Abstract
To investigate and evaluate the use of an in‐house developed diagnostic software tool using the imaging detector data for a quick daily quality assurance check of the output (dose) and lateral profile (cone) of a tomotherapy Hi•Art system. The Hi•Art treatment system is a radiation therapy machine for delivering intensity modulated radiation therapy (IMRT) in a helical fashion with an integrated CT scanner used for improved patient positioning before treatment. Since the system was developed specifically for IMRT, fat fields can be obtained by modulating the beam and therefore the fattening filter could be omitted. Because of this, the field has a cone‐like profile in both lateral and transversal directions. Patients are treated in a helical fashion with a tight pitch and a constant gantry rotation speed, while modulation is performed by a binary MLC. Consequently dose output per time‐unit (dose rate) as well as the shape of the cone‐profile are very important for correct patient treatment and should be closely monitored. However, using the company‐provided initial tools and conventional dosimetry, this can be a time consuming daily procedure. The aim of this work is to develop a fast, automated method of quality assurance based on the detector signal. A software tool called “tomocheck” running on the operation station has been developed to evaluate the output (dose rate) and the lateral cone profile (energy) of the Hi•Art system, comparing actual output and cone profile with a reference (previously approved against ionization chamber measurements). This is done by using the data of the 640 on‐board detector array that are directly retrieved and processed after a specific QA procedure. The detector file consists of the CT detector data and the three monitoring dose chamber readings over a time period of 200 sec. To evaluate the method, the system was benchmarked against ionization chamber measurements and classical IMRT QA methods. Action levels (final status “NOT ACCEPTED”) for dose ratio as well as the cone ratio are set to ±2%. The QA tool was introduced for daily QA in May 2007. For the following 24 months, a total of 931 morning checks was made on both tomotherapy machines. In 42 cases the check status was “NOT ACCEPTED”. In 34 cases the dose ratio (DR) was out of tolerance. The corrected cone ratio (CCR) was outside of specification tolerance in 8 cases. The tomocheck data was related to the ionization chamber measurements for the IMRT plan indicating a close relationship between the CCR and the off‐axis measurements. Average dose ratio against the mean value of the on‐ and off‐axis IC measurement indicates that this parameter is a good interpretation of the dose output. This tool makes it possible to perform an easy‐to‐use and fast basic daily quality assurance check featuring an output as well as an energy evaluation. Ideally this tool should offer also the combined dosimetry check of jaw width, couch speed, leaf latency, output, leaf/gantry synchrony, and lasers. This will be investigated in the future.PACS 87.55Qr
Highlights
In July 2005 we installed as one of the first hospitals in Europe a Helical Tomotherapy radiation therapy unit (TomoTherapy Inc., Madison, WI, USA)
The HiArt treatment system is a radiation therapy machine for delivering intensity-modulated radiation therapy (IMRT) in a helical fashion with an integrated CT scanner used for correct patient positioning before treatment
Tomotherapy unit and quality assurance (QA) procedure The Tomotherapy HiArt system consists of four basic components: the planning station, the optimization server, the data server, and the Radiation Delivery Subsystem (RDS)
Summary
In July 2005 we installed as one of the first hospitals in Europe a Helical Tomotherapy radiation therapy unit (TomoTherapy Inc., Madison, WI, USA). The HiArt treatment system is a radiation therapy machine for delivering intensity-modulated radiation therapy (IMRT) in a helical fashion with an integrated CT scanner used for correct patient positioning before treatment. The field has a cone-like profile in the both lateral and transversal directions. Patients are treated in a helical fashion with a tight pitch and a constant gantry rotation speed, while modulation is performed by a binary MLC. Dose output per time-unit (dose rate), as well as the shape of the cone-profile, are critical for correct patient treatment and should be closely monitored. Output check of radiation therapy delivery equipment is one of the main components of any quality assurance (QA) program. The AAPM TG-40 recommends that the output of a megavoltage radiation unit has to be checked every morning and assigns a ± 3% acceptability window.(1)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
