ESTRO 2025 - Abstract Book

S4342

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

(DSC). Treatment plans for both methods (MidV and ITV) were created and lung dosimetric parameters compared for all 30 patients.

Results: Majority of patients (16/20) had ideal IOV for GTV and PTV, with MDA <2mm and DSC >0.8. Minority of patients (4/20) had IOV within tolerance thresholds (<3mm MDA and DSC>0.7). 6/20 patients had MidV phase differences, with 4/6 attributable to IOV of GTV in 4D contouring (Table 1).

These discrepancies are within accepted thresholds of 0.7-0.8 concordance as shown in a survey of international lung SABR expert contouring 3 . All PTV margins generated were the same except for a +/-1mm difference in the Superior and Inferior directions. The treatment plans demonstrated clinically significant reduction in MidV PTV compared to the ITV PTV plans (p=0.001), with a corresponding significant reduction in mean lung dose (p=0.001) and Lung V20Gy (p=0.001) (Table 2).