Predictive Value of Dosimetric Parameters and Absolute Monocyte Count (AMC) for Acute Hematologic Toxicity in Cervical Cancer Patients Undergoing Concurrent Chemotherapy and Volumetric-Modulated Arc Therapy (VMAT)

Purpose: To identify clinical/dosimetric predictors of acute hematologic toxicity (HT) in cervical cancer patients undergoing concurrent chemotherapy and volumetric-modulated arc therapy (VMAT).Methods and Materials: We retrospectively analyzed 184 cervical cancer patients receiving concurrent chemotherapy and VMAT. Hematological parameters were collected during the treatment period. The total pelvic bone(TPB) was retrospectively delineated for each patient, and the volume of TPB receiving 10, 20, 30, 40, and 50 Gy (V10, V20, V30, V40, and V50, respectively) was calculated. We assessed the correlations between variables by the Spearman rank correlation test and compared the differences between groups by the Wilcoxon signed-rank test. Binary logistic regression analysis was used to analyze associations between HT and clinical/dosimetric parameters. The receiver operating characteristic curve(ROC) was used to determine the best cut-off values for dosimetric planning constraints.Results: The nadir of absolute monocyte count (AMC) was positively correlated with the nadir of absolute white blood cells (WBC) count (r＝0.5378, 95%CI ＝ 0.4227 to 0.6357, P<0.0001) and the nadir of absolute neutrophil count(ANC) (r＝0.5000，95%CI ＝ 0.3794 to 0.6039, P<0.0001). The decrease and increase of AMC usually occurred before the ANC and WBC. In multivariate logistic regression analysis, the chemotherapy regimen and the TPB_V20 were independent risk factors for developing Grade ≥3 hematologic toxicity. The optimal TPB_V20 cut-off value identified by ROC curves followed by Youden test was 71% (AUC = 0.788; 95%CI, 0.722–0.845; p-value＜0.001).Conclusions: The changing trend of AMC can be used as an effective predictor for the timing and severity of the ANC/WBC nadirs. Maintain TPB_V20 < 71 % and selecting single-agent cisplatin or carboplatin could significantly reduce Grade ≥3 HT in cervical cancer patients undergoing concurrent chemoradiotherapy.