5.4 - Cone Beam CT

Cone Beam CT is a special function of either EPI detectors or OBI units. By rotating around the patient and using a specialised algorithm, a 3D image of the patient can be reconstructed. The algorithm used is similar to that for a normal CT scan.

Because cone beam CT can be done with either EPI (megavoltage photons) or OBI (kilovoltage photons) it is possible to acquire kilovoltage or megavoltage images. Kilovoltage images have the advantage of increased tissue contrast and resolution. Megavoltage CBCT is less affected by artefacts from high atomic number inhomogeneity.

CBCT is checked in a similar way to EPI/OBI treatment verification techniques. Planners are able to adjust the patients position if they are not located in the correct alignment. This process is only slightly longer than for EPI/OBI checks.