Principles in positioning cross-projecting lasers.

ABSTRACT

With the increased sophistication of lasers used for patient positioning in radiotherapy comes increased possibilities for mistakes in installing the lasers, which can result in serious patient positioning errors. Two principles must be followed when mounting cross-projecting lasers (1) the horizontal line must be on the same level as the treatment unit isocenter, and the vertical line must be coplanar with the gantry rotation, and (2) If one of the lines of the cross rotates, it must be the line which is perpendicular to the line joining the two holes from which the laser beams exit the laser casing.