Our results show an increase in LETd across all structures when using daily adaptation compared to no adaptation, both in targets and organs at risk (OARs). For OARs, this increase had minimal impact on the relative differences between daily adaptation and no adaptation, independent of the dose weighting method. For the target dose, however, we observed considerable differences based on which dose weighting method is used. When moving from RBE-weighted to LET-weighted dose, the dosimetric benefits of daily adaptation decreased, especially regarding the target coverage.
Figure 1a shows LETd-volume histograms of all evaluated fractions in one example patient, indicating increased LETd for daily adaptation. Bands represent the minima/maxima across all fractions, while the solid line represents the mean. Figure 1b shows dose-volume histograms (DVHs) of all fraction doses in the same patient, comparing daily adaptation with no adaptation for both dose weighting methods. The narrow bands of the RBE-weighted dose indicate clear benefits in target coverage for daily adaptation compared to no adaptation. However, the evaluation of the LET-weighted dose does not reflect the narrow bands of the target DVHs for daily adaptation.
Figure 2 depicts DVHs of the accumulated dose distributions for two example patients, comparing daily adaptation and no adaptation for both dose weighting methods. For patient A, the dosimetric benefits of daily adaptation in the high-risk CTV diminish when moving from RBE-weighted to LET-weighted dose. For patient B, benefits in target coverage are still evident, but the prescription of 70 Gy in the high-risk CTV is missed.
