Radiation Dose to the Thoracic Vertebral Bodies and Impact on Hematologic Toxicity in Patients Receiving Concurrent Chemoradiation for Esophageal Cancer.

105 Background: Concurrent chemotherapy and radiation (CRT) for the treatment of esophageal cancer (EC) is associated with acute hematologic toxicity (HT). There are few data evaluating the relationship between radiation dose (RT) to the thoracic vertebral bodies (TVB) and the development of HT in EC patients receiving CRT. We hypothesized that increasing RT to the TVB contributes to the development of HT in EC patients receiving CRT. Methods: We identified cases of EC treated with curative intent CRT from 2007-2016. We retrospectively contoured the thoracic vertebral bodies (TVB). The TVB-mean dose and the TVB V5-V50 were calculated from the dose volume histogram. HT was graded according to the Common Terminology Criteria for Adverse Events, v4 based on leukocyte, neutrophil, and platelet nadirs during CRT. Grade≥3 HT (HT3+) was the primary endpoint. Logistic regression was used to test associations between HT3+ and dosimetric/clinical parameters. Results: We included 137 cases: 115 males (84%); median age 61 years (Interquartile range [IQR], 55-67); predominantly stage III (54%). Most patients received concurrent carboplatin/paclitaxel (N = 83). Median RT dose was 50.4 (IQR = 50.4-50.4) Gy, and the majority underwent surgery (60.6%). The rate of HT3+ was 39.4% (N = 54) at a median of 28 (IQR = 21-32) days after CRT start. On univariate analysis, a 5% increase in TVB-V40 was associated with increased odds of HT3+ (OR = 1.13, 95% CI 1.04-1.23, p = 0.0004). TVB-mean and TVB V30-V50, age (OR = 1.04, p = 0.03), males (OR = 0.38, p = 0.04), and carboplatin/paclitaxel vs. other regimen (OR = 2.66, p = 0.01) were significantly associated with HT3+, while BMI was not (OR = 1.00, p = 0.94). On multivariate analysis, TVB-V40 (OR = 1.20, p = 0.0004), carboplatin/paclitaxel (OR = 4.84, p = 0.0007), and age (OR = 1.04, p = 0.03) were independently associated with HT3+ while male gender (OR = 0.48, p = 0.16) was not. The results were similar for TVB-mean and TVB V30-V50. Conclusions: We found that increasing TVB dose was associated with HT3+ in EC patients treated with CRT. This suggests that efforts to spare RT to the TVB may reduce rates of HT3+ and prospective evaluation of these results is needed.