Miyabe Yuki, Yano Shinsuke, Okada Takashi, Nakata Manabu, Teshima Teruki, Nagata Yasushi, Hiraoka Masahiro
Department of Medical Physics & Engineering, Osaka University Graduate School of Medicine.
Nihon Hoshasen Gijutsu Gakkai Zasshi. 2004 Oct;60(10):1444-51. doi: 10.6009/jjrt.kj00003326547.
In fractionated stereotactic radiotherapy (SRT), the accuracy of patient relocation is very important. The Gill-Thomas-Cosman (GTC) re-locatable stereotactic frame is used for patient immobilization. A depth helmet and measuring probe are used to check the stability of the patient's head position relative to the GTC frame. However, displacement error caused by rotation of the patient's head is not considered in the depth-helmet measurement. Consequently, displacement of the isocenter position cannot be confirmed by the measurement obtained from the depth helmet. In this study, we evaluated the precision of reproducibility by comparing measurement values of the depth helmet with the displacement of anatomical position on a CT image. We analyzed 21 setups of 8 patients immobilized for SRT using the GTC frame, between June 2001 and June 2003. The reproducibility of the GTC frame was checked at each treatment by comparing it with the treatment planning position. The average discrepancy of the GTC frame set-up measured by the depth helmet was 0.6 mm, with a standard deviation of 0.3 mm. The result measured by CT was 0.7 mm, with a standard deviation of 0.4 mm. When the error of each measurement point was within 1.0 mm, the accuracy of relocation of the patient could be considered clinically acceptable. Displacement error not considered in the measurement of the depth helmet could be evaluated by using CT.
在分次立体定向放射治疗（SRT）中，患者重新定位的准确性非常重要。吉尔 - 托马斯 - 科斯曼（GTC）可重新定位立体定向框架用于患者固定。使用深度头盔和测量探头来检查患者头部位置相对于GTC框架的稳定性。然而，深度头盔测量未考虑患者头部旋转引起的位移误差。因此，不能通过深度头盔获得的测量来确认等中心位置的位移。在本研究中，我们通过比较深度头盔的测量值与CT图像上解剖位置的位移来评估再现精度。我们分析了2001年6月至2003年6月期间使用GTC框架固定接受SRT治疗的8例患者的21次设置。每次治疗时，通过将GTC框架与治疗计划位置进行比较来检查其再现性。深度头盔测量的GTC框架设置的平均差异为0.6毫米，标准差为0.3毫米。CT测量结果为0.7毫米，标准差为0.4毫米。当每个测量点的误差在1.0毫米以内时，患者重新定位的准确性可被认为在临床上是可接受的。可以使用CT评估深度头盔测量中未考虑的位移误差。
