ESTRO 2024 - Abstract Book

S1096

Clinical - Gynaecology

ESTRO 2024

treatment, reasons for adaptive radiotherapy were analyzed. Outcome parameters including local control , acute and late toxicities were evaluated by CTCAE4.0.

Results:

Patients were treated from 2019 to 2021 in Hong Kong Sanatorium & Hospital with indications as the following: 15 patients were MR Linac patients with cervix cancer (47%), endometrial cancer (27%), recurrent uterine cancer (6%), oligorecurrent ovarian cancers (14%) and vaginal cancer (6%). Majority of the tomotherapy cohort were cervix cancer patients (73%), and endometrial cancer patients in the remaining 27%. All patients received pelvic radiotherapy 45Gy to 50.4 Gy in 25 to 28 fractions over 5-5.5 weeks. Simultaneous integrated boost to 55Gy to 57.5Gy to pathological lymph nodes were common in 14 (47%) patients, and three patients in the tomotherapy cohort were treated with extended para-aortic fields due to advanced disease (T2b-T3bN1). In the cervix cancer cohort, ATS were required in 1-7 times (average 3 times) out of 25 fractions. The average room occupancy time is 50.6 minutes (40-58.1), and the timing of ATS occurred at various stages from first to fifth week of the course of radiotherapy. The reasons for ATS were listed in Table 1.

Table 1: reasons for ATS in the cervix cancer cohort

Modify tumor (shrinkage or shifting) Target volume (Clinical target volume – high risk or internal target volume) Organs at risk change (rectum, sigmoid, bladder) Body contour Dose escalation of pathological lymph node in one patient

In the endometrial cancer cohort, ATS was utilised less frequently, for 0-2 times. Room occupancy times was 45 minutes on average (38-50 minutes), and the timing of ATS is either on the first or last week of treatment. The reasons for ATS were modify body contour, modify organs at risk, or reduce the dose to the bowel. All patients in MR Linac and tomotherapy cohorts were followed up for a median of 16 months (2-44). There was no severe (grade 3 or above) acute toxicity in the MR Linac cohort. Grade 2 diarrhea and/or abdominal colic occurred in 2 out of 15 (13%) patients. There was no late toxicity noted. In the tomotherapy cohort, 5 out of 15 (33%) patients developed grade 2 diarrhea, and 2 patients (13%) had grade 3 diarrhea and/or abdominal colic. For the late toxicity, 3 patients in the tomotherapy cohort (20%) developed grade 2 proctitis or diarrhea. 3 patients in the MR Linac cohort and one patient in the tomotherapy cohort developed relapse. Except for one patient with an aggressive variant cervix adenocarcinoma of gastric type with residual tumor after MR Linac and brachytherapy and received salvage hysterectomy, all other patients had excellent locoregional control (97%). The relapse sites were otherwise all distant, including peritoneal, bone, lung and liver, and succumbed within 6-8 months.

Conclusion:

The results demonstrated a unique comparison of patients receiving MR Linac and tomotherapy with comparable clinical outcome and toxicity profile Patients should be carefully selected for the appropriate modality choice based on the disease extent or any potential contraindication. Implementation of MR guided imaging in the regular workflow of radiotherapy treatment should be encouraged, as there is clear advantage to allow adapt to shape to modify target/organ at risk, resulting in margin reduction and improve dosimetry. In some centers, if resources are not feasible for online adaptive MRI, a potential hybrid MRI (as baseline) and cone beam CT (during treatment) with pre-brachytherapy MRI should be advocated.