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Conclusion The study shows that a practical qRT-PCR assay can be employed to identify molecular colorectal cancer subtypes and uncover subtype-specific preoperative chemoradiotherapeutic benefit for LARC. EP-1477 Effect of anti-hypertension therapy in colorectal carcinoma patients. M.A. González Ruiz 1 , J. Quirós Rivero 1 , J.L. Muñoz García 1 , M.C. Cruz Muñoz 1 , J.J. Cabrera Rodríguez 1 , P. Simón Silva 1 , Y. Ríos Kavadoy 1 , M.F. Ropero Carmona 1 , A. Corbacho Campos 1 , F. García Urra 1 1 Infanta Cristina Hospital, Radiation Oncology Department, Badajoz, Spain Purpose or Objective To analyze the influence of anti-hypertension treatment [angiotensin-converting enzyme inhibitors (ACEIs) and/or angiotensin receptor blockers (ARBs) in survival outcomes and local control (LC) in patients (pts) with colorectal carcinoma (CRC) treated with concomitant radiochemotherapy (RCT) plus surgery with radical intention in our hospital. Material and Methods Retrospective comparative study of 181 pts with CRC in treatment with ACEIs (41 pts, 22.7%) vs no-ACEIs (140 pts, 77.3%) and pts treated with ARBs (39 pts, 21.5%) vs no- ARBs (142 pts, 78,5%) from October 2001 to February 2015. Baseline characteristics were similar in the different groups. All pts were treated with 3DCRT (total dose: 50.4 Gy / 1.8 Gy daily). The median age of the pts was 65 years-old (range 26-85); 74.6% males and 25.4% females. Lower CRC and IIIb stage were the most frequent location (39.2%) and tumor stage (43.1%). Prognostic factors such as age, sex, tumor stage (TS), KPS, margin status (MS), use of ACEIs and ARBs were related to OS, CSS and LC using Cox regression. Results The median follow-up was 63 months (range 7-168). The 10-year OS, CSS and LC were 60%, 72.4% and 80% respectively. The 10-year OS, CSS and LC in ACEIs pts was 70.1% vs 56.8% in no-ACEIs pts (p=0.168); 90.7% in ACEIs pts vs 67.6% (p=0.045) and 93.9% in ACEIs pts vs 76.5% in no-ACEIs (p=0.094), respectively. The 10-year OS, CSS and LC in ARBs pts was 69.2% vs 56.5% in no-ARBs pts (p=0.693); 87.9% in ARBs pts vs 66.5% (p=0.142) and 93.7% in ARBs pts vs 74.6% in no-ARBs (p=0.123), respectively. In the multivariate analysis, age, KPS, TS and MS were significant prognostic factors for OS; age, KPS and MS for CSS and only MS was significant prognostic factors for LC. Conclusion According to our results, CRC pts in treatment with ACEIs have better results in terms of cancer specific survival (90.7%) than pts without ACEIs (67.6%) (p= 0.045). In the multivariate analysis, age, KPS, TS and MS were significant prognostic factors for OS, CSS and LC. EP-1478 Anal cancer VMAT: Lumbosacral plexus DVHs with standard & escalated doses proposed in the ACT5 study L. Samuel 1 , T. Al-Hajri 1 , E. Findlay 2 , L. Wells 1 1 Aberdeen Royal Infirmary, Department of Clinical Oncology, Aberdeen, United Kingdom 2 Aberdeen Royal Infirmary, Department of Radiotherapy Physics, Aberdeen, United Kingdom Purpose or Objective To determine the radiation dose received by the lumbosacral plexus (LSP) in a) standard volumetric

modulated arc radiotherapy (VMAT) and b) with dose escalation proposed by the PLATO study to treat patients with anal cancer with VMAT. Material and Methods A retrospective review of the dose to the LSP was performed in all patients with anal cancer who received VMAT between 2015 and 2016. The prescription dose was between 50.4 and 53.2 Gy in 28 daily fractions. For locally advanced disease, the LSP radiation doses were also calculated assuming the patients had been allocated to each of the two dose escalation arms within the ACT5 trial. Results Fourteen patients with anal cancer were identified. The clinical stage was between stages I to IIIB. The average LSP volume was 49.0 cm³ (30 - 74.8 cm³). From the retrospective data evaluation across all patients, the average maximum dose to the LSP was 45.1 Gy (40.9 - 54.9). The average V 40Gy , V 50Gy and V 55Gy were 22.6%, 1.7% and 0% respectively. Six patients were considered for dose escalation modelling. Arm 1 and Arm 2 would receive prescription doses of 58.8 and 61.6 Gy respectively as per the PLATO study. The average maximum dose to the LSP for Arm 1 was 51.6 Gy (42.6 - 61) and for V 40Gy , V 50Gy and V 55Gy were 31.7%, 5.9% and 2.7% respectively. For Arm 2, the average maximum dose to the LSP was 53.0 Gy (42.8 - 63.6) and for V 40Gy , V 50Gy and V 55Gy were 32.7%, 5.8% and 3.3% respectively. Conclusion Dose escalation has an impact on LSP doses in cases where the LSP overlaps with multiple target volumes. Therefore it may be useful to contour this structure in patients due to receive the higher radiation doses advocated in the ACT5 or similar studies. A protocol amendment is being considered by the TMG. EP-1479 Impact of tumor regression grade in ypStage III rectal cancer after preoperative chemoradiotherapy J.H. Chung 1 , C.H. Song 1 , S.B. Kang 2 , D.W. Kim 2 , J.H. Kim 3 , K.W. Lee 3 , J.S. Kim 1 1 Seoul National University Bundang Hospital, Department of Radiation Oncology, Seongnam-si-, Korea Republic of 2 Seoul National University Bundang Hospital, Department of Surgery, Seongnam-si-, Korea Republic of 3 Seoul National University Bundang Hospital, Department of Internal Medicine, Seongnam-si-, Korea Republic of Purpose or Objective Histologic responsiveness to preoperative chemoradio- therapy (CRT) is associated with favorable prognosis in locally advanced rectal cancer patients. This study is performed to evaluate the prognostic impact of the tumor regression grade in ypStage III rectal cancer patients treated with preoperative CRT. Material and Methods In this retrospective study, 271 patients with locally advanced rectal cancer received preoperative CRT at our institution from 2003 to 2014. ypStage III patients were classified based on the combination of ypStage and Dworak tumor regression grade (TRG): ypStage III patients with TRG 3 or 4 were classified as good-responders and ypStage III patients with TRG 1 or 2 were classified as poor-responders. Results Median follow-up time was 59.4 months. 5-year overall survival (OS) and 5-year disease free survival (DFS) were 85.3% and 78.6%, respectively. When ypStage III patients were divided into good-responders (TRG 3 or 4 ypStage III groups) and poor-responders (TRG 1 or 2 ypStage III