Comparison of the photon charge between water and solid phantom depending on depth

This study assessed the clinical usefulness of the solid phantom, which may compensate for the disadvantages of the water phantom, by comparing the radiological doses between the two depending on their depths. The experimental equipment used was a linear accelerator for medical use, water phantom, solid phantom, Farmer type ion chamber and electrometer. The distance between the ray source and the center of the ion chamber was fixed to a SAD of 100 cm during the experiment. The field size was 10 x 10 cm2 and the radiation energies of the photon rays were 6 MV and 15 MV. The depth interval was 1cm (range 1-10 cm) for each energy. The relative deviation ratio of the water phantom to the solid phantom was calculated. The measurement at 100 MU was performed more than five times to calculate the average charge and absorbed dose, and the relative deviation was analyzed based on the water phantom. The results obtained at depths from 1 to 10 cm were 0.034%, -0.457%, -0.167%, 0.011%, 0.117%, 0.271%, 0.349%, 0.709%, 0.376% and 0.611% at 6 MV and those obtained at 15 MV were 1.199%, 0.033%, 0.166%, 0.496%, 0.556%, 0.705%, 0.656%, 1.071%, 0.7% and 1.057%, respectively. In conclusion, the solid phantom is useful and may complement the disadvantages of the water phantom, including the time required for its installation and errors in the measurement depth, and may precisely measure the radiological dose.