ESTRO 37 Abstract book

ESTRO 37

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palliative or as an ablative option in the oligometastatic setting. RT Efficacy in evaluable lesions was assessed through RECIST v.1.1 criteria; Progression Free Survival (PFS) and best Objective Response Rate (ORR) to Nivolumab was reported. Toxicity was assessed following the CTCAE v4.03 terminology. 2-Gy biologically equivalent dose (BED) was used to compare different RT schedules, assuming an α/β = 3 for late responding normal tissues. Results From August 2015 until September 2017 21 patients treated for a total of 27 lesions were assessed. Patients’ characteristics are summarized in Table 1 . The median duration of exposure to Nivolumab was 5 months (range 2-22), with a median of 10 cycles (range 4-45). Four patients received RT more than once and for multiple sites during the course of their treatment with Nivolumab. After a median follow up time of 6 months (range 1-24 ), a median PFS of 5 months (range 1-22) was observed. Best ORR to Nivolumab was a partial response (PR) in 3 cases (14%) and stable disease (SD) in 7 cases (34%) respectively. [ID1] At the end of the study period, 9 patients (43%) resulted alive. RT was delivered mainly for palliation in 17 lesions in total ( 63% ) whereas ablative radiotherapy was applied in 10 of lesions ( 37% ). In the palliative setting a median BED of 28 Gy (range 28- 54) was delivered while in the ablative setting a median BED of 78 Gy (range 40-129.6) was achieved. Overall concomitant treatment was well tolerated with no unexpected toxicity reported; remarkably, no life threatening toxicities occurred. An overview of treated sites and related toxicities are shown in Table 2 . In the ablative setting 10/10 were evaluable for response: 3 Complete response, 6 partial response and one stable disease were observed respectively.

Conclusion Combined RT- Nivolumab therapy appears to be a safe and a feasible choice for patients in the metastatic setting. These results encourage further prospective studies aimed to explore late effects of this combination and its clinical outcomes in terms of disease control and survival. PO-0869 Influence of cardiac implantable electronic devices onto dosimetric parameters during radiotherapy C. Straube 1 , J. Warmbrunn 1 , H.U. Haase 2 , D. Sinnecker 2 , K.L. Laugwitz 2 , S.E. Combs 1 , S. Schneider 3 , D. Habermehl 1