A film technique for the determination of output factors and end effect times for the Leksell Gamma Knife.

The relative output factors of the four helmets for a model B Leksell Gamma Knife and the end effect times for each helmet have been measured. For the three helmets with the smallest-diameter collimators a technique employing Kodak XV-2 film was used. The measured output factors are in good agreement with the values recommended by the manufacturer. The end effect times vary with the collimator size, with the shorter time occurring with the smaller collimator.