Exploring the limits of spatial resolution in radiation dose delivery.

Flexibility and complexity in patient treatment due to advances in radiotherapy techniques necessitates a simple method for evaluating spatial resolution capabilities of the dose delivery device. Our purpose in this investigation is to evaluate a model that describes the ability of a radiation therapy device to deliver a desired dose distribution. The model is based on linear systems theory and is analogous to methods used to describe resolution degradation in imaging systems. A qualitative analysis of spatial resolution degradation using the model is presented in the spatial and spatial frequency domains. The ability of the model to predict the effects of geometric dose conformity to treatment volumes is evaluated by varying multileaf collimator leaf width and magnitude of dose spreading. Dose distributions for three clinical treatment shapes, circular shapes of varying diameter and one intensity modulated shape are used in the evaluation. We show that the model accurately predicts the dependence of dose conformity on these parameters. The spatial resolution capabilities of different radiation therapy devices can be quantified using the model, providing a simple method for comparing different treatment machine characteristics. Also, as different treatment sites have different resolution requirements this model may be used to tailor machine characteristics to the specific site.