en Analytical Formula for the total scatter factor of the Small Radiation Field Size تخصصي Special پژوهشي orginal article <strong><em>Background & Aims</em></strong>: &nbsp;We present an analytical formula (AF) to calculate the total scatter factor of the MLC-shaped small radiation beams.<br> <strong><em>Materials & Methods</em></strong><em>:</em> Pinpoint, Semiflex, and Farmer ion chambers were used for MLC/Jaw-shaped fields extending from (10x10 cm²) down to (1x1 cm²). The total scatters factor, beam profiles, and penumbra was investigated for MLC/Jaw-shaped beams.<br> <strong><em>Results</em></strong><em>:</em> We found that the total scatters factor and the penumbra was clearly higher for MLC-shaped beams due to the MLC leakage, which becomes more and more significant for the small fields. The Analytical Formula was introduced as a least-square fit equation and verified against to measure data. The maximum deviation at small field size (< 4 cm²) was within 3.6% and 43.9% from both MLC and Jaw-shaped beams, respectively.<br> <strong><em>Conclusion</em></strong>: Our analytical formula shows a very good agreement with measured data at a large field size (> 4 cm²), and had small deviation with MLC-shaped small field size, emphasizing that our analytical formula is valid and reasonably good for the total scatters factor calculation of the MLC-shaped beams, especially the ultra-small field size. Small field dosimetry, Total Scatter Factor, Analytical Formula of Small Radiation Field Size 152 160 http://ijrabms.umsu.ac.ir/browse.php?a_code=A-10-164-1&slc_lang=en&sid=1 Saed Al Atawneh saed.al-atawneh@atomki.hu 10031947532846001246 10031947532846001246 Yes Department of Radiation Oncology, King Hussein Cancer Center, Amman, Jordan