Gamma KnifeŽ Treatment Plan Improvements
The Leksell Gamma KnifeŽ is used to treat intracranial lesions without invasive surgery. An array of 201 Cobalt-60 sources arranged on a semi-sphere delivers radiation in a few millimeter spot. The prototype designed by Dr. Lars Leksell debuted in 1967. Today, around 30,000 patients are treated with the Leksell Gamma Knife annually.
Gamma Plan vs. Penelope
Leksell Gamma Knife is accompanied with an integrated treatment planning package, Gamma PlanŽ. The Gamma Plan algorithm assumes passage of radiation through a uniform material. Actually, gamma radiation beams pass through tissue materials with different mass densities and atomic composition. To account for this, a Monte Carlo radiation transport code PENELOPE (Salvat et al 1996), was applied to simulate actual treatment. It was shown that Monte Carlo results are nearly identical to Gamma Plan output in a homogeneous media (see figures to the right) but substantially differ in heterogeneous media. Many millions of trajectories are needed by the nature of the Monte Carlo method for statistical accuracy. This requires increasing the speed of the simulation.
Parallelization of Penelope
A requirement of the Monte Carlo method is the independence of the statistical events and processes. Since each particle trajectory is assumed not to alter the media,
they may be considered independent and calculated in parallel. The primary modification required to the PENELOPE code was the introduction of a parallel random number
generator to insure no number correlations between processors. Dosage calculation times reduced from approximately 8 hours in serial form to several minutes using the IBM
Research SP.
For more information, visit: http://www.iupui.edu/~neurosur/GammaKnife.html/
