Abstract:
Successful radiotherapy treatments with high-energy proton beams require the
accurate positioning of patients. This paper investigates computational methods
for achieving accurate treatment setups in proton therapy based on the
geometrical differences between a double exposed portal radiograph (PR) and
a reference image obtained from the treatment planning process. The first step
in these methods involves aligning the boundary of the radiation field in the PR
with a reference boundary defined by the treatment plan. We propose using
the generalised Hough transform (GHT), followed by an optimisation routine
to align the field boundaries. It is found that this method worked successfully
on ten tested examples, and aligns up to 82% of reference boundary points onto
the field boundary. The next step requires quantising the patients anatomical
shifts relative to the field boundary. Using simulated images, a number of
intensity-based similarity measures and optimisation routines are tested on a
3D/2D registration. It is found that the simulated annealing algorithm minimising
the correlation coefficient provided the most accurate solution in the
least number of function evaluations.
