Dosimetric impact of interfractional organs at risk variation during high-dose rate interstitial brachytherapy for gynecologic malignancies

Abstract We sought to develop a framework for the identification and management of patients at risk for organs at risk (OARs) overdosing due to interfractional anatomic variation during high-dose rate interstitial brachytherapy for gynecologic malignancies. We analyzed 40 high-dose rate interstitial brachytherapy fractions from 10 patients. Planned OAR doses were compared to delivered doses, which were calculated from computed tomography scans obtained prior to each treatment fraction. Doses were converted to equivalent doses in 2 Gy fractions (EQD2) and doses to the most exposed 2 cm 3 (D 2cc ) were reviewed. Patients were risk-stratified by identifying dose thresholds corresponding to a 10% or lower risk of receiving an OAR dose exceeding the corresponding planning constraint. For each OAR, 30% to 62.5% of patients received total doses greater than planned, although the magnitude of these differences was