| 摘要 |
PROBLEM TO BE SOLVED: To obtain an accurate irradiation field by equipping a member for guiding and retaining the track of a constriction block in a track groove being provided opposingly on the proximity surface of the constriction block that orthogonally crosses the direction of radiation and approaches so that it can travel. SOLUTION: The irradiation field of radiation from a radiation source S is determined by constriction bodies 10A and 10B and constriction bodies 11A and 11B. The constriction bodies 10A, 10B, 11A, and 11B are composed by the combination of a plurality of constriction blocks 12 nearly in a plate shape. A ball bearing is arranged on the opposing surfaces of the constriction blocks 12, the opposing positions of the adjacent constriction blocks 12 are supported by the ball beating slidably. The constriction blocks 12 are driven by a drive motor 23 with an encoder 24 for detecting a position individually.
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