ESTRO 2024 - Abstract Book

S4631

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

ESTR0 2024

implemented in the TPS were also simulated. In particular for each of them a range uncertainty of ±3.5% and four values of setup uncertainty (from 0.5 mm to 2.0 mm) were used. From pRE the dose index value equivalent to the 95° percentile (both for OAR dose limit (D 1 or D 1cc ) and for target coverage (D 95 and D 98 )), of all the scenarios simulated, were extracted and compared to the same dose index in wRE result to find out which systematic setup error correlates the most and which wRE can surrogate the pRE results.

Results:

Considering the number of fractions of every plan and the number of scenarios for each pRE, 118720 dose distributions were calculated and analysed in this study. In Figure 1 an example of DVH bands comparison between wRE and pRE for a head and neck case is shown. The average (±SD) calculation time for base of skull chordoma pRE was 10.9 h (±3.3) while H&N plans needed 36.7 h (±10.3) to complete a pRE calculation (vice versa, each wRE took less than 5 min for every patient). The results showed that both in terms of target coverage and in terms of OARs sparing, the combination of setup and range uncertainty parameters in wRE that surrogated the best the pRE results were 0.5 mm / ±3.5% (p=0.905). The OAR’s dose indexes difference (D 1 /D 1cc ) between pRE and wRE0.5mm/3.5% were 0.02 (±0.65) GyRBE. They were 2.92 (±1.32) GyRBE, 1.91 (±0.96) GyRBE and 0.92 (±0.68) GyRBE (p<0.01) when pRE was compared with wRE 2.0mm/3.5% , wRE 1.5mm/3.5% and wRE 1.0mm/3.5% , respectively. In Figure 2 the linear fit and the dose differences between pRE and all the combinations of wRE parameters for OAR are shown. The analysis was repeated for the target coverage resulting in a mean target D95 difference between pRE and wRE 0.5mm/3.5% of -0.09 (±0.16) GyRBE (p=0.839). it was -1.09 (± 0.93) GyRBE, -0.71 (±0.67) GyRBE and -0.37 (±0.52) GyRBE for wRE 2.0mm/3.5% , wRE 1.5mm/3.5% and wRE 1.0mm/3.5% , respectively.