Physics Bucharest 2017
Electron beam PDD
• High surface dose (75-95)% - No skin sparing effect → Skin Targets < E means < D s (≠ photons)
• Dose builds up to a maximum at depth z max • Beyond z max the dose drops off rapidly and levels off at small low level dose component (Bremsstrahlung tail)
• Plateau region should extend to treatment depth across target region (PDD = 90% - Therapeutic Range )
• Gradient depends on energy
• Dose beyond practical range due to Bremmstrahlung (linac head, air, pt) 4 MeV < 1% 10 MeV < 2.5% 20 MeV < 4%
The Physics of Radiation Therapy (Faiz M. Khan)
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