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Detailed Analysis of TomoTherapy Quality Assurance (TQA) Before and After Dose Control System Upgrade (DCS) - 3 Year Collected Data

A Movahed

A Movahed1*, B Rabbani2, (1) Pomona Valley Hospital Medical Center, Pomoa, CA, (2) Atlas Medical Physics, Newport Beach, CA

SU-E-T-127 Sunday 3:00PM - 6:00PM Room: Exhibit Hall

Detailed data analysis, reliability comparison between the three years of collected data using TomoTherapy quality assurance (TQA) tool and software and standard manual QA test procedures. The analysis convers output, energy, magnetron arcs, noise, couch movement and overall performance of TomoTherapy unit. The analyses were performed on the data collected before and after dose control system (DCS) upgrade.

Daily, weekly and monthly QAs were performed using two different methods, basic dosimetry, step wedge and solid water slabs using two ion chambers as specified by the manufacturer. Data from TQA software and standard QAs were analyzed.

The maximum variations between the TQA and standard QA were found not to exceed 2% before DCS upgrade and within 1% after DCS upgrade. Close agreement in case of magnetron replacement and magnetron voltage adjustment by about 1.0%. The amplitude of the arcs are smaller when DCS is installed.

Based on the results, author believes TomoTherapy Quality Assurance (TQA) is a very useful tool available to the site physicist as well as to the TomoTherapy field service engineer. It is fast and provides in-depth information about, output, energy, magnetron performance, couch movement and many more. Hence it makes a very valuable tool. Since dose control system (DCS) adjusts injector current and pulse amplitude control (PAC) in order to maintain the output and dose rate variations, the arcs amplitudes are smaller compared to when DCS was not installed. It is a very handy tool when one is subjected to magnetron replacement or the prediction for the need of replacement and output adjustment as well. It is a reliable tool that provides valuable information about the performance of the machine and most of its component including couch movement, magnetron, noise, arcs, output, energy, jaws, linac and so on.

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