- 作者：Yoshihiro Ueda ; M.S. ; ueda-yo@mc.pref.osaka.jp ; Masayoshi Miyazaki ; B.S. ; Kinji Nishiyama ; Ph.D. ; Osamu Suzuki ; Ph.D. ; Katsutomo Tsujii ; M.S. ; Ken Miyagi ; M.D.
- 关键词：Stereotactic body radiation therapy for lung cancer ; Four-dimensional computed tomography ; Interfractional variations ; Electric portal imaging devise ; PTV margin
- 刊名：International Journal of Radiation Oncology*Biology*Physics
- 出版年：2012
- 期刊代码：136_03603016
- 类别：med
- 出版时间：1 July, 2012
- 卷：83
- 期：3
- 页码：1064-1069
- 文件大小：335 K
Purpose
To evaluate setup error and interfractional changes in tumor motion magnitude using an electric portal imaging device in cine mode (EPID cine) during the course of stereotactic body radiation therapy (SBRT) for non-small-cell lung cancer (NSCLC) and to calculate margins to compensate for these variations.Materials and Methods
Subjects were 28 patients with Stage I NSCLC who underwent SBRT. Respiratory-correlated four-dimensional computed tomography (4D-CT) at simulation was binned into 10 respiratory phases, which provided average intensity projection CT data sets (AIP). On 4D-CT, peak-to-peak motion of the tumor (M-4DCT) in the craniocaudal direction was assessed and the tumor center (mean tumor position [MTP]) of the AIP (MTP-4DCT) was determined. At treatment, the tumor on cone beam CT was registered to that on AIP for patient setup. During three sessions of irradiation, peak-to-peak motion of the tumor (M-cine) and the mean tumor position (MTP-cine) were obtained using EPID cine and in-house software. Based on changes in tumor motion magnitude (鈭哅) and patient setup error (鈭哅TP), defined as differences between M-4DCT and M-cine and between MTP-4DCT and MTP-cine, a margin to compensate for these variations was calculated with Stroom鈥檚 formula.
Results
The means (卤standard deviation: SD) of M-4DCT and M-cine were 3.1 (卤3.4) and 4.0 (卤3.6) mm, respectively. The means (卤SD) of 鈭哅 and 鈭哅TP were 0.9 (卤1.3) and 0.2 (卤2.4) mm, respectively. Internal target volume-planning target volume (ITV-PTV) margins to compensate for 鈭哅, 鈭哅TP, and both combined were 3.7, 5.2, and 6.4 mm, respectively.
Conclusion
EPID cine is a useful modality for assessing interfractional variations of tumor motion. The ITV-PTV margins to compensate for these variations can be calculated.