||Superiority of a soft tissue-based setup using cone-beam computed tomography over a bony structure-based setup in intensity-modulated radiotherapy for prostate cancer
Sato, Hiraku佐藤, 啓
29 , 2015-09-24 , 新潟大学
学位の種類: 博士（医学）. 報告番号: 甲第4061号. 学位記番号: 新大院博（医）甲第650号. 学位授与年月日: 平成27年9月24日
Journal of Applied Clinical Medical Physics. 2015, 16(5), 239-245.
Purpose: To test the superiority of a soft tissue-based setup using cone-beam computed tomography (CBCT) to a bony structure-based setup using the ExacTrac system in intensity-modulated radiotherapy (IMRT) for prostate cancer. Methods: We studied 20 patients with localized prostate cancer who received IMRT between November 2010 and February 2012. After the initial setup, the pelvic bony structure-based setup and ExacTrac system were applied. After that, CBCT and a soft tissue-based setup were used. A shift in the isocenter between the ExacTrac-based and CBCT-based setup was recorded in the anterior-posterior (AP), superior-inferior (SI), and left-right (LR) axes. The shift was considered an inter-fractional prostate shift. Post-treatment CBCT was also taken once a week to measure the intra-fractional prostate shift, based on the coordinates of the isocenter between pre- and post-treatment CBCT. The planning target volume (PTV) margins were determined van Herk's method. We measured the elapsed time required for soft tissue matching and the entire treatment time using CBCT. Results: The means ± standard deviation (SD) of the inter- and intra-fractional shifts were 0.9 ± 2.8 mm and −0.30 ± 1.4 mm in the AP, 0.9 ± 2.2 mm and −0.1 ± 1.2 mm in the SI, and 0.1 ± 0.7mm in the LR. The PTV margins in the cases of bony structure-based and soft tissue-based setup were 7.3 mm and 2.7 mm in the AP, 5.8 mm and 2.3 mm in the SI, and 1.9 mm and 1.2 mm in the LR. Even though the median elapsed time using CBCT was expanded in 5.9 minutes, the PTV margins were significantly reduced. Conclusions: We found the calculated PTV margins in the soft tissue-based setup using CBCT were small, and this arrangement was superior to the bony structure-based setup in prostate IMRT.