Consistency of three-dimensional planning target volumes across physicians and institutions

Purpose: Three-dimensional treatment planning depends upon exact and consistent delineation of target volumes. This study tested whether different physicians from different institutions vary significantly in their creation of planning target volumes (PTVs). Methods and Materials: Eight physicians from three different institutions created partial planning target volumes for nine clinical test cases. Their target volumes were evaluated qualitatively and quantitatively. Quantitative results were tested for significant differences. Results: Qualitative analysis showed the physicians to vary in (a) the margin placed around the clinical target volume, (b) the margin used near critical structures, and (c) handling of concavities in the clinical target volume. Quantitative analysis showed these variations to result in statistically significant differences in the measured volume of the physicians' planning target volumes. Conclusions: Individual physicians and institutions differ significantly in their creation of planning target volumes, suggesting individual and institutional differences in the working definition for the PTV. Implications of this fact are discussed, along with areas where standardization can be improved