Timing resolution for an optical fibre-based detector in a 74 MeV proton therapy beam

C Penner,C Duzenli,C Hoehr,C Lindsay,S O’Keeffe

doi:10.1088/1742-6596/1067/6/062001

Abstract

A Terbium activated Gadolinium Oxysulfide (Gd2O2S:Tb)-filled optical fibre sensor was developed and tested as a proton therapy beam dosimeter on a 74 MeV proton beam. Tests were carried out at the TRIUMF proton therapy centre, where a passively scattered beam is used for treatment. To create a clinically relevant spread-out Bragg peak, a modulator wheel with steps of varying thickness is employed. To determine the sensor’s response in a 23 mm spread out Bragg peak, the sensor signal was sampled at depth intervals of 0.79 mm along the beam axis in a water phantom. The resulting data showed a periodic variation in the signal corresponding to the rotation of the modulator wheel and related to the depth in water of the detector. This timing resolution in the sensor response could find application in quality assurance for modulated proton beams.

Highlights

Proton radiotherapy is a rapidly growing method of cancer treatment with the number of facilities as well as treatments increasing every year [1,2,3]
Materials and Methods The detector was fabricated from polymethyl methacrylate (PMMA) based plastic optical fibre, with a cavity micromachined at one end and Gd2O2S:Tb (Gadox) scintillator powder packed into the cavity (Fig. 4)
It is important to note that towards the end of the spread-out Bragg peak (SOBP), the scintillator signal is quenched (Fig. 5), which explains why the signal with the highest variation is not the highest signal

Summary

Introduction

Proton radiotherapy is a rapidly growing method of cancer treatment with the number of facilities as well as treatments increasing every year [1,2,3]. During proton therapy the beam is modulated by a rotating, stepped polymethyl methacrylate wheel [4] (Fig. 1). The modulator wheel creates a uniform distribution of dose over a specified depth range by superposition of BPs, each with a specific range and relative weight. For a 23 mm SOBP (Fig. 2), the modulator wheel consists of 20 discrete steps resulting in the superposition of 20 individual BP’s. The relative weight of the peaks increases with their range.

Methods

Results

Discussion

Conclusion