Abstract: Objective:To analyze the clinical and physical tactors associated with acute bone marrow suppression in concurrent chemo -radiotherapy for rectal cancer and to provide a reference standard for the best clinical treatment plan. Methods:Retrospective analy -sis was performed on 62patients with rectal cancer who received concurrent radiotherapy and chemotherapy in our department. The pelvis was contoured for each patient in the radiotherapy treatment planning system and divided into three subsites: lumbosacral spine, ilium, and lower pelvis. Prognostic clinical and physical factors were analyzed by univariate and multivariate analyses. Evaluated prognostic clinical factors included sex, age, clinical stage, original hemoglobin levels, and chemotherapy, operation, and radiation modes; physical factors included V5, V10, V15, V20, V25, V30, V35, V40, V45, V50, Dmax, and Dmean of lumbosacral spine, ilium, low-er pelvis, and pelvis. Results:The percentage of patients who developed acute bone marrow suppression ( ≥ 2 grade) was 61. 3% (38/ 62).Univariate analysis of related factors revealed statistically significant differences were sex, chemotherapy, lumbosacral spine V 45, il -ium V 20, and ilium V 30. Multivariate logistic regression analysis indicated that chemotherapy and ilium V30are the risk factors for acute bone marrow suppression. The receiver operating curve showed that the threshold of ilium V 30was 44% .Conclusion: Acute bone marrow suppression is influenced by more than one factor; local control rate of the tumor and acute bone marrow suppression are tradeoffs in rectal cancer treatment. An appropriate chemotherapy method should be selected, and ilium V30must be maintained below 44% to prevent bone marrow suppression in rectal cancer patients.