1. A method of radiating a moving target inside a heart, the method comprising: A acquiring sequential volumetric representations of an area of the heart; B defining a target tissue region and/or a radiation sensitive structure region in 3-dimensions (3D) for a first of the representations; C identifying the target tissue region and/or radiation sensitive structure region for another of the representations by an analysis of the area of the heart from the first representation and the other representation, including expanding the target tissue region and/or a radiation sensitive structure region with a margin based on the motion of the target tissue region and/or the radiation sensitive structure region; and D firing radiation beams to the target tissue region in response to the identified target tissue region and/or radiation sensitive structure region from the other representation; wherein the margin used has been drawn to contain the full tissue target region and/or the radiation sensitive structure region some fraction of the time, and wherein a dose calculation is altered based on the fraction of the time the full tissue target region and/or the radiation sensitive structure region is contained within the margin.