The effects of the shape and size of the clinical target volume on the planning target volume margin

Abstract

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 kr-95 and ks-95 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.