Image Guided Radiation Therapy

Images taken on EPID at plus and minus 30 degrees for treatment of the prostate with a 0.075 cm diameter linear marker.

Same images processed to enhance edges. Shown also are the markers projected from the CT scan space (gold) unto the radiographs.

One of two methods to solve for the couch shift: Trace the markers on the radiographs (red). Traces from the prior day could also be dragged for the same.

The couch shift is solved for with a least squares distance between the traced markers (red) and the markers projected onto the radiographs (gold) found from the CT scans. Alternately the couch isocenter can be dragged between the two radiographic planes to get the same match.

The couch move is now computed along with the final positions of the treatment beams.

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