Abstract Book

S814

ESTRO 37

EP-1501 Feasibility of MRgRT neoadjuvant treatment for locally advanced rectal cancer. F. Cellini 1 , G. Chiloiro 1 , L. Boldrini 1 , M. Massaccesi 1 , G. Mattiucci 1 , M.V. Antonelli 1 , V. Frascino 1 , S. Luzi 1 , S. Manfrida 1 , V. Masiello 1 , A. Petrone 1 , V. Pollutri 1 , C. Votta 1 , F. Catucci 1 , B. Fionda 1 , M. Balducci 1 , M. Gambacorta 1 , V. Valentini 1 1 Fondazione Policlinico A. Gemelli, Radiation Oncology- GemelliART, Rome, Italy Purpose or Objective Aim of this study is evaluating the feasibility of neoadjuvant radiochemotherapy (RCT) administered by tri-60-Cobalt-MRI-hybrid device (MRI-treat) in locally advanced rectal cancer (LARC). Material and Methods Patients (pts) with LARC (stage III) were considered. Absolute exclusion criteria were MR incompatibility and claustrophobia. Treatment was through simoultaneous integrated boost (SIB). Prescription included total mesorectum and drainage lymph nodes: 45 Gy at 1.8 Gy/fraction (CTV2); rectal disease and corresponding mesorectum (CTV1): 55 Gy at 2.2 Gy/fraction. A CTV to PTV margin of 5 mm has been added. Oral capecitabine, with or without weekly oxaliplatin, was administered as concomitant chemotherapy (CT). Recorded data included: PTV1-V95; PTV2-V95; Conformity Index (CI); maximum dose; bowel-V45 was calculated (dose- constraints=196cc).MRI-treat parameters for gating were set including delay time (to enable gated treatment interruption)=0 sec, ROI of target out of boundary (to enable gated treatment interruption)=5%. Beam on and total irradiation time were recorded. Pts were immobilized on MR compatible system. MRI setup images (i.e.:25 seconds TRUFI sequences with FOV LRxAPxHF 54x47x43 cm and 0.15 cm x 0.30 cm resolution) have been daily acquired for both pts positioning and organ at risk (OAR) preparation’s verification (i.e:bladder and rectal). Acute adverse events and toxicity were recorded according to v.4.0 CTCAE scale during weekly visits. Pts were planned for restaging MRI at 6 weeks after RCT, followed by surgery within 8-12 weeks. Results From March to September 2017 11 pts were enrolled (median age: 65 years [49-86]; M:F=9:2).Five pts (45.5%) were staged as cT4 with mesorectal fascia involvement in 3 cases (27.3%) and 9 pts had nodal involvement (3 pts cN1 and 6 pts cN2). Dosimetric parameters are reported in table 1. Median beam-on time and median total irradiation time were 2.55 (1.63-4.49) and 12.32 (5.7- 21.2) minutes respectively. Concomitant capecitabine was administred in 4 pts, oxaliplatin was added in 6 pts and in one case CT was not administered due to comorbidities. All the pts completed the scheduled CRT, although 4 pts interrupted it due to gastrointestinal (GI) toxicity with a mean suspension of 5.5 days (1-8).No G3 or 4 hematological, genitourinary or skin toxicity were reported. GI toxicity was observed in 9 pts (82%) with only 1 G3 case. To date 6 pts underwent restaging MRI with a complete clinical response in 1 case. Further restaging and pathological details will be later available.

Conclusion This neoadjuvant RCT SIB-IMRT schedule administered by tri-60-Cobalt-MRI-hybrid device is feasible and well tolerated in LARC pts. Such treatment approach seems interesting and deserving further analyses. Nevertheless more pathological samples are needed to evaluate the results in terms of therapy efficacy. EP-1502 Is it possible to optimize the prescription of PET/CT and MRI in anal cancer patients follow-up? D. Aloi 1 , C. Reichling 1 , C. Teyssier 1 , A. Lepinoy 2 , Z. Lakkis 3 , S. Kim 4 , J. Bosset 1 , G. Créhange 5 , B. De Bari 1 1 Hôpital Univ. Jean Minjoz CHU Minjoz Jeans & Belfort- Montbéliard Hospital, Radiation Oncology, Besançon, France 2 Paul Strauss Center, Radiation Oncology, Strasbourg, France 3 Hôpital Univ. Jean Minjoz CHU Minjoz Jeans & Belfort- Montbéliard Hospital, Surgery, Besançon, France 4 Hôpital Univ. Jean Minjoz CHU Minjoz Jeans & Belfort- Montbéliard Hospital, Medical Oncology, Besançon, France 5 Georges François Leclerc Center, Radiation Oncology, Dijon, France Purpose or Objective To analyze the pattern of prescription and the impact of PET/CT and MRI on the detection of local and distant relapse compared to physical examination alone in anal From 2007 to 2015, 104 pts received curative chemoradiotherapy (EORTC 22953 schedule). Of them, 60 received at least one PET/CT (n = 52, 70%) and/or MRI (n = 35, 58%) during their follow-up, and were included in this analysis. One, 28, 14, 16 and 1 pts were initially staged as Stage I, II, IIIA, IIIB and IV respectively (2002 UICC TMN classification). Thirty-one pts were N1-3 and 7 presented positive inguinal nodes. PET/CT or MRI were prescribed because of a suspicion of clinical relapse or because considered indicated in the follow-up of the pts (Table 1). cancer patients (pts). Material and Methods

Results Data obtained from a total of 559 follow-up visits were available (median follow-up: 31 months, range 3-120). Table 2 summarizes data about concordance between PET/CT or MRI and the clinical physical examination (expressed as number of visits).

Forty-two patients presented no signs of local or distant relapse. Nevertheless, a PET/CT was prescribed: in 35/42 (83%) PET/CT was negative. In 7/42 pts PET/CT was