Dosimetric effects of rotational offsets in stereotactic body radiation therapy (SBRT) for lung cancer

作者：Yang Yun; Catalano Suzanne; Kelsey Chris R; Yoo David S; Yin Fang Fang; Cai Jing^*

来源：Medical Dosimetry, 2014, 39(1): 117-121.

DOI：10.1016/j.meddos.2013.11.002

• Lung SBRT
• Rotation
• 6D correction
• IGRT

To quantitatively evaluate dosimetric effects of rotational offsets in stereotactic body radiation therapy (SBRT) for lung cancer. Overall, 11 lung SBRT patients (8 female and 3 male; mean age: 75.0 years) with medially located tumors were included. Treatment plans with simulated rotational offsets of 1 degrees, 3 degrees, and 5 degrees in roll, yaw, and pitch were generated and compared with the original plans. Both clockwise and counterclockwise rotations were investigated. The following dosimetric metrics were quantitatively evaluated: planning target volume coverage (PTV V-100%), max PTV dose (PTV D-max), percentage prescription dose to 0.35 cc of cord (cord D-0.35 cc), percentage prescription dose to 0.35 cc and 5 cc of esophagus (esophagus D-0.35 cc and D-5 cc), and volume of the lungs receiving at least 20 Gy (lung V-20). Statistical significance was tested using Wilcoxon signed rank test at the significance level of 0.05. Overall, small differences were found in all dosimetric matrices at all rotational offsets: 95.6% of differences were < 1% or < 1 Gy. Of all rotational offsets, largest change in PTV V-100%, PTV D-max, cord D-0.35 cc, esophagus D-0.35 cc, esophagus D-5 cc, and lung V-20 was - 8.36%, - 6.06%, 11.96%, 8.66%, 6.02%, and - 0.69%, respectively. No significant correlation was found between any dosimetric change and tumor-to-cord/esophagus distances (R-2 range: 0 to 0.44). Larger dosimetric changes and intersubject variations were observed at larger rotational offsets. Small dosimetric differences were found owing to rotational offsets up to 5 degrees in lung SBRT for medially located tumors. Larger intersubject variations were observed at larger rotational offsets.

• 出版日期2014