Dose-volume effects for pelvic bone marrow in predicting hematological toxicity in prostate cancer radiotherapy with pelvic node irradiation

Purpose To prospectively identify clinical/dosimetric predictors of acute/late hematologic toxicity (HT) in chemo-naÏve patients treated with whole-pelvis radiotherapy (WPRT) for prostate cancer. Material and methods Data of 121 patients treated with adjuvant/salvage WPRT were analyzed (static-field IMRT n = 19; VMAT/Rapidarc n = 57; Tomotherapy n = 45). Pelvic bone marrow (BM) was delineated as ilium (IL), lumbosacral, lower and whole pelvis (WP), and the relative DVHs were calculated. HT was graded both according to CTCAE v4.03 and as variation in percentage relative to baseline. Logistic regression was used to analyze association between HT and clinical/DVHs factors. Results Significant differences (p < 0.005) in the DVH of BM volumes between different techniques were found: Tomotherapy was associated with larger volumes receiving low doses (3-20 Gy) and smaller receiving 40-50 Gy. Lower baseline absolute values of WBC, neutrophils and lymphocytes (ALC) predicted acute/late HT (p ≤ 0.001). Higher BM V40 was associated with higher risk of acute Grade3 (OR = 1.018) or late Grade2 lymphopenia (OR = 1.005). Two models predicting lymphopenia were developed, both including baseline ALC, and BM WP-V40 (AUC = 0.73) and IL-V40+smoking (AUC = 0.904) for acute/late respectively. Conclusions Specific regions of pelvic BM predicting acute/late lymphopenia, a risk factor for viral infections, were identified. The 2-variable models including specific constraints to BM may help reduce HT.