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)