180. Total marrow and total lymphoid irradiation (TMI-TLI) with helical tomotherapy: Experience of Perugia's hospital. (December 2018) - Iacco, M.
Abstract: Purpose: In our centre, an on-going pilot study is testing the feasibility of TMI-TLI delivered with Helical Tomotherapy (HT) instead of TBI. We present our protocol and dosimetric results of first 28 patients treated. Methods: Head and shoulders of patient are immobilized with thermoplastic mask. Hips and legs are positioned in polyethylene foam cushion. Two supine CT scans, with feet first and head first orientation, were collected with 1 cm slice thickness. For each CT a treatment plan was optimized with the following parameters: field width 5.0 cm, pitch 0.430 and modulation factor ranging from 2 to 3 for the superior region and 5.0 cm, 0.287 and 2 for the inferior region. The overlapping region was managed with 3 sections to better control the dose accumulation. Others helps structures, like a lung contractions and RVR, were used in order to better optimise the plan. The prescribed dose was 13.5 Gy in 9 fractions to the PTV, 11.5 Gy in 8 fractions to the PTV and 13.5 Gy to the bone PTV and 11.5 Gy to lymph nodes PTV in 9 fractions respectively for 2, 5 and 21 patients. Plans were optimised to ensure 90% PTV volume received at least the 90% of the prescribed dose. Dose limits were D50% < 7.5 Gy for lungs, liver, kidneys, 8 Gy for heart, 9 Gy for small intestine, 6 Gy for eyes. Results: All plans satisfied the dose constraints. Mean dosimetric results for the 21 patients treated with two dose level were reported in table in term of D90% for PTV and mean dose for the main OARs. The mean treatment times were 17.8 and 9.8 min respectively for the superior and inferior plan. Conclusions: The TMI-TLI with HT showed good dosimetric results. Even though the patient cohort is small, treatments seemed associated with low toxicity and suitable for elderly and unfit young patient.