Abstract
When we measure the out put dose (air dose) of the deep therapy apparatus at the fixed peak voltage, we experience the unlinearity of the dose rate with the increasing tube current. We thought that this unlinearity was caused by the following two reasons. (1) The measured dose rate dose not increase expectedly, because the ion recombination in the ionization chamber becomes high with the increasing dose rate. (2) The ripples of the tube voltage increase with the increasing tube current. Then the effective value of the tube voltage decreases, following the decreasing dose rate. From our experiments we decided that the origin of the above mentioned unlinearity was this decreasing effective voltage caused by the ripples.
