On the use of a CMRP-designed fibre-optic system for HDR Brachytherapy quality assurance

Background:
Brachytherapy is an advanced cancer treatment procedure which involves the insertion of an HDR radioactive source, typically 192Ir, within the treatment volume to destroy the cancerous cell. Due to the complexity of such a technique in terms of high dose gradient and source positioning, there has been a paramount necessity to apply highly-accurate quality assurance (QA) tools to assure that treatment plan has been carried as clinically prescribed.

Purpose:
The purpose of this research study is to investigate the use of a CMRP-designed fibre-optic system for comprehensive quality assurance and real-time verification of HDR Brachytherapy source.

Methods:
A trans-impedance photodiode amplifier has been in-housed designed and prepared for this purpose. A 3mm length of Thallium Doped-Caesium Iodide CsI(Tl) (Amcrys. Ukraine) scintillation crystal has been in-lab prepared and optically coupled to a non-scintillating fibre (CK-400) as a light guide. The in-house-developed readout DAQ system was used to measure the real-time light output and simultaneous data analysis for treatment monitoring. Relying on multiple fibres and triangulation methodology, the fabricated fibre probes were placed within a solid-water phantom at varying distances above an 192Ir source located within the catheter, with dwell positions varied every 2 mm.

Results:
The response maps were developed, with profiles obtained for multiple source dwell positions were acquired in respect to 192Ir Brachytherapy source locations at different source to detector distances (SDDs). Based on our pre-clinical results obtained, it is clearly seen that the localization of an 192Ir HDR source has been feasible and CsI (Tl) crystal can track the source to within 1 mm and has been able to resolve movement of HDR source for a minimum step size of 2 mm at various distances.

Conclusions:
The designed fiber optic system, using multiple fibres, and triangulation has been devised and investigated. The developed systems show great potential in performing for in-vivo source positioning and in 3D space with a capability of real-time HDR source tracking utilizing multichannel DAQ system. The feasibility of applying such QA system for such purpose has been demonstrated, and such a system would overcome potential technical issues of other commercially available QA tools.

Mohammed Al Towairqi

University of Wollongong
PhD Student

Mohammed is currently pursuing his PhD at the Centre for Medical Radiation Physics (CMRP) at University of Wollongong (UOW) under the supervision of Distinguished Professor. Anatoly Rosenfeld. His research focuses are mainly based on the development of a fibre optic dosimetry system for HDR Brachytherapy quality assurance. He has been a[ppointed to take up a lectureship position at Taif University, More recently, he has been affiliated with Biomedical Physics Department at King Faisal Hospital & Research Centre (KFSHRC).in Riyadh.