Feasibility of atlas-based active bone marrow sparing intensity modulated radiation therapy for cervical cancer.

BACKGROUND: To test the hypothesis that atlas-based active bone marrow (ABM)-sparing intensity modulated radiation therapy (IMRT) yields similar dosimetric results compared to custom ABM-sparing IMRT for cervical cancer patients.

METHODS: We sampled 62 cervical cancer patients with pre-treatment FDG-PET/CT in training (n=32) or test (n=30) sets. ABM was defined as the subvolume of the pelvic bone marrow (PBM) with standardized uptake value (SUV) above the mean on the average FDG-PET image (ABMAtlas ) vs. the individual's PET (ABMCustom ). Both were deformed to the planning CT. Overlap between the two subvolumes was measured using the Dice coefficient. Three IMRT plans designed to spare PBM, ABMAtlas , or ABMCustom were compared for 30 test patients. Dosimetric parameters were used to evaluate plan quality.

RESULTS: ABMAtlas and ABMCustom volumes were not significantly different (p=0.90), with a mean Dice coefficient of 0.75, indicating good agreement. Compared to IMRT plans designed to spare PBM and ABMCustom , ABMAtlas -sparing IMRT plans achieved excellent target coverage and normal tissue sparing, without reducing dose to ABMCustom (mean ABMCustom dose 29.4Gy vs. 27.1Gyvs. 26.9Gy, respectively; p=0.10); however, PTV coverage and bowel sparing were slightly reduced.

CONCLUSIONS: Atlas-based ABM sparing IMRT is clinically feasible and may obviate the need for customized ABM-sparing as a strategy to reduce hematologic toxicity.