ESTRO 2023 - Abstract Book

S1729

Digital Posters

ESTRO 2023

Results Figure 1 shows the hLDf frequency distribution of tumor voxels as a function of LET threshold for two plans (small and large) where a difference in distribution between the two cases can be observed. Averaging the second moment of these distributions over all plans indicated an optimal threshold of 30 keV/ µ m.

The most significant difference of tumor’s hLDf volume histogram was observed at a relative volume of 38% (V38%), corresponding to a mean hLDf of 0.52±0.07 and 0.31±0.01 in the small and large cohort, respectively (Figure 2).

It was thus assumed that for plans with a large target, a coverage of 38% of the tumor volume with a hLDf ≥ 0.45 (which is the lower bound of hLDf in the small cohort) could be an indication for an enhanced hLDf-distribution (and closer to the distribution of small tumors, for which a better clinical outcome has been reported). Conclusion In this study the hLDf distribution in small and large tumors differed significantly. V38% was found as the most significant predictor among the investigated quantities at an LET threshold of 30 keV/ µ m, which may be used as an optimization objective in future high-LET-dose based optimization processes.