ESTRO 2024 - Abstract Book

S1103

Clinical - Gynaecology

ESTRO 2024

2829

Proffered Paper

Outcomes of pelvic reirradiation with stereotactic radiotherapy for gynaecological cancer recurrence

Benjamin J Thomas 1 , Kallol Bhadra 1 , Ian Zing Tan 1 , Lei Wang 1 , Alexandra Taylor 1,2 , Susan Lalondrelle 1,2

1 The Royal Marsden NHS Foundation Trust, Department of Radiotherapy, London, United Kingdom. 2 Institute of Cancer Research, Division of Radiotherapy and Imaging, London, United Kingdom

Purpose/Objective:

Pelvic recurrence of gynaecological cancer is associated with significant morbidity and can be challenging to treat, particularly when arising in a previously irradiated site. For cases of oligo-relapse a targeted approach is favourable, avoiding the need for systemic therapy. For instances where surgery is not feasible due to anatomical proximity of critical structures or would result in morbidity, reirradiation using highly conformal techniques such as stereotactic radiotherapy (SBRT) to radical doses is increasingly used. There is however limited published data regarding long-term efficacy and safety of pelvic reirradiation using SBRT in gynaecological malignancies 1–3 , and a lack of guidance on case selection, technique, dose and fractionation 4 . We present an analysis of our institutional experience of using SBRT for gynaecological cancer reirradiation to identify efficacy, toxicity and other factors for appropriate case selection. Patients treated with pelvic SBRT reirradiation at our institution for histologically proven gynaecological malignancies between July 2012 and January 2021 were identified from local records. Eligibility for SBRT pelvic reirradiation included lymph node or soft tissue recurrence in the pelvis or para-aortic region or positive margin after surgical resection, GTV <6cm max diameter, 1-3 sites of metastatic relapse, life expectancy >6 months, no significant toxicity from previous radiation, ideally >6 months since initial radiation treatment, WHO Performance Status ≤2. Dose constraints for previously irradiated normal tissue were crudely estimated from degree of overlap with the primary RT fields and subtracted from published SBRT constraints 5 , incorporating time repair calculation where appropriate. Treatment was delivered on C-arm linac, Cyberknife and MR-linac platforms. Data for analysis was collected from hospital electronic records and radiotherapy treatment planning systems. We recorded demographic, planning and follow up data to evaluate for the endpoints of local, regional and distant failure, PFS and OS, as well as acute and chronic toxicity data (CTCAE grading), dosimetric data, treatment site and subsequent lines of treatment. Patients were censored at their last recorded follow-up or up to September 2023. Outcome data was correlated with primary tumour site, GTV/CTV volume and time from primary radiotherapy to reirradiation. Statistical analysis was performed using written code from Python 3.10 in PyCharm CE and Lifeline package for formulating K-M curves. Material/Methods:

Results:

73 patients were identified who had undergone SBRT pelvic reirradiation: 8 patients received 2 courses of SBRT (4 receiving contemporaneous SBRT to 2 treatment sites, 4 receiving sequential SBRT due to disease progression following first SBRT course). Treatment data is included in Table 1 .