The Effects of the Shape and Size of the Clinical Target Volume on the Planning Target Volume Margin

PURPOSE: To investigate the impact of clinical target volume (CTV) shape and size on CTV to planning target volume (PTV) margin expansion. METHODS AND MATERIALS: Using numerical integration methods, margins accounting for random errors and systematic errors were calculated for CTVs of different shapes and sizes. We use [Image: see text] and [Image: see text] to represent the coefficients, for random errors and systematic errors, respectively, that ensure that every point of the CTV receives ≥95% of the prescribed dose. RESULTS: The part of the margin accounting for random errors depends on CTV shape and size; generally, a convex part of a CTV would have a larger margin than a concave part. However, the part of the margin accounting for systematic errors is independent of CTV shape and size. CONCLUSIONS: CTV shape and size should be considered when generating a PTV. For a complex CTV, the margins of the various parts of the CTV are different and related to local forms.