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

Mishra Subhalaxmi,T Palani Selvam

doi:10.1120/jacmp.v15i6.4907

Mishra Subhalaxmi, T Palani Selvam

Open Access

https://doi.org/10.1120/jacmp.v15i6.4907

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Abstract

Beam quality correction, kQQ0(r), for solid‐state detectors diamond, LiF, Li2B4O7,Al2O3, and plastic scintillator are calculated as a function of distance, r, along the transverse axis of the 60Co and 192Ir brachytherapy sources using the Monte Carlo‐based EGSnrc code system. This study also includes calculation of detector‐specific phantom scatter correction, kphan(r), for solid phantoms such as PMMA, polystyrene, solid water, virtual water, plastic water, RW1, RW3, A150, and WE210. For 60Co source, kQQ0(r) is about unity and distance‐independent for diamond, plastic scintillator, Li2B4O7 and LiF detectors. For this source, kQQ0(r) decreases gradually with r for Al2O3 detector (about 6% smaller than unity at 15 cm). For 192Ir source, kQQ0(r) is about unity and distance‐independent for Li2B4O7 detector (overall variation is about 1% in the distance range of 1–15 cm). For this source, kQQ0(r) increases with r for diamond and plastic scintillator (about 6% and 8% larger than unity at 15 cm, respectively). Whereas kQQ0(r) decreases with r gradually for LiF (about 4% smaller than unity at 15 cm) and steeply for Al2O3 (about 25% smaller than unity at 15 cm). For 60Co 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, Li2B4O7 and LiF detectors, but show distance‐dependent kphan(r) values for Al2O3 detector. PMMA phantom is water‐equivalent at all distances for Al2O3 detector, but shows distance‐dependent kphan(r) values for remaining detectors. A150 phantom shows distance‐dependent kphan(r) values for all the investigated detector materials. For 192Ir source, solid water, virtual water, RW3, and WE210 phantoms are water‐equivalent for diamond, plastic scintillator, Li2B4O7 and LiF detectors, but show distance‐dependent kphan(r) values for Al2O3 detector. All other phantoms show distance‐dependent kphan(r) values for all the detector materials.PACS numbers: 87.10.Rt, 87.53.Bn, 87.53.Jw

Highlights

296 Subhalaxmi et al.: Beam quality and phantom scatter correction brachytherapy sources,(5,6) different solid phantoms are used to overcome practical problems such as waterproofing and precise positioning of detectors
Water is recommended as the reference medium for dosimetry of a Corresponding author: Mishra Subhalaxmi, Radiological Physics & Advisory Division, Health, Safety & Environment Group, Bhabha Atomic Research Centre, Mumbai – 400 094, Maharastra, India; phone: [91] 22-25598654; fax: [91] 22-25519209; email: b.subwu@gmail.com
In another study,(8) the values of R were reported for different radiochromic films for high-energy brachytherapy sources such as 60Co, 137Cs, 192Ir, and 169Yb in liquid water, PMMA, and polystyrene phantom materials

Summary

Introduction

296 Subhalaxmi et al.: Beam quality and phantom scatter correction brachytherapy sources,(5,6) different solid phantoms are used to overcome practical problems such as waterproofing and precise positioning of detectors. Relative absorbed-dose energy response corrections, R, were reported for different solid-state detectors for 169Yb and 125I brachytherapy sources. In another study,(8) the values of R were reported for different radiochromic films for high-energy brachytherapy sources such as 60Co, 137Cs, 192Ir, and 169Yb in liquid water, PMMA, and polystyrene phantom materials. In a recently published article by Selvam et al,(9) beam quality corrections (which is the inverse of R) were reported for different solid-state detectors at 137Cs energy. Detector-specific phantom scatter corrections for different solid phantoms were reported in their study. The purpose of this study is to calculate the beam quality corrections for solid-state detectors for 60Co and 192Ir brachytherapy sources. This study includes detector-specific phantom scatter corrections for different solid phantoms for these sources. The EGSnrc-based[10] user-codes DOSRZnrc and FLURZnrc [11] are used in the study

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