A hybrid multi-particle approach to range assessment-based treatment verification in particle therapy

Abstract

Particle therapy (PT) used for cancer treatment can spare healthy tissue and reduce treatment toxicity. However, full exploitation of the dosimetric advantages of PT is not yet possible due to range uncertainties, warranting development of range-monitoring techniques. This study proposes a novel range-monitoring technique introducing the yet unexplored concept of simultaneous detection and imaging of fast neutrons and prompt-gamma rays produced in beam-tissue interactions. A quasi-monolithic organic detector array is proposed, and its feasibility for detecting range shifts in the context of proton therapy is explored through Monte Carlo simulations of realistic patient models and detector resolution effects. The results indicate that range shifts of $${1}\,\hbox {mm}$$ 1 mm can be detected at relatively low proton intensities ($$22.30(13)\times 10^{7}$$ 22.30 ( 13 ) × 10 7 protons/spot) when spatial information obtained through imaging of both particle species are used simultaneously. This study lays the foundation for multi-particle detection and imaging systems in the context of range verification in PT.

Characterization of organic glass scintillator bars and their potential for a hybrid neutron/gamma ray imaging system for proton radiotherapy range verification

“…by the prompt-gamma imaging [11], spectroscopy [12], timing [13] and peak-integration [14] methods. It has also been shown that the spatial distribution of fast neutrons (FNs) generated during treatment delivery is correlated to the proton range, and could reveal complementary information to PGs about the proton range [15,16]. To exploit this, the NOVO (NeutrOn and gamma ray imaging for real-time range VerificatiOn and image guidance in particle therapy) project was initiated with the goal of imaging the proton range using information from both PGs and FNs simultaneously.…”

“…Such a hybrid imaging system promises to reduce range uncertainties and improve treatment outcomes by exploiting the increased statistics and complementary information from both particle species. Simulation studies have shown that such a system is capable of imaging range deviations of 1 mm at proton intensities as low as 6.08 (21) • 10 6 protons/spot by using combined information from PGs and FNs [16].…”

“…For this purpose, a prototype detector array of optically segmented plastic scintillator bars must be developed, which is hereby referred to as the NOVO Compact Detector Array (NOVCoDA). As gamma rays and neutrons scatter between detector elements in the array, their energy, time-of-arrival, position and particle species information will be extracted from the detector signals [16]. Using their respective scattering kinematics, the origin of both PGs [17,18] and FNs [19,20] can be constrained to lie on the surface of a cone, assuming a single scattering interaction in each triggered detector in the array.…”

“…The spatial origin of the radiation can then be imaged using reconstruction algorithms, e.g. filtered backprojection [21,22], list-mode maximum likelihood expectation maximization (LM-MLEM) [16,23], or the stochastic origin ensembles method (SOE) [24].…”

“…Good depth-of-interaction (DOI) resolution, i.e., the position of the interaction along the bar, is essential for properly reconstructing backprojection cones of both neutrons and gamma rays, and is influenced by both the time resolution and light yield ratio between both readout ends of the detector (see 2.4 and 3.3). The energy resolution is important for accurately reconstructing event cones of scattered PGs using elastic scattering kinematics [16]. Finally, the chosen scintillator must have pulse shape discrimination (PSD) capabilities to differentiate between neutron-induced and gamma ray-induced events.…”