Trigeminal Neuralgia*

My 92 year old father was diagnosed with Trigeminal Neuralgia more than a decade ago. For a long time Amitriptyline kept the 'strikes' at bay. He became symptomatic again last October. In March they did a Gamma Knife radiation treatment. This halted his symptoms for about 6 weeks. Two weeks ago he started having daily 'strikes' again. His PCP switched him from Amitriptyline to Lyrica. Now that he is weaned completely off the Amitriptyline and on the full dose of Lyrica he is having 'strikes' several times a day. The local neurosurgeons won't consider surgery, but we are desperate. Any insights at all on any therapeutic modalities would be appreciated. Acupuncture was not effective.