Abstract
The purpose of this study was to suggest tolerance levels for IMRT DQA measurements using confidence limits determined by a multi‐institutional study in Korea. Ten institutions were grouped into LINAC (seven linear accelerators) and TOMO (three tomotherapy machines). The DQA processes consisted of point (high‐ and low‐dose regions) and planar (per‐field and composite‐field) dose measurements using an ion chamber and films (or 2D detector array) inserted into a custom‐made acryl phantom (LINAC) or a cheese phantom (TOMO). The five mock structures developed by AAPM TG‐119 were employed, but the prostate as well as the H&N structures were modified according to Korean patients' anatomy. The point measurements were evaluated in a ratio of measured and planned doses, while the planar dose distributions were assessed using two gamma criteria of 2 mm/2% and 3 mm/3%. The confidence limit (|mean + 1.96 σ|) for point measurements was determined to be 3.0% in high‐dose regions and 5.0% in low‐dose regions. The average percentage of points passing the gamma criteria of 2 mm/2% and 3 mm/3% for per‐field measurements was 92.7 ±6.5% and 98.2 ±2.8%, respectively. Thus, the corresponding confidence limit was 79.1% and 92.7%, respectively. The gamma passing rate averaged over all mock tests and institutions for composite‐field measurements was 86.1 ±6.5% at 2 mm/2% and 95.3 ±3.8% at 3 mm/3%, leading to the confidence limit of 73.3% and 87.9%, respectively. There was no significant difference in the tolerance levels of point dose measurements between LINAC and TOMO groups. In spite of the differences in mock structures and dosimetry tools, our tolerance levels were comparable to those of AAPM and ESTRO guidelines.PACS number: 87.55.Qr
Highlights
Intensity-modulated radiation therapy (IMRT) has been rapidly implemented in Korea due to recent governmental policy.[1]
The mock structures were modified according to Korean patients’ anatomy, and the dosimetry tools and phantoms used in this study were somewhat different from those of AAPM TG-119
The coefficient of variation (COV) was a normalized measurement of the dispersion of a probability distribution that was defined as a ratio of the standard deviation (STDV) to the mean
Summary
Intensity-modulated radiation therapy (IMRT) has been rapidly implemented in Korea due to recent governmental policy.[1]. 119 carried out a multi-institutional research to assess the overall accuracy of planning and delivery of IMRT, and produced quantitative confidence limits as baseline expectation values for IMRT commissioning.[8] The British group carried out a national dosimetry audit of IMRT to provide an independent check of safe implementation and to identify problems in the modeling and delivery of IMRT.[7,9,10,11]. With a rapid implementation of IMRT in Korea, ten institutions reached consensus on a multi-institutional study to provide tolerance levels of IMRT DQA measurements as a national safety guideline for the overall accuracy of IMRT planning and delivery. Ten institutions were grouped into LINAC (seven linear accelerator-based centers) and TOMO (three tomotherapy-based centers), and the results of both groups were separately analyzed
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