S346 stage I, II, IIIA, and IIIB, respectively. Median age was 61.7 years (range: 35-87). After a median planned gap of 2 weeks (range, 0-4; no gap in 25 patients since 2011), a boost dose was delivered with either IMRT (n = 16, until 2011), VMAT (n = 16), HT (n = 37) or 3D-CRT (n = 68). Concomitant CTX was delivered in 127 patients, maily using a mitomycinecapecitabine combination (n = 117). Median follow-up was 42 months (range: 2-97). Four-year LC, OS, DFS, and CFS rates were 80%, 84%, 78% and 90%, respectively. Time to progression was 4 months (range: 0-41). A total of 24 patients presented a recurrence (local only in 14, locoregional in 1, locoregional and distant in 1, local and distant in 3, regional only in 2, and distant only in 3 patients). Twelve patients underwent a colostomy because of local recurrence (n = 12) or pretreatment dysfunction (n = 2). Grade 3 acute toxicity was observed in 33 patients (2.4%); i.e. erythema (26/33) or diarrhoea (9/33). No late G3 cutaneous toxicity was recorded. At the time of analysis, 127 patients presented more than 6 months of followup and were considered evaluable for late toxicity: 5 of 127 patients present a late G3 gastrointestinal toxicity (anal incontinence). No G4 acute or late toxicity was recorded. No significant difference was observed in terms of local control or acute G3 toxicity between MRT techniques and 3D-CRT boost techniques. Conclusions: A total dose of 59.4 Gy to the anal canal and involved nodes, including 36 Gy to the uninvolved nodes, is effective and safe when delivered using modern IMRT techniques and daily IGRT. For these reasons, VMAT or HT and concurrent CTX are the standard of care in our institutions. PO-0704 Proton beam t herapy for hepatocellular carcinoma wit h ext ensive portal vein tumor thrombosis T. Okumura1, N. Fukumitsu1, M. Mizumoto1, H. Ishikawa1, K. Ohnishi1, K. Murofushi1, H. Numajiri1, K. Fukuda2, M. Abei2, T. Aihara1, T. Sakae1, K. Tsuboi1 1 University of Tsukuba, Department of Radiation Oncology, Tsukuba, Japan 2 University of Tsukuba, Department of Gastroenterology, Tsukuba, Japan Purpose/ Obj ective: To evaluate the efficacy of proton beam therapy (PBT) for hepatocellular carcinoma with extensive tumor thrombosis in the main trunk or major branches of the portal vein. Materials and Methods: Eighty patients with hepatocellular carcinoma were treated by PBT. There were 65 men and 15 women, and the median age was 65 years old (range: 25 – 88). The CTV ranged from 15.2 cm3 to 1687 cm3 (median: 238.9 cm3). The clinical stages were 3B, 3C, 4A, and 4B in 65, 1, 5, and 9 patients, respectively. Thirty-two patients had primary tumors, and 48 had recurrent tumors. The delivered total dose ranged from 70 to 80.47 Gy10 (median: 80.47Gy10) in terms of equivalent dose in 2Gy fractions. Results: Seventy-seven patients (96.3%) completed the planned treatment. Median survival rate for all the patients was 12 months. MST for the patients treated with PTV that encompassed all the detectable lesions was 26.9 months, and MST for the patients who had viable tumor outside of their PTV was 6.3 months. Local recurrence after PBT was observed in 3 patients. Forty-five patients died of tumor 3rd ESTRO Forum 2015 progression, and 28 of them had recurrence out of the PTV. Multivariate analysis revealed existence of viable tumor outside of the PTV, clinical stage, and value of des-gammacarboxy prothrombin as significant factors affecting the OS. Conclusions: PBT was effective for patients with extensive portal tumor thrombus, if the PTV encompassed all the detectable lesions. PO-0705 Could acute toxicity predict tumor regression rate in rectal cancer patients undergoing neoadj uvant treatment? E. Ozsahin1, B. De Bari1, A. Saidi1, D. Hanhloser2, D. Wagner3, P. Yan4, O. Matzinger5, J. Bourhis6 1 Centre Hospitalier Universitaire Vaudois, Department of Radiation Oncology, Lausanne Vaud, Switzerland 2 Centre Hospitalier Universitaire Vaudois, Surgery Department, Lausanne Vaud, Switzerland 3 Centre Hospitalier Universitaire Vaudois, Medical Oncology Department, Lausanne Vaud, Switzerland 4 Centre Hospitalier Universitaire Vaudois, Pathology Department, Lausanne Vaud, Switzerland 5 Riviera Hospital, Radiation Oncology Department, Lausanne Vaud, Switzerland 6 Centre Hospitalier Universitaire Vaudois, Radiation Oncology Department, Lausanne Vaud, Switzerland Purpose/ Obj ective: Some studies already showed that acute toxicity during chemo +/- radiotherapy (CT +/- RT) was correlated to the clinical response of the tumor. In this retrospective study, we report our analysis of acute toxicity of rectal cancer cancer patients treated with an homogenous schedule of CT +/- RT. Materials and Methods: Between 01/2010 and 08/2014, 83 locally advanced rectal cancer patients consecutively treated in our institution were analyzed. All these patients received long-course neoadjuvant chemoradiotherapy (45 Gy on pelvic nodes and mesorectum and 50 Gy on gross tumor volume and corresponding mesorectum, delivered with a simultaneous integrated boost). All patients were treated with helical Tomotherapy (HT) and daily image guided radiotherapy, and all of them underwent radical surgery. Concomitant chemotherapy with oral capecitabine was delivered in all the patients. Primary endpoint of this study was to report the rate of acute toxicity (G2 or more) of this therapeutic approach and to correlate