Purpose : To compare the dosimetric advantage of helical tomotherapy (HT) over intensity-modulated arc therapy (IMAT) and sliding window intensity-modulated radiation therapy (SW-IMRT) for total scalp irradiation.
Methods : Three treatment plans (SW-IMRT, IMAT and HT) were generated for a 73 year-old man with scalp angiosarcoma undergoing IMRT. The doses to the planning target volume (PTV) were 50 Gy. Conformity indexes, doses to the brain and lens, number of monitor units (MU), and treatment times were compared between techniques. Plan verification using a phantom study was also performed to compare the radiation planning results.
Results : The coverage factors of the PTV and homogeneous index were 0.99/1.10 for SW-IMRT, 0.95/1.14 for IMAT, and 0.99/1.04 for HT. The conformation numbers for the three plans were 0.74, 0.74, and 0.69, respectively. The proportions of normal brain receiving above 30 Gy/40 Gy were 43.8%/10.4% for IMRT, 40.7%/18.5% for IMAT and 20.6%/7.4% for HT. Although IMAT showed no superior dosimetric advantage over SW-IMRT, a lower number of MUs and a shorter treatment time were needed for IMAT. The phantom study had similar dosimetric results.
Conclusion : For patients receiving total scalp irradiation, these three techniques provide comparable target coverage. HT spares the brain better than IMAT and SW-IMRT.