800 / 1542
•
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%
Electron beam PDD
The Physics of Radiation Therapy (Faiz M. Khan)