Factors influencing the accuracy of beam range estimation in proton therapy using prompt gamma emission

Abstract

In-vivo imaging is a strategy to monitor the range of protons inside the patient during radiation treatment. A possible method of in-vivo imaging is detection of secondary 'prompt' gamma (PG) photons outside the body, which are produced by inelastic proton-nuclear interactions inside the patient. In this paper, important parameters influencing the relationship between the PG profile and percentage depth dose (PDD) in a uniform cylindrical phantom are explored. Monte Carlo simulations are performed with the new Geant4 based code TOPAS for mono-energetic proton pencil beams (range: 100-250 MeV) and an idealized PG detector. PG depth profiles are evaluated using the inflection point on a sigmoid fit in the fall-off region of the profile. A strong correlation between the inflection point and the proton range determined from the PDD is found for all conditions. Variations between 1.5 mm and 2.7 mm in the distance between the proton range and the inflection point are found when either the mass density, phantom diameter, or detector acceptance angle is changed. A change in cut-off energy of the detector could induce a range difference of maximum 4 mm. Applying time-of-flight discrimination during detection, changing the primary energy of the beam or changing the elemental composition of the tissue affects the accuracy of the range prediction by less than 1 mm. The results indicate that the PG signal is rather robust to many parameter variations, but millimetre accurate range monitoring requires all medium and detector properties to be carefully taken into account.

CeBr3 scintillators for 4He prompt gamma spectroscopy: Results from a Monte Carlo optimization study

“…The PS files were generated with 10 8 primary particles for each setup, then exported into a ROOT binary format and converted into a source input file for the FLUKA simulations. In the conversion, we followed the angular and longitudinal cuts similar to previous studies . In the current study, we applied: θ = 90 ± 1.5 and z = z 0 ± 0.5 cm.…”

Characterization of prompt gamma-ray emission with respect to the Bragg peak for proton beam range verification: A Monte Carlo study

“…The energy and intensity of the PG emission are sensitive to the elemental composition of tissues [9,10]. As pointed out in [20] there are many factors influencing the accuracy of beam range estimation using PG emission. Quantitative characterization of the correlation between these factors, particularly with respect to the BP, is of great importance to assess its limitation and aids in the design of a clinically reliable PG imaging system.…”

Characterization of angular detection dependence of prompt gamma-rays with respect to the Bragg peak in a water phantom using proton beam irradiations

“…There is no exact one-on-one relationship existing between PG emission and the dose deposition. As pointed out in [11] there are many factors influencing the accuracy of beam range estimation using PG emission. Quantitative characterization of the correlation between these factors, particularly with respect to the BP, is of great importance to assess its limitation and aids in the design of a clinically reliable PG imaging system.…”