11.05 - Patient Data Acquisition

The important anatomical patient data to collect for treatment planning includes:

  • Patient surface contour
  • Target volumes
  • Organs at risk
  • Inhomogeneities

The most commonly used method of acquiring patient data is CT scanning, although MRI, PET and older methods may be used.

Surface Contours

CT scanning is the ideal method of determining patient contour, as a definite change in radiation attenuation occurs at the air – tissue junction. CT also provides accurate 3D spatial information and good resolution.
MRI also provides good contrast between the air and patient surface. It is limited by inhomogeneities in the magnetic field.
PET provides poor discrimination of patient contour due to inadequate resolution.
Older methods include use of a contour plotter which used wires and paper to measure the distance from a point.

Internal Structures

CT scanning provides a balance of good resolution with poor discrimination between different soft tissue types. It provides very useful data on inhomogeneities such as bone, lung or air spaces.
MRI has provides increased discrimination between soft tissues such as muscle or brain. It also provides some information on inhomogeneities. MRI is limited by long scanning times which may lead to movement artefacts in areas such as the lung.
PET assists in localising structures which may be included in the GTV. FDG typically localises to areas of high glucose metabolism (such as tumours) and can indicate soft tissue masses that are involved with malignancy. PET must be used with CT or MRI for treatment planning to take place due to its poor resolution.