CT Simulator – Monthly QA Procedure
1. Scan Cat-Phan – fill out the density values for each plug according to the monthly
QA worksheet
2. Laser Alignment (2 mm)
a. The three axial laser lines: inner bore, outer bore, and ceiling are the most
important for patient positioning.
b. Level the laser light alignment tool using the bubble
c. Center the alignment tool to the laser in the ceiling (axial and sagittal)
d. Raise the table until it is level with the top surface of the alignment tool.
This is accomplished by centering the horizontal laser coming from the
wall to the black line running along the lateral side of the alignment tool.
e. The horizontal lasers on the left and right sides, coming from the wall,
should both be centered on the black line. If not then note the amount of
deviation.
f. The vertical lasers coming from the wall should match the vertical laser
from the ceiling. The phantom is centered to the ceiling lasers so note the
axial shift of the vertical side lasers.
g. Use the Lap-Zero laser positioning software to move the lasers (e.g. 50mm
in positive or negative x or y directions), according to the CT monthly QA
form. Make sure the lasers line up to the black line on the alignment tool
or mark the amount of shift in the monthly QA form. Laser alignment
should be within 2 mm.
h. Next, move the alignment phantom into the CT bore. Since the phantom
is centered to the outside lasers, then note the shift with respect to the bore
lasers.
3. CT number uniformity
a. Scan Cat-Phan (for protocol use “abdomen”)
b. Fill out the density values for each plug according to the monthly QA
worksheet
4. Spatial reconstruction accuracy (2 mm)
a. Register new patient, give the name as CT MONTHLYQA (first name is
CT)
b. Make zero at the center of laser alignment tool
c. Set scan ROI
d. Scan with helical mode 3 mm
e. Check for the bb and see if the bb is line up with the zero plane.
f. Evaluate and measure between two bb’s. To find the bb’s, use the page up
and page down buttons on the CT console.
5. Image transfer integrity
a. Send scan of laser alignment tool to Pinnacle.
b. On the Pinnacle planning computer, import the image from CT Goto
c. Then add a beam
d. Measure between the two bb’s
6. DRR construction accuracy (2mm)
a. Set 10 x 10 beam at 100 cm SSD in the specific plane and make Beams
Eye View (BEV) and digital reconstructed radiograph (DRR)
b. Print out the DRR image.