Dose 2016

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)

Jan Seuntjens etal, 2005, Med.Phys. 32 pp2945-

Araki etal, 2009, Med.Phys. 36 (7) pp2992-