치료조사면 및 블록 유형분석을 통한 적정다엽 콜리메이터 규모에 관한 연구

Analysis of Radiation Field and Block Pattern for Optimal Size in Multileaf Collimator

The patterns of the conventional radiation treatment fields and their shielding blocks are analysed to determine the optimal dimension of the MultiLeaf Collimator (MLC) which si considered as an essential tool for conformal therapy. Total 1169 radiation fields from 303 patients (203 from Asan Medical center, 50 from Baek Hosp and 50 from Hanyang Univ. Hosp.) were analysed for this study. Weighted case selection treatment site (from The Korean Society of Tehrapeutic Radiolog 1993). Ninety one percent of total fields have shielding blocks. Y axis is defined as leaf movement direction and it is assumed that MLC is installed on the cranial-caudal direction. The length of X axis were distributed from 4cm to 40xm (less than 21cm for 95% of cases) and Y axis from 5cm to 38cm (less than 22cm for 95% of cases). The shielding blocks extended to less than 6cm from center of the field for 95% of the cases. Start length for ninety five percent of block is less than 10cm for X axis and 11cm for Y axis. Seventy six percent of shielding blocks could be placed by either X or Y axis direction. 7.(% only by Y axis, 5.1% only X axis and It is reasonable to install MLC for Y direction. Ninety five percent of patients can be treated with coplanar rotation therapy without changing the collimator angle. Eleven percent of cases of cases were impossible to replace with MLC. Futher study of shielding technique is needed for 11% impossible cases. The treatment field dimension of MLC should be larger than 21cmX22cm. The MLC should be designed as a pair of 21 leaves with 1cm wide for an acceptable resolution and 17cm long to enable the leaf to overtravel at least 6m from the treatment field center.