Evaluating dosimetric parameters predictive of hematologic toxicity in cervical cancer patients undergoing definitive pelvic chemoradiotherapy

We performed a retrospective study of cervical cancer pelvic radiotherapy plans to explore dosimetric parameters predictive of hematologic toxicity (HT), with specific interest in evaluating metabolic parameters and identifying the best predictive model. Active marrow was retroactively contoured as pelvic bone with SUV > mean on 18F-FDG-PET. "Highly active" marrow was contoured as the hottest 10-14% volume of active marrow. Pelvic bone contour was segmented into lumbosacral, iliac crest, and lower pelvis. Predictors of HT were evaluated using logistic regression and repeated measures modeling. One hundred women were evaluated from 2009 to 2020. The plurality/majority had stage IIIC1 disease (38%) and underwent IMRT (88%) with pelvic field alone (72%). The majority received weekly cisplatin (78%), and 82% completed at least five cycles. The most common HT was leukopenia (grade 2+: 68%). Predictors of grade 2+ and 3+ HT were baseline WBC (p < 0.001), and 10- and 20-Gy dosimetric parameters to the active marrow, highly active marrow, and pelvic bone. The best predictive model of leukocyte trajectory included baseline WBC (p < 0.001), highly active marrow V20 (p < 0.001), and interactions of baseline WBC with time (p < 0.001) and highly active marrow V20 (p < 0.001), such that those with low baseline WBC experienced the greatest impact of highly active marrow V20. Baseline WBC was highly predictive of HT; dosimetric predictors included dose to the active marrow, highly active marrow, and pelvic bone, with the greatest impact from V20 to the highly active marrow, particularly in women with low baseline WBC. Future studies should consider incorporating baseline WBC and limiting dose to the most highly active marrow.