Total body irradiation using Helical Tomotherapy: Treatment technique, dosimetric results and initial clinical experience.

Purpose: Helical TomoTherapy allows precise and homogeneous tumour coverage and excellent sparing of organs at risk. We present here our treatment technique, dosimetric results, and our first clinical data for patients receiving total body irradiation as part of the conditioning regimen before hematopoietic stem cell transplantation.

Patients And Methods: The cohort consisted of 11 patients who were treated in our institution between August 2014 and January 2016. The total dose was 12Gy in six fractions in three days. We collected the dose distribution information in the treatment volumes, organs at risk and area of junction. We report retrospectively the clinical events during the first 6 months after the procedure.

Results: Median age was 31 years (range, 18-57 years). Median D98% was 11.5Gy (range: 6.6-11.9Gy). The median of the mean doses to the lungs was 8.7Gy (range: 8.5-9.3Gy). The mean dose for the junction area was 12Gy (range: 11.9-12.1Gy). All patients had the total procedure, and all underwent successful engraftment. During the first six months, nine patients had at least one grade 3 or 4 toxicity that was due essentially to graft versus host disease. No patient had radiation pneumonitis. The toxicities were both more frequent and of higher grade during the first three months.

Conclusion: Total body irradiation using helical TomoTherapy is feasible. It allows a very good homogeneity of dose and conformity with an acceptable tolerance. It could deliver higher doses to sites at high risk of recurrence (bone marrow, sanctuary sites), while sparing major normal organs like lungs, liver, and kidneys. This reduction of dose could lead to reduced severity and frequency of late complications.