A review of micro silica beads in radiation dosimetry applications

Abstract

A recent development in the field of radiation measurement is the use of silica glass beads as high performance thermoluminescent detectors. The application of using doped silica glass jewellery beads as radiation detectors was first proposed by Jafari in 2014, on the basis that it held the potential to resolve long standing issues in dosimetry, could be cheaply implemented, and had yielded good results in initial experimental work. Today the body of literature concerned with glass bead dosimeters has grown extensively, covering their behaviour in various radiation fields, as well as their handling and storage properties. The purpose of this review is to summarise the results obtained in the literature so far. Paramount among these is the finding that beads could offer excellent performance in radiotherapy applications, particularly due to their small volume (1–3 mm3), measurement reproducibility of less than 3% (k = 2), chemical inertness and low fading rate (10% over the first 30 days after irradiation). The beads are energy independent over the MV photon and MeV electron energy ranges and exhibit good linearity in electron, proton, carbon ion and photon radiation (an R2 of 0.999 having been achieved from 1 cGy to 50 Gy in a 6 MV photon beam) as well as being dose-rate and angular independent. However, significant energy dependence in the lower energy range is apparent (<300 kV), thus careful calibration is required. Irradiation of beads with neutrons has also been studied, the reported results indicate their potential use as high spatial resolution alternatives to the gas detectors presently used in industrial and scientific fields. Published use cases of silica beads have been identified and summarised in this review, these include treatment plan verification, small field dosimetry, SABR audits and kV therapy all of which demonstrating the potential use for silica bead TLDs within Radiotherapy.