In the AP lumbar positioning, if the patient is thin, how should the collimation be adjusted?

In AP lumbar positioning, when the patient is thin, the collimation should be adjusted to the iliac wings. This adjustment ensures that only the necessary anatomical structures are included in the radiographic field while minimizing exposure to surrounding tissues. The iliac wings serve as a reference point for the lower limit of the radiation field, effectively capturing the area of interest without excess scatter.

Using the iliac wings as the collimation endpoint is particularly important for thin patients, as their anatomical landmarks may be less pronounced, making it essential to clearly define the boundaries of the area being imaged. Proper collimation not only enhances image quality by reducing scatter, but it also complies with radiation safety principles by limiting unnecessary exposure to both the patient and healthcare staff.