Purpose: Brachytherapy is a vital component of definitive treatment for cervical cancer. It is common for multiple high dose rate fractions to be delivered with a single insertion and many hours between fractions. This study aims to retrospectively review the impact of any organ at risk (OAR) contour change on the dose received by those OARs due to the significant time between fractions
Method: Datasets for 14 overnight stay cervix brachytherapy patients treated between February 2017 – November 2018 were consecutively selected. The rectum, sigmoid and bladder doses and volumes from the Day 1 planning CT were recorded, then the same OARs were re-contoured on the day 2 verification CT scans. The Day 2 OAR doses and volumes were recorded and compared to departmental constraints. A correlation between OAR volume and dose was also assessed.
Results: Contour volumes varied between the Day 1 and Day 2 CT scans for all OARs. All sigmoid and all but one rectum remained under tolerance despite this change in volume. Five patients received bladder dose over tolerance however the majority of these were originally approved on Day 1 with high bladder dose for clinical reasons to achieve target volume coverage. No significant relationship was established between OAR volume change and OAR dose change.
Conclusion: OAR volume change and the impact on OAR dose in multiple fractions delivered in a single insertion is unpredictable and can vary greatly. Anatomy changes can increase the dose received by OARs in individual cases. Pre-treatment imaging is recommended for subsequent fractions, with assessment of OAR change prompting adaptive planning in select cases. Further research and larger cohorts are required to investigate other predictors of contour change and the impact on OAR doses.
Miss Gemma Busuttil –Gemma Busuttil is a Radiation Therapist with over 13 years experience as part of the Crown Princess Mary Cancer Centre team. She specialises in gynaecological radiotherapy and brachytherapy. Recently, she introduced bone marrow sparing VMAT and Acuros for EBRT gynaecological patients. She is a senior member of the Westmead Brachytherapy Team having been instrumental in the development of interstitial MRI guided cervical & vaginal brachytherapy and paediatric brachytherapy techniques at Westmead. She is actively involved in research, having previously presented at local and international conferences and is also a co-convenor of this ABG meeting.