ESTRO 2024 - Abstract Book

S4678

Physics - Optimisation, algorithms and applications for ion beam treatment planning

ESTR0 2024

Keywords: secondary particles, hadrontherapy, simulation

2275

Mini-Oral

Novel radiation quality metrics significantly increases performance of in vitro RBE proton models

Fredrik Kalholm 1,2 , Erik Traneus 3 , Niels Bassler 4,5

1 Stockholm University, Physics, Stockholm, Sweden. 2 Karolinska Institute, Oncology and Pathology, Stockholm, Sweden. 3 Raysearch Laboratories, -, Stockholm, Sweden. 4 Aarhus University, Clinical Medicine, Aarhus, Denmark. 5 Aarhus University Hospital, Danish Centre for Particle Therapy, Aarhus, Denmark

Purpose/Objective:

In proton therapy, radiation quality metrics (RQM) play a crucial role in variable Relative Biological Effectiveness (RBE) models. These models typically employ linear averaging of base metrics, such as Linear Energy Transfer (LET) or Q eff , weighted by either dose (LET d , Q eff,d ) or track contribution (LET t , Q eff,t ). Although there have been efforts to benchmark these RQM metrics, there's a possible gap in understanding the optimal construction of RQM itself. Current RQM models assume linear weighting, even though non-linear RBE effects might exist [1, 2]. This study explores the creation of new RQM metrics by applying non-linear weighting directly to underlying LET- or Q eff -spectra. This approach thereby assumes that non-linear RBE effects stem from a non-linear relationship between RBE and LET of individual particles, rather than applying non-linearities to already linearly weighted quantities such as LET d or LET t . Additionally, we develop and benchmark linear RBE models using these new RQM metrics.

Material/Methods:

In vitro cell survival data was sourced from three publications authored by a group from MD Anderson and GSI [3-5], where an in-house jig of PMMA was built with twelve different thicknesses, each corresponding to a different reported dose averaged LET value including only the primary protons (LET d,primary ). The experimental setup was simulated in SHIELD-HIT12A, and the PMMA depth corresponding to each reported LET d,primary value was found. At all these depths, the full LET spectra was scored, and new non-linear RQM metrics was calculated as:

Where n denotes the power level of LET, i denotes each individual particle in a given voxel, d denotes dose and Φ denotes fluence. Similar scoring is also performed for Q eff as a based metric instead of LET. LQ-based RBE models are subsequently created where