CT

Question 1

pros of CT in RT

Answer 1

good soft tissue delineation
fast acquisition
CT numbers to HU
cheaper compared to MRI
3D image matching, increased IGRT accuracy

Question 2

cons of CT in RT

Answer 2

increased dose
limited bore size
allergic reaction to contrast
mis-interpretation
not suitable for pregnant women

Question 3

what is the impact of changing pitch

Answer 3

• slower and reduced table movement
• slower scan time
• smaller gaps in helix —> increased image detail, but increased dose
• faster and increased table movement
• faster scan time
• bigger gaps in helix —> reduced image detail, but reduced CT dose

Question 4

how does the density of the organs change on images with no contrast, with contrast and delayed contrast

Answer 4

the density of the organs increase on images with contrast and delayed contrast. However, the density on the delayed contrast is not as high as the contrasted images due to wash out of the contrast

Question 5

why is CT important in treatment planning

Answer 5

• gives us an accurate determination of inhomogeneities/heterogeneities within the patient
• provides 3D and 4D CT data for radiation therapy treatment planning calculations
• creation of digitally reconstructed radiographs (DRRs)
• provides an accurate structure identification, targets and OAR
• enables an accurate dose calculation based on CT numbers
• cone-beam CT (CBCT) on treatment

Question 6

what is a scout scan

Answer 6

• low dose scan
• low spatial and contrast resolution
• provides reference for slice data acquisition and display
• provides information for scan length, possible bladder and rectal filling