ESTRO 2022 - Abstract Book

S1528

Abstract book

ESTRO 2022

PAT plan (Figure 1b and c), to see if the LET could be elevated in the target while still maintaining the same tumour coverage. The plans were optimized using a FLUKA Monte Carlo based optimization tool with respect to two different variable RBE models, the McNamara model (MCN), and an LET-weighted dose model (LWD), and additionally an RBE of 1.1. As the tumour was surrounding the brainstem, sparing this critical OAR had high priority during optimization. The PAT plans were compared to a reference IMPT plan in terms of their respective RBE weighted doses, physical dose and dose averaged

LET (LETd).

Results Tumour coverage was achieved for all plans in terms of (respective) RBE-weighted dose (Figure 1a). PAT resulted in lower mean physical doses in the brainstem by up to 0.9 Gy and 1.2 Gy for the full PAT plans and the pruned PAT plans compared to IMPT (Figure 2d), respectively, while there was an increase in LETd in the brainstem for the PAT plans compared to the IMPT (Figure 2f). This could be expected as the brainstem is located in the middle of the target. However, the RBE-weighted dose was lower for the PAT plans in general, compared to the IMPT plan. We also found the MCN plans providing an overall lower LETd to the brainstem compared to the LWD and the RBE 1.1 plans (Figure 2f).

Conclusion In this study we demonstrated methods for optimizing PAT plans with respect to variable RBE models, and the potential of using PAT plans in treatment planning, both with full arcs and pruned arcs. Although there was an increase of LET in the brainstem for the PAT plans, the physical doses and the RBE weighted doses were lower in the brainstem compared to the IMPT plan.

PO-1727 Robust optimization for IMPT in head and neck cancer with coupled vs. uncoupled scenarios

U.V. Elstroem 1 , O. Noerrevang 1 , K. Jensen 1

1 Aarhus University Hospital, Danish Center for Particle Therapy, Aarhus N, Denmark

Purpose or Objective For intensity modulated proton therapy (IMPT) planning, robust optimization (RO) and evaluation is used to compensate for worst case uncertainties in dose deposition due to translational changes in setup and stopping power (range). The two