After a little research I came across a publication that I believe describes the type of radiation recommended for Colleen. A link to the full text of the publication is: https://www.redjournal.org/article/S0360-3016(02)02763-3/fulltext
The paper is authored by J.A. Williams at Johns Hopkins who has published 3 papers on this topic. Radiation is delivered by linear accelerator, but is not referred to as GammaKnife or Cyberknife. He mentions that this approach is frequently used when tumors grow back after surgical removal. It appears that 5 treatments are given and the usual dose of radiation is in the range of 25 Gys. It appears it is a very effective means of eliminating further tumor growth with approximately an 18% reduction in tumor size with minimal damage to the facial nerve.
My understanding is lower doses of radiation (usually around 13 GYS) are given by Cyberknife or GammaKnife in effort to preserve hearing. However, if hearing is already gone, higher doses of radiation may be preferable with larger tumors or to control tumors that have regrown.
At any rate, the 3 publication by Dr. Williams report very good outcomes for tumor reduction with minimal damage to healthy tissue.