Validation of the TOPAS Monte Carlo toolkit for HDR brachytherapy simulations

PURPOSE

The goal of this work is to validate the user-friendly Geant4-based Monte Carlo toolkit TOol for PArticle Simulation (TOPAS) for brachytherapy applications.

METHODS AND MATERIALS

Brachytherapy simulations performed with TOPAS were systematically compared with published TG-186 reference data. The photon emission energy spectrum, the air-kerma strength, and the dose-rate constant of the model-based dose calculation algorithm (MBDCA)-WG generic Ir-192 source were extracted. For dose calculations, a track-length estimator was implemented. The four Joint AAPM/ESTRO/ABG MBDCA-WG test cases were evaluated through histograms of the local and global dose difference volumes. A prostate, a palliative lung, and a breast case were simulated. For each case, the dose ratio map, the histogram of the global dose difference volume, and cumulative dose-volume histograms were calculated.

RESULTS

The air-kerma strength was (9.772 ± 0.001) × 10-8 U Bq-1 (within 0.3% of the reference value). The dose-rate constant was 1.1107 ± 0.0005 cGy h-1 U-1 (within 0.01% of the reference value). For all cases, at least 96.9% of voxels had a local dose difference within [-1%, 1%] and at least 99.9% of voxels had a global dose difference within [-0.1%, 0.1%]. The implemented track-length estimator scorer was more efficient than the default analog dose scorer by a factor of 237. For all clinical cases, at least 97.5% of voxels had a global dose difference within [-1%, 1%]. Dose-volume histograms were consistent with the reference data.

CONCLUSIONS

TOPAS was validated for high-dose-rate brachytherapy simulations following the TG-186 recommended approach for MBDCAs. Built on top of Geant4, TOPAS provides broad access to a state-of-the-art Monte Carlo code for brachytherapy simulations.

Dosimetric characteristics of accelerated partial breast irradiation by interstitial multicatheter brachytherapy with intraoperative free-hand implantation in the treatment of early breast cancer

Introduction

The aim of this study is to evaluate the characteristics of the dosimetry and the skin dose of interstitial brachytherapy by the use of the free‐hand implantation technique toward the treatment of early breast cancer.

Materials & Methods

Seventeen patients diagnosed with early breast cancer were selected for the study. The implantation of the catheters for postoperative interstitial brachytherapy was performed using the free‐hand technique. The total tumor dose to the tumor cavity plus 2 cm margin was 3400 cGy, twice daily for 10 fractions in 5 days. The dosage to the target and the organ at risk (OAR) were recorded for analysis. The skin dose of the patient and the phantom were measured with Gafchromic film (EBT3) and the results were compared with the skin dose calculated by the brachytherapy treatment planning system.

Results

The median conformal index is 94% (range 89%–99%), and the median homogeneity index is 71%. The median skin dose measured from the skin of the patients was 20.1% lower than the skin dose calculated from the treatment planning system and consistent with the phantom surface measurement experiment. There were no grade 3 or above acute toxicity recorded.

Conclusions

Interstitial brachytherapy by the use of the free‐hand implantation technique for early breast cancer is feasible and avoids the need for a second surgical intervention. The calculated skin dose was overestimated by at least 20%. The results of this study may help in building a modification model for the prediction of skin toxicity in any future study.

Evaluation of a Proposed Biodegradable 188Re Source for Brachytherapy Application: A Review of Dosimetric Parameters

This study aimed to evaluate dosimetric characteristics based on Monte Carlo (MC) simulations for a proposed beta emitter bioglass 188Re seed for internal radiotherapy applications. The bioactive glass seed has been developed using the sol-gel technique. The simulations were performed for the seed using MC radiation transport code to investigate the dosimetric factors recommended by the AAPM Task Group 60 (TG-60). Dose distributions due to the beta and photon radiation were predicted at different radial distances surrounding the source. The dose rate in water at the reference point was calculated to be 7.43 ± 0.5 cGy/h/μCi. The dosimetric factors consisting of the reference point dose rate, D(r0,θ0), the radial dose function, g(r), the 2-dimensional anisotropy function, F(r,θ), the 1-dimensional anisotropy function, φan(r), and the R90 quantity were estimated and compared with several available beta-emitting sources. The element 188Re incorporated in bioactive glasses produced by the sol-gel technique provides a suitable solution for producing new materials for seed implants applied to brachytherapy applications in prostate and liver cancers treatment. Dose distribution of 188Re seed was greater isotropic than other commercially attainable encapsulated seeds, since it has no end weld to attenuate radiation. The beta radiation-emitting 188Re source provides high doses of local radiation to the tumor tissue and the short range of the beta particles limit damage to the adjacent normal tissue.

