Robar and Clark found that the effect of phantom scatter dose is somewhat negligible while increasing depths for field sizes less than 4 cm. It causes fewer amounts of low energies when increasing depths. For that reason the EDR2 film even though contained high Z materials obtained almost the same response of calibration curves when increasing depths for field sizes of 11 , 22 and 33 cm2.
Nevertheless the calibration curve for each depth and field size was still employed for determining dose calculation in order to minimize other variations as many as possible such as film processing conditions.
5.1.1.2 The penumbral width measured by the EDR2 radiographic film
Figure 5.1.2 (a) shows the penumbral width using EDR2 radiographic film for field size of 11, 22 and 33 cm2 at different depths. Figure 5.1.2 (b) displays the penumbral width using EDR2 radiographic film at depths of 1.5,10 and 20 cm with various field sizes. In this experiment, three repeated measurements were performed and the image J software was used for data analysis and generated penumbral width (20-80%). Table 5.1.2 shows the penumbral widths and the standard deviation obtained using the polynomial equation of degree 2.