ESTRO 36 Abstract Book

S680 ESTRO 36 _______________________________________________________________________________________________

multivariate analysis, post-CRT SUV max (≤6.5 vs. >6.5) was a significant factor for LRFS and DFS. Post-op CEA (≤2.0 vs. >2.0) was a significant factor for LRFS and OS. Conclusion This study showed the post-CRT SUV max was a significant parameter for predicting tumor recurrence. Meanwhile, post-op CEA was the only prognostic factor affecting OS among these parameters. EP-1265 Image-guided SIB-IMRT for the treatment of anal cancer patients F. Arcadipane 1 , P. Franco 1 , S. Martini 1 , G. Furfaro 1 , M. Ceccarelli 2 , M. Mistrangelo 3 , N. Rondi 4 , P. Cassoni 5 , P. Racca 6 , U. Ricardi 1 1 University of Turin- A.O.U. Citta' della Salute e della Scienza, Department of Oncology- Radiation Oncology, Torino, Italy 2 Cancer Epidemiology and CPO Piemonte - A.O.U. Citta' della Salute e della Scienza, Department of Oncology- Radiation Oncology, Torino, Italy 3 University of Turin- A.O.U. Citta' della Salute e della Scienza, Department of Surgical Sciences, Torino, Italy 4 A.O.U. Citta' della Salute e della Scienza, Department of Oncology- Radiation Oncology, Torino, Italy 5 University of Turin- A.O.U. Citta' della Salute e della Scienza, Department of Medical Sciences- Pahtology, Torino, Italy 6 A.O.U. Citta' della Salute e della Scienza, Department of Oncology- Centre for Gastrointestinal Cancers- Medical Oncology 1 Unit, Torino, Italy Purpose or Objective Concurrent chemoradiation (CT-RT) has been established as the standard of care for anal cancer patients. We explored intensity-modulated and image-guided radiotherapy (IMRT–IGRT) with a simultaneous integrated boost (SIB) approach reporting on clinical outcomes within a mono-istitutional observational study. Material and Methods Between April 2007 and April 2015, 87 patients with biopsy proven squamous cell anal cancer were treated with SIB- IMRT. Radiotherapy was delivery using a schedule of 50.4/54 Gy to the primary tumor and involved lymphnodes and 42/45 Gy to the elective volumes. Dose prescription varied according to clinical stage, following Radiation Therapy Oncology Group (RTOG) 0529 indications. Concurrent 5-Fluorouracil and Mitomycin-C were given. Clinical data and toxicity are herein reported. Results A total of 87 patients (stage I 6%; II 56%; III 38%) were treated and observed for median time of 34 months (range: 9-102). CT-RT with MMC and 5-FU was administered in 90.8% of patients. One patient received MMC only, two patients 5-FU only and five patients underwent exclusive RT, after consderation of age, comorbidities and performance status. The 3-year rates of colostomy-free survival, local control, disease free and overall survival were 71% (95% CI 0.59-0.80), 69% (95% CI 0.57-0.79), 64% (95% CI 0.52-0.75), and 79% (95% CI 0.66- 0.87) respectively (Figure 1). At the time of analysis 20/87 (23%) patients were dead and 14 death were related to cancer. Up to 23 patients recurred; ten failed locally, 7 failed both locally and distantly and 6 developed systemic failure only. Seventy-seven patients reached a clinical complete response six months after treatment (88.5%). Major acute toxicity events (>G3) were recorded for gastrointestinal (6.9%), genitourinary (1.2%) and hematologic (neutropenia: 19.6%) aspects. Borderline significance as prognostic factors with respect to CFS were found for gender and stage (Table 1).

Conclusion Image-guided IMRT with a SIB approach concomitant to 5- FU/MMC based chemotherapy is a safe and well tolerated treatment strategy in an unselected anal cancer patient population. EP-1266 In silico evaluation of subcutaneous skin dose associated to use of MRIdian MRI- 60Co System G.C. Mattiucci 1 , L. Boldrini 2 , D. Cusumano 3 , L. Azario 4 , M. Ferro 2 , S. Chiesa 2 , G. Chiloiro 2 , N. Dinapoli 2 , M.A. Gambacorta 1 , C. Masciocchi 5 , E. Placidi 6 , D. Piccari 7 , M.V. Antonelli 7 , M. Rapisarda 7 , S. Teodoli 6 , M. Balducci 1 , A. Piermattei 4 , F. Cellini 2 , V. Valentini 1 1 Università Cattolica del Sacro Cuore, Gemelli ART - Radiation Oncology, Rome, Italy 2 Fondazione Policlinico A. Gemelli, Gemelli ART - Radiation Oncology, Rome, Italy 3 Fondazione Policlinico A. Gemelli, UOC di Fisica Sanitaria - Gemelli ART - Radiation Oncology, Rome, Italy 4 Università Cattolica del Sacro Cuore, Rome, Italy 5 Fondazione Policlinico A. Gemelli, KBO Labs - Gemelli ART - Radiation Oncology, Rome, Italy 6 Fondazione Policlinico A. Gemelli, UOC Fisica Sanitaria - Gemelli ART - Radiation Oncology, Rome, Italy 7 Fondazione Policlinico A. Gemelli, TSRM - Gemelli ART - Radiation Oncology, Rome, Italy Purpose or Objective The MRIdian MRI- 60 Co radiotherapy system (ViewRay, Oakwood, Ohio) combines an open split-solenoid MRI scanner equipped for parallel imaging and three 60 Co gamma-ray sources. The dose delivered to the subcutaneous tissues of skin by such system should be evaluated: the lower mean beam