Simulation of proton range monitoring in an anthropomorphic phantom using multi-slat collimators and time-of-flight detection of prompt-gamma quanta

Abstract

Prompt-gamma (PG) imaging has the potential for monitoring proton therapy in real time. Different approaches are investigated. We focus on developing multi-slat collimators to image PG quanta, aiming at optimizing collimator performance to detect deviations in treatment delivery. We investigated six different multi-slat configurations, which have either optimal (analytical) intrinsic spatial resolution at fixed efficiency, or otherwise; at different distances from the proton pencil-beam axis (15 cm-35 cm). We used Geant4 to simulate irradiations of the head (energy: 130 MeV) and pelvis (200 MeV) of an anthropomorphic phantom, with and without physiologic/morphologic or setup changes of clinical dosimetric relevance. The particles escaping the phantom were transported through each of these multi-slat configurations and the gamma counts profiles were recorded at the collimator exit. Median filtering was applied to the registered PG-profiles to mitigate the effects of septa shadowing and statistical fluctuations. Time-of-flight discrimination was used to enhance the signal-to-background ratio, which appeared crucial for 200 MeV irradiations. Visual detection of the artificially introduced changes was possible by comparing the PG to the depth-dose profiles. Moreover, 2 mm range shifts could be detected in the head irradiation case using a simple linear regression fit to the falloff of the PG-profile. The influence of changes in complex, patient-like dose distributions on the PG-profiles obtained with multi-slat collimation is first studied in this work, which further gives insight on collimator design optimization and highlights its potential and simplicity for detecting proton treatment deviations over a wide range of Bragg peak positions.

Distal edge determination precision for a multi-slat prompt-gamma camera: A comprehensive simulation and optimization of the detection system

“…The proton beam was simulated as a single pencil beam of zero width. The proton energy was set to 130 MeV, corresponding to a typical head irradiation scenario [12]. One PT frame was simulated with 1•10 8 protons organized in bunches of 310 protons with a period of 10 ns, which is representative of the most distal pencil-beam in a typical cyclotron-based treatment plan [18].…”

“…The PG-based techniques do not rely on detection of delayed emission, as the PET-based imaging does, and, therefore, are unaffected by biological processes such as the activity washout [11], which is a significant advantage considering accurate range monitoring. In the previous study performed by our group [12], a PGI imaging system with a multi-slat collimator oriented orthogonally to the beam direction has been investigated. This imaging approach is hereafter referred to as O-PGI.…”

Design and performance evaluation of a slit‐slat camera for 2D prompt gamma imaging in proton therapy monitoring: A Monte Carlo simulation study

“…7,13 PGI systems either utilize physical collimation such as gamma cameras or non-physical collimation such as Compton cameras (CCs). 5,15,16 Compton cameras provide the possibility of 3D imaging and are currently investigated for applications to particle therapy dose monitoring. 17,18 The detection efficiency of CCs are ranging from 10 −6 to 10 −3 in proton therapy and nuclear medicine imaging.…”

Prompt-gamma emission in GEANT4 revisited and confronted with experiment

“…Monte-Carlo simulations play a crucial role in the design and optimization phase o f detection setups, including those dedicated for prompt-gamma imaging (PG I) [8][9][10][11][12]. Not only the detector response is modelled this way, but also the characteristics o f gamma quanta induced in the irradiated object by a proton beam, which depend on the description o f the underlying processes in a given implementation o f a Monte-Carlo engine.…”