Figure 1: Sketch showing the concept behind the study. In the second fraction CT the registered organs of the 1st fraction maintain their positions with respect to the bony anatomy after image registration. The applicator has however changed its position and geometry in the second fraction image. The dose to the 1st fraction organs when calculated from the 2nd fraction CT is the hypothetical dose that will result if the only change between the two fractions was the change in applicator position and geometry. The actual organ position in the 2nd fraction is depicted in dark grey. 
