title: Surface dose measurements and comparison of unflattened and flattened photon beams.
abstract: The purpose of this study was to evaluate the central axis dose in the build-up region and the surface dose of a 6 MV and 10 MV flattened photon beam (FB) and flattening filter free (FFF) therapeutic photon beam for different square field sizes (FSs) for a Varian Truebeam linear accelerator using parallel-plate ionization chamber and Gafchromic film. Knowledge of dosimetric characteristics in the build-up region and surface dose of the FFF is essential for clinical care. The dose measurements were also obtained empirically using two different commonly used dosimeters: a p-type photon semiconductor dosimeter and a cylindrical ionization chamber. Surface dose increased linearly with FS for both FB and FFF photon beams. The surface dose values of FFF were higher than the FB FSs. The measured surface dose clearly increases with increasing FS. The FFF beams have a modestly higher surface dose in the build-up region than the FB. The dependence of source to skin distance (SSD) is less significant in FFF beams when compared to the flattened beams at extended SSDs.
authors.affiliation: Division of Medical Physics, School of Advanced Sciences, VIT University, New Delhi, India.
authors.forename: Ashokkumar
authors.initials: A
authors.lastname: Sigamani
authors.affiliation: Division of Medical Physics, School of Advanced Sciences, VIT University, New Delhi, India.
authors.forename: Arunai
authors.initials: A
authors.lastname: Nambiraj
authors.affiliation: Department of Radiation Oncology, Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, India.
authors.forename: Girigesh
authors.initials: G
authors.lastname: Yadav
authors.affiliation: Department of Radiation Oncology, Krishna Institute of Sciences, Hyderabad, Telangana, India.
authors.forename: Ananda
authors.initials: A
authors.lastname: Giribabu
authors.affiliation: Department of Radiation Oncology, BGS Global Hospital, Bengaluru, Karnataka, India.
authors.forename: Karthikeyan
authors.initials: K
authors.lastname: Srinivasan
authors.affiliation: Department of Radiation Oncology, Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, India.
authors.forename: Venkadamanickam
authors.initials: V
authors.lastname: Gurusamy
authors.affiliation: Department of Radiation Oncology, Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, India.
authors.forename: Kothanda
authors.initials: K
authors.lastname: Raman
authors.affiliation: Division of Medical Physics, School of Advanced Sciences, VIT University, New Delhi, India.
authors.forename: Kaviarasu
authors.initials: K
authors.lastname: Karunakaran
authors.affiliation: Division of Medical Physics, School of Advanced Sciences, VIT University, New Delhi, India.
authors.forename: Rajesh
authors.initials: R
authors.lastname: Thiyagarajan
keywords: Flattening filter-free; Gafchromic films; NACP chamber; photon beams; surface dose