A fast Monte Carlo code for proton transport in radiation therapy based on MCNPX

An important requirement for proton therapy is a software for dose calculation. Monte Carlo is the most accurate method for dose calculation, but it is very slow. In this work, a method is developed to improve the speed of dose calculation. The method is based on pre-generated tracks for particle transport. The MCNPX code has been used for generation of tracks. A set of data including the track of the particle was produced in each particular material (water, air, lung tissue, bone, and soft tissue). This code can transport protons in wide range of energies (up to 200 MeV for proton). The validity of the fast Monte Carlo (MC) code is evaluated with data MCNPX as a reference code. While analytical pencil beam algorithm transport shows great errors (up to 10%) near small high density heterogeneities, there was less than 2% deviation of MCNPX results in our dose calculation and isodose distribution. In terms of speed, the code runs 200 times faster than MCNPX. In the Fast MC code which is developed in this work, it takes the system less than 2 minutes to calculate dose for 10(6) particles in an Intel Core 2 Duo 2.66 GHZ desktop computer.

Dosimetric aspects of 103Pd radioactive stent source

This study aims to determine AAPM TG-60 dosimetric quantities in regions surrounding the 103Pd stent wall by MCNP5 Monte Carlo code. The Palmaz-Schatz stent was modeled by a hollow cylinder of 17.89mm length (2mm diameter) with net surface very similar to real stent. The Dose deposited per photon (Gy), relative dose, Anisotropy function, F(r,θ), and radial dose function, gL(r), were described at AAPM TG-60 protocol were generated from these values and listed in tabular format. For benchmarking, the relative dose values were verified with TG-43 and EGS4 code results at identical conditions, relative to the radial distances from surface of the stent. There were noticeable results. These physical dosimetric parameters can be used in future treatment planning systems for IVBT.

Novel dose calculation and characterization of 32P intravascular brachytherapy stent source

Derived from AAPM task group No. 60/149 protocol, applicable in treatment planning In this study, the two-dimensional dose distributions in water for a 32P intravascular brachytherapy stent have been calculated. The pure beta emitter source 32P which has been coated on Palmaz-Schatz stent is discussed. The dosimetric parameters required by the AAPM TG-60/149 formalism are discussed and calculated. Version 5 of the (MCNP) Monte Carlo radiation transport code was used to calculate the dosimetry parameters around the source. The Monte Carlo calculated dose rate at the reference point is found to be 2.8 Gy/μCi. Also in this study, the geometry function, G(r,θ), radial dose function, g(r), and the anisotropy function, F(r,θ), have been calculated at distances from 1.8 to 9 mm. The results of these calculations have been compared with other published calculated and measured values for an actual same source. High dose variants were visible near the 32P stent surface, but these values decreased with depth in water rapidly. There is an acceptable agreement between the calculated data in this study and other published data for the same source, which validate our simulations method.

Dosimetric characteristics of three new design 125I brachytherapy sources

For roughly 25 years, 125I sources have been used in the treatment of various malignant diseases such as prostate cancer. Three new brachytherapy sources, IR01-125I, IR02-125I and IR03-125I, have been developed and are designed for permanent implant application. The Monte Carlo radiation transport code version MCNP 5 was used to calculate the dosimetry parameters around the sources in accordance with the updated report of the American Association of Physicists in Medicine (AAPM), Task Group No. 43. For each source, the dose rate constant Λ, the radial dose function gL(r), and the anisotropy function F(r, θ), were obtained. The results indicated a dose rate constant of 0.932 ± 0.01, 0.934 ± 0.01 and 0.939 ± 0.01 Gy h−1 U−1 for the IR01-125I, IR02-125I and IR03-125I sources respectively. With the goal of determining an optimal design for a 125I source, each seed's parameters were compared with other seeds. In this study, the optimal source IR03-125I provides the most isotropic dose distribution in water. Finally, the results for optimal source were compared with published results for those of other commercial sources.

Thermoluminescent and Monte Carlo dosimetry of IR06-103Pd brachytherapy source

This work presents experimental dosimetry results for a new P103d brachytherapy seed, in accordance with the AAPM TG‐43U1 recommendation that all new low‐energy interstitial brachytherapy seeds should undergo one Monte Carlo (MC) and at least one experimental dosimetry characterization. Measurements were performed using TLD‐GR200A circular chip dosimeters using standard methods employing thermoluminescent dosimeters in a Perspex phantom. The Monte Carlo N‐particle (MCNP) code, version 5 was used to evaluate the dose‐rate distributions around this model P103d source in water and Perspex phantoms. The consensus value for dose‐rate constant of the IR06‐P103d source was found equal to 0.690 cG⋅h−1⋅U−1. The anisotropy function, F(r, θ), and the radial dose function, gL(r), of the seed were measured in Perspex phantom and calculated in both Perspex and liquid water phantom. The measured values were also found in good agreement with corresponding MC calculations.

PACS number: 87.53.Jw

Monte Carlo calculated TG-60 dosimetry parameters for the beta- emitter 153Sm brachytherapy source

PURPOSE

The formalism recommended by Task Group 60 (TG-60) of the American Association of Physicists in Medicine (AAPM) is applicable for beta sources. Radioactive biocompatible and biodegradable 153Sm glass seed without encapsulation is a beta- emitter radionuclide with a short half-life and delivers a high dose rate to the tumor in the millimeter range. This study presents the results of Monte Carlo calculations of the dosimetric parameters for the 153Sm brachytherapy source.

