Selection of suitable beam orientations in radiation therapy using entropy and Fourier transform measures

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Abstract
Two different measures for the selection of advantageous beam directions in radiation therapy have been investigated. The two measures are based on the size and shape of the tumour and make use of the optimal dose distributions derived using the inverse radiation therapy planning technique. The first measure employs the entropy of the optimal beam profiles to find the beam orientations having the largest amount of structure and information content and thus the lowest entropy. The second measure uses the integral of the low frequency part of the Fourier transform of the optimum beam profiles to find the beam orientations containing the largest amount of gross beam structure. For comparison, a biological measure has been used which identifies beam directions and single beam dose distributions giving the largest probability of complication-free tumour control. The calculations show good agreement between the new methods presented and this biological measure. Furthermore, the agreement is also good for target volumes of simple shapes where optimal beam orientations are well known, indicating that the results for more complicated target shapes may also be useful, as illustrated by sample calculations.

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