||Dose Distribution Evaluation of Internal Target Volume in Stereotactic Body Radiotherapy for Lung Cancer
Yuri, Shimizu ,
Naoya, Saotome ,
Masahiko, Futaguchi ,
Shinobu, KumagaiAtsuro Terahara
44 , 2016-6 , The Medical Society of Toho University
Background: Three-dimensional computed tomography (3DCT) is used in planning stereotactic body radiotherapy (SBRT) for lung cancer (3D plan). To accurately evaluate dose distribution for internal target volume (ITV), we recalculated a 3D plan using all breathing phases for four-dimensional computed tomography (4DCT). Methods: The study included 8 patients with one tumor each who underwent SBRT for stage I lung cancer. After performing free-breathing 3DCT, 4DCT was performed. The prescription dose in the 3D plan was 48 Gy/4 fr or 56 Gy/7 fr for the ITV mean in 3DCT. We recalculated 3D plan radiation conditions for each breathing phase of 4DCT and accumulated dose distributions for all breathing phases (4D plan) with deformable image registration. A dose-volume histogram and a dose distribution map were used to evaluate dose distribution. Results: For all patients, the maximum difference between the 3D and 4D plans for the minimum dose applied to 2% of the ITV or ITV mean was 2.6% and 1.7% respectively. For the 3 patients who exhibited substantial respiratory movement of the tumor, the dose distribution changed in accordance with the observed differences in tumor shadows for registered 4DCT and primary 3DCT during dose accumulation, and the difference between plans for the minimum dose applied to 98% of the ITV was relatively large, －6.7% to 2.9%. Conclusions: We used 4D plan evaluation to confirm that the intended doses were applied to the ITV using the 3D plan. When using a 4D plan with deformable image registration to evaluate the dose distribution of a 3D plan, the selection of primary computed tomography for dose accumulation is important.