Abstract
The purpose of this study was to determine the reproducibility of patient‐specific, intensity‐modulated radiation therapy (IMRT) quality assurance (QA) results in a clinical setting. Six clinical patient plans were delivered to a variety of devices and analyses, including 1) radiographic film; 2) ion chamber; 3) 2D diode array delivered and analyzed in three different configurations (AP delivery with field‐by‐field analysis, AP delivery with composite analysis, and planned gantry angle delivery); 4) helical diode array; and 5) in‐house‐designed multiple ion chamber phantom. The six clinical plans were selected from a range of treatment sites and were of various levels of complexity. Of note, three of the plans had failed at least preliminary evaluation with our in‐house IMRT QA; the other three plans had passed QA. These plans were delivered three times sequentially without changing the setup, and then delivered two more times after breaking down and rebuilding the setup between each. This allowed for an investigation of reproducibility (in terms of dose, dose difference or percent of pixels passing gamma) of both the delivery and the physical setup. This study showed that the variability introduced from the setup was generally higher than the variability from redelivering the plan. Radiographic film showed the poorest reproducibility of the dosimeters investigated. In conclusion, the various IMRT QA systems demonstrated varying abilities to reproduce QA results consistently. All dosimetric devices demonstrated a reproducibility (coefficient of variation) of less than 4% in their QA results for all plans, with an average reproducibility of less than 2%. This work provides some quantification for the variability that may be seen for IMRT QA dosimeters.PACS numbers: 87.55.Qr, 87.56.Fc
Highlights
Intensity-modulated radiation therapy (IMRT) has become ubiquitous in radiation therapy clinics
A number of devices have been developed to measure doses from IMRT patient plans, which are compared with the intended dose distribution calculated by the treatment planning system (TPS)
Two of these metrics are percent difference and percent of pixels passing the gamma criterion.(1) Percent difference is often used with point measurements, such as with an ion chamber, whereas gamma analysis is used for planar measurements, such as film or a diode array
Summary
Intensity-modulated radiation therapy (IMRT) has become ubiquitous in radiation therapy clinics. For the sake of convenience, several metrics have been adopted that allow for the sorting of plans as passing (the delivered dose distribution adequately reflects the intended dose distribution, as calculated by the TPS) or failing. Two of these metrics are percent difference and percent of pixels passing the gamma criterion.(1) Percent difference is often used with point measurements, such as with an ion chamber, whereas gamma analysis is used for planar measurements, such as film or a diode array. A robust IMRT QA system, requires good reproducibility of the measured dose
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