Organic Scintillator-Fibre Sensors for Proton Therapy Dosimetry: SCSF-3HF and EJ-260

Abstract

In proton therapy, the dose from secondary neutrons to the patient can contribute to side effects and the creation of secondary cancer. A simple and fast detection system to distinguish between dose from protons and neutrons both in pretreatment verification as well as potentially in vivo monitoring is needed to minimize dose from secondary neutrons. Two 3 mm long, 1 mm diameter organic scintillators were tested for candidacy to be used in a proton–neutron discrimination detector. The SCSF-3HF (1500) scintillating fibre (Kuraray) and EJ-260 plastic scintillator (Eljen Technology) were irradiated at the TRIUMF Neutron Facility and the Proton Therapy Research Centre. In the proton beam, we compared the raw Bragg peak and spread-out Bragg peak response to the industry standard Markus chamber detector. Both scintillator sensors exhibited quenching at high LET in the Bragg peak, presenting a peak-to-entrance ratio of 2.59 for the EJ-260 and 2.63 for the SCSF-3HF fibre, compared to 3.70 for the Markus chamber. The SCSF-3HF sensor demonstrated 1.3 times the sensitivity to protons and 3 times the sensitivity to neutrons as compared to the EJ-260 sensor. Combined with our equations relating neutron and proton contributions to dose during proton irradiations, and the application of Birks’ quenching correction, these fibres provide valid candidates for inexpensive and replicable proton-neutron discrimination detectors.

A Multi-Point Optical Fibre Sensor for Proton Therapy

“…Five sensors were fabricated as described by Penner et al (2023) [37] using 3 mm lengths of 1 mm diameter SCSF-3HF (1500) scintillating fibre (Kuraray) as the radiosensitive element, and 15 m fibre lengths of Eska Premier 1 mm Simplex Optical Fibre (Mitsubishi Chemical Corporation, Chiyoda-ku, Tokyo, Japan) for light transport, as shown in Figure 1. The exposed scintillator/fibre-coupled ends were coated with a liquid electrical tape (Gardner Bender, New Berlin, Wisconsin, United States) to eliminate ambient light contamination.…”

“…Many scintillation dosimeters are fabricated using plastic or silica optical fibres as transport fibres and organic or inorganic scintillators for radiation sensing [31][32][33][34][35][36][37]. When irradiated, scintillator atoms (inorganic scintillators) or molecules (organic scintillators) are excited, and as the product of the scintillator returning to a neutral state, light is emitted and radiation-induced luminescence (RIL) is detected.…”

“…The scintillator employed in this study was the SCSF-3HF (1500) double-clad plastic scintillator fabricated by Kuraray (Chiyoda-ku, Tokyo, Japan), which was selected due to its sharp scintillation peak at 530 nm as well as its formulation for radiation hardness. A single sensor fabricated in the same manner as those used in this study was previously characterized using the TRIUMF 74 MeV proton therapy research centre (PTRC) beam, and shown to exhibit a linear dose and dose rate response as well as quenched but correctable (via Birks' formula) raw and spread-out Bragg peaks [37].…”