摘要目的:探索直肠癌新辅助调强放化疗患者骨盆骨髓剂量体积参数( Vx)与急性血液学不良反应(HT)的相关性，为降低放疗相关的血液不良反应风险，优化放疗计划提供临床数据。 方法:回顾性分析2017年10月至2019年5月在贵州医科大学附属肿瘤医院行新辅助同步放化疗(CCRT)的41例局部进展期直肠癌(LARC)患者。所有患者均行5野调强放疗(IMRT)，计划靶区(PTV)的处方剂量为45~50.4 Gy/25~28次。放疗期间同步卡培他滨或5－氟尿嘧啶(5-FU)化疗。根据通用不良反应标准5.0 (NCI-CTC.V 5.0)评估放疗期间的急性HT。采用logistic回归分析评估骨盆(髋骨、骶骨、股骨)骨髓低剂量受照体积 Vx与急性HT的关系，采用广义相加模型(GAM)和分段回归分析进一步确定两者之间的非线性关系和阈值效应。 结果:多因素logistic回归分析显示，骨盆骨髓低剂量( V5、 V10)受照总体积( TV)、髋骨骨髓受照体积( CV)与≥2度白细胞降低存在显著相关性( P<0.05)。骶骨骨髓低剂量( V5、 V10)受照体积( SV)与≥2度白细胞降低存在显著负相关( P<0.05)。阈值效应分析显示， CV10与≥2度白细胞降低存在阈值效应，阈值为575 ml， OR(95% CI)为1.85(1.08, 3.16)。 结论:在直肠癌新辅助调强放疗中，与 TV相比， CV是预测急性HT的更优指标。与急性HT相关的 CV主要集中在低剂量水平( CV5、 CV10)。本研究中的阈值( CV10＝575 ml)可作为盆腔放疗中降低急性HT风险优化放疗计划的参考。

abstractsObjective: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.