Incorporating ¹⁸FDG-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 ¹⁸FDG-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 ¹⁸FDG-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 ¹⁸FDG-PET; plan D accounted only for the active BM subregions outlined with ¹⁸FDG-PET. Dose received by active bone marrow within the pelvic (^ACTPBM) and in different subregions such as lumbar-sacral (^ACTLSBM), iliac (^ACTIBM) and lower pelvis (^ACTLPBM) bone marrow was analyzed.

Results: A significant difference was found for ^ACTPBM in terms of D_mean (p = 0.014) V₂₀ (p = 0.015), V₂₅ (p = 0.030), V₃₀ (p = 0.020), V₃₅ (p = 0.010) between Plan A and other plans. With respect to specific subsites, a significant difference was found for ^ACTLSBM in terms of V₃₀ (p = 0.020)), V₃₅ (p = 0.010), V₄₀ (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 ^ACTLSPBM and ^ACTIBM 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 ¹⁸FDG-PET imaging. The subset of patients with a benefit in terms of dose reduction to active BM through the inclusion of ¹⁸FDG-PET in the planning process needs further investigation.