Dosimetric study and verification of total body irradiation using helical tomotherapy and its comparison to extended SSD technique.

The American College of Radiology practice guideline for total body irradiation (TBI) requires a back-up treatment delivery system. This study investigates the development of helical tomotherapy (HT) for delivering TBI and compares it with conventional extended source-to-surface distance (X-SSD) technique. Four patients' head-to-thigh computed tomographic images were used in this study, with the target defined as the body volume without the left and right lungs. HT treatment plans with the standard TBI prescription (1.2 Gy/fx, 10 fractions) were generated and verified on phantoms. To compare HT plans with X-SSD treatment, the dose distribution of X-SSD technique was simulated using the Eclipse software. The average dose received by 90% of the target volume was 12.3 Gy (range, 12.2-12.4 Gy) for HT plans and 10.3 Gy (range, 10.08-10.58 Gy) for X-SSD plans (p < 0.001). The left and right lung median doses were 5.44 Gy and 5.40 Gy, respectively, for HT plans and 8.34 Gy and 8.95 Gy, respectively, for X-SSD treatment. The treatment planning time was comparable between the two methods. The beam delivery time of HT treatment was longer than X-SSD treatment. In conclusion, HT-based TBI plans have better dose coverage to the target and better dose sparing to the lungs compared with X-SSD technique, which applies dose compensators, lung blocks, and electron boosts. This study demonstrates that HT is possible for delivering TBI. Clinical validation of the feasibility of this approach would be of interest in the future.