What is the relationship between source-to-image distance (SID) and patient dose when using the same technical factors?

What is the relationship between source-to-image distance (SID) and patient dose when using the same technical factors?

• A. Patient dose increases with SID
• B. Patient dose decreases with SID
• C. Patient dose remains unchanged
• D. Patient dose is irrelevant to SID

Answer: (B)

As the source-to-image distance (SID) increases, the radiation dose received by the patient decreases. This relationship is primarily due to the inverse square law, which states that the intensity of radiation is inversely proportional to the square of the distance from the source. When SID is increased while keeping the technical factors, like kilovoltage and milliampere-seconds, constant, the amount of radiation reaching the patient is diminished because the x-rays spread out over a larger area as they travel the greater distance. As a result, the total exposure the patient receives is lower. Therefore, an increase in SID, while maintaining the same exposure settings, effectively reduces the dose the patient experiences.

As the source-to-image distance (SID) increases, the radiation dose received by the patient decreases. This relationship is primarily due to the inverse square law, which states that the intensity of radiation is inversely proportional to the square of the distance from the source. When SID is increased while keeping the technical factors, like kilovoltage and milliampere-seconds, constant, the amount of radiation reaching the patient is diminished because the x-rays spread out over a larger area as they travel the greater distance. As a result, the total exposure the patient receives is lower. Therefore, an increase in SID, while maintaining the same exposure settings, effectively reduces the dose the patient experiences.