ESTRO 2022 - Abstract Book

S450

Abstract book

ESTRO 2022

Survival outcomes after definitive chemoradiation were comparable between HIV negative and HIV positive patients, but PLWH had higher rates of G3+ neutropenia and thrombocytopenia. Dynamics of hematologic toxicity showed significant association with the irradiated volume of ABM with stronger and continuous correlation of TTN in lymphocyte count in PLWH. Platelet dynamics suggest volume thresholds affecting TTR in both groups. Strategies to improve functional bone marrow sparing including dose de-escalation in low-risk disease are ongoing.

PD-0501 Patterns of failure in anal cancer after IMRT and chemotherapy: Impact of 1 vs 2 doses of Mitomycin.

Z. Al Habsi 1 , K. Joseph 2 , A. Abraham 3 , M. Al Balushi 3 , G. Tankel 4 , K. Mulder 5 , H. Warkentin 6 , D. Schiller 7 , K. Tankel 8 , N. Usmani 8 , D. Severin 3 , K. Paulson 3 , H. Karachiwala 9 , C. Wong 10 , T. Nijjar 3 , C. Doll 11 1 Cross Cancer Institute , Radiation Oncology, Edmonton, Canada; 2 Cross Cancer Institute, Radiation Oncology, Edmonton , Canada; 3 Cross Cancer Institute, Radiation Oncology, Edmonton, Canada; 4 University of Alberta, Research, Edmonton, Canada; 5 Cross Cancer Institute, Medical Oncology, Edmonton, Canada; 6 Cross Cancer Institute, Medical Physics, Edmonton, Canada; 7 Royal Alexandra Hospital, General Surgery, Edmonton, Canada; 8 Cross Cancer Institute, Radiation Oncology , Edmonton, Canada; 9 Cross Cancer Institute, Medical Oncology , Edmonton, Canada; 10 Royal Alexandra Hospital, Gastroenterology, Edmonton, Canada; 11 TOM BAKER CANCER CENTRE, Radiation Oncology, Calgary, Canada Purpose or Objective Concurrent chemoradiation (CRT) with 2 doses of 5-fluorouracil (5-FU) and mitomycin C (MMC) is the standard of care for anal canal cancer (ACC) in North America, while 1 dose of MMC has been standard in Europe. Given the lack of randomized data of 1 vs. 2 doses of MMC on disease outcomes, we have conducted a population-based study to elucidate the impact of 1 vs. 2 doses of MMC on patterns of treatment failure (POF) and outcomes in ACC treatment. Materials and Methods Data was collected from the provincial cancer registry of patients with stage I-III ACC who were treated with concurrent CRT from 2000 to 2018. Primary outcome measures were patterns of failure, recurrence free survival (RFS) and overall survival (OS). Results 428 patients with a median age of 58 years (29-88 years) were included in this analysis. 234 (54.7%) patients received 1 dose of MMC and 194 (45.3%) received 2 doses of MMC. At a median follow-up of 78.5 months (5-252 months), 89 (20.8%) patients developed disease recurrence: 44 (10.3%) loco-regionally, 39 (9.1%) distally and 6 (1.4%) had both local and distant recurrences. Cox regression analysis showed that the dosage of MMC did not have an impact on overall recurrence (HR=0.883, p=0.561), with the exception of patients with stage III disease who had a significantly higher risk of recurrence (HR=5.238, p=0.021). Subgroup analysis showed an association between stage IIIB and IIIC with recurrence (HR=13.33, p=0.008 and HR=6.933, p=0.011 respectively), but was not impacted by the use of 1 vs. 2 doses of MMC. The dosage of MMC was not associated with incidence of local recurrence (HR=1.136, p=0.655) or distant recurrence (HR=0.743, p=0.267). However, in Stage IIIC patients, 2 doses of MMC showed a trend towards improved distant RFS (HR=0.626, p=0.084). The median RFS and OS were not reached for either groups. The mean RFS was 192.2 and 200.6 months for 2 MMC and 1 MMC respectively (p=0.864). The mean OS was 171.8 and 182.4 months for 2 MMC and 1 MMC respectively (p=0.758). Conclusion Our analysis showed that the patterns of failure and the risk of loco-regional and distant failures were similar between ACC patients who received 1 vs. 2 doses of MMC for stage groups I to IIIC disease. These finding support routine use of single dose of MMC with 5FU and radiotherapy for definitive CRT. However, a trend towards better RFS was demonstrated with a second dose of MMC in patients with stage IIIC disease. 1 GenesisCare UK, Centre for Radiotherapy at Cromwell Hospital, London, United Kingdom; 2 GenesisCare UK, Centre for Radiotherapy at University Oxford Hospital, Oxford, United Kingdom Purpose or Objective Stereotactic MR guided online adaptive radiotherapy (SMART) offers significant dosimetric advantages in the treatment of abdominal and pelvic malignancies due to complex surrounding anatomy and mobile organs at risk 1,2 Here, we report patient tolerability, acute toxicity and dosimetric outcomes of SMART in a cohort of patients with abdominal and pelvic lymph node metastases. Materials and Methods Patients who underwent SMART between 01.01.2020 and 31.09.2021 were retrospectively included. Acute toxicity was prospectively assessed using Common Terminology Criteria for Adverse Events (CTCAE) v4.0. Dose-volume histograms (DVHs) for target volumes and OARs were obtained for every treatment course at the following time points: 1. Baseline: simulation plan applied to anatomy at simulation 2. Pre-adaptation: simulation plan applied to the anatomy of the day prior to each treatment fraction 3. Post-adaptation: re-optimized plan applied to the anatomy of the day prior to each treatment fraction PD-0502 Stereotactic MR guided online adaptive radiotherapy for abdominal and pelvic lymph node metastases K. Owczarczyk 1 , H. Harford-Wright 1 , S. Shergill 1 , T. Sevitt 1 , J. Lynch 1 , J. Harris 1 , B. George 2 , A. Gaya 1 , J. Good 2