Impact of Pre-Irradiation on Quenching In Optical Fibres: Proton Therapy Dosimetry
Abstract
Purpose
To map the saturation behaviour of quenching in multiple CeTb-doped optical fibres, with different levels of X-rays pre-irradiation, under proton irradiation.
Methods
Two sets of five CeTb-doped optical fibres were irradiated with X-rays to different doses, ranging from 0 Gy to 1700 Gy. The fibres were placed in a water phantom, at the end of a passive proton beamline, and tested with a 74 MeV proton beam. With a 3D stage, the fibres were centred to the entrance window and then moved in the beam direction to record Bragg peaks, as a function of time. Each doped fibre was connected to a transport cable and the signals were recorded with an MPPC and a collection software. Five Bragg peak measurements for each fibre were taken. The signals were normalized to the plateau region and to the current profiles.
Results
The quenching indicators, expressed as peak-to-plateau ratios, were plotted against pre-irradiated doses (0-1700 Gy). A reduction in the quenching was observed, as peak-to-plateau ratios increased with the pre-irradiation and a saturation behaviour was observed at high pre-irradiated doses. The saturation was mapped with an exponential saturation, and the peak-to-plateau ratios increased from 2.8 (0 Gy) to 3.4 (1700 Gy). The saturation fits results were compatible between different batches, and time scale effects were not observed.
Conclusion
The results suggest that pre-irradiation of optical fibres can open radiative pathways and reduce quenching, leading to higher-precision dosimetry. The saturation behaviour indicates that after a certain level of pre-irradiation, optical fibres could offer quenching-free dosimetry, effectively reducing the main drawbacks of optical fibres dosimetry, offering a great candidate for proton dosimetry, with excellent spatial resolution and potential for real-time dosimetry.