ABSTRACT
Objective:To analyze the correlation between the volume of irradiated pelvic bone marrow and acute hematologic toxicity (HT), in order to provide clinical data to reduce the risk of acute HT and optimize the radiotherapy plan.Methods:From October 2017 to May 2019, 41 LARC patients who received neoadjuvant concurrent chemoradiotherapy (CCRT) were retrospectively reviewed in our center. All patients were treated with 5-field intensity-modulated radiotherapy (IMRT), and the prescription dose delivered to PTV was 45-50.4 Gy in 25-28 fractions. Capecitabine or 5-fluorouracil (5-FU) wasadministered daily 5 days a week during radiotherapy. Different HTswere recorded according to National Cancer Institute Common Toxicity Criteria Version 5.0 (NCI-CTC.V5.0) based on laboratory tests. The volume of PBM or each site (coxal, sacrum, femoral) receiving more than x Gy refers to as TVx, CVx, SVx, and FVx, respectively. Logistic regression was performed to evaluate the association between the volume of irradiated pelvic bone marrow and different HT. Generalized additive model (GAM) and piecewise regression were used to further analyze the possible nonlinear relationship and threshold effect between them. Results:Multivariate logistic regression analysis showed that low-dose of irradiated total pelvic bone marrow volume ( TV5) and coxal bone marrow volume ( CV5, CV10) were significantly correlated with Grade ≥2 leukopenia( P<0.05). There was a significant negative correlation between the sacrum bone marrow volume ( SV5, SV10) and Grade ≥2 leukopenia ( P<0.05). A thresholdeffect has been observed between CV10 and Grade ≥2 leukopenia by Generalized additive model (GAM) and piecewise linear regression. The threshold between CV10 and Grade ≥2 leukopenia was 575 ml, OR (95% CI) was 1.85 (1.08, 3.16). Conclusions:In neoadjuvant IMRT of rectal cancer, CV is a better predictor of acute HT induced by CCRT than TV. The irradiated volume of CV associated with acute HT was mainly low-dose levels ( CV5, CV10). The thresholds of our study ( CV10= 575 ml) could be a good reference for the optimization of the radiotherapy plan.