Comments on "Sampling techniques for the evaluation of treatment plans" [Med. Phys. 20, 151-161 (1993)].

We believe that, for the purpose of evaluation and optimization of treatment plans, quasirandom sampling is superior to grid sampling and should be the method of choice. We believe it to be on average more efficient than grid sampling (i.e., more accurate for any given number of dose estimates) and, even more importantly, more reliable in that it is subject to less variability due to shape and orientation of the particular VOI--as demonstrated in Fig. 2. As a rule of thumb we recommend using about 400 quasirandom samples per volume of interest. For many situations this number is a conservative estimate; for a few situations more samples might be necessary. Optimal sampling for the purpose of calculation and presentation of the dose distribution is a different story which we have addressed elsewhere.