Monte Carlo‐based beam quality and phantom scatter corrections for solid‐state detectors in 60Co and 192Ir brachytherapy dosimetry

Abstract

Beam quality correction, $k_{{\mathit{\text{QQ}}}_0}\left(r\right)$, for solid‐state detectors diamond, LiF, ${\text{Li}}_2{\mathrm{B}}_4{\mathrm{O}}_7,{\text{Al}}_2{\mathrm{O}}_3$, and plastic scintillator are calculated as a function of distance, r, along the transverse axis of the ${}^{60}\text{Co}$ and ${}^{192}\text{Ir}$ brachytherapy sources using the Monte Carlo‐based EGSnrc code system. This study also includes calculation of detector‐specific phantom scatter correction, $k_{\mathit{\text{phan}}}\left(r\right)$, for solid phantoms such as PMMA, polystyrene, solid water, virtual water, plastic water, RW1, RW3, A150, and WE210. For ${}^{60}\text{Co}$ source, $k_{{\mathit{\text{QQ}}}_0}\left(r\right)$ is about unity and distance‐independent for diamond, plastic scintillator, ${\text{Li}}_2{\mathrm{B}}_4{\mathrm{O}}_7$ and LiF detectors. For this source, $k_{{\mathit{\text{QQ}}}_0}\left(r\right)$ decreases gradually with r for ${\text{Al}}_2{\mathrm{O}}_3$ detector (about 6% smaller than unity at 15 cm). For ${}^{192}\text{Ir}$ source, $k_{{\mathit{\text{QQ}}}_0}\left(r\right)$ is about unity and distance‐independent for ${\text{Li}}_2{\mathrm{B}}_4{\mathrm{O}}_7$ detector (overall variation is about 1% in the distance range of 1–15 cm). For this source, $k_{{\mathit{\text{QQ}}}_0}\left(r\right)$ increases with r for diamond and plastic scintillator (about 6% and 8% larger than unity at 15 cm, respectively). Whereas $k_{{\mathit{\text{QQ}}}_0}\left(r\right)$ decreases with r gradually for LiF (about 4% smaller than unity at 15 cm) and steeply for ${\text{Al}}_2{\mathrm{O}}_3$ (about 25% smaller than unity at 15 cm). For ${}^{60}\text{Co}$ source, solid water, virtual water, RW1, RW3, and WE210 phantoms are water‐equivalent for all the investigated solid‐state detectors. Whereas polystyrene and plastic water phantoms are water‐equivalent for diamond, plastic scintillator, ${\text{Li}}_2{\mathrm{B}}_4{\mathrm{O}}_7$ and LiF detectors, but show distance‐dependent $k_{\mathit{\text{phan}}}\left(r\right)$ values for ${\text{Al}}_2{\mathrm{O}}_3$ detector. PMMA phantom is water‐equivalent at all distances for ${\text{Al}}_2{\mathrm{O}}_3$ detector, but shows distance‐dependent $k_{\mathit{\text{phan}}}\left(r\right)$ values for remaining detectors. A150 phantom shows distance‐dependent $k_{\mathit{\text{phan}}}\left(r\right)$ values for all the investigated detector materials. For ${}^{192}\text{Ir}$ source, solid water, virtual water, RW3, and WE210 phantoms are water‐equivalent for diamond, plastic scintillator, ${\text{Li}}_2{\mathrm{B}}_4{\mathrm{O}}_7$ and LiF detectors, but show distance‐dependent $k_{\mathit{\text{phan}}}\left(r\right)$ values for ${\text{Al}}_2{\mathrm{O}}_3$ detector. All other phantoms show distance‐dependent $k_{\mathit{\text{phan}}}\left(r\right)$ values for all the detector materials.

PACS numbers: 87.10.Rt, 87.53.Bn, 87.53.Jw