Total Marrow and Lymphoid Irradiation with Helical Tomotherapy: a Practical Implementation Report

Objective To standardize the technique and resources for total marrow and lymphoid irradiation (TMLI) as part of the conditioning regimen before allogenic bone marrow transplantation (ABMT) using helical tomotherapy.Methods We used this technique in our first 5 patients requiring TMLI. Patients were immobilized using a mask and a whole-body vacuum cushion. CT scanning was performed in head first supine (HFS) and feet first supine (FFS) orientations with an overlap at mid-thigh. Target consisted of the entire skeleton, spleen, sanctuary sites and major lymphatics whereas lungs, kidneys, aero-digestive tract, bowel, parotids, heart and liver were defined as organs at risk (OAR). Treatment was performed in two parts based on 2 different plans generated in HFS and FFS orientations with an overlap at the mid thigh. Patients along with the immobilization device were manually rotated by 180° to change the orientation after the delivery of HFS plan. The dose at the junction was contributed by a complementary dose gradient from each of the plans. Plan was to deliver 95% of 12Gy to 98% of CTV with dose heterogeneity < 10% and pre-specified OAR doe constraints. Megavoltage-CT was used for position verification before each fraction. Patient specific quality assurance and an in-vivo film dosimetry to verify junction dose were performed in all patients.Results Treatment was delivered in two daily fractions of 2Gy each for 3 days with at least 8-hours gap between each fraction. The target coverage goals were met in all the patients. The average person-hours per patient were 16.5, 21.5 and 25.75 for radiation oncologist, radiation therapist and medical physicist respectively. Average in-room time per patient was 9.25 hours with an average beam-on time of 3.32 hours for all the six fractions. Conclusion This report comprehensively describes technique and resource requirements for TMLI and would serve as a practical guide for departments keen to start this service. Despite being time and labor intensive, it can be implemented safely and robustly. We will be using this methodology in a prospective phase II trial to study safety and feasibility of dose escalated TMLI as part of conditioning regimen before ABMT.