‰ͺŽRˆγŠw‰ο Acta Medica Okayama 0030-1558 102 1-2 1990 “dŽqόŽ‘—ΓŽž‚Ι‚¨‚―‚ιƒGƒlƒ‹ƒM[’αŒΈ•ϋ–@‚ΙŠΦ‚·‚ιŒŸ“’ 217 225 EN Yoshitada Nakagiri Toshiharu Yamada Katsuhiko Sugita Yasutaka Mikami Yoshihiro Ohkawa Kenji Inamura Nobuhiro Oguri Isao Nagaya Toshiaki Noriyasu Yoshio Okazaki Nobuhiro Inoue Izumi Togami Yoshio Hiraki The declerator and bolus, which reduce radiant energy in electron beam radiotherapy, were investigated with respect to the interrelation between their quality of material, thickness and position, and the mean energy anf depth-dose rate curve pattern. The data obtained indicated that an acryl decelerator fitted to the tube aperture had the disadvantage of entailing bremsstrahlung x-ray intervention as well as increased depth dose. An elastomeric bolus placed on the phantom surface, however, resulted in an increase surface dose and minmal x-ray intervention. When radiation was performed with the phantom surface held apart from the bolus, a build-up phenomenon occurred on the phantom surface with a consequent diminution of surface dose. It was concluded that a bolus is more effective than a decelerator fitted to the tube aperture for attenuation of radiant energy. It is more advantageus to irradite with the bolus in contact with the skin in cases in which the target is localized in the superficial layer of the skin, and with the bolus apart from the skin in cases in which the target is situated deeper below the skin. No potential conflict of interest relevant to this article was reported.