Physics of the Use of Small Sealed Sources in Brachytherapy

Need of independent dose verification in brachytherapy

“…(f ak,wat ) is the air kerma to dose in water conversion factor and is approximately 1.11 for 192 Ir and 137 Cs gamma energies. [ 3 ] The main difference between g(r), used in TG-43 formalism, and WPF(r) is that g(r) is the dose in water, normalized at 1 cm, along the perpendicular bisector of the actual source whereas WPF(r) is the ratio of dose in water to the dose in air for a point isotropic source. Both g(r) and WPF(r) vary only marginally with distance from the source up to about 5 cm for 192 Ir gamma energies, and may be ignored for manual dose verification.…”