Generation of uniformly distributed dose points for anatomy-based three-dimensional dose optimization methods in brachytherapy

We have studied the accuracy of statistical parameters of dose distribution s in brachytherapy using actual clinical implants. These include the mean, minimum and maximum dose values and the variance of the dose distribution i nside the PTV (planning target volume), and on the surface of the PTV. Thes e properties have been studied as a function of the number of uniformly dis tributed sampling points. These parameters, or the variants of these parame ters, are used directly or indirectly in optimization procedures or for a d escription of the dose distribution. The accurate determination of these pa rameters depends on the sampling point distribution from which they have be en obtained. Some optimization methods ignore catheters and critical struct ures surrounded by the PTV or alternatively consider as surface dose points only those on the contour lines of the PTV. D-min and D-max are extreme do se values which are either on the PTV surface or within the PTV. They must be avoided for specification and optimization purposes in brachytherapy. Us ing D-mean and the variance of D which we have shown to be stable parameter s, achieves a more reliable description of the dose distribution on the PTV surface and within the PTV volume than does D-min, and D,,. Generation of dose points on the real surface of the PTV is obligatory and the considerat ion of catheter volumes results in a realistic description of anatomical do se distributions. (C) 2000 American Association of Physicists in Medicine. [S0094-2405(00)01105-6].