ESTRO 2025 - Abstract Book

S211

Brachytherapy - Gynaecology

ESTRO 2025

Conclusion: This is the first French cohort to report results on LACC with DP involvement. We show that the use of a uterovaginal device with adequate parametrial implantation allows good coverage of target volumes and a clinical response consistent with previously published results.

Keywords: Parametrial involvement, Interstitial needles

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Digital Poster Dosimetric impact of translational and rotational applicator displacement on intracavitary/interstitial brachytherapy for cervical cancer Natalie Kar Wei Yip 1 , Tsz Ching Fok 1 , Cheuk Lam Chung 1 , Tin Lok Chiu 1 , Siu Ki Yu 1 , Amy Tien Yee Chang 2 1 Medical Physics, Hong Kong Sanatorium & Hospital, Hong Kong, Hong Kong. 2 Comphrehensive Oncology Centre, Hong Kong Sanatorium & Hospital, Hong Kong, Hong Kong Purpose/Objective: In clinical practice of cervix intracavitary brachytherapy, workflow duration of two to four hours often occurs between the acquisition of planning images and treatment delivery. Location of CT/MR imaging is not in proximity to brachytherapy site; patient transport between the two sites may introduce applicator displacement within patient. As no current guideline exists for the need of further verification images after planning CT/MRI, and treatment plans are created before brachytherapy treatment, potential applicator displacements may be undermined. This study aims to investigate the potential difference in planned versus actual administered therapy and dosimetric impact of intracavitary/interstitial applicator displacements. Material/Methods: Eleven cervical cancer patients who have completed EBRT and brachytherapy with Geneva applicator were retrospectively recruited, amounting to 33 treatment plans, of which 17 plans with needles and 16 plans without needles. Virtual displacements of the entire applicator set (including needles if present) were simulated on Oncentra TPS by offsetting the applicator reconstruction. Inferior translational displacements (caudal direction) of 1, 2, 3, 5, 8, 10 mm and rotational displacements in axial plane of ±1, 2, 3, 5, 8, 10º were investigated. Dose normalisation, source dwell positions and times were kept consistent with the originally planned. DVH metrics of target and OARs were calculated for each displacement, then compared with original plans. Results: Translational displacement of 5 mm results in >5% dose reductions in IR-CTV D90 for needles subgroup. In the without-needles subgroup, 1-10 mm displacements result in <5% dose reductions in GTV, HR-CTV D90 and Point A. Most significant dose increases are seen in rectum D2cc for both subgroups, a 2 mm displacement results in >5% dose increases; +67.63% and +29.86% at 10 mm for without-needles and needles subgroups respectively. All rotational displacements result in <5% dose changes for target and OARs. Specifically, for GTV, HR-CTV, IR-CTV D90, dose changes are well within ±1% for both subgroups. Despite the changes, dose constraints of targets and OARs are still within the defined limits and no violation has been noticed.