The thermoluminescence response of Ge-doped optical fibres to X-ray photon irradiation

Abstract

Thermoluminescence dosimetry (TLD) is useful in medical application to determine dose received by patient in cancer treatment. The interest is to introduce optical fibres as a new thermoluminescence (TL) material. This paper presents preliminary results on the TL response reproducibility with various doses and fading of Ge-doped optical fibres to X-ray photon irradiation. The optical fibres investigated were typical single-mode fibres, with a core diameter of 130 (a.m. Prior to X-ray photon irradiation, the calibration of diagnostic X-ray machine doses was made using ionization chamber. Dose rate of 58.31 mGy s'1 was delivered to the Ge-doped optical fibre using 49.8 kVp and 986 (iA current setting. During irradiation, a retort stand was used to hold the plastic container in order to get uniform exposure. TL response of Ge-doped optical fibre following X-ray irradiations was found to be linear in medical radiotheraphy dose range up to 10 Gy. In fading studies, a total of 30 samples of Ge- doped optical fibres were simultaneously irradiated, first to 2 Gy of X-rays and then subsequently to 10 Gy of X-ray dose. The performance of Ge-doped optical fibres was then compared against the currently available TL material i.e. TLD-700 (LiF:Mg,Ti). The average reading from five repeated measurements on both types of TL material were recorded on a daily basis over a period of six days. After irradiation, and until readout, the samples were kept in the lightproof container at a room temperature. Six days after irradiation, the Ge-doped optical fibre exposed to 2 Gy showed a 26.2 % loss of signal compared to the yield obtained 24 hours after irradiation, while at 10 Gy the fibre showed a loss of 19.7 %. Conversely, for TLD-700 the respective values were 75.9% and 36.1 %.