ESTRO 2020 Abstract Book

S296 ESTRO 2020

N+ rectal disease for curative-intent treatment received one of 4 neoadjuvant regimens consisting of short-course (5 x 5 Gy) or long-course radiotherapy (RT) (25 x 2 Gy) with or without concurrent or sequential chemotherapy (capecitabine, 5-fluorouracil, and/or oxaliplatin) followed by immediate surgery or delayed surgery.Whole post- neoadjuvant surgical specimens were assessed to analyze the global tumor pathologic regression grades, residual tumor distribution patterns, the extent of lymphovascular permeation, lymph node positivity, and the overall density of lymphocyte infiltration in the tumor microenvironment. These factors were further examined to identify possible correlations with clinical outcomes. Results Among the 4 neoadjuvant treatment groups, including 2 conventional regimens, we found a significant increase in the post-neoadjuvant stromal lymphodensities in the 3 groups with delayed surgery after different chemoradiation regimens compared to the group with immediate surgery after a short course of RT alone. Independent of neoadjuvant chemoradiation regimens, the postinduction high-intermediate-low stromal- infiltrating CD8+ T-cell densities corresponded to tumor regression grades, distant metastasis rates and disease- free survival and were prognostic factors for the further stratification of AJCC stage III rectal cancer patients into different risk groups after surgery.

Conclusion The effectiveness of induction strategies on tumor remission and disease recurrence in advanced rectal cancer was significantly correlated with an enhanced cytotoxic immune response in the tumor microenvironment. PD-0536 Bone-marrow sparing IMRT for anal cancer patients: a prospective phase II trial F. Arcadipane 1 , P. Silvetti 2 , C. Fiandra 3 , E. Gallio 4 , S. Martini 2 , F. Giglioli 4 , A. Sardo 4 , G.C. Iorio 2 , F. Olivero 2 , A. Gastino 2 , V. De Luca 2 , U. Ricardi 2 , P. Franco 2 1 AOU Citta' della Salute e della Scienza, Department of Oncology- Radiation Oncology, Torino, Italy ; 2 University of Turin, Department of Oncology- Radiation Oncology-, Turin, Italy ; 3 University of Turin, Department of Medical Physics- Radiation Oncology-, Turin, Italy ; 4 AOU Citta' della Salute e della Scienza, Department of Medical Physics- Radiation Oncology, Torino, Italy Purpose or Objective This study investigated how to decrease the acute hematologic toxicity (HT) profile in anal cancer patients treated with chemoradiation (CRT), employing a tailored Volumetric Modulated Arc Therapy approach in order to spare hematopoietic bone marrow (BM) identified with (18F)-FDG positron emission tomography (18FDG-PET) Material and Methods A one-armed two-stage Simon’s design was selected to test the hypothesis that BM sparing approach would improve by 20% the rate of G0–G1 (vs G2-G3) HT from 27% of RTOG 0529 historical data to 47% (α=0.05 and the β=0.20). At the first stage, among 21 enrolled patients, at least 9 should have been scored as G0– G1 acute toxicity to further proceed with the trial. At the second stage, another 18 patients will be accrued for an overall sample size of 39 patients. The study was conducted in patients eligible for concurrent CRT following Nigro protocol, dose and constraints of RTOG 0529 trial. We employed 18FDG-PET to identify active BM within pelvic structures (active PBM) detached in 3 subsites: active iliac bone marrow (IBM), active lumbosacral bone marrow (LSBM), active lower pelvis bone marrow (LPBM). Active BM was defined according to the segmentation identifying regions within the pelvis with higher SUV than the mean SUV for that bony region, for each patient. Dose constraints were: V10< 90% and V20<75% for active PBM, V40< 41% and mean dose <32 Gy for active LSBM. Acute HT events and non-hematologic toxicity were recorded. Results From December 2017 to October 2019, 27 patients met the eligibility criteria and were enrolled onto the protocol. In March 2019 we complete the first stage of the trial and we reached the target required by the design of the study and we continued the enrolment. Patients characteristics are