Optimisation of the SiFi-CC Compton camera for range verification in proton therapy through a genetic algorithm

• Optimierung der SiFi-CC Compton-Kamera zur Reichweitenüberprüfung in Protonentherapie mittels eines genetischen Algorithmus

Kasper, Jonas; Stahl, Achim (Thesis advisor); Schulz, Volkmar (Thesis advisor)

Aachen : RWTH Aachen University (2022, 2023)
Dissertation / PhD Thesis

Dissertation, RWTH Aachen University, 2022

Abstract

Proton therapy is a modality of cancer radiotherapy that has become more important in the past decade. The proton beams exhibit a favourable energy deposition pattern, which allows the preservation of healthy tissue and yields a better conformality of the deposited dose. To fully exploit this advantage, a method of real-time beam range monitoring and hence on-line supervision of the deposited dose distribution would be needed. This work contributes to the development of a detector design that is intended to be used for beam range verification in proton therapy. The concept of the SiPM and scintillating Fiber-based Compton Camera (SiFi-CC) is proposed for the reconstruction of spatial dose distributions based on the detector response to prompt-gamma radiation originating from nuclear interactions of the proton beam with the tissue of the patient. The depth profile of their vertices reveals a characteristic distal fall-off, the position of which is correlated with the position of the Bragg peak of the proton beam. A multistage simulation framework was designed to simulate the interactions of proton-beam secondaries in different versions of the SiFi-CC setup. The simulated response of the SiFi-CC detector included the generation, propagation, and recording of optical photons. For the analysis of the data obtained from the simulations, a complex processing chain was developed. This chain converted the simulated detector response into reconstructed images of the prompt-gamma distributions and derived resolutions on the distal fall-off positions of these distributions. After the simulation parameters were adjusted to reproduce laboratory measurement results and the analysis chain was optimised, the simulation and processing frameworks were used in the course of a genetic algorithm. The aim was to optimise the geometric setup of the SiFi-CC. The genetic algorithm yielded the best performance for a SiFiCC setup with 16 layers of scintillating fibres in the scatterer, 36 layers in the absorber, a distance between the scatterer and the source of 150 mm and a distance between the scatterer and the absorber of 120 mm. Based on these results, two different fibre stacking methods in the detector design were assessed. A SiFi-CC setup that uses the parameters derived from the genetic algorithm and in which all fibres are aligned along the same direction is capable of detecting a 5 mm shift in the range of a proton beam, based on the prompt-gamma rays produced by 5 proton beam spots. The setup shows a detection efficiency of 0.0000558(1). This performance makes it a promising candidate for the task of on-line monitoring of proton therapy.

Institutions

• Department of Physics [130000]
• Chair of Experimental Physics III B [133510]