IJMPCERO  Vol.7 No.1 , February 2018
Variations in Tomotherapy Beam Outputs: A Multiple-Institutional Investigation
This study aimed to determine variations in tomotherapy beam outputs at multiple institutions. Measurements were obtained at 22 radiotherapy institutions. The first parameter was the absolute dose to water (Dfmsrw, Qmsr) in the machine-specific reference field (fmsr), which indicated a static field in the tomotherapy reference conditions defined by the International Atomic Energy Agency (IAEA) study group. The second measured parameter was the difference between the measured and the planed doses in the intensity modulated radiotherapy (IMRT) verification plans, which were created using a solid phantom by the vendor during tomotherapy apparatus installation to adjust the beam output. The IMRT verification plan error at each institution was defined as the systematic error of the beam output; Dfmsrw, Qmsr was subsequently modified. The Dfmsrw, Qmsr values of four institutions with a modified energy fluence per ideal open time (EFIOT) were lower than the values at other institutions. The mean value of all institutions except those four was 0.994 ± 0.013 Gy (range: 0.974 Gy, 1.017 Gy). When the
Dfmsrw, Qmsr value was corrected by the IMRT verification error, this variation decreased. In addition, the mean IMRT verification errors in the TomoDirectTM and TomoHelicalTM modes with the TomoEDGETM mode were 1.2% ± 0.8% (range: -0.6%, 1.8%) and 0.2% ± 0.5% (range: -0.6%, 0.9%), respectively (p < 0.05). Those without the TomoEDGE mode were 0.6% ± 1.0% (range: -1.0%, 1.7%) and -0.7% ± 0.7% (range: -2.3%, 0.4%), respectively (p < 0.001). The variations in tomotherapy beam output across multiple facilities were very low, except at facilities where the EFIOT was modified. The beam output was affected by the mode (e.g., TomoHelical), and it would be recommended to investigate the difference of the beam output due to differences in the mode in order to equalize the beam output.
Cite this paper: Shimizu, H. , Sasaki, K. , Sugi, K. , Fukuma, H. , Nakabayashi, T. , Isomura, T. , Tachibana, H. and Kodaira, T. (2018) Variations in Tomotherapy Beam Outputs: A Multiple-Institutional Investigation. International Journal of Medical Physics, Clinical Engineering and Radiation Oncology, 7, 87-99. doi: 10.4236/ijmpcero.2018.71008.

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