Depth shifting ionization curves for gradient effects (TG-51)

Figure 1: Effect of shifting depth-ionization data measured with cylindrical chambers upstream by 0.6 for photon beams (panel a) and 0.5 for electron beams (panel b) (with = 1.0 cm). The raw data are shown by curve I (long dashes) in both cases and the shifted data, which are taken as the depth-ionization curve, are shown by curve II (solid line). The value of the % ionization at point A (10 cm depth) in the photon beam gives and the depth at point B (solid curve, 50% ionization) in the electron beam gives from which can be determined (see section VIII.C). For the photon beams, curve II is effectively the percentage depth-dose curve. For the electron beams, curve II must be further corrected (see section X.D) to obtain the percentage depth-dose curve shown (short dashes - but this is not needed for application of the protocol).