A formalism for independent checking of Gamma Knife dose calculations

For stereotactic radiosurgery using the Leksell Gamma Knife system, it is i mportant to perform a pre-treatment verification of the maximum dose calcul ated with the Leksell GammaPlan((R)) (D-LGP) stereotactic radiosurgery syst em. This verification can be incorporated as part of a routine quality assu rance (QA) procedure to minimize the chance of a hazardous overdose. To imp lement this procedure, a formalism has been developed to calculate the dose D-CAL(X,Y,Z,d(av),t) using the following parameters: average target depth (d(av)), coordinates (X,Y,Z) of the maximum dose location or any other dose point(s) to be verified, 3-dimensional (3-dim) beam profiles or off-center -ratios (OCR) of the four helmets, helmet size i, output factor O-i, plug f actor Pi, each shot j coordinates (x,y,z)(i,j), and shot treatment time (t( i.j)). The average depth of the target d(av) was obtained either from MRI/C T images or ruler measurements of the Gamma Knife Bubble Head Frame. D-CAL and D-LGP were then compared to evaluate the accuracy of this independent c alculation. The proposed calculation for an independent check of D-LGP has been demonstrated to be accurate and reliable. and thus serves as a QA tool for Gamma Knife stereotactic radiosurgery. (C) 2001 American Association o f Physicists in Medicine.