for a new 32P brachytherapy source using FLUKA code

GPU-accelerated Monte Carlo simulation of electron and photon interactions for radiotherapy applications

Objective. The Monte Carlo simulation software is a valuable tool in radiation therapy, in particular to achieve the needed accuracy in the dose evaluation for the treatment plans optimisation. The current challenge in this field is the time reduction to open the way to many clinical applications for which the computational time is an issue. In this manuscript we present an innovative GPU-accelerated Monte Carlo software for dose valuation in electron and photon based radiotherapy, developed as an update of the FRED (Fast paRticle thErapy Dose evaluator) software.Approach. The code transports particles through a 3D voxel grid, while scoring their energy deposition along their trajectory. The models of electromagnetic interactions in the energy region between 1 MeV-1 GeV available in literature have been implemented to efficiently run on GPUs, allowing to combine a fast tracking while keeping high accuracy in dose assessment. The FRED software has been bench-marked against state-of-art full MC (FLUKA, GEANT4) in the realm of two different radiotherapy applications: Intra-Operative Radio Therapy and Very High Electron Energy radiotherapy applications.Results. The single pencil beam dose-depth profiles in water as well as the dose map computed on non-homogeneous phantom agree with full-MCs at 2% level, observing a gain in processing time from 200 to 5000.Significance. Such performance allows for computing a plan with electron beams in few minutes with an accuracy of ∼%, demonstrating the FRED potential to be adopted for fast plan re-calculation in photon or electron radiotherapy applications.

Surface dose rate variations in planar and curved geometries of 106Ru/106Rh plaque sources for ocular tumors

PURPOSE

Investigation of surface dose rate variation with respect to the source configuration of ¹⁰⁶Ru/¹⁰⁶Rh eye plaque. To explore an alternate way to determine activity of brachytherapy plaques.

METHODS

The surface dose rates of ¹⁰⁶Ru/¹⁰⁶Rh plaque developed indigenously were measured by extrapolation chamber. To rule out possibility of any error in the activity distribution and quantity, same source was used in two different configurations namely planar and curved. EBT3 Gafchromic film was used for determination of uniformity in activity. Monte Carlo-based Codes EGSnrc and FLUKA were used to calculate dose rate in tissue, percentage depth dose and for determination of activity. Parameters and correction factors were estimated using simulations.

RESULTS

The measured reference absorbed dose rates for planar and curved ¹⁰⁶Ru/¹⁰⁶Rh eye plaques are found to be 589 ± 29 mGy/h and 560 ± 28 mGy/h, respectively. The difference in the reference absorbed dose rate of curved eye plaque is about ~5% as compared to planar configuration. The FLUKA-calculated dose values are almost independent of cavity length of the extrapolation chamber for both eye plaques. The FLUKA-based dose rates per μCi ¹⁰⁶Ru/¹⁰⁶Rh are about 17.28 ± 0.08 mGy/h and 16.48 ± 0.06 mGy/h, respectively for planar and curved eye plaques which match well with the measurements. The calculated activities for planar and curved eye plaques are 34.08 μCi and 33.98 μCi, respectively.

CONCLUSIONS

Surface dose rates for a prototype ¹⁰⁶Ru/¹⁰⁶Rh eye plaque with different configurations were estimated using simulations and measured experimentally. An alternate way to determine activity of beta-gamma brachytherapy plaque has been proposed.

Development of GATE Monte Carlo Code for Simulation and Dosimetry of New I-125 Seeds in Eye Plaque Brachytherapy

Purpose

Dose distributions are calculated by Monte Carlo (MC) simulations for two low-energy models ¹²⁵I brachytherapy source-IrSeed-125 and IsoAid Advantage (model IAI-125A)-loaded in the 14-mm standardized plaque of the COMS during treatment of choroid melanoma.

Methods

In this study, at first, the radial dose function in water around ¹²⁵I brachytherapy sources was calculated based on the recommendations of the Task Group No. 43 American Association of Physicists in Medicine (TG-43U1 APPM) using by GATE code. Then, brachytherapy dose distribution of a new model of the human eye was investigated for a 14-mm COMS eye plaque loaded with these sources with GATE Monte Carlo simulation.

Results

Results show that there are good agreements between simulation results of these sources and reporting measurements and simulations. Dosimetry results in the designed eye phantom for two types of iodine seeds show that the ratios of average dose of tumor to sclera, vitreous, and retina for IrSeed (IsoAid) source are 3.7 (3.7), 6.2 (6.1), and 6.3 (6.3), respectively, which represents the dose saving to healthy tissues. The maximum percentage differences between DVH curve of IsoAid and IrSeed seeds was about 8%.

Conclusions

Our simulation results show that although new model of the ¹²⁵I brachytherapy source having a slightly larger dimension than IAI-125A, it can be used for eye melanoma treatment because the COMS eye plaque loaded with IrSeed-125 could produce similar results to the IsoAid seeds, which is applicable for clinical plaque brachytherapy for uveal melanoma.

A Monte Carlo investigation of the dose distribution for new I-125 Low Dose Rate brachytherapy source in water and in different media

Permanent and temporary implantation of I-125 brachytherapy sources has become an official method for the treatment of different cancers. In this technique, it is essential to determine dose distribution around the brachytherapy source to choose the optimal treatment plan. In this study, the dosimetric parameters for a new interstitial brachytherapy source I-125 (IrSeed-125) were calculated with GATE/GEANT4 Monte Carlo code. Dose rate constant, radial dose function and 2D anisotropy function were calculated inside a water phantom (based on the recommendations of TG-43U1 protocol), and inside several tissue phantoms around the IrSeed-125 capsule. Acquired results were compared with MCNP simulation and experimental data. The dose rate constant of IrSeed-125 in the water phantom was about 1.038 cGy·h−1U−1 that shows good consistency with the experimental data. The radial dose function at 0.5, 0.9, 1.8, 3 and 7 cm radial distances were obtained as 1.095, 1.019, 0.826, 0.605, and 0.188, respectively. The results of the IrSeed-125 is not only in good agreement with those calculated by other simulation with MCNP code but also are closer to the experimental results. Discrepancies in the estimation of dose around IrSeed-125 capsule in the muscle and fat tissue phantoms are greater than the breast and lung phantoms in comparison with the water phantom. Results show that GATE/GEANT4 Monte Carlo code produces accurate results for dosimetric parameters of the IrSeed-125 LDR brachytherapy source with choosing the appropriate physics list. There are some differences in the dose calculation in the tissue phantoms in comparison with water phantom, especially in long distances from the source center, which may cause errors in the estimation of dose around brachytherapy sources that are not taken account by the TG43-U1 formalism.