Sci—Fri PM: Delivery — 08: Total Marrow Irradiation Using Helical Tomotherapy in Treating\ a Multiple Myeloma Patient: A Case Study

The Ottawa Hospital Cancer Centre has embarked on a phase I/II dose escalation study of IG‐IMRT using Helical Tomotherapy (HT) for Total Marrow Irradiation (TMI) of multiple myeloma patients prior to autologous hematopoietic stem cell transplantation. In this work we outline the technical and physical hurdles related to planning and dose delivery and summarize our experience to date. Limitations with the scanning and planning systems required that patients have two CT scans; one of the upper body and one of the lower body with at least a 20 cm overlap. They must also have a separate treatment plan for each region. PTVs and OARs were defined on both CT sets and image fusion using ImageJsoftware was used to link the two scan sets. The treatment plan for the upper body used a 2.5 cm beam to provide good sup‐inf dose conformation, while a 5.0 cm beam was used for the lower body. DQA was planned, delivered and analyzed, showing good agreement between the planned and measured dose distributions in the junction region. We demonstrate the technical feasibility of our method in overcoming the challenges related to the planning system, including junctioning and summing the dose clouds of longitudinally adjacent plans created on different CTdata sets. The treatment was well‐tolerated by the patient and no severe acute toxicity was noted. Scaling to the QUANTEC data (V20 of 30–35%) for lungs, we estimate that with the present CTV‐PTV margins it should be possible to safely deliver 25 Gy TMI.