ESTRO 38 Abstract book

S193 ESTRO 38

Purpose or Objective Definitive radiotherapy combined with chemotherapy (CRT) is the standard treatment for patients with loco- regional squamous-cell carcinoma of the anal canal. There are different contouring guidelines for anal caner, which still vary concerning recommendations for radiation margins in different anatomical regions, especially on inguinal site. PET-imaging has become more important in primary staging of anal cancer, as it is a very sensitive method to detect lymph node (LN) metastases. Using PET- imaging, we evaluated patterns of LN spread, and examined the differences of the respective contouring guidelines on the basis of our results. Material and Methods We carried out a retrospective study of 37 anal cancer patients treated with RCHT who underwent FDG-PET imaging for primary staging in our department between 2011 and 2018. Patients showing PET-positive LNs were included in this analysis. LN metastases of all patients were delineated in one patient’s dataset. Using a color- code, LNs were divided indicating whether its location was in- or out-field of the standard clinical target volume as recommended by Radiation Therapy Oncology Group (RTOG), Australasian Gastrointestinal Trials Group (AGITG) or British National Guidance (BNG). Furthermore, a detailed analysis of the location of LNs of the inguinal region was performed. Results Twenty-two out of 37 AC patients with pre-treatment PET- imaging had PET-positive LN metastases, accumulating to a total of 154 LNs. The most commonly affected anatomical region was inguinal (49 LNs, 32%). All para- rectal, external & internal iliac and pre-sacral LNs were covered by the recommended CTVs of the three different guidelines. Twenty-six out of the 154 positive LNs (17%) were above all three CTVs (13 para-iliac, 13 para-aortic). Of 49 involved inguinal LNs, 14 (29%), 7 (14%) and 5 (10%) inguinal LNs were outside the recommended CTVs by RTOG, AGITG and BNG. Inguinal LNs could be located up to 5.7cm inferiorly to the femoral saphenous junction and 2.8cm medial or laterally to the big femoral vessels.

Conclusion Following neoadjuvant chemoradiotherapy for LARC, women had higher risk of developing lung metastasis, while men were more prone to develop liver metastasis. In a cohort consisting of rectal cancer patients that either proceeded directly to surgery or to standard neoadjuvant chemoradiotherapy, men’s tumors had lower blood perfusion and wider IMV diameter. The latter was strongly associated with development of liver metastasis. Even though the LARC patients received study cohort-specific neoadjuvant treatments, the results indicate that women and men with rectal cancer have different outcomes of tumor-directed therapies, which may be related to hemodynamic factors in both the tumor and the pelvic cavity. OC-0386 A PET-based patterns of failure analysis in the context of contouring guidelines in anal cancer H. Dapper 1 , K. Schiller 1 , S. Münch 1 , J. Peeken 1 , K. Borm 1 , W. Weber 2 , S.E. Combs 1,3,4 1 Klinikum rechts der Isar- TU München, Department of Radiation Oncology, München, Germany ; 2 Klinikum rechts der Isar- TU München, Department of Nuclear Medicine, München, Germany; 3 Deutsches Konsortium für Translationale Krebsforschung DKTK, Partner Site Munich, München, Germany; 4 Helmholtz Zentrum München, Institute for innovative Radiotherapie iRT, München, Germany