en Radiobiology Radiobiology تحقيق بديع Original Research <div style="text-align: justify;">Background: Small photon beams are increasingly used in modern radiotherapy modalities. In small photon fields, the dosimetric field size will deviate from the nominal field size. An effective field size (FSeff) for use in small field dosimetry has been defined to overcome this issue. The present study aims to investigate the suitability of two ionization chambers and two semiconductor diodes in the measurement of 6MV photon beam profiles and to analyze the variations of FSeff in smaller fields. Materials and Methods: Measurements were made at 6 MV photon beams of a Siemens Artiste linear accelerator and transverse profiles were acquired for nominal square field sizes of side 1&times;1 to 10&times;10 cm² via the irradiation of detectors and radiochromic film. Full&nbsp;width&nbsp;at&nbsp;half&nbsp;maximum (FWHM) at the 50% isodose level was used to calculate FSeff. Results: The uncertainty of the FWHM values derived from the in-plane and cross-plane profiles (&Delta;FWHM%) were below 6% for all the detectors were below 6% except for Semiflex in the 1&times;1 field size. In small field sizes (less than 3 &times; 3 cm²), larger differences occurred between the dosimetric and nominal field sizes in all detectors. No significant differences between nominal and effective field sizes were observed in a field rage of 4&times;4 - 10&times;10 cm². Conclusion: In the acquisition of small field profiles, selection of an appropriate detector is influential in accurate measurements. The findings of present study support the argument that both the size and composition of detectors affect the small field profile measurements.</div> Effective field size, small field dosimetry, ionization chamber, diode. 163 168 http://ijrr.com/browse.php?a_code=A-10-2188-77&slc_lang=en&sid=1 H. Keivan 7900319475328460020860 7900319475328460020860 No School of Allied Medical Sciences, Shahroud University of Medical Sciences, Shahroud, Iran R. Maskani 7900319475328460020861 7900319475328460020861 No School of Allied Medical Sciences, Shahroud University of Medical Sciences, Shahroud, Iran D. Shahbazi-Gahrouei shahbazi@med.mui.ac.ir 7900319475328460020862 7900319475328460020862 Yes Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran A. Shanei 7900319475328460020863 7900319475328460020863 No Department of Medical Physics, School of Medicine, Isfahan University of Medical Sciences, Isfahan, Iran S. Pandesh 7900319475328460020864 7900319475328460020864 No Department of Radiology Technology, School of Allied Medicine, Birjand University of Medical Sciences, Birjand, Iran E. Tarighati Sereshke 7900319475328460020865 7900319475328460020865 No Department of Medical Physics, School of Medicine, Iran University of Medical Sciences, Tehran, Iran