A methodology for incorporating functional bone marrow sparing in IMRT planning for pelvic radiation therapy

Background and purpose: The purpose of this study was to design a radiation therapy treatment planning approach that would spare hematopoietically active bone marrow using [¹⁸F]FLT PET imaging. Materials and methods: We have developed an IMRT planning methodology to incorporate functional PET imaging using [¹⁸F]FLT scans. Plans were generated for two simulated cervical cancer patients, where pelvic active bone marrow regions were incorporated as avoidance regions based on the ranges: SUV4 ≥ 4; 4 > SUV3 ≥ 3; and 3 > SUV2 ≥ 2. Dose objectives were set to reduce bone marrow volume that received 10 (V₁₀) and 20 (V₂₀) Gy. Results: Active bone marrow regions identified by [¹⁸F]FLT with an SUV ≥ 2, SUV ≥ 3, and SUV ≥ 4 represented an average of 43.0%, 15.3%, and 5.8%, respectively of the total osseous pelvis for the two cases studied. Improved dose-volume histograms for all identified bone marrow SUV volumes and decreases in V₁₀, and V₂₀ were achieved without clinically significant changes to PTV or OAR doses. Conclusions: Incorporation of [ ¹⁸F]FLT PET in IMRT planning provides a methodology to reduce radiation dose to active bone marrow without compromising PTV or OAR dose objectives in pelvic malignancies.