Automatic Estimation of Patient Set-up Errors in Radiotherapy by Region-based Alignment of Portal and Pre-treatment Images

Q. Su, M.R. Varley, B.J. Matuszewski, L.-K. Shark, G.S. Shentall, and M.C. Kirby (UK)


Medical image analysis, Patient set-up error inradiotherapy, Image registration, Mutual information


In radiotherapy, eradication of a tumour without causing complications in normal tissues surrounding the tumour depends on the accuracy of patient set-up, i.e. the position of the patient with respect to the radiation beams. In this paper, an automatic method is presented to estimate patient set-up errors by region-based alignment of portal images captured during treatment delivery and pre-treatment images obtained from conventional X-ray film by digitisation. The method utilises the axes and grid lines produced by the collimating system on both images to achieve automatic extraction of the corresponding sub image pairs, and exploits the mutual information between the corresponding sub-image pairs to achieve automatic alignment. Using real radiotherapy images, the patient errors estimated are shown to be consistent with manual alignment.

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