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Summary: TPS modelling of small & composite fields
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Modelling of the direct beam source becomes important in narrow collimated
modulated fields due to source occlussion
•
In small and modulated fields the MLC is more involved in shaping primary energy
fluence, so modelling this becomes important
•
Explicit modelling of the direct beam source size and the effects due to the MLC is
not common in most TPS. Implementations (approximations) vary.
•
Fine resolution is required in dose but also energy fluence calculations for small
field modelling
•
Only at very high beam energies (or in low density regions) lateral electron
transport alone dominates dose in the penumbra
→
a beam model that accounts
for finite source size and collimating jaw effects plays a primary role in the dose
calculated by the TPS
•
Most TPSs do not require small field measured data as default input to their beam
configuration engines.
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