Towards machine learning aided real-time range imaging in proton therapy

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 $$\gamma $$ γ -ray energies spanning up to 5–6 MeV, rather low $$\gamma $$ γ -ray emission yields and very intense neutron induced $$\gamma $$ γ -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 $$\gamma $$ γ -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$$_{3}$$ 3 crystals, when compared to other similar systems based on LYSO, CdZnTe or LaBr$$_{3}$$ 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$$_{3}$$ 3 monolithic crystals, thereby achieving a high efficiency in coincidence of 0.2% for a point-like 1 MeV $$\gamma $$ 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 10$$^{8}$$ 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 $$\gamma $$ γ -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.

In-Beam PET And Compton Imaging For Enhanced Accuracy Proton-Range Verification

“…On average, both resolution and repeatibility are better in PET than in Compton imaging. Rather than the angular or spatial resolution itself, it is the sensitivity of the imaging apparatus to range shifts or variations what matters when it comes to addressing range verification 18 . The latter is more related to repeatibility than resolution, although a higher image resolution is expected to deliver also a more reliable range monitoring.…”

“…More details can be found in Ref. 18 . The add-back energy-calibrated energy spectrum between detectors of the different i-TED modules during the beam-off period is displayed in Fig.…”

“…For a point-like 1 MeV γ-ray source at 5 cm distance from the front face of the module, the coincidence detection efficiency is ∼0.2%. Regarding neutron-induced background suppression, LaCl 3 (Ce) ensures a small sensitivity to neutron interactions in the detection volume itself 18 , while offering also a large intrinsic detection efficiency. Finally, the high time-resolution obtained with the implemented acquisition system (PETsys Front-End Board D version 2 (FEB/D-1024)), with coincidence-time resolutions of CTR∼500 ps, help to reduce random coincidences and other related backgrounds that could degrade the Compton imaging.…”

Hybrid PET/Compton-camera imaging: an imager for the next generation

“…Within the frame of particle therapy, event selection instead of compensation during the reconstruction is often attempted to reduce the impact of accidental coincidences and fortuitous events [69], and/or to compensate for the wrong estimation of the unknown initial energy [126]. Machine learning, in particular deep neural networks, has also shown some potential in this regard [127][128][129][130].…”

Simultaneous Gamma-Neutron Vision device: a portable and versatile tool for nuclear inspections

“…The system consists of a compact and handheldportable device capable of measuring and simultaneously imaging both thermal-and slowneutrons and γ -rays, both of them with a high efficiency. The proposed device consists of an upgrade of the i-TED Compton imager [16][17][18][19] developed within the ERC project HYMNS [20], in such a way that simultaneous imaging of both γ -rays and slow neutrons becomes feasible with the same device.…”