ESTRO 2025 - Abstract Book

S240

Brachytherapy - Gynaecology

ESTRO 2025

BT schedule consists of two applications for the delivery of 2x2 fractions (one treatment plan per application). BT plans were optimized (EMBRACEII, NCT03617133) and MRL plans were simulated for all patients (MARGARITA, NCT05937958), both with OAR hard constraints being dose limiting. MRI-scans without applicator in place, acquired before the first BT-application, were used for the MRL treatment plans and a PTV-margin of 3mm around CTV-HR and GTV was added. For one MRL plan six identical fractions were assumed. EQD2-doses for targets and OARs and dose volumes were compared, statistical significance was determined using a Wilcoxon signed-rank test (p-value<0.05). The 5th percentile of all distances from every point on the target to the closest point of the OAR was used as the shortest distance between (PTV)CTV-HR and OAR. Results: Median CTV volumes for group 1 and 2 were 53cc and 20cc, respectively. In group 1, GTV D98% was significantly higher (p-value:0.0059) for BT. In group 2, BT doses were significantly higher for all target volumes. In both groups, MRL rectum 2cc doses were significantly closer to the constraint. For both groups combined, median V150% was 34cc and 0cc for BT and MRL, respectively.