Development of an immobilization device for Total Marrow Irradiation.

Abstract Introduction A body frame dedicated to total marrow (lymph node) irradiation (TMI/TMLI) could minimize patient motion during the potentially extended beam-on time with this technique. We present the development of a dedicated immobilization system for TMI/TMLI using volumetric modulated arc therapy (VMAT). Materials&Methods Since 2010, 59 adult patients were treated with TMI/TMLI using a multi-isocenter VMAT technique. Two CTs were required (one head-first-supine, and one feet-first-supine (FFS)) to cover the whole volume. For the first ten patients, two standard commercial frames with personalized masks (with/without personalized vacuum cushion for the lower extremities) were used without specific inter-fixation (Frame A). For the next 49 patients a homemade three-frame immobilization system was adopted (Frame B), where each frame was interlocked with the next one and thermoplastic masks used to fix the patient. The effectiveness of the two immobilization systems was assessed by offline/online matching between daily cone-beam CT (CBCT) of each isocenter and the simulation CTs. Results Mean offline shifts for Frame A were: 3-12 mm in anterior-posterior, 2-5 mm in cranial-caudal, and 2-6 mm in left-right directions. Larger shifts were found for FFS series (shifts up to 23 mm). In Frame B, mean offline shifts were: 1-4 mm in anterior-posterior, 1-4 mm in cranial-caudal, and 1-4 mm in left-right directions. Mean online adjustments were: -1±4mm in anterior-posterior, 0±2mm in cranial-caudal, and 0±4 mm in left-right directions. Conclusion The patient positioning shifts for TMI/TMLI irradiation were mitigated by a homemade immobilization system and the use of individualised masks.