ESTRO 2022 - Abstract Book

S398

Abstract book

ESTRO 2022

Figure 1 illustrates the dependence of NTCP and delivery time on number of ELs K and beams B . We found that 360 ELs distributed over 30 beams generated proton arc plans with minimal NTCP. Relative to corresponding IMPT plans, an average reduction of 21±3% in integral dose was observed. The average NTCP for grade ≥ 2 and grade ≥ 3 xerostomia at six months after treatment decreased with 4.7 ± 1.8% and 2.3 ± 0.8%, respectively, while the average NTCP for grade ≥ 2 and grade ≥ 3 dysphagia decreased with 4.3 ± 2.9% and 0.8 ± 0.4%, respectively. Figure 2 shows the expected reduction in NTCP per patient, when proton arc therapy is employed.

Figure [1]: The dependence of average reduction in plan toxicity with respect to clinical IMPT plans ( ∆ NTCP), (graph A,B) and average estimated "step and shoot" delivery time (graph C,D) on the number of beams B , in proton arc plans with 360 energy layers (graph A,C) and on the number of energy layers K , in proton arc plans with 30 beams (graph B,D) for 3 oro-pharynx patients. The dashed lines in gaph B represent the average ∆ NTCP when all available enegy layers were used. The red line in graphs C and D show the average delivery time for clinical 6 field IMPT.

Figure [2]: NTCP values at six months after treatment for grade ≥ 2 toxicity (top) and grade ≥ 3 toxicity (bottom) for clinical IMPT and proton arc plans employing 30 beams and 360 energy layers of 10 oropharyngeal patients. Conclusion Proton arc therapy demonstrates potential to further reduce toxicity relative to clinical IMPT, especially when 360 ELs and 30 beams are employed for oropharyngeal patients.

OC-0454 A simple ion-type-independent in-vitro RBE description to improve proton RBE modelling

L. Tian 1 , A. Lühr 1

1 Technical University Dortmund, Physics, Dortmund, Germany