Flynn, S; Manolopoulos, S; Rompokos, V; Poynter, A; Toltz, A; Beck, L; Ballisat, L; Velthuis, J; Allport, P; Green, S; Thomas, R; Price, T (2022) Monitoring Pencil Beam Scanned proton radiotherapy using a large format CMOS detector. Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 1033. 166703

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Abstract

Pencil beam scanning is an effective form of proton radiotherapy for cancer treatment. Small beams of protons are magnetically deflected in order to conform to a tumour shape, and exploiting the Bragg peak in order to minimise dose deposited in healthy tissues. Compared to other therapy modalities, it presents many dosimetric challenges requiring new methods of quality-assurance to ensure the best patient outcome possible. Position Sensitive Detectors (PSD) made from Complementary-Metal Oxide Semiconductor (CMOS) technology offer one such solution for in-situ and in-vivo dosimetry, taking advantage of the development of high resolution imaging panels that are tolerant to high levels of ionising radiation. To further evaluate the suitability of CMOS technology, the vM2428 detector, a large-format CMOS device with 50 um pixel pitch, was investigated at the University College London Hospital (UCLH) proton beam centre using a 220 MeV proton beam at clinical beam currents. The shape of the proton beam was intentionally distorted, enabling the comparison of the vM2428 detector and EBT3 film in a fault-finding scenario for QA purposes. For stationary beams, it was found that the vM2428 detector was capable of acquiring beam profiles comparable to EBT3 film within a single frame (~4 ms) in addition to the 2D dose profile. The detector was then exposed to laterally displaced beams of the same spot size ("spot scanning") that emulates a clinical beam delivery and was found able to record the beam displacement in real time. The measured spot-to-spot separation was measured to be 5.35+-0.03 mm, in agreement with the planned 5.356 mm. No deterioration of the detector performance due to radiation induced damage (radiation ageing) was observed. These results highlight the versatility and potential of large-format CMOS detectors to proton beam therapy.

Item Type:	Article
Subjects:	Ionising Radiation > Dosimetry
Divisions:	Medical, Marine & Nuclear
Identification number/DOI:	10.1016/j.nima.2022.166703
Last Modified:	15 Oct 2025 13:47
URI:	https://eprintspublications.npl.co.uk/id/eprint/10250