If the patient dose is 0.5 mGy at a 50-inch SSD, what would be the dose at a 64-inch SSD?

To determine the patient dose at a different Source-to-Skin Distance (SSD), the inverse square law is commonly applied. This law states that the intensity of radiation from a point source is inversely proportional to the square of the distance from that source.

In this case, if the initial dose at a 50-inch SSD is 0.5 mGy, you can calculate the new dose at the 64-inch SSD using the relationship:

Dose2 = Dose1 × (SSD1² / SSD2²)

Plugging in the values:

Dose at 64-inch = 0.5 mGy × (50² / 64²)

Calculating the squares gives:

50² = 2500 and 64² = 4096

Now, substituting these into the equation:

Dose at 64-inch = 0.5 mGy × (2500 / 4096)

Calculating the fraction:

2500 / 4096 ≈ 0.6104

Then:

Dose at 64-inch ≈ 0.5 mGy × 0.6104 ≈ 0.3052 mGy

This rounds to approximately 0.31 mGy, aligning with the value indicated in the