Which of the following statements about semi-annual testing for collimator light field and x-ray field alignment is correct?

• A. 1, 2, and 3
• B. 1 and 2
• C. 2 and 3
• D. 1 and 3

Answer: (A)

The key idea is to ensure geometric accuracy of the imaging system: the light field must accurately represent the actual x-ray field so what you see guides what is exposed. This matters because you want to expose exactly the intended anatomy and avoid irradiating areas outside the target, while also ensuring the area of interest is fully captured on the image.

Semi-annual checks verify three essential aspects: that the light field boundary matches the radiation field across the central axis and at the field edges; that the x-ray beam is centered to the system’s reference so the field sits correctly with the patient or table; and that the field shape remains appropriately sized and symmetrical so there are no edge or corner misalignments. When all of these are confirmed, you have a reliable indication that mechanical wear, drift, or misalignment hasn’t degraded the congruence between the light and actual beam.

Omitting any one of these aspects could allow gradual misalignment to go unnoticed, compromising both patient safety and image quality.