ESTRO 2021 Abstract Book

S1042

ESTRO 2021

Royal Marsden Hospital, Fulham Road, Department of Oncology, London, United Kingdom; 3 University of Oxford, Centre for Statistics in Medicine, Oxford, United Kingdom; 4 Mount Vernon Hospital, Mount Vernon for Cancer Treatment, Northwood, United Kingdom; 5 University of Leeds, Department of Colorectal Surgery, Leeds, United Kingdom; 6 University of Glasgow, Institute of Cancer Sciences, Glasgow, United Kingdom; 7 St Mark’s Hospital, Department of Colorectal Surgery, London, United Kingdom; 8 Bowel Cancer UK, Patient Representative, London, United Kingdom Purpose or Objective A diagnosis of locally recurrent rectal cancer (LRRC) is associated with considerable morbidity and a poor prognosis. While surgical series demonstrate a median survival of 37 months; the median survival of non- operative management is approximately 10 months. The use of re-irradiation stereotactic ablative body radiotherapy (SABR), offers an alternative to extensive surgery. However designing trials in this setting is challenging due to the limited available data. We performed a multicentre, retrospective case series of patients treated with SABR reirradiation, with a view to identifying appropriate outcome measures in clinical trials. Materials and Methods All patients in three centres treated with 30Gy in 5 fractions reirradiation were identified through local radiotherapy systems. Patients were treated with 30Gy in 5 fractions prescribed to D95. Both gantry based linear accelerators and Cyberknife were acceptable platforms for treatment delivery. Follow up consisted of review with CT scans at 3, 6, 12, 18 and 24 months. Radiotherapy systems provided details of treated lesions, appropriate local hospitals and general practitioners were contacted for information regarding site of relapse, date of relapse, details on last follow up and death. Statistical analysis was carried out using R version 3.6.1 (R Core Team (2019). R: A language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. URL https://www.R-project.org/) Results 70 patients received reirradiation SABR for rectal cancer between the 3rd August 2015 and 2nd September 2020. 8 patients were excluded, 7 received SABR for an R1 resection, 1 patient had lung metastasis at outset; 62 patients remained with 73 lesions. Using the reverse Kaplan-Meier method, median FU was 31 months. Median age was 65 years (range 36 to 86). Male to female ratio 60/40. 59 patients had lymph node recurrences, 1 bony recurrence, 1 penile and 1 perianastomotic recurrence. Median GTV volume of the largest lesion in each patient was 13.4cm3 (1 to 122cm3). Other than survival data, results are based on 61 patients as one patient moved out of area and only date of death is available. Median (95% CI) PFS was 12.1months (10.4, 16.6) with 2 year PFS rate of 0.23 (0.14, 0.40). 42 of 61 (69%) had progressed, initial sites of progression were local, distant and both local and distant in 18, 11 and 12 patients. 23 (37%) had died, 14 (64% of deaths) with consequences of uncontrolled pelvic disease contributing to death; for example tumour related fistulas, irretractable pain, hydronephrosis and issues associated with stents, bowel obstruction and recurrent PR bleeds. 28 of 61 (48%) had a local recurrence at the time of death or last follow up. Of 39 patients alive at FU, 14 (36%) were living with a local relapse. Median OS was 38.7months (28.8 -), 2 year OS rate 0.76 (0.64, 0.90). Conclusion Historic median OS in non-operative management of LRRC is approximately 10 months. The high rate of eventual local recurrence, percentage of deaths due to consequences of local disease and the encouraging median OS of 38.7 months in our series; suggests dose escalation using a SABR technique may be beneficial and OS may be an appropriate primary endpoint for a trial. Given the high percentage of patients living with a local recurrence at last follow up, with all the associated morbidity, quality of life must form a major part of future trials. PO-1263 Exclusive radiotherapy in early stage anal cancer - outcomes, patterns and predictors of relapse A. Briens 1 , C. Neuzillet 2 , F. Huguet 3 , E. Rivin Del Campo 3 , V. Guimas 4 , E. Fallet 5 , S. Garcia Molina 6 , E. François 7 , L. Montagne 8 , U. Schick 9 , P. Lesueur 10 , L. Siphroudis 11 , J. Edeline 12 , J. Castelli 1 , R. de Crevoisier 1 , A. Lièvre 11 , K. Gnep 1 1 Centre Eugène Marquis, Radiation Oncology, Rennes, France; 2 Institut Curie, Medical Oncology, Saint-Cloud, France; 3 Tenon Hospital, Radiation Oncology, Paris, France; 4 Institut de Cancérologie de l'Ouest, Radiation Oncology, Nantes, France; 5 Quimper Hospital, Gastroenterology, Quimper, France; 6 Poitiers University Hospital Center, Radiotherapy, Poitiers, France; 7 Centre Antoine Lacassagne, Medical Oncology, Nice, France; 8 Centre Antoine Lacassagne, Radiotherapy, Nice, France; 9 Brest University Hospital Center, Radiation Oncology, Brest, France; 10 Centre François Baclesse, Radiation Oncology, Caen, France; 11 Rennes University Hospital Center, Gastroenterology, Rennes, France; 12 Centre Eugène Marquis, Medical Oncology, Rennes, France Purpose or Objective While chemoradiotherapy (CRT) is well-validated in advanced anal cancers, the management of early-stage tumors remains debated and exclusive radiotherapy (RT) is a therapeutic option. Our objectives were to report clinical outcomes and to analyze patterns of failures and predictors of relapses in a cohort of early- stage anal cancers treated with exclusive RT. Materials and Methods We included patients treated with exclusive RT in a curative intent for T1 or small T2 (≤ 3cm), node negative (N0), non metastatic squamous cell carcinoma of the anus (SCCA) between 1999 and 2015 in 8 French centers. Univariate and multivariate analyses were performed to identify factors related to patients, tumors or treatments, impacting locoregional control (LRC), disease free survival (DFS) and cancer specific survival (CSS) using Cox proportional Hazard Regression to estimate Hazard Ratios (HR). LRC, DFS and CSS between groups were estimated using the Kaplan-Meier method. Results We identified 141 consecutive patients treated with exclusive RT for T1 or small T2 (≤ 3cm), N0, SCCA. After a