If the patient dose is 1 mGy at a 72 inch SID, what is the estimated patient dose at a 40 inch SID?

When considering how the patient dose changes with distance, it is critical to understand the inverse square law. The inverse square law states that the intensity of radiation exposure (and consequently the dose received by the patient) is inversely proportional to the square of the distance from the radiation source. This means that as you move closer to the radiation source, the dose significantly increases, while moving further away decreases the dose.

In this scenario, the original patient dose is measured at a source-to-image distance (SID) of 72 inches, yielding a dose of 1 mGy. To find the estimated patient dose at a closer SID of 40 inches, you can apply the inverse square law, using the formula:

[ \text{Dose}_2 = \text{Dose}_1 \times \left(\frac{D_1}{D_2}\right)^2 ]

Where:

• ( \text{Dose}_1 ) is the initial dose (1 mGy at 72 inches),

• ( D_1 ) is the initial distance (72 inches),

• ( D_2 ) is the new distance (40 inches).

Plugging in the values:

[ \text{Dose}_2 = 1 , \text