This work investigated the absorbed dose to
water rate under reference conditions in a Cyberknife VSI system using
radiochromic films EBT3 and MD-V3 and three ionization chambers: an Exradin A12
and two FC65P Welhöfer Scanditronix
with different serial numbers. The correction factor,, was studied using a
Varian iX linac and the Cyberknife system. The measurements in the Varian iX
were performed in a 10 × 10 cm2 field, 10 cm depth in
liquid water at 90 cm and 70 cm SSD and in a 5.4 × 5.4 cm2
field, 10 cm depth at 70 cm SSD to simulate the Cyberknife conditions. In the
Cyberknife system, measurements were performed using ionization chambers and
both film types at 70 cm SSD and 10 cm depth in its 6 cm diameter reference
field. The results indicate that？is independent of the dosimeters and the
evaluation methods. Maximum differences of 0.22% - 0.55% (combined
uncertainties of 1.22% - 1.98%, k = 1) are obtained on ？using Varian iX,
whereas discrepancies of 2.08% - 2.09% (combined uncertainties of 1.87% - 2.13%, k = 1) are observed using the Cyberknife system. Given the agreement
between detectors and the combined standard uncertainties, the data from Varian
iX could be considered the most accurate and consequently a weighted average
factor of 0.902 ± 0.006 could be used for the Cyberknife VSI system reference
field. Within measurement uncertainties, the absorbed dose rate measured in the
Cyberknife VSI system reference field was found to be independent of the
dosimeters used. These results suggest that the absorbed dose measured at a
point within a given field size should be the same, regardless the dosimeter
used, if their dosimetric characteristics are well known. This highlighted the
importance of
References
[1]
Cabrera-Santiago, A. and Massillon-JL, G. (2016) Track-Average LET of Secondary Electrons Generated in LiF: Mg, Ti and Liquid Water by 20-300 kV X-Ray, 137Cs and 60Co Beams. Physics in Medicine and Biology, 61, 7919-7933. https://doi.org/10.1088/0031-9155/61/22/7919
[2]
Massillon-JL, G., Minniti, R., Mitch, M.G., Maryanski, M.J. and Soares, C.G. (2009) Use of Gel Dosimetry to Measure the 3D Dose Distribution of a 90Sr/90Y Intravascular Brachytherapy Seed. Physics in Medicine and Biology, 54, 1661-1672. https://doi.org/10.1088/0031-9155/54/6/017
[3]
IAEA (2005) Absorbed Dose Determination in Photon and Electron Beams; An International Code of Practice. Technical Report Series, Vol. 277, Viena.
[4]
Almond, P.R., Biggs, P.J., Coursey, B.M., Hanson, W.F., Huq, M.S., et al. (1999) AAPM’s TG-51 Protocol for Clinical Reference Dosimetry of High-Energy Photon and Electron Beams. Medical Physics, 26, 1847-1870. https://doi.org/10.1118/1.598691
[5]
Alfonso, R., Andreo, P., Capote, R., Huq, M.S., Kilby, W., et al. (2008) A New Formalism for Reference Dosimetry of Small and Nonstandard Fields. Medical Physics, 35, 5179-5186. https://doi.org/10.1118/1.3005481
[6]
Massillon-JL, G., Cueva-Procel, D., Diaz-Aguirre, P., Rodriguez-Ponce, M. and Herrera-Martinez, F. (2013) Dosimetry for Small Fields in Stereotactic Radiosurgery Using Gafchromic MD-V2-55 Film, TLD-100 and Alanine Dosimeters. PLoS ONE, 8, e63418. https://doi.org/10.1371/journal.pone.0063418
[7]
Francescon, P., Kilby, W., Satariano, N. and Cora, S. (2012) Monte Carlo Simulated Correction Factors for Machine Specific Reference Field Dose Calibration and Output Factor Measurement Using Fixed and Iris Collimators on the Cyber Knife System. Physics in Medicine and Biology, 57, 3741-3758. https://doi.org/10.1088/0031-9155/57/12/3741
[8]
Pantelis, E., Moutsatsos, A., Zourari, K., Kilby, W., Antypas, C., Papagiannis, P., Karaiskos, P., Georgiou, E. and Sakelliou, L. (2010) On the Implementation of a Recently Proposed Dosimetric Formalism to a Robotic Radiosurgery System. Medical Physics, 37, 2369-2379. https://doi.org/10.1118/1.3404289
[9]
Massillon-JL, G. and Zúñiga-Meneses, L. (2010) The Response of the New MD-V2-55 Radiochromic Film Exposed to 60Co Gamma Rays. Physics in Medicine and Biology, 55, 5437-5449. https://doi.org/10.1088/0031-9155/55/18/011
[10]
Massillon-JL, G., Muñoz-Molina, I.D. and Díaz-Aguirre, P. (2016) Optimum Absorbed Dose versus Energy Response of Gafchromic EBT2 and EBT3 Films Exposed to 20-160 Kv X-Rays and 60Co Gamma. Biomedical Physics & Engineering Express, 2, Article ID: 045005.
[11]
Image J (2016). http://imagej.nih.gov/ij/
[12]
Kilby, W., Dooley, J.R., Kuduvalli, G., Sayeh, S. and Maurer, J.R. (2010) The CyberKnife Robotic Radiosurgery System in 2010. Technology in Cancer Research and Treatment, 9, 433-452. https://doi.org/10.1177/153303461000900502
[13]
Bewley, D.K., Bradshaw, A.L., Burns, J.E., Cohen, M., Day, M.J., Godden, T.J., Greene, D., Jennings, W.A., Lillicrap, S.C., Smith, C.W. and Williams, P.C. (1996) Central Axis Depth Dose Data for Use in Radiotherapy. The British Journal of Radiology, 104, 114.
[14]
ANSI/NCSL Z540-2-1997 1997 U.S. Guide to the Expression of Uncertainty in Measurement. American National Standard for Expressing Uncertainty NCSL, Boulder.
[15]
Kawachi, T., Saitoh, H., Inoue, M., Katayose, T., Myojoyama, A. and Hatano, K. (2008) Reference Dosimetry Condition and Beam Quality Correction Factor for CyberKnife Beam. Medical Physics, 35, 4591-4598. https://doi.org/10.1118/1.2978228
[16]
Aragón-Martínez, N., Gómez-Muñoz, A. and Massillon-JL, G. (2014) Characterization of Radiation Beams Used to Determinate the Correction Factor for a CyberKnife Unit Reference Field Using Ionization Chambers. AIP Conference Series, 1626, 55-60.
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