新しい原理，装置によるLinear Acceleratorを用いたRadiosurgery—その原理・装置と臨床経験

A New Principle and Device for Radiosurgery Using a Linear Accelerator; Its principle, devices and clinical trials

I．はじめに

　細い放射線東を脳定位的手技を用いて脳内の病巣部に集中させ，開頭手術をすることなしに病巣を破壊・治療する方法はmdiosurgeryと名付けられ，脳神経外科領域での新しい治療法として脚光を浴びている．radiosur—geryの開発・発展と普及はKarolinska InstittiteのLek—sellおよびその一門の大きな貢献によるものである．Leksellらは1950年代初めよりLinear acceleratorよりのphoton，cyciotronよりのproton beamなどを用いてradiosurgeryの開発を試み，最終的には半球面上に配置した179個または201個の₆₀CO線源よりのγ線束を頭蓋内の病巣部に集中させる装置：gamma unitda—破壊部と非破壊部の境界がナイフで切ったような鋭さをもっているのでgamma knifeともよばれる—を完成させた．この装置は極めて高価であるにもかかわらず，現在田1界で10カ所以上の施設に設置され，一定の条件のAVMや各種腫瘍にradiosurgery治療が行われ，成果をあげている．わが国でも第1号機が東大病院に導入され，1990年6月より臨床的試用が開始されていることは周知の通りである．

Abstract

The authors have developed new devices for stereotactic radiosurgery using a conventional linear accelerator (LINAC). The system of devices consists of a rotatory chair with a base ring holder, a Brown Robert Well's stereotactic apparatus (BRW's apparatus) with a double set of base rings and a number of precise collimators which eliminate penumbra to the greatest extent. A study rotatory chair was manufactured, whose vertical axis of rotation is always set and stable. A strongly built, adjustable holder for the BRW's base ring is attached to the chair.

The principle and flow of procedures step by step is as follows ; 1) . The rotatory chair is carried in under the linear accelerator and the vertical rotatory axis of the chair is precisely adjusted to align with the vertical center of the photon beam from the LINAC. 2) A base ring and a locator of BRW's apparatus are mounted on a patient's head and three coordinates of a target are determined by CT scans. 3) The target indicator of thedummy set of BRW's apparatus is positioned according to X, Y, Z coordinates of the target. The tip of a rod in-dicator fixed on an instrument bloc on the arc device is precisely adjusted to touch at the tip of the target in-dicator. 4) The base ring and arc device with rod in-dicator are transfered together from the BRW's dummy set to the rotatory chair and fixed to the base ring hol-der. The tip of the rod indicator is precisely adjusted to be positioned at the isocenter of the LINAC. 5) The base ring and arc device are removed and replaced by another base ring mounted on the head of a patient, who is made to sit on the rotatory chair. The target in the brain is now located at the isocenter of the LINAC. Stereotactic radiation is started with rotation of the chair and circular movement of the gantry of the LINAC. The chair is rotated at a speed of 100° per second, and the gantry of the LINAC is moved slowly on a circular trajectory from +115° to -115°. Fourteen cases, including AVM, cavernous angioma, acoustic tumor and glioma have been treated so far. Three cases of large AVM were treated by a combina-tion of artificial embolization and stereotactic radiosurgery. The follow-up period of these cases is not yet long enough for final evaluation of therapeutic efficacy, however, disappearance or marked decrease in size of lesions has been confirmed so far in 3 AVMs, 2 cavernous angiomas, 1 acoustic tumor and 1 glioma. Advantages of stereotactic radiosurgery using our de-vices are its simplicity and economical benefits.