Dose 2016

When can a plastic phantom be considered water-equivalent?

In MeV beams

Depths have to be scaled so that the spectra at the measuring point are similar, the same Sw,air is applicable.

Measuring at a scaled depths, electron fluences differ between two materials, due to different scattering powers. → Need of a fluence correction factor h m (may vary with depth)

Phantoms that are electrical insulators: Charge storage effects, which modify the electron fluence incident on the ion chamber; cylindrical chambers more affected than plane parallel chambers

Recommended to use thin slabs (<2 cm thick) of plastic

McEwen, Med Phys 33(4), 2006, p876-