ESTRO 36 Abstract Book

S676 ESTRO 36 _______________________________________________________________________________________________

EP-1256 Local ablative radiotherapy for liver metastasis: factors affecting local control and survival C. Petersen 1 , T. Gauer 1 , T. Frenzel 1 , M. Todorovic 1 , A. Krüll 1 , M. Blaschczyk 1 1 University Medical Center Hamburg - Eppendorf UKE, Department of Radiation Oncology, Hamburg, Germany Purpose or Objective The liver is a common site of metastases from most common solid malignancies. Currently available systemic treatment regimens, result in transient to long-term disease control, raising the question of further local management. Secondary resection and thermo-ablation may contribute to long-term survival or allow at least a relevant chemotherapy-free interval. These approaches are often limited. With stereotactic body radiotherapy metastases can be treated with high efficiency in only a few sessions. Here we evaluate the feasibility of high-dose stereotactic body radiation therapy for liver metastases in patients not eligible for surgery focussing on colorectal cancer patients. Material and Methods Between July 2012 and December 2015, 33 patients with 56 liver metastases (range 1-4) were treated with SBRT. Primary tumor mostly consists of colorectal cancer (59%) and others (lung-, breast-, pancreatic cancer). Median time between diagnosis of liver metastases and SBRT was 11 months (range 0-57 months). To receive precise information about target localization, 3 gold fiducial markers were implanted in 30 out of 56 lesions (54%). To analyze respiratory tumor motion, 4D-CT scans were performed for all patients. Gross tumor volume contours of 10 breathing cycles were transferred to the average CT of the CD-CT data, forming the internal target volume (ITV). Planning target volume was obtained by adding a 4 mm margin. SBRT was delivered in VMAT technique using Varian TrueBeam linear accelerator. Most common fractionation schedule was 5 x 11 Gy (90% isodose covering the PTV). Results The median follow-up for all patients was 13 months. The overall local control rate for all 56 metastases was 86% with a total of 7 failures. In univariate analysis, the implantation of fiducial markers was predictive for local control (p=0.029). During follow up period, tumor progression developed in 28 cases (83%). In 13 cases new intrahepatic lesions occurred (47%), in 10 cases extra hepatic lesions (36%) and in 5 cases intra- and extra hepatic lesions (18%). Overall survival rate was 58%, median overall survival was 21 months. Univariate analysis showed statistical significance for OS concerning histology (colorectal vs. other) and gross tumor volume ( 20 ccm). Conclusion Liver SBRT is effective and yielded good local control. The SBRT procedure is a valid option for patients with oligometastatic disease and should be considered as an alternative to surgical treatment or other local ablative techniques.

Purpose or Objective Neoadjuvant chemoradiotherpy (CRT) has become standard in the treatment of rectal cancer patients with stage 3 disease. This approach has shown to reduce both local recurrence rates and increase the rate of sphincter preservation procedures. Up to 20% of patients 6 weeks post neoadjuvant CRT have a complete histological response (pCR). PCR has shown to correlate with better and sustained oncological outcomes. The feasibility of the emerging watch and wait management strategy for patients with pCR will depend on the reliability of restaging assessments post CRT. We looked the accuracy of pre-operative MRI in predicting the rectal cancer tumour stage, node status and complete clinical response in patients who have undergone neoadjuvant chemoradiotherapy using histopathologic analysis as the reference standard. Material and Methods We retrospectively identified all patients who underwent neoadjuvant CRT (50.4 Gy, 1.8 Gy/fraction, in 5.5 weeks, with continuous infusional fluorouracil 225 mg/m2daily) for rectal cancer and proceeded to standard TME at our institution over a 16 month period. Their initial cTNM staging was collected as was their restaging ycTNM post CRT (based on diffusion weighted MRI pelvis). The sensitivity and specificity of the latter at predicting tumour, nodal and complete clinical response compared to surgical histology was analysed. Results 43 patients underwent CRT and subsequent TME over the time period at our institution. Overall histopathological response rate was 93% with a pCR rate of 14%. MRI had a sensitivity of 58% and specificity of 94% at assessing compete clinical response, 95 CI 40-93%, 80-99% respectively. At predicting tumour response MRI had sensitivity of 53% and specificity of 85%, 95 CI 45-80%, 74- 94% respectively. Accuracy of predicting nodal response were lower with a sensitivity of 43% and specificity of 40% , 95 CI 30-88%,32-58% respectively. The average modal time interval between CRT and MRI was 5 weeks while the average modal time between CRT and surgery was 8 weeks Conclusion Our study suggests that MRI alone may not be accurate enough in assessing clinical stage post neoadjuvant CRT, and particularly the clinical node status. Imaging alone will likely be needed to be combined with clinical, biochemical and endoscopic assessments in order to improve reliability of post treatment rectal staging. EP-1258 High precision SIB-IMRT versus conventional radiotherapy in anal cancer: a propensity score analysis F. Arcadipane 1 , A. Lepinoy 2 , P. Franco 1 , M. Ceccarelli 3 , B. De Bari 2 , L. Lestrade 2 , G. Furfaro 1 , M. Mistrangelo 4 , G. Créhange 5 , U. Ricardi 1 1 Radiation Oncology, Oncology, Turin, Italy 2 Radiation Oncology, Radiation Oncology, Besançon, France 3 Cancer Epidemiology and CPO Piemonte, Epidemiology, Turin, Italy 4 Surgery, Surgical Sciences, Turin, Italy 5 Radiation Oncology, Radiation Oncology, Dijon, France Purpose or Objective To evaluate clinical outcomes of a simultaneous integrated boost- intensity modulated radiotherapy (SIB- IMRT) approach in patients with non-metastatic anal cancer compared to those of a set of patients treated with 3-dimensional conformal radiation and sequential boost (CRT). Material and Methods A retrospective cohort of 190 anal cancer patients consecutively treated between March 2007 and October

Electronic Poster: Clinical track: Lower GI (colon, rectum, anus)

EP-1257 A look at pre-operative MRI accuracy at predicting rectal cancer staging post chemoradiotherapy K. Nugent 1 , R. McDermott 1 , M. Higgins 1 , B. O'Neill 1 1 St Lukes Radiation Network, Radiation Oncology, Dublin, Ireland