AbstractID: 7748 Title: Iterative Optimization of Beam Positions for IMRT
Intensity modulated Radiotherapy (IMRT) generally only involves the optimization of fluence intensity for a series of pre-chosen
beam positions. In theory optimization of beam positions is also possible, however the requirement for a time consuming
stochastic method to achieve the global minimum has limited this in practice. In this study a deterministic method has been
investigated for establishing beam positions. The results may not produce the global minimum however they do show a vast
improvement on no optimization. The process relies on gradually reducing the number of beams used based on the average
fluence delivered by each beam. To investigate this a 2-dimensional simulation was performed. An initial large number of evenly
spaced beams were set up and a small number of iterations used to determine the optimal fluence intensity pattern for each beam.
The average fluence was then calculated for each beam and those with the lowest average fluence removed. This process is
repeated until the desired number of beams is reached. Investigations were made into the number of beams required initially, the
number of beams removed, and the initial number of iterations. For the situation of 180 initial beams, gradually reduced by three
beams at a time based on the average fluence following 10 iterations, a plan vastly improved on that using evenly spaced beams
can be achieved. This improvement is obviously reduced for situations where beam positioning is limited due to physical
constraints, however it is particularly useful for the situation when beam angles are not intuitive.