TY - JOUR ID - 13030 TI - Interpretation of In-air Output Ratio of Wedged Fields in Different Measurement Conditions JO - Iranian Journal of Medical Physics JA - IJMP LA - en SN - AU - Biglari, Faride AU - Mehnati, Parinaz AU - Jomehzadeh, Ali AD - Department of Medical Physics, Tabriz University of Medical Sciences, Tabriz, Iran. AD - Medical Radiation Sciences Research Team, Department of Medical Physics, Tabriz University of Medical Sciences, Tabriz, Iran. AD - Department of Medical Physics, Kerman University of Medical Sciences, Kerman, Iran. Y1 - 2018 PY - 2018 VL - 15 IS - Special Issue-12th. Iranian Congress of Medical Physics SP - 366 EP - 366 KW - Head Scatter Factor KW - Wedge KW - Ionization Chamber KW - Build-up cap DO - 10.22038/ijmp.2018.13030 N2 - Introduction: The head scatter factor (Sc) is one of the important parameters for monitor unit (MU) calculation. There are multiple factors that impact the Sc values, such as, head structures, back scattering in to dose monitoring chambers, wedges and so on. This study aimed to investigate the variations of SC with different build-up cap materials, wall thickness, Source to Skin Distance (SSDs), ionization chambers and variation of the SC  with wedge angles in 6MV photon beam. Materials and Methods: In this study, Copper and Perspex build-up caps were designed and fabricated with two different thicknesses for each build-up cap. Measurements were performed on an Elekta Compact medical linear accelerator (6 MV) using RK with sensitive volume of 0.12 cc and Farmer-type ion chamber with sensitive volume of 0.65 cc. In all measurements, build-up caps and ionization chambers were positioned in a stand vertical to the beam central axis. It is also investigated the effect of different SSDs on SC. Results: The presence of wedge influences the SC values significantly. Variation of SC in open and wedged fields had maximum deviation of 0.9% and 6.8% and minimum of 0.4% and 2.7% for 30° and 60° angles of wedge, respectively. different SSD and type of ion chamber had no significant influence on the SC. In small field sizes, the SC values in copper build-up cap is higher than Perspex and in large field sizes, measured SC in perspex build-up cap is higher than copper. Conclusion: It was found that the presence of internal wedge has significant contribution to head scatter factor and it increases with increasing wedge angle. Therefore, it should be takes into account in manually MU calculations. UR - https://ijmp.mums.ac.ir/article_13030.html L1 - ER -