ESTRO 2021 Abstract Book

S645

ESTRO 2021

Conclusion Five-fraction SBRT treatment seems to induce notable prostate swelling during the treatment, which should be considered when applying CTV-to-PTV margins. Extra care should be taken when the prostate delineation is based solely on MRI (e.g. MR-only protocol), where 1-2 mm extra margin could be needed to cover the possible swelling. Poor image quality due to patient motion may partly explain the observation of decreasing prostate volume relative to the baseline with some of the patients. The results of the current study agree with and confirm previous findings from the HYPO-RT-PC trial with 7 x 6.1 Gy fractionation scheme [1]. [1] Gunnlaugsson A et al, Change in prostate volume during extreme hypo-fractionation analysed with MRI. Radiat Oncol 2014;9:22 PD-0812 Brachytherapy of locally advanced cervical cancer using the hybrid applicator VeneziaTM - results S. Saicic 1 , F. Walter 2 , M. Rottler 2 , J. Well 2 , L. Nierer 2 , K.-.M. Niyazi 2 , C. Belka 2 , S. Corradini 2 1 University Hospital of Ludwig-Maximilians-Universität (LMU) Munich, Department of Radiation Therapy and Radiation Oncology, Munich, Germany; 2 University Hospital of Ludwig-Maximilians-Universität (LMU) Munich, Department of Radiation Therapy and Radiation Oncology, Munich, Germany Purpose or Objective Following external beam radiation therapy (EBRT) with platinum-based chemotherapy, MR-guided brachytherapy (BT) has been shown to significantly improve overall survival and local control of cervical cancer. Recent innovations in applicator technology, such as the hybrid Venezia TM applicator, have expanded the availability of combined intracavitary and interstitial BT. This allows targeting tumor extensions that are not sufficiently covered by intracavitary BT alone. We report preliminary clinical results of advanced adaptive BT in the treatment of patients with locally advanced cervical cancer. Materials and Methods Between 03/2017 and 06/2020, a total of 53 patients with cervical cancer were treated using the hybrid Venezia TM applicator following a definitive chemoradiation protocol. Cumulative dose coverage after combined EBRT and MR-guided brachytherapy was analysed regarding the D98 GTV, D90 HR-CTV, D98 HR-CTV and D98 IR- CTV (EQD2; α/β = 10). Additionally, organ at risk (OAR) doses at D2cc for bladder, rectum, sigmoid, and small intestine were evaluated (EQD2; α/β = 3). The median follow-up time was 20 months. Results The median age at diagnosis was 50 years (range: 30- 85years). Overall, 45 patients (85%) were treated with a combination of IS/IC brachytherapy using interstitial needles, while in cases of a HR-CTV volume of > 30cc a total of 89.6% of patients received combined IS/IC treatment. The cumulative mean dose to the GTV D98 was 110.5Gy (range: 78.1 – 253.1Gy), HR-CTV D90: 91.4Gy (range: 72.2 – 100.8Gy), and HR-CTV D98: 81.5Gy (range: 62.9 – 90.1 Gy). In cases of a HR-CTV volume <30cc, the constraint D90 >90Gy was accomplished in 95.8% of patients. In cases of larger HR-CTV volumes >30cc the D90 > 85Gy was reached in a total of 96.4% of cases. Regarding the IR-CTV D98 a mean dose of 65.9Gy (range 57.2 – 85.1Gy) was reached. Mean D2cc doses for OARs were 74.9Gy (range: 56.6 – 89.7Gy) for the bladder, 59.5 Gy (range: 49.6–72.4 Gy) for rectum, 60.8 Gy (range:47.2 – 75 Gy) for sigmoid, and 55.6Gy (range: 44.1–72.1Gy) for the small intestine. The constraint bladder D2cc < 80 Gy was attained in 71.7% of patients, whereas rectum D2cc < 65 Gy was reached in 79.2%. The overall survival for the cohort was 95.2%, with a metastasis free survival of 87.7% and a recurrence free survival of 95.9% at 20 months. Conclusion Our preliminary clinical data confirm the importance of advanced MR-guided brachytherapy in the treatment of patients with locally advanced cervical cancer, with excellent early results. Advances in image-guidance and hybrid applicator technologies such as the Venezia TM enable risk-adaptive combined treatment protocols. Poster discussions: Poster discussion 15: Gynaecological (endometrium, cervix, vagina, vulva)