Abstract
Purpose: To assess the feasibility of image guided radiation therapy to reduce functional bone marrow (FBM) dose for cervical cancer patients with positive para‐aortic lymph nodes undergoing extended field intensity modulated radiotherapy (EF‐IMRT). Method and Materials: Three patients were enrolled on a prospective study to test image‐guided FBM‐sparing EF‐IMRT (IG‐EF‐IMRT). Patients underwent CT simulation plus (1) whole body 18F‐FDG‐PET and (2) quantitative MRI using iterative decomposition of water and fat with echo asymmetry and least‐squares estimation (MRI‐IDEAL). Regions of high standardized uptake value (SUV) (increased glucose metabolism) on PET and low fat fraction (high cellularity) on MRI‐IDEAL indicated higher FBM concentrations. The PET and MRI‐IDEAL were registered with the simulation CT. FBM was segmented based on the patient's individual mean SUV and fat fraction within lumbosacral spine and pelvis. For each patient, 2 plans were compared: non‐IG‐EF‐IMRT(CT defined BM as the sparing objective) vs. IG‐EF‐IMRT(FBM as the sparing objective). Results: The mean FBM volume, as a proportion of lumbosacral spine and pelvis, was 23% (s.d. 0.6%). IG‐EF‐IMRT significantly reduced the volume of FBM receiving ≥ 10 Gy and ≥ 20 Gy (V10 and V20) compared to non‐IG‐EF‐IMRT. With PET and MRI‐IDEAL guidance, the mean FBM V10 was reduced from 94% to 89%, mean FBM V20 was reduced from 86% to 73%. IG‐IMRT plans did not compromise target coverage or increase dose to normal organs. One patient was treated with IG‐EF‐IMRT, with FBM V10 and V20 of 82% and 70%, respectively. She received all 5 cycles of weekly cisplatin (40 mg/m2) and had grade 2 HT during CRT. The other two patients were treated with non‐IG‐EF‐IMRT and planned with IG‐EF‐IMRT. Conclusion: IGRT for FBM sparing is clinically feasible and significantly reduces FBM dose compared to standard IMRT. This novel technique may reduce HT and is being tested in a clinical trial.
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