The influence of grid size on accuracy in radiotherapy dose plotting.

The recent article by Niemierko and Goitein [Med. Phys. 16, 239-247 (1989)] illustrates well the errors which are occurring in plotting isodose lines. We wish to augment their analysis with similar work done at Cardiff a few years ago; to indicate some practical treatment outcomes they have omitted; to propose even more stringent requirements of the grid size used; and thus to further alert users and software manufacturers to this problem.