ESTRO 2020 Abstract Book

S582 ESTRO 2020

PO-1101 Intensity-modulated radiotherapy treatment of anal cancer: single-institution outcomes E. Scott 1 , A. Kar 1 , H. Ariyaratne 1 1 Royal Free London NHS Foundation Trust, Clinical Oncology, London, United Kingdom Purpose or Objective To evaluate local control and survival in patients with localised anal cancer treated with intensity-modulated radiotherapy (IMRT) and concurrent chemotherapy. Material and Methods We retrospectively reviewed clinical records of patients treated with radiotherapy for anal cancer between April 2014 and September 2019 in a tertiary referral centre in the United Kingdom. All patients had biopsy-confirmed squamous cell carcinoma staged according to TNM 7. IMRT was planned on Pinnacle® TPS and delivered on a Varian® linac platform. Patients received concurrent chemotherapy unless contraindicated. Results 83 patients had radiotherapy for anal cancer, with 76 included in the analysis. Patients excluded had non-IMRT or palliative treatment. 66% of patients were female. Median age was 62 years (range 28-90 years). The percentages of patients with T1, T2, T3 and T4 disease were 21%, 30%, 29% and 19% respectively. The percentages of patients with N0, N1, N2 and N3 disease were 44%, 22%, 16% and 17% respectively. Most patients had moderately differentiated histological grade (64%). Seven patients had basaloid subtype. The radiotherapy treatment schedule was 50.4 Gy in 28 fractions to involved regions. 40 patients (53%) with higher stage disease had simultaneous integrated boost to primary to 53.2 Gy in 28 fractions. 4% of patients received 41.4 Gy in 23 fractions as part of the PLATO clinical trial for low-risk disease. 13% of patients had a defunctioning stoma prior to radiotherapy. 80% of patients received concurrent mitomycin C and capecitabine. Capecitabine alone (3%) or mitomycin C/5-FU (1%) were used infrequently. 16% of patients did not have chemotherapy. 8% started on a reduced dose of chemotherapy due to co-morbidities, and 11% had reduced dose intensity during treatment. Reasons for chemotherapy interruption included thrombocytopaenia, renal impairment and skin toxicity. There was no Grade 4 toxicity. Median follow-up was 16 months (range 1-61 months). Nine patients (12%) had local recurrence. Seven of these patients had T3/4 disease or nodal involvement. Three did not receive chemotherapy during treatment. Five patients with local recurrence were successfully treated with salvage surgery, while the others declined or were not fit for surgery. The rate of metastatic progression was 13%, and all these patients had T3/4 disease or nodal involvement at presentation. For the whole cohort, 12- month overall survival was 88% and 24-month overall survival was 84%. Conclusion IMRT with concurrent chemotherapy was well tolerated and resulted in very good local control and overall survival, despite a high proportion of stage III disease in this cohort. Local and distant recurrences were associated with advanced stage at presentation. PO-1102 Dose-volume analysis and sphincter-related toxicity of radiation therapy for rectal cancer N. Jullian 1 , F. Charlier 1 , D. Van Gestel 1 , F. Otte 1 , L. Moretti 1 1 Institut Jules Bordet, Radiotherapy, Bruxelles, Belgium Purpose or Objective The purpose of this study was to evaluate the dose delivered to the anorectal sphincter and to evaluate its impact on sphincter toxicity/fecal incontinence after

preoperative chemoradiation for locally advanced rectal cancer. Material and Methods We reviewed 36 patients with a locally advanced rectal adenocarcinoma treated between 2013 and 2015 with preoperative chemoradiation (45-50Gy+5FU) followed by sphincter-sparing surgery. Four different structures were delineated on the dosimetry/simulation CT-scan: the levator ani muscle (LAM), the pubo-rectal muscle (PRM), the external anal sphincter muscle (EAS), and the internal anal sphincter muscle (IAS). The correlation between the dose delivered to these sphincter structures and the significance of fecal incontinence was evaluated using the CTCAE v5.0 incontinence grade score and the Low Anterior Resection Syndrome Score (LARS Score) Results The median age at the time of the study was 67 year (IQ 25-75: 64-74), the majority were men (64%), and the most represented cTNM was T3N1 (56%). All patients received preoperative chemoradiation with at least 45Gy delivered to the CTV, most (72%) benefited from an integrated boost (50Gy) to the GTV. Mean doses (Dmean) (IQ 25 – 75) were 45Gy (44.2 – 46.7) for the PRM, 48.4Gy for the LAM (46.5 – 48.8), 45.1Gy (42 – 47.7) for the EAS, and 45.6Gy (44.1 - 47.5) for the IAS. There was a linear correlation between the dose delivered to the IAS and the distance from the IAS to the inferior part of the tumor. The majority of patients (64%) had some degree of fecal incontinence (CTCAE) with 30% of patients having grade I incontinence, 28% grade II, and 6% grade III. Thirty-six percent of patients had a major LARS, 17% a minor LARS, and 47% had no LARS. The Spearman correlations performed to evaluate the relationship between the LARS Score and the different dosimetric parameters (Dmean, D0.01cc) of each muscle were inconclusive graphically (r <0.4). However, the p value was significant (p<0.05) for EAS and IAS Dmean and for LAM D0.01cc. Conclusion No anal sphincter dose-volume relationship was found for the development of LARS, although limitations in sample size may have prevented a statistically significant clinical correlation. Nevertheless, this study proved particularly informative in terms of dose received by the different muscles. PO-1103 The Energy Metabolism Changes In Rectal Cancer Patients After Neoadjuvant Radiochemotherapy J. Acosta 1 , E. Rodríguez 1,2 , A. Moreno 2 , J. Gomez 1 , L. Torres 1 , Y. López 1 , J. Trilla 1 , G. Baiges 2 , A. Hernández 2 , J. Joven 2 , J. Camps 2 , M. Arenas 1,2 1 Hospital Universitari Sant Joan de Reus, Department of Radiation Oncology, Reus, Spain ; 2 Institut d’Investigació Sanitària Pere Virgili- Universitat Rovira i Virgili, Unitat de Recerca Biomèdica, Reus, Spain Purpose or Objective The aim of this study was to investigate changes in energy metabolism associated with neoadjuvant radiochemotherapy (NRCT) in patients with locally advanced rectal cancer (RC). Material and Methods Thirty-two patients (men, n= 22; women, n= 10) with locally advanced RC had been included in the study between 2014 and 2018. Blood samples were collected before and one month after NRCT. A Gas Chromatography/Mass Spectrometry sequence was used to determine plasma concentration of energy balance- associated metabolites. Metabolites involved in the glycolysis, citric acid cycle and amino acid metabolism were analysed. All statistical calculations and graph representations were performed with the statistical