Benchmarking novel optical fibre sensors for applications in radiation therapy

Abstract

Detecting ionising radiation using scintillation light is a long-established technique, yet scintillator-based dosimetry in radiotherapy was not commercially available until recently. Scintillator materials can be organic or inorganic. Organic based scintillator detectors suffer from low light conversion efficiency and Cerenkov light ratio (CLR) coefficient energy dependence. The aim of this study was to characterise novel optical fiber sensors (OFS) based on an inorganic scintillating material for external beam radiotherapy due to the high sensitivity and high light conversion efficiency of inorganic scintillators. The sensor was constructed using a polymethyl methacrylate (PMMA) plastic optical fibre. The core of the PMMA was micro machined to make a cavity with a 700 μ m diameter and a 3 mm depth. The cavity was filled with the scintillating material terbium doped gadolinium oxysulphide (Gd2O2S:Tb) and then sealed with an epoxy. The scintillation material fluoresces on exposure to ionising radiation and the resultant emitted fluorescent light is detected using a multi-pixel photon counting module. Essential dosimetric properties were quantified, including the repeatability of the OFS system response, linearity of the output signal with radiation doses and dose rate and dose per pulse (DPP) dependency of the system. Percentage depth dose (PDD) and lateral dose profiles were measured for different field sizes and compared to the commercial W1 plastic scintillator and Monte Carlo simulations using BEAMnrc/DOSXYZnrc codes.