Journal of Medical Physics
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Year : 2016  |  Volume : 41  |  Issue : 2  |  Page : 85-91

Surface dose measurements and comparison of unflattened and flattened photon beams

1 Division of Medical Physics, School of Advanced Sciences, VIT University, New Delhi, India
2 Department of Radiation Oncology, Rajiv Gandhi Cancer Institute and Research Centre, New Delhi, India
3 Department of Radiation Oncology, Krishna Institute of Sciences, Hyderabad, Telangana, India
4 Department of Radiation Oncology, BGS Global Hospital, Bengaluru, Karnataka, India

Correspondence Address:
Ashokkumar Sigamani
Division of Medical Physics, School of Advanced Sciences, VIT University, Vellore, Tamil Nadu
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/0971-6203.181648

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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.

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