An investigation of eye lens dose of stereotactic radiosurgery for trigeminal neuralgia using Leksell Gamma Knife model C.

Abstract

The authors conducted a study to assess the eye lens dosimetry in trigeminal neuralgia (TN) treatment when using the Leksell Gamma Knife model C. Phantom studies were used to measure the maximal dose reaching the eye lens with and without eye shielding. Six consecutive patients with TN were evaluated for Gamma Knife surgery (GKS). The maximum prescribed dose of 80 Gy was delivered with a single shot using the 4-mm collimator helmet. High-sensitivity thermoluminescence dosimeter chips (TLDCs) were used to measure the dosimetry. In vitro, the Leksell GammaPlan (LGP) system predicted the mean maximal doses of 1.08 +/- 0.08 and 0.15 +/- 0.01 Gy (mean +/- standard deviation) to the lens ipsilateral to the treated trigeminal nerve without and with eye shielding, respectively. The TLDCs-measured dosimetry indicated the mean maximal doses of 1.12 +/- 0.09 and 0.17 +/- 0.01 Gy without and with eye shielding, respectively. The maximal doses to the lens contralateral to the nerve were similar. In vivo, the LGP predicted the mean maximal doses to the lens ipsilateral to the treated nerve as 1.1 +/- 0.07 and 0.16 +/- 0.02 Gy, respectively, without and with eye shielding. The dosimetry measured by TLDCs indicated the mean maximal dose to the lens ipsilateral to the treated nerve as 0.17 +/- 0.02 Gy with eye shielding. The mean maximal doses to the lens contralateral to the nerve were similar. Using the 110 and 125 degrees gamma angles, the LGP predicted the mean maximal doses of 0.32 +/- 0.04 and 0.12 +/- 0.04 Gy to the lens without and with eye shielding, respectively. Patients with TN undergoing GKS without eye shielding may develop cataracts due to the high radiation dose to the eye lenses. The authors suggest the routine use of bilateral eye shielding for the patients.