Vertebral body irradiation during chemoradiation therapy for esophageal cancer contributes to acute bone marrow toxicity

Background: Hematologic toxicity (HT) commonly occurs during chemoradiation therapy (CRT) for esophageal cancer. We sought to determine radiation doses that correlate with declines in blood counts due to vertebral body (VB) irradiation during CRT. Methods: We analyzed 53 esophageal cancer patients who were treated with weekly neoadjuvant carboplatin, paclitaxel and RT with weekly complete blood counts (CBC) available during treatment. HTs were graded according to the Common Terminology Criteria for Adverse Events version 4.0 (CTCAE v4.0). Dose volume histogram (DVH) parameters of V-x, defined as percentage of entire bony vertebra (body, pedicles, laminae, processes) receiving at least x Gy of radiation, were collected for VB V-5 (VBV5), VBV10-VBV60 in increments of 10, and mean vertebral dose (MVD). Linear and logistic regressions were performed to identify associations between leukopenia nadirs and DVH parameters. Receiver operator curves identified thresholds to avoid grade >= 3 leukopenia. Results: A proportion of 32.1% of patients (n=17) developed grade 3 leukopenia and 5.7% (n=3) developed grade 4 leukopenia. VBV5, VBV10, VBV20, VBV30, and MVD were significantly associated with worsening leukopenia on univariate and multivariate analysis. Associations with leukopenia were not seen with VBV40 and VBV50 DVH values. Thresholds to avoid grade >= 3 leukopenia were VBV10 < 49.1%, VBV20 < 45.6%, and MVD < 17.2 Gy. Conclusions: VBV5, VBV10, VBV20, VBV30 associate with leukopenia during CRT for esophageal cancer patients. Improved radiation sparing of the VB may decrease HT and may improve tolerability of concurrent chemotherapy and allow for intensification of systemic therapy during RT.