Lung sparing and ribcage coverage in total body irradiation delivered by helical tomotherapy

PURPOSE: Helical tomotherapy (HT) is a viable method for delivering total body irradiation (TBI) when preparing patients for allogenic stem cell or bone-marrow transplantation. TBI can be planned to reduce the amount of radiation delivered to organs at risk, such as the lungs, with the aim of decreasing toxicity. However, it is important for the ribcage to receive the prescribed radiation dose in preparation for bone-marrow transplantation. In this retrospective study, we analyzed radiation dose coverage of the lungs and ribcage in patients who underwent TBI delivered by HT to achieve lung dose sparing. METHODS: Thirty-five patients were included in the analysis and divided into three groups based on their prescribed radiation dose (4, 8, or 12 Gy). HT was performed using a rotating gantry to reduce radiation to the lungs. Dosimetric parameters for the lungs and ribcage as well as dose-volume histograms were calculated. RESULTS: The mean lung D(95) was 60.97%, 54.77%, and 37.44% of the prescribed dose for patients receiving 4 Gy, 8 Gy, and 12 Gy, respectively. Ribcage coverage was most optimal for patients receiving 4 Gy, with a D(95) of 91.27% and mean homogeneity index of 1.17, whereas patients receiving 12 Gy had a mean D(95) of 78.65% and homogeneity index of 1.37, which is still within the range recommended by treatment guidelines. CONCLUSIONS: Using HT to achieve lung tissue sparing is a viable approach to minimizing pulmonic complications in patients undergoing TBI. As this planning adjustment does not compromise the dose and quality of coverage received by the ribcage, it is a feasible tool within conditioning regimens for allogeneic bone-marrow transplantation.