In semi-annual collimator alignment testing, which device is used as the primary test device?

• A. Alignment Template
• B. 9 Pennies Image
• C. Tape Measure
• D. Ruler

Answer: (A)

Ensuring the light field matches the radiation field and is centered over the image receptor is the key idea. The alignment template is built specifically for this purpose because it provides precise reference marks and field edges you can compare directly with the projected light field and the detector. By placing the template in the beam path (or overlaying it with the cassette), you can see exactly where the light field falls relative to the template’s marks and center. If the boundaries or the central line don’t line up, the collimator is off and adjustments are needed to bring the light field, radiation field, and image receptor into agreement. A tape measure or ruler can only measure distances and won’t verify the actual alignment of the light field to the beam, and the pennies image approach isn’t as standardized or precise for this purpose.