ESTRO 2021 Abstract Book

S986

ESTRO 2021

Conclusion In this retrospective dosimetric study, IFI significantly decreased doses to organs at risk compared to ENI. The use of mediastinal IFI, instead of ENI, in the adjuvant setting for N2 disease could potentially translate into a survival benefit by combining improved locoregional control with decreased rate of toxic deaths. This should be further investigated in prospective clinical studies. PO-1189 Stereotactic radiotherapy for lung oligometastases from colorectal cancer A. Fodor 1 , C.L. Deantoni 1 , R. Tummineri 1 , C. Fiorino 2,3 , I. Dell'Oca 1 , M. Mori 2 , S. Broggi 2 , M. Pasetti 1 , L. Perna 2 , S.L. Villa 1 , G. Mandurino 1 , A. Sanchez Galvan 1 , S. Baroni 1 , P. Pacifico 1 , A. Del Vecchio 2 , N.G. Di Muzio 1,3 1 IRCCS San Raffaele Scientific Institute, Department of Radiation Oncology, Milan, Italy; 2 IRCCS San Raffaele Scientific Institute, Medical Physics, Milan, Italy; 3 Vita-Salute San Raffaele University, Radiotherapy, Milan, Italy Purpose or Objective Lung oligometastases (LOM) from colorectal cancer (CRC) have a higher radioresistance than those from other cancers. The objective of this retrospective analysis is to evaluate toxicity and local control (LC) of stereotactic radiotherapy in the management of LOM from CRC performed in our institution. Materials and Methods From 01/2006 to 07/2020, 70 metastases (mts) of 38 LOM patients from CRC were treated with SRT (37 with 4D helical/VMAT IG-IMRT and 32 with real time-tracking robotic radiosurgery). Median age was 65.0 (48.7- 84.0) years. Median interval between primary treatment and LOM was 14 (1-117) months. A single LM was treated in 19 pts, two in 11 pts, three in five pts, four in one patient, and five in two patient (one with 2 lesions treated in one PTV for a total of four PTVs), respectively. Median gross tumor volume (GTV) was 5 (0.16-88.6) cc, and median planning treatment volume (PTV) was 21.35 (1.97-180) cc. Median prescribed dose 54 (36-60) Gy, in a median number of 6 (2-8) fractions. Fifty-eight lesions were peripheral and 11 centrally located. The Biologically Effective Dose (BED), considering an alpha/beta ratio of 10 was 102.6 (72-180) Gy. Acute and late toxicities were graded according to the National Cancer Institute Common Terminology Criteria (CTCAE) v. 5. Results Median follow up was 15.2 (3-86.4) months. The treatment was well tolerated and no grade (G) ≥ 2 acute toxicity was reported: two pts presented G1 cough (the patient treated on four lesions) and another patient G1 dyspnea. Five patients presented late toxicity: a late G3 pulmonary toxicity was observed in one patient treated on five LOM (total PTV = 82.71 cc). The patient treated on four lesions registered with G1 acute cough presented G1 fibrosis during the follow up. Three pts (treated on two, two and three lesions respectively) presented G1 dyspnea. Fifteen pts (39.5%) were dead at the last follow up, one for brain metastases, one for bacterial pneumonia, one for a second (urothelial) tumor progression and all others for systemic progression (none for local progression). Median overall survival (OS), cancer specific survival (CSS) and Local progression free survival (LPFS) were 38.2 months, 38.7 months and 15.2 months, respectively. Kaplan Meyer estimates of OS were 87% at 12 months and 72% at 24 months, CSS 88.8% at 12 months and 73.5% at 24 months, while LPFS 72% at 12 months and 42% at 24 months. Of the relapsed lesions 4 were treated with surgery, four with a second course of SRT, 9 with chemotherapy and one with immunotherapy. Conclusion SRT in lung oligometastases from colorectal cancer have a low toxicity profile at a median BED of 102 Gy, but a better patient selection, avoiding important volumes of disease treated concomitantly, is necessary to prevent any toxicity. A higher BED is necessary to improve local control. PO-1190 Lung lesions treated with CyberKnife: An Indian single centre experience A. Sasidharan 1 , R. Kamath 1 , P. KU 1 , A. R 1 , S. K Reddy 1 , H. Nair 1 , A. E H 2 , D. Dutta 1 1 Amrita Institute of Medical Sciences, Radiation Oncology, Kochi, India; 2 Amrita Institute of Medical Sciences, Medical Physics, Kochi, India Purpose or Objective To assess outcome after stereotactic body radiotherapy (SBRT) with CyberKnife (CK) in Indian primary lung cancer and lung oligometastasis patients. Materials and Methods Analysis of data from a prospectively maintained database of patients with primary lung cancer and lung oligometastasis treated with SBRT on CK was done. Results From 2017 - 2020, 42 patients were treated with CK for lung lesion (20 primary lung & 22 lung