im not very familiar with tomotherapy, but from what i have read of the literature, survival for patients with brain metastases (depending on the histology, # of lesions, pre-rx KPS, etc) treated with GKSRS and linac based RS are fairly similar. moreover, since GKSRS is more prevalent in the united states than tomotherapy is, it is readily available to the general public, who may not have the opportunity to be treated at places such as hopkins or the brigham with cutting edge technology. ive trained/studied/rotated at institutions where GKSRS was the preferred treatment over linac based RS, with bigger names in the field (suh, shaw, steiner).