Dose Course 2018_Flipping book

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