What happens to margin when performing 2 or more lesions with CSI?

What happens to margin when performing 2 or more lesions with CSI?

• A. Margin becomes very high
• B. Margin decreases
• C. Margin unchanged
• D. Margin becomes negative

Answer: (A)

Margins in treatment planning must cover microscopic spread and setup uncertainties. When two or more lesions are treated with CSI, the overall target area becomes larger, and you need to expand the margin around that area to ensure all disease is encompassed and to account for any positioning or delivery variations. This added uncertainty and larger treatment field drive the margin to increase, sometimes described as a higher margin. If margins were reduced or left the same, there’d be a greater risk of missing cancer cells between lesions. A negative margin isn’t meaningful in this context, since margins are buffers to ensure coverage, not negative values.

Margins in treatment planning must cover microscopic spread and setup uncertainties. When two or more lesions are treated with CSI, the overall target area becomes larger, and you need to expand the margin around that area to ensure all disease is encompassed and to account for any positioning or delivery variations. This added uncertainty and larger treatment field drive the margin to increase, sometimes described as a higher margin. If margins were reduced or left the same, there’d be a greater risk of missing cancer cells between lesions. A negative margin isn’t meaningful in this context, since margins are buffers to ensure coverage, not negative values.