A Dosimetric Correlation Between Radiation Dose to Bone and Reduction of Hemoglobin Levels After Radiation Therapy for Prostate Cancer

Abstract

The aim of this work was to investigate the correlation between dose to pelvic bone marrow and anemia when treating prostate cancer (PC) with definitive radiation. Patients were selected from a prospective institutional database of patients with PC treated between 2008 and 2021. Pelvic bone (L3/L4 interface through ischial tuberosities) was contoured, and the dose to this structure was calculated. Doses were converted to 2-Gy equivalent doses using an α/β of 10. Exploratory analysis suggested dichotomizing into low-volume exposures of ≤1000 cc (LVE) and high-volume exposures of >1000 cc (HVE). Nonparametric kernel regressions were performed evaluating the effects of time, dose, and androgen deprivation therapy use on hemoglobin (Hgb) values. Reoptimization of plans was performed to evaluate the feasibility of adjusting significant dose levels. A total of 203 patients were included in the final analysis. Median baseline Hgb was 14.9 g/dL (interquartile range, 14.1-15.6). Patients with bone marrow HVE ≥15 Gy were found to have significantly lower predicted Hgb levels compared with those with LVE at day 90: 12.8 g/dL (95% CI, 12.4-13.3) versus 14.5 g/dL (95% CI, 14.0-14.9), respectively (P < .05). When normalizing starting Hgb levels, HVE patients still had significantly lower predicted Hgb levels than LVE at day 90: 86.1% (95% CI, 83.2%-89.7%) versus 96.2% (95% CI, 92.4%-100%), respectively. Reoptimizing 20 plans with high volume of bone marrow receiving 15 Gy resulted in a mean reduction from 1422 cc to 997 cc without compromise of other organs at risk or target coverage. Patients with >1000 cc of bone marrow receiving ≥15 Gy had significantly lower predicted Hgb levels than those with ≤1000 cc. Reoptimization of plans demonstrated that this dose constraint is achievable without impairing plan quality. This dose constraint can be considered to limit acute marrow toxicity in patients with PC.