Study of Parameters Affects the Dosimetry System

Purpose: This paper evaluates the mechanical parameters for three dimensions PTW automatic water phantom system (MP3-S) and its computer controlled measuring system (MEPHYSTO software version 7.3). Material and Methods: This study compares the scanning overall speed using the PTW water phantom and PTW MEPHYSTO software at different levels of overall speed 5, 10, 15, 20,30, 40, and 50mm/sec. These measurements are done for depth dose curve, beam profile and diagonal profile using different step intervals and different spatial resolutions (low, medium, and high). Results: The scanning overall speed for depth dose measurements using PTW water phantom is about 19% to 86% less than the scanning overall speed of MEPHYSTO software at different overall speed levels 5 to 50mm/sec at 1mm step size. There is no difference in scanning overall speed between beam profile and depth dose measurements using PTW water phantom, while the scanning overall speed at diagonal profile is about 21% to 55% less than PDD. Conclusion: This study compared between scanning overall speed using the PTW automated water phantom and PTW MEPHYSTO software. It showed that the scanning overall speed using the PTW water phantom is affected by changing the spatial resolution (low, medium and high) and by changing the scanning type (depth dose and diagonal profile). The facilities in the PTW MEPHYSTO software for increasing the scanning overall speed and saving the measurements time have not achieved its aim. Our recommendations first of all is to add a time factor beside the distance present in hand control of PTW water phantom to enable the user to know the true scanning overall speed, and second is doing quality assurance between the software and mechanical water phantom during the system calibration regularly. On the other hand to move from measurement to others using big step size the system is achieve it's aimed.