Selective Beam Shielding Method of Gamma-Knife Unit Using Various Plugging Patterns

Jang,  Geon Ho; Lim,  Young Jin; Shin,  Dong Oh; Choi,  Doo Ho; Hong,  Seong Eon; Leem,  Won

J Korean Soc Ther Radiol > Volume 11(2); 1993 > Article

Original Article

Journal of the Korean Society for Therapeutic Radiology 1993;11(2): 439-448.

Selective Beam Shielding Method of Gamma-Knife Unit Using Various Plugging Patterns

Geon Ho Jang, Young Jin Lim, Dong Oh Shin, Doo Ho Choi, Seong Eon Hong, Won Leem

¹Department of Therapeutic Radiology, Kyung Hee University School of Medicine, Seoul, Korea.
²Department of Neurosurgery, Kyung Hee University School of Medicine, Seoul, Korea.

ABSTRACT

The B-type gamma knife unit was installed at Kyung-Hee University Hospital in March 1992. The selective beam plugging method can be used to reduce the low percentage isodose profiles of normal sensitive organ and to codify the isodose cuties of treatment volume for better shaping of the target volume. For representing the changes of the law percentage isodose profiles, the variations of dose distribution for several cases were discussed in this paper. The film dosimetry was performed for the evaluation of calculated isodose profiles predicted by KULA dose planning system. The results were verified by RFA-3 automatic densitometry. The clinical application of selective beam shielding method was performed in 17 patients in 100 patients who have undergone gamma knife radiosurgery for a year. The calculated and the measured isodose profiles for the high percentage regions were well consistent with each other. When the target of pituitary tumor is macro-size, the selective beam shielding method is the most applicable method. When the target size, however, is small, the correct selection of the proper helmet size is very important. All patients were exposed almost about 3~12 Gy for brain stem, and 3~11.2 Gy for optic apparatus. It is recommended that the same or other plugging patterns with multiple isocenters should be used for protection of the radiosensitive normal structures with precise treatment of CNS lesions.

Key Words: Stereotaclic radiosurgery, Selective beam shielding method, Plugging pattern, Multiple isocenters