ESTRO 2025 - Abstract Book

S2989

Physics - Image acquisition and processing

ESTRO 2025

Material/Methods:

Ten 5-fraction prostate patients (recruited to a single-centre trial 1 ) were identified with suitable diagnostic MRI acquired a median 159 days (range 105-237) prior to treatment including a small field-of-view T2w and large field-of view T1w for target, OAR, bones and body autosegmentation (MVision AI, Contour+ prototype, Finland). MRL reference plans, REF diag , were generated on the diagnostic MR, as in Figure 1 1,2 . If the T1w showed cropped body extent, the image was extended as in Figure 2.

REF diag was used to simulate the first fraction (#1) online plan adaption, creating ATS diag as shown in Figure 1. The autosegmented bones and body contours deformed to the #1 MR, while the targets and OAR used clinically on #1 were used for ATS diag , mimicking clinician recontouring online. ATS diag was then compared against the clinically treated adapted plan, ATS clin , in terms of number of passing clinical goals. To test the dose calculation accuracy, ATS diag , was recalculated using patient specific electron densities (ED) and clinically-used bones and body contours, ATS ED , assessing PTV ΔD50%, and 3D gamma analysis at 2mm/2%.