Ge-doped optical fibres as thermoluminescence dosimeters for LDR I-125 brachytherapy sources
F. M. ISSA 1*, R. P. Hugtenburg 2, D. A. Bradley 1, A. Nisbet 1,3
1 Department of Physics, University of Surrey, Guildford, GU2 7XH, UK
2 Department of Medical Physics & Clinical Engineering, Abertawe Bro Morgannwg UHB and School of Medicine, Swansea University, Swansea, SA2 8PP, UK
3 Department of Medical Physics, Royal Surrey County Hospital NHS Foundation Trust, Guildford, GU2 7XX, UK
Brachytherapy is that form of radiotherapy in which, depending on clinical considerations and access, sealed radioactive sources are placed either within or next to the tissue to be treated. The intent is to deliver as high a tumour dose as possible, limited only by surrounding normal tissue tolerance. The method is effective for many kinds of cancer, including cervical, prostate, breast and skin cancer.
Given the associated high dose gradients, at distances within a few cm from the source it is quite difficult to perform dose measurements. In particular, use is required of very small dosimeters of adequate sensitivity (Jones, 2007) or possibly to make use of calculation formalisms eg that of AAPM TG 43, or to use validated Monte Carlo simulations.
Ge-doped optical fibre TL dosimeters have been investigated in a previous study (Issa et al., 2010), showing good dosimetric response for low photon energies, good reproducibility, low fading and linear dose response up to 45 Gy. In addition, Ge-doped silica fibres offer good spatial resolution (~120 µm), low cost and are impervious to water. These desirable characteristics persuade us that these TL fibres can be used as dosimeters for brachytherapy applications.
In the present work Ge-doped optical fibre thermoluminescence dosimeters are used in order to measure the dose distribution around a Low Dose Rate (LDR) I-125 seed (model 6711) for distances from 1 mm to 10 cm. The irradiations are performed in a Perspex phantom with full scattering condition. The results have been verified, making comparisons with results of EGSnrc \ DOSRZnrc Monte Carlo code simulations. Agreement is obtained within 2%.
ISSA, F., LATIP, N. A. A., BRADLEY, D. A. & NISBET, A. 2010. Ge-doped optical fibres as thermoluminescence dosimeters for kilovoltage X-ray therapy irradiations. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, In Press, Corrected Proof.
JONES, C. 2007. Calibration and Quality Assurance of Brachytherapy Sources. Handbook of Radiotherapy Physics. Taylor & Francis.