CT sim terms

def. Accuracy of patient setup and localization

laser alignment
Key word: positioning accuracy

def. Accuracy of distances within an image (x-y plane)

in plane spatial integrity

key word: geometry accuracy

def. Accuracy of image thickness in the z-axis

slice thickness

key word: z axis accuracy

def. Correct HU values assigned to materials

CT number accuracy

def. Accuracy of HU values over time

CT number constancy

def. Same material gives same CT number throughout image

term. Uniformity

def. Random variation in pixel values/ CT numbers

term Noise

key word: image graininess

def. Ability to see small objects with large density differences

term. High-contrast resolution

key word: detail

def. Ability to distinguish subtle tissue differences

term. Low-contrast resolution

key word: soft tissue visibility

def. Radiation output/dose from scanner

CTDI

key word: dose

def. Accuracy of table position and movement

term. Couch movement accuracy

key word: Patient positioning

def. Accuracy of coordinates transferred to treatment planning

term. Localization system accuracy

5 things that must be checked daily

• Lasers (alignment / localization)

• CT # constancy (water)

• Basic image quality constancy

• Quick in-plane spatial integrity check (geometry check→ x OR y)

• Safety systems (intercom/visual monitoring)

“Positioning + water + basic geometry = daily”

6 things that must be checked monthly

• In-plane spatial integrity (FULL x AND y directions) ← VERY important

• Slice thickness accuracy

• CT # accuracy (multiple materials, not just water)

• Uniformity

• Noise

• Laser alignment (more detailed check)

image quality or geometry accuracy → think MONTHLY

5 things that must be checked annually

• High-contrast resolution

• Low-contrast resolution

• CTDI (dose measurements)

• Full system performance evaluation

• Mechanical/couch comprehensive checks

dose or resolution testing → annual