Abstract
Compton imaging represents a promising technique for range verification in proton therapy treatments. In this work, we report on the advantageous aspects of the i-TED detector for proton-range monitoring, based on the results of the first Monte Carlo study of its applicability to this field. i-TED is an array of Compton cameras, that have been specifically designed for neutron-capture nuclear physics experiments, which are characterized by gamma -ray energies spanning up to 5–6 MeV, rather low gamma -ray emission yields and very intense neutron induced gamma -ray backgrounds. Our developments to cope with these three aspects are concomitant with those required in the field of hadron therapy, especially in terms of high efficiency for real-time monitoring, low sensitivity to neutron backgrounds and reliable performance at the high gamma -ray energies. We find that signal-to-background ratios can be appreciably improved with i-TED thanks to its light-weight design and the low neutron-capture cross sections of its LaCl_{3} crystals, when compared to other similar systems based on LYSO, CdZnTe or LaBr_{3}. Its high time-resolution (CRT sim 500 ps) represents an additional advantage for background suppression when operated in pulsed HT mode. Each i-TED Compton module features two detection planes of very large LaCl_{3} monolithic crystals, thereby achieving a high efficiency in coincidence of 0.2% for a point-like 1 MeV gamma -ray source at 5 cm distance. This leads to sufficient statistics for reliable image reconstruction with an array of four i-TED detectors assuming clinical intensities of 10^{8} protons per treatment point. The use of a two-plane design instead of three-planes has been preferred owing to the higher attainable efficiency for double time-coincidences than for threefold events. The loss of full-energy events for high energy gamma -rays is compensated by means of machine-learning based algorithms, which allow one to enhance the signal-to-total ratio up to a factor of 2.
Highlights
Compton imaging represents a promising technique for range verification in proton therapy treatments
Discussion and conclusion i-TED is a Compton camera array that has been designed for neutron-capture nuclear physics experiments
Several design aspects of i-TED, such as its high time resolution, high efficiency and relatively low neutron sensitivity may become of interest in order to address some of the current challenges in Prompt Gamma Imaging for range verification in proton therapy treatments
Summary
Compton imaging represents a promising technique for range verification in proton therapy treatments. Each i-TED Compton module features two detection planes of very large LaCl3 monolithic crystals, thereby achieving a high efficiency in coincidence of 0.2% for a point-like 1 MeV γ-ray source at 5 cm distance This leads to sufficient statistics for reliable image reconstruction with an array of four i-TED detectors assuming clinical intensities of 108 protons per treatment point. In-vivo range monitoring remains still an issue for most of the Compton cameras under development[16,18–29] These limitations are related to the limited coincidence efficiency of some of the detectors[20,21,25], the high counting rates in clinical c onditions[16,24,30], the spatial resolution[22], the signal-to-background ratio that is challenged by contaminant r eactions[18,31], and the CPU processing-time required by the corresponding image-reconstruction a lgorithm[26]
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