A Monte Carlo study of the relationship between the time structures of prompt gammas and the in-vivo radiation dose in proton therapy

Abstract

For the in vivo range verification in proton therapy, it has been tried to measure the spatial distribution of the prompt gammas generated by the proton-induced interactions with the close relationship with the proton dose distribution. However, the high energy of the prompt gammas and background gammas are still problematic in measuring the distribution. In this study, we suggested a new method determining the in vivo range by utilizing the time structure of the prompt gammas formed with the rotation of a range modulation wheel (RMW) in the passive scattering proton therapy. To validate the Monte Carlo code simulating the proton beam nozzle, axial percent depth doses (PDDs) were compared with the measured PDDs with the varying beam range of 4.73-24.01 cm. And the relationship between the proton dose rate and the time structure of the prompt gammas was assessed and compared in the water phantom. The results of the PDD showed accurate agreement within the relative errors of 1.1% in the distal range and 2.9% in the modulation width. Average dose difference in the modulation was assessed as less than 1.3% by comparing with the measurement. The time structure of prompt gammas was well-matched 2 within 0.39 ms with the proton dose rate, and this could enable the accurate prediction of the in vivo range.

Independent dose verification system with Monte Carlo simulations using TOPAS for passive scattering proton therapy at the National Cancer Center in Korea

“…To recalculate patient dose with the MC method, accurate modeling and commissioning of the therapeutic beam nozzle must be performed. The passive scattering mode of the proton beam nozzle (Proteus235, IBA) installed at the KNCC was modeled and validated based on the detailed manufacturers blueprint and a Geant4 code developed in a previous study (Shin et al 2015). TOPAS (2.0.p03 version) was employed with various dose calculation functions provided for MC simulations of proton therapy.…”

Precision modeling of the IBA Universal Nozzle double scattering mode at the University Proton Therapy Dresden for Monte Carlo simulation

“…The field width and plateau are matched within ±3% [26]. Another example is the modelling of the IBA system at the National Cancer Center in Korea (KNCC) for which results have been reported [15,27]. The setup seems very similar to the MGH setup.…”