Abstract Book

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ESTRO 37

survival (PFS) rate and overall survival (OS) rate of dual- agent therapy was higher than that of single-agent therapy (59.6% and 43%, 76.4% and 61.2%, respectively), but there were no significant differences (P = 0.260 and 0.387, respectively). Furthermore, patients treated with adjuvant chemotherapy after concurrent chemoradio- therapy exhibited significant improvements in both OS and PFS (P = 0.04 and 0.042, respectively). Multivariate analysis showed that sex, age, radiotherapy dose, and adjuvant chemotherapy had no significant effects on OS or PFS. Only disease stage was associated with OS and PFS in the multivariable analysis (P = 0.007 and 0.006, respectively). Conclusion We conclude that the 5-year PFS and OS rates of dual- agent therapy were higher than those of single-agent concurrent chemoradiotherapy for patients with unresectable esophageal squamous cell carcinoma; however, there were no significant differences in univariate analysis and multivariable analysis. The better PFS and OS might be attributable to the younger age of patients in the double-agent group. Therefore, we hypothesize that double-agent therapy is not better than single-agent therapy. In the future, we aim to confirm our hypothesis through a prospective randomized study. EP-1414 Stereotactic body radiotherapy with image- guided delivery for liver metastasis F. Ricchetti 1 , S. Fersino 1 , R. Mazzola 1 , A. Fiorentino 1 , N. Giaj Levra 1 , D. Aiello 1 , F. Gregucci 1 , U. Tebano 1 , G. Sicignano 1 , S. Naccarato 1 , R. Ruggieri 1 , F. Alongi 1 1 Ospedale Sacro Cuore-Don Calabria, Radiation Oncology, Negrar, Italy Purpose or Objective Stereotactic body radiation therapy (SBRT) is an emerging treatment option for liver metastasis (LM) unsuitable for ablation or surgery. An accurate treatment planning with risk-adapted dose prescription and the identification of specific constraints for organs at risk (OARs), daily Cone Beam CT (CBCT) as image-guidance, could allow an effective and safe treatment delivery. The diagnostic accuracy of 18 F-FDG PET-CT as imaging pre-SBRT and post-SBRT is a very useful tool to evaluate the response to treatment. Here, feasibility and efficacy of SBRT in LM treated in our Cancer Care Center are reported. Material and Methods Between October 2014 and February 2017, 41 LM on 22 patients underwent SBRT. The clinical target volume (CTV) was identified on planning contrast-enhanced CT scan and PET-CT. An additional margin of 3-5 mm was added for the planning target volume (PTV). The dose- volume constraints for duodenum and stomach were D 1cc <36Gy and D 3cc <36Gy, respectively. Volume of healthy liver receiving 15 Gy was kept lower than 700cm 3 , and in order to reduce interfraction liver deformation a thermoplastic mask with abdominal compression was used. In order to achieve OARs dose-constraints a risk- adapted dose prescription strategy was adopted, choosing between schedules with biologically effective dose (BED) <70Gy or >70Gy, according to ICRU83. SBRT was delivered with volumetric modulated arc technique (VMAT) using RapidArc and flattening filter-free (FFF) mode. Daily CBCT was performed. The patients were evaluated at the end of treatment for acute toxicity and at 3, 6 and 12 months for late toxicity and treatment response with 18 F- FDG PET-CT. Results Primary site was colorectal in the majority of lesions (16 out of 41), mean metastasis diameter was 20 mm (range 10-60). At a median follow up of 12 months (range 2-30), 15 of 22 (68%) patients are alive. BED >70Gy was prescribed in 83% of cases. At 3 months (m) complete response (CR), partial response (PR), stability of disease

(SD) and progression of disease (PD) was observed in 66%, 27%, 3% and 4%, respectively. At 6m 46% of patients had a CR, 3% a PR and 22% a PD. At 12m there were 27% CR and 7% PD. 65% of liver recurrences were out of field. No cases of ≥ G3 acute and late toxicity were reported. Conclusion Risk-adapted dose prescription and image-guided SBRT is an effective and safe option for LM. The role of PET-CT parameters as predictors of response after SBRT for these patients is a very interesting aspect to investigate in the future; however, further clinical evaluation is warranted. EP-1415 SBRT for unresectable locally advanced pancreatic cancer: risk-adapted dose prescription F. Gregucci 1 , S. Fersino 1 , R. Mazzola 1 , D. Aiello 1 , U. Tebano 1 , S. Corradini 2 , M. Cirillo 3 , R. Ruggieri 1 , F. Alongi 4 1 Sacro Cuore Don Calabria Cancer Care Center, Radiation Oncology, Negrar, Italy 2 LMU Munich, Radiation Oncology, Munich, Germany 3 Sacro Cuore Don Calabria Cancer Care Center, Medical Oncology, Negrar, Italy 4 University of Brescia- Sacro Cuore Don Calabria Cancer Care Center, Radiation Oncology, Negrar, Italy Purpose or Objective As stated by the ASCO 2016 guidelines, Stereotactic Body Radiation Therapy (SBRT) represents a new treatment option for locally advanced pancreatic cancer (LAPC). An accurate treatment planning with risk-adapted dose prescription with adherence to specific dose constraints for organs at risk (OARs), and the use of daily Cone Beam CT (CBCT) for image-guidance, could allow an effective and safe treatment delivery. Here, feasibility and efficacy of SBRT in LAPC treated in our Cancer Care Between August 2014 and December 2016, 33 unresectable LAPC patients underwent SBRT. In order to respect OAR dose-constraints a risk-adapted dose prescription strategy was adopted, choosing between the following schedules: 42 Gy or 45 Gy in 6 daily fractions with a biologically effective dose (BED) >70 Gy 10 and 36 Gy in 6 fractions (estimating a BED 57.6 Gy 10 ). SBRT was delivered with volumetric modulated arc technique (VMAT) using RapidArc and flattening filter-free (FFF) mode. Image guidance was performed by means of CBCT before every treatment session. The patients were evaluated at the end of treatment for acute toxicity and at 3, 6 and 12 months for late toxicity and treatment response. Results At the time of analysis, the median follow up was 18 months (range, 5-34 months). Prior to SBRT, 24 out of 33 patients received induction chemotherapy. Although all patients were previously judged as unresectable, 6 out of 33 (18%) underwent surgery after SBRT; all of them received a BED >70 Gy 10 . One-year LC and OS were 81% and 75%, respectively. A total of 12 patients (37%) had an extra-pancreatic progression. No cases of ≥G3 acute and late toxicity were reported. Conclusion In our experience, the risk-adapted dose prescription and image-guided SBRT represent an effective treatment option for LAPC patients. The present results, showed good tolerability without severe toxicity. Probably, in case of dose reductions below BED <70 Gy due to OAR dose limits, an early combination with systemic therapies could optimize the oncological outcome. EP-1416 Postoperative proton therapy for pancreas cancer patients on the Proton Collaborative Group registry R. Nichols 1 , C. Morris 1 , K. Prabhu 2 , W. Hartsell 3 , O. Cahlon 4 , S. Apisarnthanarax 5 , L. McGee 6 , C. Vargas 6 1 University of Florida Proton Therapy Institute, Radiation Center are reported. Material and Methods