ESTRO 36 Abstract Book

S678 ESTRO 36 2017 _______________________________________________________________________________________________

22 patients (9 prostate and 13 rectal cancer) received pelvic re-irradiation with SBRT between 25.07.2011 and 20.04.2016. Median age was 66 years (range 30-85 years). Median follow up was 18.5 months (range 3-58 months). The median time between primary EBRT and SBRT re- irradiation was 26 months (range 4-162 months). Median SBRT dose was 30Gy/3# (range 24Gy-44Gy/3-5#). Prior EBRT dose ranged from 20Gy/4#-70Gy/35# (median BED 63.72, range 30-84 assuming α/β = 10). 55% patients reported no measurable toxicity. No patients experienced ≥Grade 3 toxicity.10/22 (45%) patients experienced acute Grade 1/Grade 2 toxicities including fatigue, sciatica, nausea, diarrhoea, rectal haemorrhage and urinary symptoms. Only 1 patient experienced late toxicity (asymptomatic pelvic insufficiency at 21 months post SBRT, not requiring intervention). The 1 and 2 year LC rate were 90%, 85% and DPFS rate 92%, 71% respectively. OS at 1 and 2 years were 91% and 71% respectively. Conclusion Pelvic re-irradiation with SBRT is well tolerated and effective at controlling local disease. No ≥Grade 3 toxicity has been observed to date in our patient cohort although longer term follow up is needed. Further research to establish safe maximum cumulative doses to OARs for pelvic re-irradiation is warranted. EP-1274 Impact of concomitant radiotherapy boost in locally advanced rectal cancer: dose escalation M.A. Estornell 1 , D. Martinez 2 , V. Morillo 3 , M. López 1 , M. Soler 1 , J.L. Monroy 1 , A.V. Navarro 1 , A. Soler-Rodriguez 1 1 Hospital Universitario de la Ribera, Radiation Oncology Department., Alzira, Spain 2 University Hospital.Valladolid, Department of Medical Physics and Radiation Protection., Valladolid, Spain 3 Provincial Hospital. Castellon., Radiation Oncology Department, Castellon., Spain Purpose or Objective The standard preoperative radiation dose for locally advanced rectal cancer (LARC) is 45-50.4 Gy in 25-28 fractions. The aim of this study is to analyze the correlation between escalation radiotherapy dose, pathological complete clinical response (pCR) and downstaging rate or even its relation with other parameters of interest as toxicity, surgical margins, locoregional recurrence-free survival (LRFSD), distant metastasis free survival (DMFS) and overall survival (OS). The efficacy of the dose escalation in terms of pathological tumor response was evaluated as main end- point. Material and Methods Between 2000 and 2013, 287 patients were treated with preoperative chemoradiotherapy and surgical resection for LARC in our hospital. 233 patients underwent the standard chemoradiation schedule (median age 67 years; stage III 73.3%, stage IV 1.7%; 41.1% low third rectum; 45- 50.4 Gy; 1.8-2 Gy/fraction) and 54 patients were treated with simultaneous integrated boost-SIB (median age 66 years; stage III 74.5%, stage IV 1.8%; 21.8 % low third rectum; 45 Gy to the pelvis volume with a 2.17 Gy SIB on the tumor and macroscopical nodes). Results Dose escalation radiotherapy treatment reports a benefit in pCR (9.5 % vs 20 % p= 0.029), tumoral downstaging rate (42.7 % vs 60% p=0.020), nodal downstaging rate (62.9% vs 7.7% p= 0.173) and ypT0 rate (10.3% vs 20 p= 0.049). Complete microscopical resection increses on integrated boost group (93.4% vs 98% statistically non-significant). In the comparison between both groups by Contingency Table , no statistically significant differences were found on toxicity (G2 27.5% vs 37%; G3 3.1 % vs 9%) or surgical complications (35.7% vs 40%). With a follow up of 181 months, the study reports a statistically significance on disease free survival (56.1% vs 76.7 % p= 0.036 Kaplan-

Meier Test), and overall survival (21% vs 46.65 p=0.02) in the SIB group. Locorregional recurrence-free survival also improves but without statistical significance (88% vs 94.9 % Kaplan-Meir method). Tumoral downstaging was considered as an independent factor on DFS (HR 1.914 p=0.004 Cox model.) Conclusion Escalation dose radiotherapy group achieved statistical differences in pCR (ypT0 yN0), tumoral downstaging rate, overall survival (OS) and distant disease free survival (DFS). pCR could be considered as a prognostic factor on OS. The variable tumoral downstaging demonstrate a great value as an independent factor on DFS. EP-1275 Patients with locally advanced rectal cancer (larc): predictive factors of pathological response S. Montrone 1 , A. Sainato 1 , R. Morganti 2 , C. Vivaldi 3 , B. Manfredi 1 , C. Laliscia 1 , M. Cantarella 1 , G. Coraggio 1 , G. Musettini 3 , A. Gonnelli 1 , G. Masi 3 , P. Buccianti 4 , F. Pasqualetti 1 , F. Paiar 1 1 OSPEDALE SANTA CHIARA, Radiotherapy, PISA, Italy 2 OSPEDALE SANTA CHIARA, Oncology- Biostatistical Consulting, PISA, Italy 3 OSPEDALE SANTA CHIARA, Oncology, PISA, Italy 4 OSPEDALE CISANELLO, Colon-rectal Surgery, PISA, Italy Purpose or Objective Preoperative RTCT followed by total mesorectal excision (TME) is the standard of cure in patients (pts) with LARC. After neoadjuvant RTCT the rate of complete pathologic response (pCR) range between 15%-30% and many studies are trying to find predictive factors of response in order to select pts who could benefit from organ-preserving options (local excision or “wait and see approach”). This study aim to identify predictive factors of T and N response of neoadjuvant RTCT. Material and Methods We analyzed retrospectively the data of 119 pts affected by LARC (all of them cT3-T4 and 90,7% cN+) treated by neoadjuvant RTCT (50.4 Gy in 28 FF + capecitabine 1650 mg/mq/day) followed by TME surgery, between January 2008 and April 2014, in Pisa Universitary Hospital. Based on MR-images, we analyzed T characteristics (clinical stage, site respect to anal verge, cranio-caudal extension, number of involved quadrants, volume, distance from mesorectal fascia) and N characteristics (clinical stage, number of nodes with short axis ≥ 5mm and distance from mesorectal fascia), at diagnosis and at restaging (before surgery) and their variations, in order to find a correlation with pathological T and N stage. Results All pts completed planned RTCT. The overall pCR rate was 25,2%. In the multivariate analysis (T parameters) only the number of involved quadrants (p=0,002) and the cranio- caudal extension at diagnosis (p=0,043) resulted to be predictive of pCR. At the pathological findings, the rate of pN+ was 21% compared to 90,7% of the clinical stage. In the multivariate analysis (N parameters) only the number of nodes (short axis ≥ 5mm) at diagnosis was shown to be predictive of pN0, both as a continuous variable (p=0,004) that as dichotomous variable (p<0,0001) with a threshold value of 3 nodes. T and N variations, at pre-surgical restaging, were not significantly correlated to pathological outcomes. Conclusion To know predictive factors of pCR and pN0 after neoadjuvant RTCT could influence the surgical approach. T size and T distance from the anal verge seem to be two well established predictive factors of response . Based on our retrospective analysis, we can add that the number of involved quadrants and the number of nodes (≥5mm) at diagnosis could be additional predictive parameters. EP-1276 Clinic and radiobiology of hypofractionated radiotherapy for metastatic liver tumors. Pilot results.