SUFJ12: Dosimetrical Characteristics of a 2.5 MV Megavoltage Photon Beam
Abstract
Purpose: To evaluate the accuracy of modeling scatter factor (SF) and primary offaxis 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 offaxis profiles measured for a slit field (3cm ×35 cm) for 5 depths: 0.6, 5, 10, and 20, 30 cm. Primary offaxis 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 beamhardening 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 »
 Authors:

 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 00942405
 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. SUFJ12: 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. SUFJ12: 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 .
"SUFJ12: Dosimetrical Characteristics of a 2.5 MV Megavoltage Photon Beam". United States. doi:10.1118/1.4955920.
@article{osti_22632148,
title = {SUFJ12: 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 offaxis 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 offaxis profiles measured for a slit field (3cm ×35 cm) for 5 depths: 0.6, 5, 10, and 20, 30 cm. Primary offaxis 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 beamhardening 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 = {00942405},
number = 6,
volume = 43,
place = {United States},
year = {2016},
month = {6}
}