Dynamic region-of-interest cone-beam CT for image-guided postmastectomy radiotherapy

The results from a single patient setup with simulated reconstruction results are presented as a proof of concept. For this patient it was decided that a roughly hemi-thoracic ROI would be ideal for providing sufficient information for patient setup and sparing the contralateral breast. AP aligned parallel chords were chosen for the reconstruction geometry. We found that by shifting approximately 7 cm both anteriorly and to the patient's left, we are able to image over approximately a 190 degree arc. The collision prediction model is shown in Figure 1. In Figure 3 the full data sinogram is shown with the data ranges required for a traditional full-fan/half-scan, a half-fan/full-scan and the proposed conformal ROI technique. A summary of results is given in Table I. Note that, with this patient setup, a typical half-fan/full-scan geometry would cause a patient collision. With a symmetric detector full-fan/half-scan geometry the collision could be avoided but would require an 82 cm wide detector, more then double what is on the current system.