SummaryHematologic toxicity (HT) is a common adverse effect in patients with cervical cancer treated with concurrent chemoradiation therapy. In this study, we used 18 F-fluorodeoxyglucose positron emission tomography to quantify changes in functional bone marrow (BM) in unirradiated (extrapelvic) and irradiated (pelvic) BM in cervical cancer patients treated with concurrent chemotherapy of varying intensities. We found that patients have varying Purpose: To quantify longitudinal changes in active bone marrow (ABM) distributions within unirradiated (extrapelvic) and irradiated (pelvic) bone marrow (BM) in cervical cancer patients treated with concurrent chemoradiation therapy (CRT). Methods and Materials: We sampled 39 cervical cancer patients treated with CRT, of whom 25 were treated with concurrent cisplatin (40 mg/m 2 ) and 14 were treated with cisplatin (40 mg/m 2 ) plus gemcitabine (50-125 mg/m 2 ) (C/G). Patients underwent 18 F-fluorodeoxyglucose positron emission tomographic/computed tomographic imaging at baseline and 1.5 to 6.0 months after treatment. ABM was defined as the subvolume of bone with standardized uptake value (SUV) above the mean SUV of the total bone. The primary aim was to measure the compensatory response, defined as the change in the log of the ratio of extrapelvic versus pelvic ABM percentage from baseline to after treatment. We also quantified the change in the proportion of ABM and mean SUV in pelvic and extrapelvic BM using a 2-sided paired t test. Results: We observed a significant increase in the overall extrapelvic compensatory response after CRT (0.381; 95% confidence interval [CI]: 0.312, 0.449) and separately in patients treated with cisplatin (0.429; 95% CI: 0.340, 0.517) and C/G (0.294; 95% CI: 0.186, 0.402). We observed a trend toward higher compensatory response in patients treated with cisplatin compared with C/G (PZ.057). Pelvic ABM percentage