According to Sterling's formula, two fields are considered equivalent based on what parameter?

Sterling's formula is used in radiation therapy to evaluate the equivalence of different radiation fields in terms of their dose distribution characteristics. The parameter that determines whether two fields are considered equivalent according to Sterling's formula is their area or perimeter.

When fields have the same area or perimeter, it indicates that they can deliver a similar dose distribution to the target tissue, despite possibly differing in shape or orientation. This characteristic is crucial in treatment planning because it allows clinicians to use different field configurations while still achieving the desired dose to the tumor while sparing surrounding healthy tissue.

The significance of the area or perimeter lies in its relationship to the overall coverage and dose delivery of the radiation fields. If two fields occupy the same area or share the same perimeter value, they can be assumed to impart similar dose distributions, which enhances treatment flexibility and planning efficiency.