ESTRO 2025 - Abstract Book

S3555

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

ESTRO 2025

Results:

Figure 1 shows the instantaneous dose-rate as function of time in the central spot as well as 2D maps of DR eq,const for three proton PBS fields used in the mice experiments. Although all fields had identical doses of 40Gy and mean dose rates of 60Gy/s, their time structure and DR eq,const were very different. For the transmission PBS proton beam without repainting [1], the dose delivery was concentrated in a short time interval, giving a DR eq,const that was 2.6 times higher than DR mean (Figures 1A,D) When the dose delivery was distributed more evenly over the field duration by repainting [1] DR eq,const approached DR mean (Figures 1B,E). For the SOBP field without repainting [3], much wider spots resulted in an intermediate DR eq,const being 1.6 times higher than DR mean (Figures 1C,F). For pulsed electron beams, DR eq,const was generally lower than DR mean and approached DR mean for large number of pulses. The acute skin toxicity observed in mice after 40Gy irradiation with different beam structures followed very similar trends as function of DR eq,const (Figure 2 bottom) in clear contrast to DR mean (figure 2 top), demonstrating the radiobiological relevance of DR eq,const .