Abstract
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 p
Highlights
Tomotherapy (Accuray, Inc., Sunnyvale, CA, USA) is a unique machine for delivering intensity modulated radiation therapy (IMRT) treatments using multileaf collimators (MLCs) of 64 leaves while synchronizing with the gantry rotation and moving the patient into the beam plane at constant speed [1]
It is impossible with this machine to measure the absorbed dose to water under standard reference conditions composed of a 10 cm × 10 cm square field and 100 cm source-to-surface distance (SSD) or source-to-axis distance (SAD)
The Exradin A1SL ionization chamber was used for measurement in this investigation, which was routinely used for all institutions
Summary
Tomotherapy (Accuray, Inc., Sunnyvale, CA, USA) is a unique machine for delivering intensity modulated radiation therapy (IMRT) treatments using multileaf collimators (MLCs) of 64 leaves while synchronizing with the gantry rotation and moving the patient into the beam plane at constant speed [1]. The International Atomic Energy Agency (IAEA) study group defined new reference conditions for treatment units, such as tomotherapy and CyberKnifeTM (Accuray Inc., Sunnyvale, CA, USA), that cannot establish standard reference conditions [2]. The tomotherapy reference conditions were defined as a 5 cm × 10 cm field and 85 cm SSD or SAD. The present study aimed to determine variations in these beam outputs among multiple institutions, based on the tomotherapy reference conditions. In this report, it aimed to clarify the effect of errors due to delivery mode by investigating errors among multiple institutions.
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