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Conclusion This data on a large series of oligometastatic patients treated by SBRT point out the usefulness of the functional evaluation of the response that seems to be predictive of encouraging local control at 2 years

maximum tolerable dose has been reached if one third of patients experience a dose-limiting toxicity. Preliminary data about acute toxicity and late toxicity, tumor response and early local control were investigated and reported§

Results 282 consecutive patients (M/F: 166/116; median age: 69, range 35-90) with 376 lesions were treated. Of these, 119 were primary or metastatic lung tumors, 13 were metastatic liver tumors and 188 were nodal metastases. Median follow-up was 19 months (2-157). Maximum tolerated dose was defined in 4 (a, b, c and f) of the 7 arms of the study, while recruitment of other arms (d, e, g) is still ongoing (Table). Grade 2 acute toxicity rate was 5.6%. Overall response rate was 82.2 % (CI 95%: 77.2- 86.3) with a complete response rate of 58.8% (CI 95%: 52.8-64.4). 12-and 24-months actuarial local control (freedom from progression in the irradiated site) were 84.3% and 73.7%, respectively. Four patients (all previously irradiated in the same site) had severe (>grade 3) late toxicity Conclusion SBRT delivered in 5 consecutive fractions up to the doses evaluated in the first part of this trial is well tolerated. The maximum tolerable dose has reached in four of seven study arm PV-0472 Role of SBRT in the treatment of liver metastases: clinical results and prognostic factors E. Clerici 1 , T. Comito 1 , C. Franzese 1 , L. Di Brina 1 , C. Iftode 1 , A. Tozzi 1 , F. De Rose 1 , P. Navarria 1 , G.R. D'Agostino 1 , M. Scorsetti 1 1 Istituto Clinico Humanitas, Radiotherapy and Radiosurgery, Rozzano Milan, Italy Purpose or Objective To evaluate feasibility and efficacy of Stereot actic Body Radiation Therapy for unresectable liver metastasis in oligometastatic patients. Material and Methods Oligometastatic patients with up to 3 liv er metastases, maximum diameter of 6 cm and Karnofsky Performance Status ≥70 were treated with Stereotactic Body Radiation Therapy. Total dose was 75 Gy in 3 consecutive fractions and Volumetric Modulated Arc Therapy by RapidArc (Varian, Palo Alto, CA) technique was used. The primary end-point was infield local control. Secondary end points were to define overall survival, prognostic factors and radiation treatment- related toxicity. Results Between February 2010 and December 2016, we enrolled in this trial study 202 patients with 268 liver metastases. Number of treated lesions was 1 in 150 patients (74.5%), 2 in 38 patients (18.8%), and 14 in 3 patients (6.9 %). Median follow-up time from SBRT was 33 months (5-87

PV-0471 An interim analysis of a phase I dose escalation clinical trial on extracranial SBRT F. Deodato 1 , G. Macchia 1 , S. Cilla 2 , A. Ianiro 2 , V. Picardi 1 , M. Ferro 1 , G. Tolento 3 , G. Siepe 3 , A. Arcelli 3,4 , M. Buwenge 3 , S. Bisello 3 , G. Maselli 5 , G. Sallustio 5 , S. Ciabatti 3 , R. Frakulli 3 , S. Cammelli 3 , G.P. Frezza 4 , V. Valentini 6 , A.G. Morganti 3 1 Fondazione di Ricerca e Cura “Giovanni Paolo II”, Radiotherapy Unit, Campobasso, Italy 2 Fondazione di Ricerca e Cura “Giovanni Paolo II”, Medical Physics Unit, Campobasso, Italy 3 Department of Experimental- Diagnostic and Specialty Medicine – DIMES- University of Bologna- S. Orsola- Malpighi Hospital, Radiation Oncology Center, Bologna, Italy 4 Ospedale Bellaria, Radiotherapy Department, Bologna, Italy 5 Fondazione di Ricerca e Cura “Giovanni Paolo II”- Università Cattolica del S. Cuore, Radiology Unit, Campobasso, Italy 6 Policlinico Universitario “A. Gemelli”- Università Cattolica del S. Cuore, Radiation Oncology Department, Rome, Italy Purpose or Objective To present the interim results in terms of safety and efficacy of a multi-arm phase I study on stereotactic body radiotherapy (SBRT) delivered by means fixed non- coplanar fields or volumetric arc therapy in patients with primary or metastatic tumors in various extra-cranial body sites. The trial was aimed to determine the maximum tolerated dose (MTD) of 5 fractions SBRT treatment Material and Methods The clinical trial design was very articulated including seven arms (Table). Each patient was sequentially enrolled in a given study arm, according to tumor site and clinical stage. The total dose, prescribed to the target isocenter (ICRU 62), ranged from 20 to 50 Gy (biologic effective dose=28-100 Gy, α/β=10) according to different arms of the protocol; the doses per fraction ranged from 4 to 10 Gy along 5 days. Dose escalation was based primarily on acute and subacute toxicity because late toxicity can occur months or years later. Dose limiting toxicities (DLT) were defined as any treatment- related non haematological adverse effects rated as Grade > 3 or any haematological toxicity rated as > 4 by Radiation Therapy Oncology Group (RTOG) criteria. The