Technical note: The effect of the 4-mm-collimator output factor on gamma knife dose distributions

We present results of investigations of the clinical significance of variations in the value of the 4-mm-collimator output factor, OF4/18. Changes in treatment volume, dose-volume histograms (DVHs), and isodose distributions were studied, by varying OF4/18 up to 20. The variations were performed on a sample of clinical patient treatment plans for which the 4 mm collimator was used. Although smaller effects are noted for the prescription isodose line, greater dosimetric changes occur for higher dose regions within the target. 2003 American College of Medical Physics.