IJMPCERO  Vol.4 No.4 , November 2015
Visual Analysis of the Daily QA Results of Photon and Electron Beams of a Trilogy Linac over a Five-Year Period
ABSTRACT
Data visualization technique was applied to analyze the daily QA results of photon and electron beams. Special attention was paid to any trend the beams might display. A Varian Trilogy Linac equipped with dual photon energies and five electron energies was commissioned in early 2010. Daily Linac QA tests including the output constancy, beam flatness and symmetry (radial and transverse directions) were performed with an ionization chamber array device (QA Beam Checker Plus, Standard Imaging). The data of five years were collected and analyzed. For each energy, the measured data were exported and processed for visual trending using an in-house Matlab program. These daily data were cross-correlated with the monthly QA and annual QA results, as well as the preventive maintenance records. Majority of the output were within 1% of variation, with a consistent positive/upward drift for all seven energies (~+0.25% per month). The baseline of daily device is reset annually right after the TG-51 calibration. This results in a sudden drop of the output. On the other hand, the large amount of data using the same baseline exhibits a sinusoidal behavior (period = 12 months; amplitude = 0.8%, 0.5% for photons, electrons, respectively) on symmetry and flatness when normalization of baselines is accounted for. The well known phenomenon of new Linac output drift was clearly displayed. This output drift was a result of the air leakage of the over-pressurized sealed monitor chambers for the specific vendor. Data visualization is a new trend in the era of big data in radiation oncology research. It allows the data to be displayed visually and therefore more intuitive. Based on the visual display from the past, the physicist might predict the trend of the Linac and take actions proactively. It also makes comparisons, alerts failures, and potentially identifies causalities.

Cite this paper
Chan, M. , Li, Q. , Tang, X. , Li, X. , Li, J. , Tang, G. , Hunt, M. and Deasy, J. (2015) Visual Analysis of the Daily QA Results of Photon and Electron Beams of a Trilogy Linac over a Five-Year Period. International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 4, 290-299. doi: 10.4236/ijmpcero.2015.44035.
References
[1]   Eric, E.K., et al. (2009) Task Group 142 Report: Quality Assurance of Medical Accelerators. Medical Physics, 36, 4197-4212.
http://dx.doi.org/10.1118/1.3190392

[2]   Kutcher, G.J., et al. (1994) Comprehensive QA for Radiation Oncology: Report of AAPM Radiation Therapy Committee Task Group 40. Medical Physics, 21, 581-618.
http://dx.doi.org/10.1118/1.597316

[3]   Smith, K., et al. (2015) AAPM Medical Physics Practice Guideline #8: Minimum Practice Requirements for Linac QA. Journal of Applied Clinical Medical Physics. In Press.

[4]   Polgar, I. (1999) Quality Control and Quality Assurance of Linear Accelerators. In: Mayles, W.P.M., Lake, R., McKenzie, A., Macaulay, E.M., Morgan, H.M., Jordan, T.J. and Powley, S.K., Eds., IPEM 81 Physics Aspects of Quality Control in Radiotherapy, The Institute of Physics and Engineering in Medicine, York.

[5]   Chang, W. (2012) R Graphics Cookbook, Practical Recipes for Visualized Data. O’Reilly Media, Sebastopol.

[6]   Grattan, M.W.D. and Hounsell, A.R. (2011) Analysis of Output Trends from Varian 2100/D and 600C/D Accelerators. Physics in Medicine and Biology, 56, N11-N19.
http://dx.doi.org/10.1088/0031-9155/56/1/N02

[7]   Bartolac, S. and Letourneau, D. (2015) Assessment of Seasonal Linear Accelerator Output Variations and Associated Impacts. Medical Physics, 42, 3363.
http://dx.doi.org/10.1118/1.4924497

[8]   Hossain, M. (2014) Output trends, Characteristics, and Measurements of Three Megavoltage Radiotherapy Linear Accelerators. Journal of Applied Clinical Medical Physics, 5, 1-15.

[9]   Uddin, M.T. (2012) Quality Control of Modern Linear Accelerator: Dose Stability Long and Short-Term. Proceedings of IPAC2012, New Orleans.

[10]   Luketina, I.A. and Greig, L. (2004) Linear Accelerator Output Variability. Australasian Physics & Engineering Sciences in Medicine, 27, 155-159.
http://dx.doi.org/10.1007/BF03178676

 
 
Top