Irradiation of Anatomically-Defined Pelvic Subsites and Acute Hematologic Toxicity in Anal Cancer Patients Undergoing Chemoradiation

Publication date: Available online 23 March 2017
Source:Practical Radiation Oncology
Author(s): Brent Rose, Devarati Mitra, Theodore S. Hong, Kyung-Wook Jee, Andrzej Niemierko, Lorraine N. Drapek, Lawrence S. Blaszkowsky, Jill N. Allen, Janet E. Murphy, Jeffrey W. Clark, David P. Ryan, Jennifer Y. Wo
PurposeChemoradiation (CRT) for the treatment of anal cancer is known to cause significant hematologic toxicity (HT). We sought to investigate if radiation dose to specific pelvic subsites is associated with increased HT risk.Methods and MaterialsForty-five patients with non-metastatic anal cancer who received definitive CRT with intensity modulated radiation therapy (IMRT) and concurrent mitomycin-C and 5-fluorouracil were studied. Total pelvic bone marrow (TBM) was divided into three subsites: lumbosacral bone marrow (LSBM), including the entire sacrum and L5 vertebral body; iliac bone marrow (IBM) extending from the iliac crests to the superior border of the femoral head; and lower pelvic bone marrow (LPBM) including the pubic bones, ischia, acetabula, and proximal femurs. The primary endpoint was absolute neutrophil count (ANC) nadir during or within 2weeks of treatment completion. Generalized linear modeling was used to analyze the correlation between the equivalent uniform dose (EUD, with an "a" value of 0.5) to the individual pelvic subsites and the various hematologic endpoints. Age, body mass index, sex, baseline blood counts and immunosuppression were analyzed as potential covariates.ResultsMean±SD ANC nadir was 0.77 x 10⁹/L (±0.66 x 10⁹/L). Grades 3+ and 4+ neutropenia occurred in 71.1% and 44.4% of patients, respectively. In addition to radiation dose to pelvic bone marrow, baseline ANC was the only significant predictor of hematologic toxicity on multivariable analysis and was included in all models. The EUD of TBM, LSBM and IBM were each significantly associated with neutropenia. The model performance of TBM (adjusted R²=0.226) was similar to both LSBM (adjusted R²=0.206) and IBM (adjusted R²=0.249).ConclusionsRadiation dose to TBM, LSBM and IBM were each individually associated with HT, suggesting that sparing just a portion of pelvic bone marrow is insufficient to decrease rates of clinically significant bone marrow suppression.



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