Session Item

To report our dosimetric results in planning total marrow and lymphatic irradiation (TMLI) and total body irradiation (TBI) in patients with hematologic malignancies using helical tomotherapy.

In the present study, helical tomotherapy planning was performed for 7 patients using intensity modulated radiation therapy for TMLI and TBI target volumes, separately.  All patients were treated with conventional TBI technique and then re-planned. CT scanning was performed in head-first supine (HFS) and feet-first supine (FFS) orientations with overlap at mid-thigh. The TMLI planning target volume (PTV) consisted of whole body bones (excluding mandible, hands and foots) in the body including brain, scrotum, spleen and all lymphatics (head and neck, waldeyer axilla, mediasten, abdomen, pelvic). The organ at risk (OAR) included the lens, lungs, kidneys, heart, liver, bowels, rectum and bladder. On the other hand, the TBI PTV consisted of whole body without lungs, kidneys and lenses. The plans were prescribed to ensure 100% of the prescribed dose to cover 90% of the PTV. The prescription dose was set to 12 Gy. Planning parameters were set as follows; a pitch of 0.397, field width of 5 cm, a modulation factor of 2- 2.3. Homogeneity index was calculated for each plan.

 The mean OAR doses for each patient are listed in Table 1 and Table 2 for the TMLI and TBI, including statistical comparison results. For the all patients, the mean PTV D₉₈, D₂, D₅₀ and body maximum dose for the TMLI plans was 9.98 Gy, 13.65 Gy, 12.97 Gy and 14.87 Gy, respectively. In addition, the mean PTV D₉₈, D₂, D₅₀ and body maximum dose for the TBI plans was 10.19 Gy, 13.28 Gy, 12.60 Gy and 14.87 Gy, respectively. The mean homogeneity index was 0.28 and 0.24 for TMLI and TBI, respectively.

In this study, our results exhibited that TMLI and TBI treatments can be planned using the helical tomotherapy, effectively. HT based TMLI and TBI treatments improve homogeneous dose distribution to target volume while significantly decreasing organ at risks doses. Dose homogeneity was provided successfully for TMLI and TBI techniques using helical tomotherapy. In addition, while kidney doses were slightly lower in TMLI planning than TBI, lungs and lenses were getting slightly lower doses with TBI planning.