18F-FDG PET-defined therapy response to predict acute hematologic toxicity for anal cancer patients treated with chemoradiation.

775Background: Hematologic toxicities (HT) induced during chemoradiotherapy (CRT) for anal cancer can lead to increased infection rates, bleeding, asthenia, and unplanned breaks compromising treatment efficacy. We hypothesize that HT in anal cancer patients treated with CRT correlate with change in active bone marrow (ABM) characterized by pre- and post-CRT 18F-FDG PET/CT (PET). Methods: Twenty-eight locally advanced anal cancer patients treated with definitive CRT from 2011-2016 were identified. PET scans were obtained 0-2 weeks pre- and 6-8 weeks post-CRT. HT was evaluated by weekly white blood cell count, absolute neutrophil count (ANC), hemoglobin (Hg) and platelet nadirs. Total bone marrow (TBM) was defined on CT images, and segmented into three subregions: lumbosacral (LS), left and right iliac pelvis. PET images were normalized to bone outside of the TBM uptakes. ABM was characterized in all PET images as the volume having standard uptake value SUV > 40% of SUVmax in the TBM. Image variables (globa...