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 .sup.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 .sup.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 .sup.18FDG-PET; plan D accounted only for the active BM subregions outlined with .sup.18FDG-PET. Dose received by active bone marrow within the pelvic (.sup.ACTPBM) and in different subregions such as lumbar-sacral (.sup.ACTLSBM), iliac (.sup.ACTIBM) and lower pelvis (.sup.ACTLPBM) bone marrow was analyzed. Results A significant difference was found for .sup.ACTPBM in terms of D.sub.mean (p = 0.014) V.sub.20 (p = 0.015), V.sub.25 (p = 0.030), V.sub.30 (p = 0.020), V.sub.35 (p = 0.010) between Plan A and other plans. With respect to specific subsites, a significant difference was found for .sup.ACTLSBM in terms of V.sub.30 (p = 0.020)), V.sub.35 (p = 0.010), V.sub.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 .sup.ACTLSPBM and .sup.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 .sup.18FDG-PET imaging. The subset of patients with a benefit in terms of dose reduction to active BM through the inclusion of .sup.18FDG-PET in the planning process needs further investigation. Keywords: Anal cancer, Hematologic toxicity, Radiotherapy, Dose-painted IMRT, Bone-marrow sparing radiation