Radiation dose enhancement at tissue-tungsten interfaces in HDR brachytherapy

Abstract

HDR BrachyView is a novel in-body dosimetric imaging system for real-time monitoring and verification of the source position in high dose rate (HDR) prostate brachytherapy treatment. It is based on a high-resolution pixelated detector array with a semi-cylindrical multi-pinhole tungsten collimator and is designed to fit inside a compact rectal probe, and is able to resolve the 3D position of the source with a maximum error of 1.5 mm. This paper presents an evaluation of the additional dose that will be delivered to the patient as a result of backscatter radiation from the collimator. Monte Carlo simulations of planar and cylindrical collimators embedded in a tissue-equivalent phantom were performed using Geant4, with an 192 Ir source placed at two different sourcecollimator distances. The planar configuration was replicated experimentally to validate the simulations, with a MOSkin dosimetry probe used to measure dose at three distances from the collimator. For the cylindrical collimator simulation, backscatter dose enhancement was calculated as a function of axial and azimuthal displacement, and dose distribution maps were generated at three distances from the collimator surface. Although significant backscatter dose enhancement was observed for both geometries immediately adjacent to the collimator, simulations and experiments indicate that backscatter dose is negligible at distances beyond 1 mm from the collimator. Since HDR BrachyView is enclosed within a 1 mm thick tissue-equivalent plastic shell, all Institute of Physics and Engineering in Medicine

A Novel Perineal Shield for Low-Dose Rate Prostate Brachytherapy

“…Increased dose to the patient due to backscatter is possible. However, prior studies attempting to quantify backscatter exposure with Iridium-192, a higher energy source than Iodine-125 have revealed that the backscatter dose is essentially negligible at > 1 mm [31]. For our shield, it is practically difficult to measure the radiation exposure on the patient's side of the shield due to the radiation emitted directly from the sources inside the prostate.…”

A simulation study of BrachyShade, a shadow-based internal source tracking system for HDR prostate brachytherapy

“…Ir HDR brachytherapy source. The core consists of pure iridium with a uniform distribution of 192 Ir, surrounded by a steel shell (Borg et al, 1999a;Han et al, 2014).…”