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Penner, Crystal

University of British Columbia

As the technology to deliver precise and very high radiotherapeutic doses with narrow margins grows to better serve patients with complex radiotherapeutic needs, so does the need for sensor systems that can reliably deliver multi-point information for enhanced safety and access. Requirements for such tools include near-water equivalence, flexibility, robustness and fast timing. Sensors should exhibit dose and dose rate independence, and adequate spatial resolution for measuring beams in axial and transverse directions. To this end, two organic fibre-based arrays were developed: one five scintillator array for conventional dose rates applications, and one of seven PMMA fibres for FLASH dose rates. A 16 channel MPPC was employed as photodetector for both arrays. For the scintillator array, two 3 mm long organic scintillators were tested: the SCSF-3HF(1500) scintillating fibre (Kuraray) and the EJ-260 plastic scintillator (Eljen Technology) were studied for dose and dose rate, Bragg peak and spread-out Bragg peak response. Both fibres exhibited linear dose and dose rate response and correctable (via Birks’ equation) depth doses. The SCSF-3HF scintillator was then expanded to the 5-sensor array. The five-point scintillator system was tested in a 74 MeV proton beam. We studied response across beam diameters from 25 mm to 5 mm and at multiple depths to observe beam penumbrae, output factors and depth-dose. We found through comparison to ionisation chambers and radiochromic film that the array is capable of measurements accurate to within 8% in the centre of proton beams, and within 2% at 3.5 cm depth in water with excellent repeatability over 3 trials. The seven PMMA fibre array was developed to interrogate FLASH proton beam profiles. 1 mm diameter fibres were embedded in a custom phantom and irradiated at proton dose rates from 7.5 to 101 Gy/s. The array was able to record beam profiles in relative agreement with measurements from radiochromic films (between 5 and 13% in the transverse beam centre) and Monte Carlo simulation (axial direction). A decrease in light output over time was observed—possibly caused by radiation damage in the matrix of the fibre—and characterized with an exponential decay function (decay constant: 0.00032 ± 0.00002).

Text

2024-08-21

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/88981

Electrical and Computer Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/