During treatment, the helmet s 201 ports will focus the unit s carefully collimated gamma rays to converge simultaneously and precisely at the target tumor, with accuracy within 0.1 millimeter. The arrangement of radiation sources and the exacting collimation ensure minimal exposure to surrounding tissue. The total length of treatment is related to the size and location of the lesion, but the standard exposure time is between five and twenty minutes. At the end of the treatment, the couch automatically slides the patient from the unit and the stereotactic frame is removed. Observation continues for a short period, and the hospital stay is usually only overnight.
Patients are able to return to their usual daily routine immediately upon discharge.
As with any medical procedure, some risks are involved. Immediate side effects are extremely rare. The risks of traditional brain surgery, such as hemorrhage, infection, and stroke, are avoided with Gamma Knife radiosurgery. Because the positive effects of Gamma Knife treatment are realized over time, periodic imaging studies are conducted to confirm that growth of the tumor has been arrested and to ascertain whether shrinkage has occurred. In the case of AVMs, imaging will confirm that occlusion has taken place or that the malformation has disappeared.