Preliminary investigations of two types of silica-based dosimeter for small-field radiotherapy

Two thermoluminescent dosimeters (SiO2-GeO2 doped fibres and glass beads (GB)) were used to measure small photon field doses and compared against GAFCHROMIC film, a small ionisation chamber (RK-018) and a p-type silicon diode (SCANDITRONIX, F1356), as well as Monte Carlo simulations with FLUKA and BEAMnrc/DOSXYZnrc. Ge-doped SiO2 fibres have been shown by this group to offer a viable system for use as dosimeters. The fibres and GB offer good spatial resolution (similar to 120 mu m and 2 mm respectively), large dynamic dose range (with linearity from tens of mGy up to well in excess of many tens of Gy), are nonhygroscopic and are of low cost. Measurements of beam profiles for field sizes of 10 mm x 10 mm, 20 mm x 20 mm, 30 mm x 30 mm, 40 mm x 40 mm, and 100 mm x 100 mm were carried out. Through the use of a customised solid water phantom, doped optical fibres and GBs were placed at defined positions along the x-and y-axes to allow accurate beam profile measurement. The maximum difference between FWHM measurements was 1.8 mm. For penumbra measurements (measured between 80% and 20% isodoses), the maximum difference was <1 mm. These measurements indicate good agreement, within measurement uncertainty, with Gafchromic film, data obtained from the use of two commonly used detectors and FLUKA and BEAMnrc/ DOSXYZnrc simulations. (C) 2014 Elsevier Ltd. All rights reserved.