Harnessing the thermoluminescence of Ge-doped silica flat-fibres for medical dosimetry

Study has been made of key thermoluminescence (TL) properties of Ge-doped silica flat-fibre, including TL glow curves, dose-rate dependency and reproducibility, the fibres being photon irradiated over the dose range 0.5- to 8 Gy, use being made of a medical linear accelerator (LINAC) operated at either 6- or 10 MV. Percentage depth doses (PDD) were also studied, comparison being made of fibre-measured PDD values against those obtained using an ionization chamber and standard TLD-100 and TLD-700 chips. The flat-fibre samples displayed a single prominent TL glow curve dosimetry peak at 249 °C, the structure of this remaining unchanged during repeat cycles of annealing and irradiation at different doses. For fixed dose, the TL responses of the samples also remained practically constant in use of five different dose-rates in the range100 MU/min to 500 MU/min. The effective atomic number (Zeff) of the flat-fibre was calculated to be 13.37, greater than soft tissue (7.42) but within the range of values for human bone (11.6-13.8). Using the 6 MV photon beam, PDD studies yielded a dmax of 1.5 cm, consistent with the value attained using the ionization chamber and the standard TLD chips. At 2 cm depth, the optical fibre samples showed good agreement to within −4%, 1.3% and 4% respectively with measurements made in use of the ionization chamber, standard TLD-100 chips and TLD-700 chips. The study represents part of an overall plan towards development of silica fiber-based dosimeters for radiotherapy and diagnostic radiology applications.