An investigation of eye lens complication for gamma knife radiosurgery of trigeminal neuralgia

We report in-vivo dosimetry and phantom study results for determining complication rate of the eye lens for trigeminal neuralgia (TN) patients treated using gamma knife radiosurgery. This study is driven by the observation that a large dose such as 70-80 Gy was generally prescribed for trigeminal neuralgia, and, therefore, a small percentage (2-3%) of scattering dose to the lens of the eye could reach or even exceed its tolerance dose. In-vivo dosimetry measurements on six patients and a head phantom were performed to investigate these effects. The average lens dose was measured to be 0.077/spl plusmn/0.006 Gy. This value is significantly lower than the 1-2% as predicated from the gamma knife treatment planning system. Using an empirical biological model, the probability of the lens complication was determined to be 0.1%. This low rate confirms our clinical findings that few TN patients develop cataracts.