title: Measurement and comparison of head scatter factor for 7 MV unflattened (FFF) and 6 MV flattened photon beam using indigenously designed columnar mini phantom.
abstract: OBJECTIVE
  To measure and compare the head scatter factor for 7 MV unflattened and 6 MV flattened photon beam using a home-made designed mini phantom.
  
  
  BACKGROUND
  The 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.
  
  
  METHODS
  A 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 cm and d max dose water equivalent thickness.
  
  
  RESULTS
  The 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 cm × 10 cm to 40 cm × 40 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.
  
  
  CONCLUSIONS
  There were significant differences in Sc values measured for 6MV-FB and unflattened 7MV-UFB photon beams over the range of field sizes from 10 cm × 10 cm to 40 cm × 04 cm. Different results were obtained for measurements performed with low-Z and high-Z mini phantoms.
authors.affiliation: Department of Radiation Oncology, Rajiv Gandhi Cancer Institute & Research Centre, New Delhi, India ; School of Advanced Sciences, VIT University, Vellore, India.
authors.forename: Sigamani
authors.initials: S
authors.lastname: Ashokkumar
authors.affiliation: School of Advanced Sciences, VIT University, Vellore, India.
authors.forename: Arunai
authors.initials: A
authors.lastname: Nambiraj
authors.affiliation: Department of Radiation Oncology, Rajiv Gandhi Cancer Institute & Research Centre, New Delhi, India.
authors.forename: Sujit Nath
authors.initials: SN
authors.lastname: Sinha
authors.affiliation: Department of Radiation Oncology, Rajiv Gandhi Cancer Institute & Research Centre, New Delhi, India.
authors.forename: Girigesh
authors.initials: G
authors.lastname: Yadav
authors.affiliation: Department of Radiation Oncology, Rajiv Gandhi Cancer Institute & Research Centre, New Delhi, India.
authors.forename: Kothanda
authors.initials: K
authors.lastname: Raman
authors.affiliation: Department of Radiation Oncology, Rajiv Gandhi Cancer Institute & Research Centre, New Delhi, India.
authors.forename: Manindra
authors.initials: M
authors.lastname: Bhushan
authors.affiliation: Department of Radiation Oncology, Rajiv Gandhi Cancer Institute & Research Centre, New Delhi, India ; School of Advanced Sciences, VIT University, Vellore, India.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Thiyagarajan
keywords: 6MV-FB; 7MV-UFB; Linear accelerators; Mini phantom; Sc factor