Figure 3.1. Penumbral widths increased linearly with chamber diameters. The first three lines represent P 10-90 and the last three lines illustrate P 20-80 at depths of 5, 15, and 25 cm for 6 MV photon beams.
Mark R. Arnfield et al. studied the accuracy of the calculation in IMRT techniques which contain many small fields of Varian Eclipse planning by improving the commissioning beam data at the penumbral region using higher spatial resolution such as film dosimeter for measurement. They compared the result of IMRT fields between the original beam data set collected by IC-10 chamber and those measured by Kodak XV-2 film and found that the latter can achieve better accuracy of IMRT dose calculation by 18-20% especially at high dose gradient, except peak B and C, as shown in Figure 3.2. Therefore, the accuracy of the measured penumbral width was essential in order to ensure the accuracy of treatment planning calculation.