Room: AAPM ePoster Library
A novel methodology to reconstruct, in full 3D, the proton beam range, through prompt gamma (PG) rays detection, is presented.
The present technique utilizes the 2.741 - 6.128 MeV (p, ¹6O) PG-rays couples, emitted in cascade. Within the limitation of spectroscopy detector/electronic systems, these rays are emitted simultaneously in time and position. When protons impinge tissues couples are produced. Their detection, coupled with a reconstruction algorithm, allows the identification of the common emission point. The PG-ray distribution has a maximum intensity located few millimetres prior to the Bragg peak. For a beam crossing tissues with constant oxygen concentration, the range can be determined from the couples emission points.
The detection system is comprised of 16 LaBr3(Ce) detectors, symmetrically arranged. The position reconstruction capability was investigated with Geant4 simulations. Both the spectrometer, with realistic energy and temporal resolution, and a water phantom were modelled. The beam stops in the phantom within the spectrometer central volume. To reconstruct the PG-rays emission positions, the information recorded by each detector is fed into an in-house developed algorithm.
The detector/algorithm performance, for a 180 MeV beam and an 8 cm spectrometer internal radius, was evaluated. The centroid, µ, and the lateral spread, s, of the algorithm-reconstructed PG-rays emission positions is 21.37 ± 4.17. Keeping fixed the beam energy (180 MeV), this analysis was repeated for two different radii, 15 and 25 cm, obtaining 21.41 ± 5.65 and 21.45 ± 6.36, respectively. Subsequently, keeping fixed the radius (8 cm), a 175 / 177.5 MeV beam was modelled; translating into a 5 / 10 mm range undershoot. Results were: 20.84 ± 4.31 and 20.31 ± 5.47, respectively.
A novel methodology for proton range verification is developed. A prototype is under construction. The final goal is a clinically compliant system for on-line, real-time verification.