[1] Natl Hosp Neurol & Neurosurg, Gamma Knife Ctr, Queen Sq, London, England
[2] Univ Oxford, Green Templeton Coll, Oxford, England
[3] UCL, Dept Med Phys & Biomed Engn, Wellcome EPSRC Ctr Intervent & Surg Sci, London, England
[4] UCL, Dept Med Phys & Biomed Engn, Ctr Med Image Comp, London, England
[5] Kings Coll London, Sch Biomed Engn & Imaging Sci, London, England
[6] Mayo Clin & Mayo Fdn, Dept Neurosurg, Rochester, MN USA
[7] Univ Calif San Francisco, Dept Radiat Oncol, San Francisco, CA USA