My mother had breast cancer and metastasis into brain. She has completed IMRT Radiation Theraphy (16 sittings) 3 weeks before. I recently came to know about SRS-Gammaknife Radio surgery for Brain which is effective than normal RT. Pls need details.

Imrt vs gamma knife. Both are useful for different situations depending on the number, size and location of the lesions. Sometimes may be difficult to compare the roles without looking at the scans.
Poor prognosis. Brain mets represents late stage disease, If solitary then resection can be tried or if large lesion shrinks with IMRT then resection may be tried. When lesion is solitary then best RT is Gamma knife which is high intensity, low dose volume at about 2-3 cm. For larger lesion the high intensity localized RT is known as Cyberknife, delivered in a rotation system in which the patient is centered.
Depends on how many. Stereotactic Radiosurgery otherwise know as Gammaknife, Cyberknife, etc. is highly effective and in many ways safer treatment than IMRT Radiation therapy. But it cannot be used on everyone and depends on the numbers of metastasis and the size of them. If the tumors are bigger than 3 cm and/or numerous than SRS is not recommended.