Abstract
A constant relative biological effectiveness (RBE) of 1.1 is currently used in clinical proton therapy. However, the RBE varies with factors such as dose level, linear energy transfer (LET) and tissue type. Multiple RBE models have been developed to account for this biological variation. To enable recalculation of patients treated with double scattering (DS) proton therapy, including LET and variable RBE, we implemented and commissioned a Monte Carlo (MC) model of a DS treatment nozzle. The main components from the IBA nozzle were implemented in the FLUKA MC code. We calibrated and verified the following entities to experimental measurements: range of pristine Bragg peaks (PBPs) and spread-out Bragg peaks (SOBPs), energy spread, lateral profiles, compensator range degradation, and absolute dose. We recalculated two patients with different field setups, comparing FLUKA vs. treatment planning system (TPS) dose, also obtaining LET and variable RBE doses. We achieved good agreement between FLUKA and measurements. The range differences between FLUKA and measurements were for the PBPs within ±0.9 mm (83% ⩽ 0.5 mm), and for SOBPs ±1.6 mm (82% ⩽ 0.5 mm). The differences in modulation widths were below 5 mm (79% ⩽ 2 mm). The differences in the distal dose fall off (D80%–D20%) were below 0.5 mm for all PBPs and the lateral penumbras diverged from measurements by less than 1 mm. The mean dose difference (RBE = 1.1) in the target between the TPS and FLUKA were below 0.4% in a three-field plan and below 1.4% in a four-field plan. A dose increase of 9.9% and 7.2% occurred when using variable RBE for the two patients, respectively. We presented a method to recalculate DS proton plans in the FLUKA MC code. The implementation was used to obtain LET and variable RBE dose and can be used for investigating variable RBE for previously treated patients.
Highlights
The majority of long-term follow-up data from proton therapy are from patients treated with double scattering (DS) proton therapy
We evaluated the differences between the measurements and the simulations at the 90% to 10% dose level in 10% intervals, in addition to the 80%–20% lateral penumbras
We presented the first implementation of an IBA DS proton therapy nozzle in the FLUKA Monte Carlo (MC) code
Summary
The majority of long-term follow-up data from proton therapy are from patients treated with double scattering (DS) proton therapy. This delivery technique employs scattering and range shifting components to spread and confirm the beam. A particular increase in RBE towards the end of the proton beam range due to elevated LET has been suggested by in vivo experiments (Saager et al 2018). This increase could be problematic for patients with organs at risk (OARs) located near the distal end of treatment fields. Further investigations are required to understand how and if elevation in LET/RBE influence the toxicity in OARs
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call