Wong V Y W, Tung S Y, Leung T W, Ho K H S
Department of Clinical Oncology, Tuen Mun Hospital, Hong Kong, People's Republic of China.
Clin Oncol (R Coll Radiol). 2003 Aug;15(5):280-7. doi: 10.1016/s0936-6555(03)00091-8.
This study introduces a non-invasive method based on computed tomography (CT) verification to ensure patients are accurately positioned before fractionated stereotactic radiotherapy. It enables quality control of mask positioning with reference to the CT images of the treatment plan.
A mask system, together with a dental impression moulded mouth bite, was used for patient immobilisation. In order to facilitate relevant image comparison, special alignment during CT localisation was discussed in the study. The accuracy of patient set-up was studied by assessing the isocentre position in relation to the patient's anatomical structure. The planning CT images were applied as a reference and the study was applied to 261 cranial applications.
The results show that the mean and the maximum overall displacements at the isocentre were 0.7 and 2.5 mm, respectively. The mean and the maximum rotational displacement in the axial plane were 0.56 degrees and 2 degrees, respectively. The mean translational displacement and rotational displacement were close to zero when considering the direction of movement.
The results indicate that the systematic error of the mask system and the verification method are minimal. Advantages of this technique include the simple set-up, three-dimensional quantification and short study time (10-15 min). It is therefore practical to implement on a routine basis. Investigation of the ability to relocate the mask is also recommended to justify the required safety margin between the clinical and planning target volumes.
本研究介绍一种基于计算机断层扫描（CT）验证的非侵入性方法，以确保患者在分次立体定向放射治疗前准确就位。它能够参照治疗计划的CT图像对面罩定位进行质量控制。
使用面罩系统以及牙科印模制成的口咬器来固定患者。为便于进行相关图像比较，本研究讨论了CT定位期间的特殊对齐方式。通过评估等中心位置相对于患者解剖结构的情况来研究患者摆位的准确性。将计划CT图像用作参考，该研究应用于261例颅脑治疗。
结果显示，等中心处的平均总位移和最大总位移分别为0.7毫米和2.5毫米。轴向平面内的平均旋转位移和最大旋转位移分别为0.56度和2度。考虑运动方向时，平均平移位移和旋转位移接近零。
结果表明面罩系统和验证方法的系统误差极小。该技术的优点包括设置简单、三维定量以及研究时间短（10 - 15分钟）。因此，在常规基础上实施是可行的。还建议对面罩重新定位的能力进行研究，以确定临床靶区与计划靶区之间所需的安全 margins。 （注：原文中“margins”可能表述有误，根据语境推测可能是“margin”，意为“边缘、余量”等，这里按“安全 margin”翻译，具体含义需结合完整医学背景确定）
