48 以下何種放射手術治療技術無法處理顱外（extracranial）的腫瘤或病變？
(A) X-knife
(B) Gamma Knife
(C) Tomotherapy
(D) Proton therapy

Gammanknife

-         nThe gamma knife delivers radiation to a target lesionnin the brain by simultaneous irradiation with a large number of isocentric gamma ray beams.

-         nIn a modern unitn201 Co-60 sources are housed in a hemispherical shield and the beamsnare collimated to focus on a single point at a source-to-focus distance of 40.3cm.

-         nGamma knife can only be used for small lesions because of its field size limitation (max. diameter = 18mm), although several isocenter can benplaced with the same target to expand or shape dose distribution.

-         nFor the same reasons, gamma knife can produce a more conformal dose distributionnthan that possible with x-ray knife unless the latter is equipped with specialnfield-shaping collimators such as the dynamic MLC.

<出處>

 ”ThenPhysics of Radiation Therapy”, 3^rd edition, P.514-515