D'Souza H, Joshi R C, Ganesh T, Subramani V, Vasu G, Kumar R, Julka P K, Rath G K
Department of Radiation Oncology, Institute Rotary Cancer Hospital, All India Institute of Medical Sciences, Ansarinagar, New Delhi, India.
Australas Radiol. 1999 Aug;43(3):342-5. doi: 10.1046/j.1440-1673.1999.433691.x.
Stereotactic irradiation, either in the form of stereotactic radiosurgery (SRS) or stereotactic radiotherapy (SRT) of brain lesions requires high precision and submillimetre accuracy in the isocentre, the main determinants being gantry and couch rotations. It is thus necessary to evaluate the isocentre variation due to gantry and couch rotations in the particular setup for SRS/SRT. This paper describes variation in the isocentre of a Philips (now Elekta) SL-20 linear accelerator modified for adapting a couch-mounted radiosurgery system. By considering the isocentre as defined by a mechanical index as the standard, the variations in the isocentre of the linear accelerator were independently measured for the gantry and for couch rotations. The variation in the isocentre for gantry rotation was found to be between 0.1 mm and 0.9 mm, conforming to the submillimetre accuracy required for SRS/SRT. However, the isocentre variation due to couch rotation varied considerably, possibly because the couch is of the RAM type. The isocentre variation due to couch rotation is rectified by microadjusting the couch mount at the time of treatment using a laser target localizing frame. It is our conclusion that a modified linear accelerator can be used for performing SRS/SRT after careful and separate evaluation of the isocentre stability due to gantry and couch rotations.
立体定向放射治疗，无论是采用立体定向放射外科手术（SRS）还是立体定向放射治疗（SRT）来治疗脑部病变，都需要在等中心具备高精度和亚毫米级的准确性，主要的决定因素是机架和治疗床的旋转。因此，有必要在SRS/SRT的特定设置中评估由于机架和治疗床旋转而导致的等中心变化。本文描述了一台为适配安装在治疗床上的放射外科手术系统而改装的飞利浦（现为医科达）SL-20直线加速器等中心的变化情况。以由机械指标定义的等中心作为标准，分别测量了直线加速器在机架旋转和治疗床旋转时等中心的变化。发现机架旋转时等中心的变化在0.1毫米至0.9毫米之间，符合SRS/SRT所需的亚毫米级精度。然而，由于治疗床旋转导致的等中心变化差异很大，这可能是因为治疗床是RAM类型的。在治疗时使用激光靶点定位框架对治疗床支架进行微调，可以纠正由于治疗床旋转导致的等中心变化。我们的结论是，经过改装的直线加速器在仔细且分别评估了由于机架和治疗床旋转导致的等中心稳定性之后，可以用于进行SRS/SRT。
