Cobalt-60 systems, like the Gamma Knife, deliver radiation beams through 192 circular pinholes in a fixed helmet worn by the patient. The pinhole radiation meets at the tumor site, delivering a high dose, while the surrounding healthy tissue and critical brain structures receive minimal radiation. These systems offer treatment options with proven effectiveness and high precision and for decades were the only dedicated radiosurgery systems for the treatment of brain metastases.
The cobalt-60 system is designed to deliver radiation in the shape of a sphere. To cover irregularly shaped tumors, several of these radiation spheres have to be used. If a metastasis is pear-shaped, for example, then two different sized spheres must be used to mimic the shape of the tumor. Newer systems automatically change the width of radiation beams and the position of the patient to create more variations and improve the overall delivery process. With this technology, physicians can also treat multiple brain metastases one after another in one automated procedure. Although the total required treatment time increases with every metastasis, new Cobalt-60 systems offer very precise treatment options with proven effectiveness.
In the morning before treatment, a head frame is secured to the patient’s skull so there is no chance of movement later during the treatment. The patient is then scanned. The brain metastases are carefully outlined on the scans and a radiosurgery plan is made. The goal of the plan is to focus as much of the radiation dose as possible on the metastasis and, at the same time, spare the healthy tissue surrounding the metastasis. Once the patient is positioned on the table with the head frame fixed into place, all metastases are treated one after the other.