ESTRO 37 Abstract book

ESTRO 37

S408

7 Guy's and St Thomas' Hospital NHS Trust, Department of Upper GI Surgery, London, United Kingdom Purpose or Objective Neoadjuvant chemotherapy (CT) and chemoradiotherapy (CRT) have a survival benefit over surgery alone in oesophageal cancer. However, the rates of pathological complete response (pCR) are relatively low, ranging between 15-25% in clinical trials. Currently there is no established means of predicting, which patients will achieve a good pathological outcome following induction treatment. The aim of this study was to determine whether magnetic resonance imaging (MRI) biomarkers either at baseline or following neoadjuvant CT/CRT can predict pathological response. Material and Methods Following IRB approval and informed consent, 25 prospective patients (median age 67 years (range 41-78), 20 male) with newly diagnosed oesophageal carcinoma (21 adenocarcinomas, 4 squamous cell carcinomas) underwent a 1.5T MRI before and after neoadjuvant CT/CRT, which included T2-weighted, dynamic contrast enhanced (DCE) T1-weighted and a diffusion weighted (DWI) sequence (b values: 50-900 s/mm). Tumour was outlined an all sequences generating corresponding 3D volumes of interest (VOI) from which the following values were derived: T2w voxel signal intensity histogram features (mean, skewness, kurtosis and entropy); DCE transfer constant (K trans ), DCE extravascular-extracellular space (V e ); DWI apparent diffusion coefficient (ADC). Primary outcome was good pathological response: pathCR or near-pathCR (Mandard tumor regression grade [TRG] 1 or 2). Predictive value was assessed using a linear regression model with Huber-M-estimation (to reduce the sensitivity to outliers given relatively small sample size), p values were adjusted for multiple comparison using Benjamin Hochberg correction (FDR<5%). Results 22 patients received induction CT, 3 patients received CRT. 6 patients (26%) had a good pathological response. Simple linear regression incorporating all 7 imaging variables at 2 timepoints (14 factors) identified post CT/CRT T2w entropy and kurtosis to be significantly associated with continuous Mandard TRG (FDR p-value 0.03, R 2 0.39 and FDR p value 0.03, R 2 0.25, respectively). Analysis of variance on dichotomized pathological outcome, confirmed good pathological Response (Mandard TRG 1-2) to be significantly associated with higher post CT/CRT T2 entropy and lower post CT/CRT T2 kurtosis (FDR p-value 0.006 and 0.02, respectively). In addition, good pathological response was significantly associated with an increase in T2w entropy post CT/CRT (median 11.2% versus 3.3%, p=0.02). Conclusion Higher post-treatment T2w intra-tumoural entropy (marker of lesional heterogeneity) and a greater increase in T2w entropy following CT/ CRT were associated with good pathologic response in our study. Greater heterogeneity may reflect cancer cell regression, development of fibrosis and influx of immune cells.

2 Centre Bayard Lyon-Villeurbanne, Radiothérapie, Lyon- Villeurbanne, France 3 Centre Antoine Lacassagne, Radiophysique, Nice, France 4 Centre Antoine Lacassagne, Clinical Research Department, Nice, France Purpose or Objective Following the randomized trial Lyon R96.02 (1) CXB is validated as a safe and efficient treatment for rectal cancer. Combining CRT (50 Gy+ capecitabine) and CXB boost with Papillon 50 Tm provides a high probability of organ preservation. We report the experience of three French institutions using this strategy. Material and Methods Selection was based on digital rectal examination, colonoscopy, MRI (and/or Endorectal-ultrasound, 18FDG Pet-CT). Inclusion was: adenocarcinoma (distal, middle rectum), T2 T3a-b, tumor diameter ≤ 4cm, N0, M0. Treatment used CXB (80-110 Gy/3-4 fr) followed by CRT (CAP 50). Tumor response was assessed 8 to 10 weeks after start of treatment using DRE, rigid rectoscopy and MRI. A clinical complete response (cCR) was defined as no visible tumor, supple rectal wall and TRG 1-2 on MRI. In case of cCR or near cCR a close surveillance or local excision was proposed. Results Between 2002 -2016, 84 patients were treated (2). Median age: 75 years, Male: 59, Female: 25. Operable patients: 69 (83%). Median follow-up time : 53 months. cCR was achieved in 91% of cases. Local excision was performed in 16 patients (ypT0/pT1: 14). At 4 years, the cancer specific survival was 82% [CI:96-70] and the local relapse rate 12% [CI: 2-22]. No isolated perirectal lymph node relapse was observed. After 4 years, 3 more local relapses were observed after 4, 6 and 7 years. Acute grade 3 toxicity was seen in 9 patients mainly related to CRT. Main late toxicity (> 6 months after treatment) was rectal bleeding (radiation telangiectasia) which required plasma argon coagulation in 5 patients. No TME surgery was performed and organ preservation was achieved in all cases. Bowel function was good in 85% of patients. Conclusion After adequate selection and treatment, rectal cancer T2T3a-b N0 ≤4cm can achieved a high rate of cCR (≥85%) with organ preservation with good bowel function and a low rate of local relapse (< 15%) with low toxicity. Prolonged follow-up is mandatory. As rectal adenocarcinoma is radioresistant tumor, the treatment must combine CRT and CXB boost. Like anal squamous cell carcinoma, planned organ preservation can be proposed to operable patients. The ongoing European OPERA trial aims at bringing evidence to this option. Reference 1. Gérard JP et al. Improved sphincter preservation Lyon R96 trial. J Clin Oncol 2004;22:2404-9. PO-0790 Texture features to assess response to neoadjuvant therapy in locally advanced rectal cancer S. Mazzetti 1 , A. Di Dia 2 , V. Giannini 1 , C. Bracco 2 , S. Cauda 3 , E. Delmastro 4 , P. Gabriele 4 , M. Stasi 2 , T. Varetto 3 , D. Regge 1 1 Candiolo Cancer Institute -IRCCS, Imaging Unit, Candiolo, Italy 2 Candiolo Cancer Institute -IRCCS, Medical Physics Unit, Candiolo, Italy 3 Candiolo Cancer Institute -IRCCS, Nuclear Medicine Unit, Candiolo, Italy 4 Candiolo Cancer Institute -IRCCS, Radiotherapy Unit, Candiolo, Italy 2. Frin AC et al. Organ or sphincter preservation for rectal cancer. The role of contact X-ray. Eur J Cancer. 2017 Feb;72:124-136.

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

PO-0789 Contact X Ray (CXB) boost for planned organ preservation in T2 T3 rectal cancer. French Experience. J.P. Gérard 1 , N. Barbet 2 , C. Dejean 3 , K. Benezery 1 , R. Coquard 2 , Y. Chateau 4 , J. Gal 4 , J. Doyen 1 1 Centre Antoine Lacassagne, Radiotherapie, Nice, France