ESTRO 2025 - Abstract Book

S4408

RTT - Treatment planning, OAR and target definitions

ESTRO 2025

senior Radiation Therapist (RTT) to create user-adjusted auto-contours (UA-ACs). Time for adjustment was recorded, and a Clinical Oncologist (CO) independently reviewed a UA-AC subset.

Results: CBCTs of 114 patients were screened for suitability for GTV contouring, having excluded patients with mis-coded staging or incomplete DICOM data. Thirty-eight cases (33.3%) were deemed unsuitable (Table 1), most frequently because the GTV boundary was not discernible secondary to effacement of similar-density normal tissues, or peri tumoural consolidation (Figure 1). UA-AC GTVs were generated on 553 scans (n=72 AVIP, n=4 3D planning CT, n=477 CBCT). Median AC adjustment time on CBCT was 83 seconds (range: 0–460 seconds), with no significant time differences between CBCTs according to the timepoint during treatment (p=0.79, ANOVA). Mean AC adjustment time on planning CT was significantly shorter than day 1 CBCT (59 vs. 92 seconds, p<0.001, Wilcoxon signed-ranks test). Agreement of the CO and RTT delineations (20% of scans were audited) was good, with “no revision” ratings in 81.1% of scans, “minor revisions” in 16.2% and “major revisions” in 2.7% for CBCTs. 37 planning CTs were reviewed and “minor revision” was noted in one case (2.7%)