| 摘要 |
<p>PURPOSE:To achieve elimination of adverse effect on back scattered rays caused by a stop or the like and moreover, higher accuracy of a dose distribution control by setting a dosimeter on the outlet side of an irradiation port of a spot-shaped collimator. CONSTITUTION:The outlet of a gantry 6 is provided with a collimator 10 for releasing spot-like X rays. The collimator 10 has an incident port 10A into which a rectangular X-ray beam is impinged and a spot hole 10B for releasing spot-like X rays. The spot hole 10B is a small hole which larger in opening toward the outlet side and a radiation shielding body such as lead is arranged in the perimeter thereof. A dosimeter 4 is set at the tip of the collimator 10. The dosimeter 4 is of a X-ray transmission type and, for example, employs a radiation detector integrated. In this case, as X rays pass, a current matching a passage thereof flows and, by monitoring the current, the dose of the spot-like X rays can be measured. This achieves a higher accuracy of dose distribution control while enabling the prevention of erroneous measurement of the dosimeter as caused by the scattered rays.</p> |
