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Physician Inquiry - Physics: How does it Work?
-- Courtesy of NASA |
The gamma knife has 201 Co-60 sources of equal activity totalling 2.2X10
GBq. They are positioned to emanate gamma rays through a primary and a
secondary collimator such that the gamma rays focus to an oblate spheroid of
from 4 - 18mm average diameter. The 4mm focal ellipsoid has a penumbre of
1mm from the 50%-10% of its maximum profile. With careful positioning and
weighting of the 4,8,14, and 18mm focal spheroids, extremely sharp dose
volume histograms can be attained for the target and nearby critical
structures. Blocking of up to half of the 201 sources affords even tighter
control of dose shaping to the target and adjacent critical structures. |
