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Summary:

equivalence between square, rectangular,

circular or irregular fields

• Output in air ratio, S

c

, in air is not symmetric in X and Y

Equivalent squares with individual weighting of collimator elements can lead

to sufficiently accurate approximation

For elongated fields less accurate

• Phantom (volume) scatter factor, S

p

, is symmetric in X and Y

Traditional equivalent square formula lead to sufficiently accurate

approximation for S

p

, TPR, RDD, PDD

For elongated fields less accurate

• Irregular blocked or MLC shaped fields require more sophisticated models