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Two‐film brachytherapy reconstruction algorithm
Author(s) -
Siddon Robert L.,
Chin Lee M.
Publication year - 1985
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.595738
Subject(s) - algorithm , brachytherapy , centroid , point (geometry) , point set registration , matching (statistics) , computer science , mathematics , computer vision , artificial intelligence , geometry , surgery , medicine , statistics , radiation therapy
We have developed a new isocentric two‐film reconstruction algorithm for brachytherapy seed and needle implants. The algorithm has no requirements that the two films be orthogonal, symmetric, or even be taken in a transverse plane. In addition, there is no requirement that the two films even have the same number of images. We have found removal of these usual constraints useful for head and neck implants where images are often obscured by patient anatomy. The inherent image matching ambiguities associated with traditional two‐film techniques are minimized by considering the image end points, rather than just the image centroids. For two films, the new algorithm, which considers all image combinations at one time, matches all the end‐point images on one film with those on the other, and then reconstructs the end‐point positions of the seeds. The algorithm minimizes the difference between the actual images and the projected images from the reconstructed seeds. The new two‐film image matching problem is shown to be equivalent to the well‐known assignment problem. For an implant of N seeds, this equivalence allows the two‐film problem to be solved by an algorithm (ACM algorithm 548) that scales with a polynomial power of N , rather than N ! as is usually assumed. An implant of N seeds can be matched and reconstructed in approximately ( N /20) 2 s on a VAX 11/780.