ESTRO 2023 - Abstract Book

S1874

Digital Posters

ESTRO 2023

morbidity. The method was explored on grade 2 rectal morbidity data from a sub-cohort (n=111) of a large passively scattered PT prostate cancer cohort (n=1214), treated to 78 Gy(RBE 1.1) and morbitities recorded prospectively up to 8 years (incidence ~15% for both full and sub-cohort). MC simulations in FLUKA with a validated implementation of the gantry were conducted with 200 million primaries per treatment field, scoring LETd and dose (figure 1). Results Figure 2 shows the resulting distributions using four different pairs of dose and LETd thresholds. The distributions visualize the extent of variation in different areas of the dose and LETd volume space, and thus where potential differences between patients with vs. without morbidity can be observed. E.g. for the D10% and LETd10% thresholds, the D10% of the rectum for our cohort varied from 30 Gy to above 80 Gy, with the majority above 60 Gy. The LETd10% for the high dose region of the rectum ranged from 1.5 keV/um to above 3.5 keV/um. However, there were no observed differences between with patients with vs. patient without grade 2 rectal morbidity.