659 / 1245
-2
-1
1
•
2
TPR
20/10
=0.80
20%->80%=0.52 cm
TPR
20/10
=0.68
20%->80%=0.23 cm
g/cm
2
0
Fluence profile: finite source size 0.70 cm
Fluence profile: finite source size 0.35 cm
• Penumbra width influenced by source size
• Only at very high beam energies (or in low
density regions) lateral electron transport
alone dominates penumbra shaping
Modelling of source size & electron transport
Nyholm
et al
Rad. Onc. 78, pp 347-51 and PMB 51 pp 6245-62
(Anders Ahnesjö)
energy fluence profile for an ideal point source