over-response correction of snc 350p roos and ptw markus chambers in the surface dose and build-up region dosimetry of 6mv photon beam

Introduction: the design characteristics of ionization chambers are critical for the accurate measurement of percentage surface dose (psd) and percentage depth dose (pdd) in the build-up region. this study assesses the over-response correction in psd and pdd for different field sizes, using markus and roos fixed separation parallel-plate ionization chambers.material and methods: the sun nuclear corporation snc 350p roos and ptw markus parallel plate ionization chambers were used to measure 6 mv photon beam pdd along the central axis in the build-up region.the experiment was performed on a solid water® he phantom with a density of 1.032 g/cm3.the measurements were taken at a source surface distance (ssd) of 100 cm with field sizes of 10x10cm2,20x20 cm2, and 30x30cm2 and at variable depths.results: for field sizes of 10x10 cm2, 20x20 cm2, and 30x30 cm2 at a source-to-axis distance (sad) of 100 cm, the psd values obtained with the markus chamber, before and after applying rawlinson’s equation for over-response correction, were as follows: 35.11%, 42.92%, 50.72% (before correction) and 28.37%, 36.19%, 44.05% (after correction). similarly, the psd values measured using the roos chamber, before and after applying over-response correction, were as follows: 41.61%, 50.50%, 58.04% (before correction), and 33.96%, 42.87%, 50.38% (after correction).conclusion: the application of over-response correction using rawlinson’s equation improved the accuracy of measurements for both chambers, emphasizing the significance of employing appropriate correction techniques to ensure precise dose measurements in the build-up region using ionization chambers.