acute toxicity to the Mandard tumor regression rate (TRG). Toxicity were retrospectively scored using CTC-AE score (v. 4.0). The considered acute toxicity were: skin toxicity, diarrhoea, blood loss, cystitis, anorectal pain. We performed logistic regression analyses, and we correlated the TRG with the presence of acute toxicity (any grade), the presence of any acute toxicity grade > 2, and with a 'sum of toxicity' (ST) of each toxicity grades (i.e: this ST in a patient presenting a G2 bladder toxicity , a G1 pain and a G3 diarrhoea was 6, 2+1+3). Results: Globally, 22/83 patients presented an acute > G2 toxicity (26.5%), with only one patients presenting a G3 acute skin toxicity. Data about TRG were available for 69 patients. Logistic regression showed that better TRG have been found in patients presenting higher TS, both when TRG was considered as an ordinal (p=0.028) or as a continuous variable (p=0.03). 3rd ESTRO Forum 2015 S347 Conclusions: Long-course chemo-radiotherapy with simultaneous integrated boost is safe in the treatment of rectal cancer patients. Patients presenting more pronounced and/or several toxicity showed a significant trend toward a better TRG. Immunological local reactions could potentially explain these results, and should be further explored. PO-0706 Individualised margin calculations for different regions in anal cancer IMRT target L. Durrant1, F. Van den Heuvel1, M. Robinson1, M.A. Hawkins1, R. Muirhead1 1 CRUK/MRC Oxford Institute for Radiation Oncology, Department of Oncology, Oxford, United Kingdom Purpose/ Obj ective: UK IMRT anal cancer treatment uses large fields to uninvolved nodal groups (40Gy) with simultaneous integrated boost to the primary tumour (50.4Gy T1/T2; 53.2Gy T3/T4) and involved nodes (50.4Gy). With a simple bony match online, iliac nodes are well covered and the margins required are well documented, however the margins for prophylactic inguinal nodes (pIN) and primary tumour are not well established as data from daily imaging are limited; these form the focus of this study. Materials and Methods: Anal cancer patients treated at a single institution under current UK IMRT guidelines were screened; 11 consecutive inguinal node negative patients were studied. Supine treatment comprised 28 fractions with daily imaging: CBCT fractions 1-5, 10, 15, 20 and 25; orthogonal kV imaging all other fractions. 99 CBCT’s were re-matched automatically to the planning CT. A bony match was performed using a clipbox encompassing the bony pelvis. Re-matches were performed within the same clipbox using the clinician defined tumour (GTVA) as a region of interest (ROI), then repeated with the pIN ROI. Accuracy of auto-matches were assessed visually to ensure clinical relevance. Bony match values were subtracted from the GTVA and pIN measurements to evaluate differences in the optimal treatment position for the tumour or the nodes relative to a simple bony match. Margins were calculated using van Herk’s recipe. Results: Differences (mm) between GTVA/ bony matches were larger than inguinal/ bony matches in all axes ( lat -3.1 to 4.2; -2 to 1.5, vert- 6.9 to 12.7; -3.6 to 2.9, long -13.3 to 17.2; -8.5 to 7.3 in GTV and pIN respectively). This was statistically significant in the long axis (p<0.05) shown in Fig.1. GTVA had consistently larger systematic and random errors than pIN, reflected in the margin calculations (mm): GTVA lat 2.8, long 9.8, vert 5.8; pIN lat 1.5, long 3.1, vert 3.1. Conclusions: With a simple bony match, the margin around pIN can be reduced to 1.5mm laterally and 3.1mm in all other directions potentially reducing toxicity to the groin, genitalia and bladder. The GTVA to PTV margin incorporates microscopic disease, the motion of the soft tissues of the anus which can be affected by tumour size, location, bowel filling and BMI; and the set up error. The margin reported in this study covers set up error and soft tissue motion of the anus. An individualised margin incorporating these factors can be calculated and applied during the treatment course with the aim of reducing toxicity in adjacent organs such as vagina, bladder and penile bulb. Further investigation is warranted to demonstrate reduced toxicities with these strategies. PO-0707 Multidisciplinary clinic models deliver higher value care for patients with pancreatic cancer S. Elnahal1, B. Luber2, A.T. Wild3, A. Dholakia1, H. Wang2, T. Pawlik4, J.M. Herman1, S. Alcorn1 1 Johns Hopkins Kimmel Comprehensive Cancer Center, Radiation Oncology, Baltimore, USA 2 Johns Hopkins Kimmel Comprehensive Cancer Center, Biostatistics, Baltimore, USA 3 Memorial Sloan Kettering Cancer Center, Radiation Oncology, New York City, USA 4 Johns Hopkins Kimmel Comprehensive Cancer Center, Surgery, Baltimore, USA Purpose/ Obj ective: Multidisciplinary clinics (MDCs) offer patients an initial evaluation by all three oncologic specialists, radiologists, pathologists, and others. The costs and overall value (defined as quality divided by costs) of care in MDCs are not well-described. For patients with pancreatic cancer, we compared direct care costs, patient retention rates, patient phone calls with symptoms, patient ED visits with symptoms, and survival outcomes for patients treated in a pancreatic MDC to patients evaluated outside of the MDC. Materials and Methods: Two cohorts of patients with pancreatic cancer seen at our institution were analyzed and