MULTICENTRIC POOLED ANALYSIS OF STEREOTACTIC RADIOTHERAPY IN OVARIAN CANCER: (MITO-RT1 PROJECT).

Aims Stereotactic body radiotherapy (SBRT) represents an interesting opportunity in the treatment of ovarian cancer (OC) isolated recurrences or residual lesions after systemic treatment, as well as a valid tool to lengthen the free time of re-challenge with platinum. However, studies on this topic are sporadic and with few cases. The aim of this multicentric retrospective pooled analysis was to collect the largest unselected real-life dataset of OC patients treated with SBRT in the attempt to define the safety and efficacy. Secondary objectives were to identify the best dose/fractionation regimen in terms of local control as well as to describe acute and late toxicities. Methods Eight Italian cancer Centers were firstly started the project giving their adhesion to this retrospective pooled analysis. A specific data-set for standardized data collection for ovarian cancer SBRT treatment was developed. Participants were required to fill a data sets including: age, histotype, site of irradiation, previous treatments, best response, toxicity as well as technical/dosimetric data about SBRT treatment. Patients' data were obtained from the historical database of radiation oncologists who joined the study. Results Data on 73 OC patients (median age: 63.5, range 40-83) carrying a total of 120 lesions were considered suitable for analysis. Between 2005 and 2018 all patients underwent SBRT in single or multiple fractions with a median biological equivalent dose (BEDα/β 10) of 76.8 Gy (range 7.5-262.5). Patient and treatment characteristics as well as acute toxicity are detailed in Table 1. Safety. 52 patients (71.3%) did not experience acute toxicity, the others 21 (28.7%) experienced low grade acute toxicity with no patient showing > grade 2 toxicity. With a median follow-up of 18 months (range: 1 - 120), 68 patients (93.1%) did not experienced late toxicity, the others 5 (6.9%) experienced low grade late toxicity with no patient showing > grade 2 toxicity. Efficacy. On a per-lesion basis, the 12-and 24-months actuarial local control inside SBRT field were 88.3% and 86.2%, respectively. BED10 > 50Gy was correlated with a better 12-months local control (91.7% versus 72.9%, p=0.034). Conclusions Preliminary results on a population-level confirm that SBRT delivered in 1-10 consecutive fractions is safe and well tolerated notwithstanding several previous surgical and systemic treatments. Therefore, this treatment can be considered as a further resource in order to lengthen the free time of re-challenge with platinum. [ABSTRACT FROM AUTHOR]