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In the FF
•
Photons are absorbed
→
reduced efficiency
•
Photons are scattered (head scatter 3-10% of photon fluence)
→
increased
contamination radiation
•
Neutrons are produced (high MV)
→
increased contamination radiation
Flat profile
•
Only flat at one depth
•
Patients and tumors aren’t flat
Flattening Filter
Wang Y, JACMP2012