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18F-FDG PET-Defined Therapy Response Predicts Acute Hematologic Toxicity for Anal Cancer Patients Treated with Chemoradiation

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Y Yue

Y Yue1*, J David1 , Q Li1 , K Blas2 , B Fraass1 , P Kabolizadeh2 , R Tuli1 , (1) Cedars-Sinai Medical Center, Los Angeles, CA, (2) Beaumont Health System, Royal Oak, MI


TH-AB-FS4-1 (Thursday, August 3, 2017) 7:30 AM - 9:30 AM Room: Four Seasons 4

Purpose: Irradiation-induced hematologic toxicities (HT) during radiotherapy(RT) for anal cancer can lead to increased infection rates, bleeding, asthenia, and decreased treatment intensity via unplanned breaks. We hypothesize that HT in anal cancer patients treated with chemoradiation(CRT) correlates with change in active bone marrow (ABM) characterized by pre- and post-CRT PET/CT.

Methods: Twenty-one locally advanced anal cancer patients treated with CRT from 2011-2016 were identified. 18F-FDG PET/CT scans were obtained 2 weeks pre- and 6 weeks post-CRT. HT was evaluated by weekly white blood cell count, absolute neutrophil count(ANC), hemoglobin 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 by liver uptakes. ABM was characterized in all PET images as the volume having standard uptake value (SUV) larger than mean uptakes in the TBM. Image variables (global, subregional SUVmean, SUVmax, ABMs) of pre- and post-CRT and their differential changes were evaluated as potential predictors of HT. Locoregional radiomics features were calculated using a 3D kernel-based approach. HT prediction was modeled by logistic regression with the Lasso algorithm with 10-fold cross-validation. HT endpoints were defined as change between baseline blood nadir and the lowest nadir values during and up to 2 weeks after treatment.

Results: The lasso regression identified 5 predictors (pre-SUVmax, post-LS-ABM, LS-ABM change, homogeneity texture change, and variance). Ratios of LS-ABMs to TBM were reduced from 18.9% (pre-CRT) to 16.3% (post-CRT). This reduction of LS-ABM is significantly correlated to acute HT measured by ANC (p=0.023) and hemoglobin (p=0.012) nadirs.

Conclusion: 18F-FDG-PET-derived active BM changes between pre- and post-CRT is significantly associated with HT in anal cancer patients undergoing CRT. LS-ABM is a robust surrogate for evaluation of HT and can be used to develop BM-sparing radiotherapy for reduction of potential HT.

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