CBCT: Technical and Practical Stuff

• Acquisition Modes:

  • full scan
  • half scan
• Full Scan:

  • CBCT - gantry completes full rotation (360 degrees) around patient
  • used to gather a complete field of view that includes patient's external body contour
  • include: pelvis, low dose thorax
• Half Scan:

  • CBCT - gantry completes a partial rotation around patient
  • used to gather centrally located field of view that is incomplete - may not encompass external contour of patient
  • includes:
  • pelvis spotlight (often used for prostate)
  • low dose head
  • standard dose head
  • high quality head
• Filters: bow tie filter

  • physical filter placed in path of CBCT beam to improve image quality
  • types:
  • full fan (for half scan CBCT)
  • half fan (for full scan CBCT)
• Full Fan:

  • full fan bow tie filter
  • 2D detector is centrally positioned and full fan filters the beam equally on both sides of the central axis
  • used in centrally located applications
  • used in half scan CBCT
• Half Fan:

  • uses half fan bow tie filter
  • x ray beam and 2D detector are offset laterally to include patient's external contour
  • used in full scan CBCT
• CBCT Image Analysis

  • image quality
  • abnormalities
  • pre - treatment prep
  • rotation (pitch, roll, yaw)
  • automatch to soft tissue
  • perform manual image match for fine tuning automatch (evaluate primary and secondary match structures)
  • perform image shifts as needed