Measurement and comparison of head scatter factor for 7MV unflattened (FFF) and 6MV flattened photon beam using indigenously designed columnar mini phantom

AimTo measure and compare the head scatter factor for 7[[ce:hsp sp="0.25"/]]MV unflattened and 6[[ce:hsp sp="0.25"/]]MV flattened photon beam using a home-made designed mini phantom.BackgroundThe head scatter factor (Sc) is one of the important parameters for MU calculation. There are multiple factors that influence the Sc values, like accelerator head, flattening filter, primary and secondary collimators.Materials and methodsA columnar mini phantom was designed as recommended by AAPM Task Group 74 with high and low atomic number material for measurement of head scatter factors at 10[[ce:hsp sp="0.25"/]]cm and dmax dose water equivalent thickness.ResultsThe Sc values measured with high-Z are higher than the low-Z mini phantoms observed for both 6MV-FB and 7MV-UFB photon energies. Sc values of 7MV-UFB photon beams were smaller than those of the 6MV-FB photon beams (0.6–2.2% (Primus), 0.2–1.4% (Artiste) and 0.6–3.7% (Clinac iX (2300CD))) for field sizes ranging from 10[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]10[[ce:hsp sp="0.25"/]]cm to 40[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]40[[ce:hsp sp="0.25"/]]cm. The SSD had no influence on head scatter for both flattened and unflattened beams. The presence of wedge filters influences the Sc values. The collimator exchange effects showed that the opening of the upper jaw increases Sc irrespective of FF and FFF.ConclusionsThere were significant differences in Sc values measured for 6MV-FB and unflattened 7MV-UFB photon beams over the range of field sizes from 10[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]10[[ce:hsp sp="0.25"/]]cm to 40[[ce:hsp sp="0.25"/]]cm[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]04[[ce:hsp sp="0.25"/]]cm. Different results were obtained for measurements performed with low-Z and high-Z mini phantoms