METHODS

Version 5 of the (MCNP) Monte Carlo radiation transport code was used to calculate two-dimensional dose distributions around the source. The dosimetric parameters of AAPM TG-60 recommendations including the reference dose rate, the radial dose function, the anisotropy function, and the one-dimensional anisotropy function were obtained.

RESULTS

The dose rate value at the reference point was estimated to be 9.21 +/- 0.6 cGy h(-1) microCi(-1). Due to the low energy beta emitted from 153Sm sources, the dose fall-off profile is sharper than the other beta emitter sources. The calculated dosimetric parameters in this study are compared to several beta and photon emitting seeds.

CONCLUSIONS

The results show the advantage of the 153Sm source in comparison with the other sources because of the rapid dose fall-off of beta ray and high dose rate at the short distances of the seed. The results would be helpful in the development of the radioactive implants using 153Sm seeds for the brachytherapy treatment.

Monte Carlo calculation of dosimetry parameters for the IR08-103Pd brachytherapy source

PURPOSE

For the treatment of some cancerous tumors using brachytherapy methods and low-energy photon sources, such as 125I and 103Pd, the American Association of Physicists in Medicine Task Group No. 43U1 report recommends that the dosimetric parameters of a new brachytherapy source must be determined in two experimental and Monte Carlo theoretical methods before using each new source clinically. This study presents the results of Monte Carlo calculations of the dosimetric parameters for IR08-103Pd brachytherapy source design. IR08-103Pd seed has been manufactured at the Agricultural, Medical and Industrial Research School.

METHODS

Version 5 of the (MCNP) Monte Carlo radiation transport code was used to calculate the dosimetry parameters around the source. Three geometric models of the seed, based on different locations of beads inside the titanium capsule, were simulated. The seed contains five resin beads of 0.6 mm diameter having 103Pd uniformly absorbed in the bead volume, which were contained within a cylindrical titanium capsule having 0.8 mm outside diameter and 4.8 mm length.

RESULTS

The Monte Carlo calculated dose rate constant of the IR08-103Pd seed was found to be 0.695 +/- 0.021 cGyU(-1) h(-1). Also in this study, the geometry function G(r, theta), line and point-source radial dose functions gL(r) and gP(r), and the anisotropy function F(r, theta), have been calculated at distances from 0.25 to 7 cm. The results of these calculations have been compared with measured values for an actual IR08-103Pd seed.

CONCLUSIONS

There are no statistical significant dosimetric differences among the three seed orientations in this study (i.e., ideal, vertical, and diagonal). However, the observed differences between the calculated and measured values could be explained by the measurement uncertainty and the configuration of the resin beads within the capsule and capsule orientation.

Study of the IsoAid ADVANTAGE (125)I brachytherapy source dosimetric parameters using Monte Carlo simulation

Monte Carlo calculations have been performed using the MCNP4C code for an iodine seed design. As the ADVANTAGE I-125, Model IAI-125 source is commercially available for interstitial brachytherapy treatment, dosimetric characteristics (dose rate constant, radial dose function and anisotropy function) of this source were theoretically determined following the updated AAPM task group 43 (TG-43U1) recommendations. The dose distribution around the seed was calculated with Monte Carlo simulation in liquid water. The Monte Carlo calculated dose rate constant of this source in water was found to be 0.986cGyh(-1)U(-1), with an approximate uncertainty of 0.4%. The obtained result has been compared with the previous study. Comparison of the calculated dose rate constant with the value presented by Meigooni et al. shows a very good agreement. Also the anisotropy function and the radial dose function for this source are graphically compared.

Dosimetric comparison of four new design 103Pd brachytherapy sources: optimal design using silver and copper rod cores

Four new brachytherapy sources, IRA1-103Pd, IRA2-103Pd, IRA3-103Pd, and IRA4-103Pd, have been developed at Agricultural, Medical, and Industrial Research School and are designed for permanent implant application. With the goal of determining an optimal design for a 103Pd source, this article compares the dosimetric properties of these sources with reference to the authors' earlier IRA-103Pd source. The four new sources differ in end cap configuration and thickness and in the core material, silver or copper, that carries the adsorbed 103Pd. Dosimetric data derived from the authors' Monte Carlo simulation results are reported in accordance with the updated AAPM Task Group No. 43 report (TG-43U1). For each source, the authors obtained detailed results for the dose rate constant lambda, the radial dose function g(r), the anisotropy function F(r, theta), and the anisotropy factor phi(an)(r). In this study, the optimal source IRA3-103Pd provides the most isotropic dose distribution in water with the dose rate constant of 0.678(+/-0.1%) cGy h(-1) U(-1). The IRA3-103Pd design has a silver rod core combined with thin-wall, concave end caps. Finally, the authors compared the results for their optimal source with published results for those of other source manufacturers.