Correlation between pelvic bone marrow dose volume parameters and acute hematologic toxicity in neoadjuvant intensity-modulated radiotherapy for locally advanced rectal cancer

Abstract

Objective To explore the correlation between pelvic bone marrow dose volume parameters (Vx) and acute haematological toxicity (HT) in patients undergoing neoadjuvant intensity- modulated radiotherapy for locally advanced rectal cancer(LARC), and to provide clinical data to reduce the risk of radiotherapy-associated HT and to optimise radiotherapy planning. Methods Seventy-five patients with LARC who underwent neoadjuvant concurrent radiotherapy (CCRT) from October 2019 to November 2023 at the Affiliated Cancer Hospital of Guizhou Medical University were retrospectively analysed. All patients underwent 5-field intensity- modulated radiotherapy (IMRT) with a prescribed dose of 45-50.4 Gy/25–28 times in the planned target (PTV). Simultaneous capecitabine or 5-fluorouracil (5-Fu) chemotherapy was delivered during radiotherapy. Acute HT during radiotherapy was assessed according to the National Cancer Institute Common Toxicity Criteria Version 5.0 (NCI-CTC.V5.0). Logistic regression analyses were used to assess the relationship between the dose-volume of bone marrow in the pelvis (Vx of hip, sacrum, and femur) and acute HT, and the non-linear relationship and threshold effect between the two were further analysed using the generalised additive model (GAM) and segmental regression. Results Multifactorial logistic regression analysis showed that there was a significant correlation between total pelvic bone marrow irradiated volume (TV) and coxal bone marrow irradiated volume (CV) at low doses (V₅, V₁₀) and ≥ 2 degrees of leukocyte reduction and neutrophil reduction (P < 0.05).There was a significant negative correlation between low-dose (V₅, V₁₀, V₁₅) sacral bone marrow irradiated volume (SV) and ≥ 2 degrees of leukocyte reduction (P < 0.05). Threshold effect analysis showed that there was a threshold effect of CV₁₀ with both ≥ 2 degrees of leukopenia and neutropenia, with similar thresholds of 483–495 ml for both. Conclusion In neoadjuvant intensity-modulated radiotherapy for rectal cancer, CV is a better predictor of acute HT compared with TV. CV associated with acute HT is mainly concentrated at low dose levels (CV₅, CV₁₀, CV₁₅). The threshold of 483 ml for CV₁₀ can be used as a reference for reducing the risk of acute HT and optimising radiotherapy planning in pelvic radiotherapy.