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Title: SU-F-J-12: Dosimetrical Characteristics of a 2.5 MV Megavoltage Photon Beam

Abstract

Purpose: To evaluate the accuracy of modeling scatter factor (SF) and primary off-axis ratio (POAR) for 2.5 MV megavoltage photon beams using an empirical model, which can be used as a dose calculation model for low energy EPID imaging. Methods: Scatter photon parameters were calculated for 2.5 MV photon beam from a Varian TrueBeam by fitting the product of depth dose, PDD, and the phantom scatter factor, Sp, for a range of square field sizes between 2 and 40 cm and depths between 0 and 30 cm. The model is then applied to off-axis profiles measured for a slit field (3cm ×35 cm) for 5 depths: 0.6, 5, 10, and 20, 30 cm. Primary off-axis ratio (POAR) values were determined based on the fitting to data using the empirical model. Results: The fitting to PDD*Sp has a maximum error of 14%, mostly near surface, where backscattering of photons dominate and has a standard deviation of 4.7%. The attenuation coefficient and beam-hardening coefficient of the beam is determined to be 0.095 1/cm and 0.0038 1/cm, respectively. POAR for 2.5 MV has a peak in the center, corresponding to a beam without sufficient material to flatten the beam. Conclusion: This work illustratesmore » a deficiency of the current empirical model to fit SF for a 2.5 MV photon beams. Most of the errors are near the surface region and an improved model that incorporate better modeling of backscattering can be developed to improve the model accuracy.« less

Authors:
; ; ;  [1]
  1. University Pennsylvania, Philadelphia, PA (United States)
Publication Date:
OSTI Identifier:
22632148
Resource Type:
Journal Article
Journal Name:
Medical Physics
Additional Journal Information:
Journal Volume: 43; Journal Issue: 6; Other Information: (c) 2016 American Association of Physicists in Medicine; Country of input: International Atomic Energy Agency (IAEA); Journal ID: ISSN 0094-2405
Country of Publication:
United States
Language:
English
Subject:
60 APPLIED LIFE SCIENCES; 61 RADIATION PROTECTION AND DOSIMETRY; ACCURACY; ATTENUATION; BACKSCATTERING; BIOMEDICAL RADIOGRAPHY; DEPTH DOSE DISTRIBUTIONS; ERRORS; PHANTOMS; PHOTON BEAMS; RADIATION DOSES; SIMULATION

Citation Formats

Anamalayil, S, Liu, H, Kim, M, and Zhu, T. SU-F-J-12: Dosimetrical Characteristics of a 2.5 MV Megavoltage Photon Beam. United States: N. p., 2016. Web. doi:10.1118/1.4955920.
Anamalayil, S, Liu, H, Kim, M, & Zhu, T. SU-F-J-12: Dosimetrical Characteristics of a 2.5 MV Megavoltage Photon Beam. United States. doi:10.1118/1.4955920.
Anamalayil, S, Liu, H, Kim, M, and Zhu, T. Wed . "SU-F-J-12: Dosimetrical Characteristics of a 2.5 MV Megavoltage Photon Beam". United States. doi:10.1118/1.4955920.
@article{osti_22632148,
title = {SU-F-J-12: Dosimetrical Characteristics of a 2.5 MV Megavoltage Photon Beam},
author = {Anamalayil, S and Liu, H and Kim, M and Zhu, T},
abstractNote = {Purpose: To evaluate the accuracy of modeling scatter factor (SF) and primary off-axis ratio (POAR) for 2.5 MV megavoltage photon beams using an empirical model, which can be used as a dose calculation model for low energy EPID imaging. Methods: Scatter photon parameters were calculated for 2.5 MV photon beam from a Varian TrueBeam by fitting the product of depth dose, PDD, and the phantom scatter factor, Sp, for a range of square field sizes between 2 and 40 cm and depths between 0 and 30 cm. The model is then applied to off-axis profiles measured for a slit field (3cm ×35 cm) for 5 depths: 0.6, 5, 10, and 20, 30 cm. Primary off-axis ratio (POAR) values were determined based on the fitting to data using the empirical model. Results: The fitting to PDD*Sp has a maximum error of 14%, mostly near surface, where backscattering of photons dominate and has a standard deviation of 4.7%. The attenuation coefficient and beam-hardening coefficient of the beam is determined to be 0.095 1/cm and 0.0038 1/cm, respectively. POAR for 2.5 MV has a peak in the center, corresponding to a beam without sufficient material to flatten the beam. Conclusion: This work illustrates a deficiency of the current empirical model to fit SF for a 2.5 MV photon beams. Most of the errors are near the surface region and an improved model that incorporate better modeling of backscattering can be developed to improve the model accuracy.},
doi = {10.1118/1.4955920},
journal = {Medical Physics},
issn = {0094-2405},
number = 6,
volume = 43,
place = {United States},
year = {2016},
month = {6}
}