You are asking your neurosurgeon a very valid question about why he is choosing only one CK session. I find it disturbing that he couldn't or wouldn't give you an answer. Have you met with the radiation oncologist? Being Kaiser, my fear would be that one session was chosen because it is less expensive than three.
Do you have the option of getting a second opinion elsewhere? Redwood City is half an hour from Stanford, where CK was pioneered. I had mine done there in 2017 with Dr. Stephen Chang, and his standard procedure is three sessions.
As for CK itself, it's pretty much a walk in a park. It works like this: Lie there with your comfy mask and heated blankets. Listen to music. Have a little rest afterward, probably taking a steroid tablet with a glass of juice. Get up and go to lunch. After my first session, I was stunned that my tinnitus disappeared within hours. (That's unusual.) Otherwise, I felt nothing. However, after the third session, I was bone tired and couldn't wait to take a nap. That hit-the-wall fatigue lasted for a number of weeks--fixed each day with a nap--but gradually it disappeared.
Keep us posted on your journey.