Cylindrical dose distributions in pseudodynamic rotation radiosurgery: an experimental study.

A linac-based radiosurgical technique is reported which produces cylindrical isodose distributions covering cylindrical targets of arbitrary orientations within the patient's head. The technique uses rectangular collimators and 4 degrees of freedom: gantry and couch rotation, as defined by a previously known dynamic rotation technique, collimator rotation, and collimator length adjustment. The relationship between the four parameters is derived and because of its complexity, the cylindrical dynamic rotation technique is introduced as a pseudodynamic technique. For cylindrical targets, the cylindrical pseudodynamic technique is comparison to the standard spherical technique produces considerable dose savings to healthy tissue surrounding the target and gives a similar or better dose fall-off outside the target.