The invention concerns a method for determining the filling of a lung, wherein
the movement of an anatomical structure which moves with breathing, or one or more
points on the moving anatomical structure whose movement trajectory is highly correlated
with lung filling, is detected with respect to the location of at least one anatomical
structure which is not spatially affected by breathing, and wherein each distance
between the structures is assigned a particular lung filling value. It further
concerns a method for assisting in radiotherapy during movement of the radiation
target due to breathing, wherein the association of lung filling values with the
distance of the moving structure which is identifiable in an x-ray image and the
structure which is not spatially affected by breathing is determined by means of
an above-named method, the current position of the radiation target is detected
on the basis of the lung filling value, and wherein radiation exposure is carried
out, assisted by the known current position of the radiation target.
