Hematologic Nadirs During Chemoradiation for Anal Cancer: Temporal Characterization and Dosimetric Predictors
- Department of Radiation and Cellular Oncology, University of Chicago, Chicago, Illinois (United States)
- Department of Radiation Oncology, The Ohio State University, Columbus, Ohio (United States)
- Department of Radiation Oncology, Stanford University, Stanford, California (United States)
Purpose: Pelvic bone marrow (BM) constraints may offer a means to reduce the toxicity commonly associated with chemoradiation for anal cancer. We conducted a bi-institutional analysis of dose-volume metrics in a time-sensitive fashion to devise practical metrics to minimize hematologic toxicity. Methods and Materials: Fifty-six anal cancer patients from 2 institutions received definitive radiation therapy (median primary dose of 54 Gy) using intensity modulated radiation therapy (IMRT, n=49) or 3-dimensional (3D) conformal therapy (n=7) with concurrent 5-fluorouracil (5-FU) and mitomycin C. Weekly blood counts were retrospectively plotted to characterize the time course of cytopenias. Dose-volume parameters were correlated with blood counts at a standardized time point to identify predictors of initial blood count nadirs. Results: Leukocytes, neutrophils, and platelets reached a nadir at week 3 of treatment. Smaller volumes of the pelvic BM correlated most strongly with lower week 3 blood counts, more so than age, sex, body mass index (BMI), or dose metrics. Patients who had ≥750 cc of pelvic BM spared from doses of ≥30 Gy had 0% grade 3+ leukopenia or neutropenia at week 3. Higher V40 Gy to the lower pelvic BM (LP V40) also correlated with cytopenia. Patients with an LP V40 >23% had higher rates of grade 3+ leukopenia (29% vs 4%, P=.02), grade 3+ neutropenia (33% vs 8%, P=.04), and grade 2+ thrombocytopenia (32% vs 7%, P=.04) at week 3. On multivariate analysis, pelvic BM volume and LP V40 remained associated with leukocyte count, and all marrow subsite volumes remained associated with neutrophil counts at week 3 (P<.1). Conclusions: Larger pelvic BM volumes correlate with less severe leukocyte and neutrophil nadirs, suggesting that larger total “marrow reserve” can mitigate cytopenias. Sparing a critical marrow reserve and limiting the V40 Gy to the lower pelvis may reduce the risk of hematologic toxicity.
- OSTI ID:
- 22645768
- Journal Information:
- International Journal of Radiation Oncology, Biology and Physics, Vol. 97, Issue 2; Other Information: Copyright (c) 2016 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; Country of input: International Atomic Energy Agency (IAEA); ISSN 0360-3016
- Country of Publication:
- United States
- Language:
- English
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