“…Significant variation exists in the prescribed radiation doses in previously published series. 1,3,13,17,28,29 It must be emphasized that the actual delivered dose might be different from the prescribed maximal dose from one GK unit to another due to variations in the output factor for the 4-mm collimator, 0.8-0.85, depending on the institution and medical physics techniques used to measure the output factor. 19 In addition, several other parameters such as advanced patient age, the presence of concomitant vasculopathy, systemic diseases such as multiple sclerosis, a small trigeminal cistern, and/or a history of previous radiosurgical treatments may lead to the use of a lower radiation dose.…”