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When can a plastic phantom be considered water-equivalent?
In MV photon beams
(where energy deposition is mainly due to Compton interactions → O’Connor scaling theorem is applicable)
•
Depth scaling proportional to
the ratio of mass attenuation coefficients.
•
Measurements in
polystyrene
can show differences from water of up to
3%
(Christ
1995), depending on photon beam quality and depth.T
•
The agreement in dosimetric quantities (depth doses, TPR, TMR, OF) between the
epoxy-resin phantom materials
and water are generally within 1% (energy range
between Co-60 and 18 MV X-rays)
Araki etal, 2009, Med.Phys. 36 (7) pp2992-
Jan Seuntjens etal, 2005, Med.Phys. 32 pp2945-