ESTRO 36 Abstract Book

S685 ESTRO 36 _______________________________________________________________________________________________

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. T. Latusek 1 , L. Miszczyk 1 , J. Rembak-Szynkiewicz 2 1 Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Radiotherapy, Gliwice, Poland 2 Maria Sklodowska-Curie Memorial Cancer Center and Institute of Oncology, Radiology, Gliwice, Poland Purpose or Objective Liver metastases are the most common tumor in this organ and majority of them are metastases of adenocarcinomas of the gastrointestnal tract. Radiotherapy is often used as alternative method to surgery. Due to promising results of the extracranial stereotactic radiotherapy used to treat primary metastatic tumors of the lung it is applied also for primary or metastatic liver lessions. The aim was to evaluate the efficacy of hypofractionated radiotherapy for Clinical material consists of 28 liver malignant liver lesions treated with stereotactic hypofractonated radiotherapy at the Cancer Center, MSC Memorial Institute in Gliwice. Tumor size and volume reflecting initial numer of cancer cells were estimated Patient’s age was in the range of 33- 84 years (median 64). All liver metastases were irradiated with a total dose of 45 Gy given in 3 fractions in 8 days. Method of respiratory gating and CyberKnife were used. Follow-up ranges from 1 to 12 months. Results Early 3-months results show 64% regression (14 cases), 4% stagnation (1 case) and 32% progression (7- cases). However, total dose of 45 Gy does not result in early complete regression. Even in case of „twin tumores” with the same initial volume (the same initial numer of cancer cells) suprisingly showed different response: regression vs progression what is difficult to interpret from the radiobiological point of view. Conclusion Total dose of 45 Gy should result in complete regression, but it doesn’t. From theoretical calculation it seem that D10 dose may arise even to 21 Gy what seems not very logical. It can not be excluded that reason for such early answer could be „Hallo Phenomenon”- inflamation around irradiated area suggesting false stagnation or even regression. EP-1277 Optimising RT dose for anal cancer – the development of three clinical trials in one platform D. Sebag-Montefiore 1 , R. Adams 2 , S. Bell 3 , L. Berkman 4 , D. Gilbert 5 , R. Glynne-Joones 6 , V. Goh 7 , W. Gregory 3 , M. Harrison 6 , L. Kachnic 8 , M. Lee 9 , L. McParland 3 , R. Muirhead 10 , B. O'Neil 11 , G. Hutchins 1 , S. Rao 12 , A. Renehan 13 , A. Smith 3 , G. Velikova 1 , M. Hawkins 14 1 Leeds Institute of Cancer and Pathology University of Leeds, Leeds Cancer Centre, Leeds, United Kingdom 2 Cardiff University and School of Medicine, Velindre Hospital, Cardiff, United Kingdom 3 Leeds Institute of Clinical Trials Research, Clinical Trials Research Unit, Leeds, United Kingdom 4 NCRI, Consumer Forum, London, United Kingdom metastatic liver tumors. Material and Methods