ESTRO 2021 Abstract Book

S1058

ESTRO 2021

Conclusion Our data shows that outcome for radically treated cervical cancer depends on the stage and the total D90 dose delivered to the tumour. The use of image guided brachytherapy allows for escalation of the D90 dose. The new FIGO 2018 staging which takes nodal status into consideration may show better prognostic discrimination in future studies.

PO-1283 Does Radiotherapy planning factors impact para-aortic recurrence in IIIC1 cervical cancer patients?

Abstract withdrawn

PO-1284 MR-guided radiotherapy of gynecologic cancer – preliminary outcome data from a small cohort study A. Ør Knudsen 1 , G. Nyvang 1 , P. Krause Møller 1 , U. Bernchou 1 , A. Smedegaard Bertelsen 2 , T. Schytte 3

1 University Hospital Odense, Oncology Department, Odense, Denmark; 2 University Hospital Odense, Oncology department, Odense, Denmark; 3 University Hosptial Odense, Oncology Department, Odense, Denmark

Purpose or Objective Curative radiotherapy of gynecologic malignancies is challenging due to internal motion of radiation sensitive organs at risk (OAR) close to the target within minutes. Using the 1.5 Tesla magnetic resonance imaging linear accelerator (MRL) daily MRI enables the delineation of OAR and subsequent adaptation of the plan before each treatment fraction compensating for some of the motion. During dose delivery, target and OAR position can be monitored using cine MRI, and treatment may be interrupted if necessary. Thus with the MRL it is possible to deliver stereotactic boosts to the target while sparring critical OAR. The current study reports on our experience and the initial preliminary clinical outcome data of MRL-based treatment in a small cohort of patients with gynecologic malignancies. Materials and Methods Patients with gynecologic malignancies have been treated on the MRL at our institution since March 2019. At each treatment fraction, the radiotherapy plan was adapted to the position and shape of the OAR and tumor including deformable image registration, manual contour editing, and plan optimization. Inhomogeneous dose distribution with high maximum dose within the tumor was tolerated, while strict constraints to OAR was enforced. The toxicity was scored according to CTC_AE vs 5 at baseline, 2, 4, and 12 weeks after radiotherapy. Results So far, thirteen patients have been treated: Four with cervical cancer, six with uterine cancers, two with ovarian cancer (re-irradiation), and one with vaginal cancer. The patients with cervical cancer had treatment on MRL instead of brachytherapy (BT) as an emergency solution, due to difficult anatomy or because the patient could not cooperate to BT. Based on OAR tolerance doses and desired dose to the target, prescribed doses of 20 Gy/10f, 30 Gy/5-6f, 35 Gy/5-7f or 50 Gy/5f were used. For patients who also had conventional external radiotherapy (EBRT), and received MLR boost treatment instead of BT the OAR constraints for BT were applied. No grade 3 or 4 toxicities were observed at the end-of treatment or follow-up at 2-4 weeks compared to baseline. Fatigue and anorexia were the most common grade 2 toxicities at any time. Five patients had complete response, three partial response, one had progressive disease, two just finished treatment and two was lost to follow-up at three months. Follow-up beyond three months is not consistent. Five patients are dead. Conclusion Treatment on MRL for gynecologic cancer seems to be feasible. For patients where treatment on MRL is combined with conventional EBRT, constraints from BT for OAR can be applied. In this small cohort, local control rate was high and toxicity did not exceed grade 2 and was manageable, but more data on less inhomogeneous cohorts is needed before any conclusions can be drawn.