Incorporating 18 FDG-PET-defined pelvic active bone marrow in the automatic treatment planning process of anal cancer patients undergoing chemo-radiation.

Background: To investigate whether the incorporation of ¹⁸ FDG-PET into the automatic treatment planning process may be able to decrease the dose to active bone marrow (BM) for locally advanced anal cancer patients undergoing concurrent chemo-radiation (CHT-RT).
Methods: Ten patients with locally advanced anal cancer were selected. Bone marrow within the pelvis was outlined as the whole outer contour of pelvic bones or employing ¹⁸ FDG-PET to identify active BM within osseous structures. Four treatment planning solutions were employed with different automatic optimization approaches toward bone marrow. Plan A used iliac crests for optimization as per RTOG 05-29 trial; plan B accounted for all pelvic BM as outlined by the outer surface of external osseous structures; plan C took into account both active and inactive BM as defined using ¹⁸ FDG-PET; plan D accounted only for the active BM subregions outlined with ¹⁸ FDG-PET. Dose received by active bone marrow within the pelvic ( ^ACT PBM) and in different subregions such as lumbar-sacral ( ^ACT LSBM), iliac ( ^ACT IBM) and lower pelvis ( ^ACT LPBM) bone marrow was analyzed.
Results: A significant difference was found for ^ACT PBM in terms of D _mean (p = 0.014) V ₂₀ (p = 0.015), V ₂₅ (p = 0.030), V ₃₀ (p = 0.020), V ₃₅ (p = 0.010) between Plan A and other plans. With respect to specific subsites, a significant difference was found for ^ACT LSBM in terms of V ₃₀ (p = 0.020)), V ₃₅ (p = 0.010), V ₄₀ (p = 0.050) between Plan A and other solutions. No significant difference was found with respect to the investigated parameters between Plan B,C and D. No significant dosimetric differences were found for ^ACT LSPBM and ^ACT IBM and inactive BM subregions within the pelvis between any plan solution.
Conclusions: Accounting for pelvic BM as a whole compared to iliac crests is able to decrease the dose to active bone marrow during the planning process of anal cancer patients treated with intensity-modulated radiotherapy. The same degree of reduction may be achieved optimizing on bone marrow either defined using the outer bone contour or through ¹⁸ FDG-PET imaging. The subset of patients with a benefit in terms of dose reduction to active BM through the inclusion of ¹⁸ FDG-PET in the planning process needs further investigation.