ESTRO 2020 Abstract book

S320 ESTRO 2020

(HR=0.52[0.37, 0.73]), younger age (Table) and 15 more lymph nodes examine compared to those with fewer than 15 lymph nodes (HR=0.82[0.74-0.90]). Moreover, a total radiation dose of 45-50.4 Gy (HR=0.79[0.70-0.89]) was superior to doses of 44-45 Gy, but further escalation in dose above 50.4 Gy was not significantly better. Tumor characteristics found to be associated with worse OS were grade 3 (HR=1.71[1.41-2.08]), T4 tumor stage (HR=1.87[1.42-2.45]), N2 nodal stage (HR=1.88[1.29- 2.75]), N3 nodal stages (HR=1.20[1.02-1.41]), presence of LVSI (HR=1.59[1.42, 1.79]), number of positive lymph nodes (p<0.0001), number of days between diagnosis and start of treatment (p<0.0001). Conclusion We found that OS is better in patients who are female, treated at an academic institution, come from higher- income families, had 15 or more lymph nodes examined, treated with radiation of 45-50.4 Gy and multi-agent chemotherapy. OS is worse with increasing age at diagnosis, increasing CDCC score, grade 3, T4 tumor stage, N2/N3 nodal stage, presence of LVSI, larger number of positive lymph nodes, increasing number of days between diagnosis and start of treatment.

PD-0538 Rectal cancer: world-wide use of radiotherapy and the importance of more strict lymph node staging K. Hammarström 1 , B. Glimelius 2 , T. Sjöblom 2 , A. Mezheyeuski 3 , N. Korsavidou Hult 4 , I. Imam 2 , J. Ekström 2 1 Uppsala University, Dept. of Immunology- Genetics and Pathology, Solna, Sweden ; 2 Uppsala University, Dept. of Immunology- Genetics and Pathology, Uppsala, Sweden ; 3 Uppsala Uiversity, Dept. of Immunology- Genetics and Pathology, Uppsala, Sweden ; 4 Uppsala University, Dept. of Surgical Sciences- Radiology, Stockholm, Sweden Purpose or Objective Pre-operative radiotherapy (RT) or chemoradiotherapy (CRT) is frequently used prior to rectal cancer surgery to enable radical surgery of a non-resectable tumour and to improve local control (LR) and survival. There is no international consensus regarding which tumour and nodal stages that belong to the different risk groups (early, intermediate or locally advanced) and what therapy is recommended. Although the use is administered according to guidelines, the use varies considerably around the world because the recommendations vary significantly. Using an unselected population-based Swedish cohort of rectal cancer patients, it was possible to estimate the proportions of non-metastatic patients recommended to RT/CRT according to different guidelines in the world to better understand the wide variability between countries. Presence of lymph node metastases is important for the treatment decision in most guidelines. We investigated how the proportions of patients with (N+) and without (N0) lymph node metastases have changed during the study period 2010-2016 and if this influenced the number of patients recommended to radiotherapy. Material and Methods Selected guidelines from different countries and regions were applied to a population-based material of 686 primary non-metastatic rectal cancers completely staged by MRI. The fraction of patients assigned to surgery alone or surgery following pre-treatment with (C)RT was determined according to the respective guideline. RT/CRT administered to rectal cancer patients for other reasons, for example, for organ preservation or palliation, was not considered. The proportion of N0 vs N+ per year during the study period was investigated and the study cohort was divided into two groups (2010-2013 and 2014-2016) to see whether the stricter diagnostic criteria of lymph node metastases have effects on the number of irradiated patients. Results The fraction of patients with a clear recommendation for pre-treatment with (C)RT varied between 38% and 77% according to the different guidelines. If treatment was to be given only to non-resectable tumours, 9% would be recommended CRT. The proportion of patients with lymph node metastases increased until 2013 but has since then decreased due to stricter diagnostic criteria. As a result, fewer patients are recommended to radiotherapy in all guidelines but two. Conclusion Differences in the guideline recommendations illustrate the uncertainty of what an appropriate use of radiotherapy is. The different recommendations may have impact on LR rates, but likely not on survival. Finding clinical markers of tumour remission are important for a personalised treatment approach and a more appropriate use of radiation therapy.