West Asia Organization for Cancer Prevention (WAOCP), APOCP's West Asia Chapter. Asian Pacific Journal of Cancer Prevention 1513-7368 19 11 2018 11 01 Calculation of Equivalent Square Fields in Radiation Therapy by an Improved Vadash Correction Factor for Collimator Exchange Effects 3053 3057 73919 10.31557/APJCP.2018.19.11.3053 EN Mohammad Javad Tahmasebi Birgani Department of Radiotherapy and Oncology, Golestan Hospital, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. Nahid Chegni Department of Medical Physics, Medical School, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. Marziyeh Tahmasbi Department of Radiology Technology, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. Raziye Fayazi Department of Medical Physics, Medical School, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. Jafar Fatahi Asl Department of Radiology Technology, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. Mohammad Ali Behrouz Department of Medical Physics, Medical School, Ahvaz Jundishapur University of Medical Sciences, Ahvaz, Iran. Journal Article 1999 11 30 Background and objectives: To determine the head scatter factor, a formalism presented by Vadash and Bjärngard<br />has been employed to assess collimator exchange effects. The aim of this study was to determine the best Vadash<br />correction factor (A) by introducing a new method based on the output factor measured in air for different square and<br />rectangular fields. Materials and Methods: A new simple mathematical method based on selection of the best dosimetric<br />data was proposed to obtain the A value for Vadash to predict the equivalent square field size. Measurements were<br />performed with a Farmer c https://journal.waocp.org/article_73919_dcbfcde9191090ae21a5c45c9d5fec35.pdf