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DOI: 10.1055/s-0044-1798209
VALIDATION OF A QUALITY ASSURANCE METHODOLOGY IN SMALL FIELD IRRADIATION
Introduction: The TRS-483/IAEA publication purposes a new method for dosimetry in small field irradiation (SF). Nevertheless, we observe a lack of recommendations in quality assurance (QA) protocols of SF, usually used in stereotactic radiosurgery (SRS). We proposed a QA methodology for SF dosimetry comparing measured dose with calculated dose in Treatment Planning System (TPS). Methodology: For nine SRS treatment plans, we irradiated all treatment fields (TF) together (Method 1), measuring the total dose. The dose was measured with a pinpoint ionization chamber (IC). We then applied the influence factors and the correction factors proposed by TRS-483. These irradiations were realized in distinct days, with different ambient conditions. After that, in a single-day event (with stable ambient conditions), again for all nine SRS plans, we irradiated the IC with the TFs, but this time field by field (Method 2). The measured doses were corrected by specific influence quantities for each TF. Results: The mean number of TFs per treatment plan was 17.1 (SD: 3.1), and the total mean dose was 15.0 Gy (SD: 4.0 Gy). The mean difference between the total measured dose, and the total calculated dose was 2.04% (SD 0.76 %). In one of the plans, the difference was 3.8 %. In this specific plan, the mean field size was bigger than 3.0 cm. This difference was observed only in Method 1. We hypothesized that the methodology would not be suitable for TFs bigger than 3.0 cm. However, when we irradiated the individual TFs and applied the specific influence quantities and correction factors, field by field, we did not found a difference greater than 3.0 %. Conclusion: We observed that the methodology is reproducible and consistent. We recommend Method 2, including for TFs bigger than 3.0 cm. The quality of measurement is hugely dependent on Ktp, so the setup shall be settled in stable ambient condition to minimize differences in measurements.
No conflict of interest has been declared by the author(s).
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Publication History
Article published online:
23 October 2019
© 2019. The Author(s). This is an open access article published by Thieme under the terms of the Creative Commons Attribution 4.0 International License, permitting copying and reproduction so long as the original work is given appropriate credit (https://creativecommons.org/licenses/by/4.0/)
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Tiago Batista de Oliveira, André Ezequiel Lobo de Abreu, Gerson Hiroshi Yoshinari, Mariana Paranhos Alvarenga, James Wagner Morais, Harley Francisco de Oliveira. VALIDATION OF A QUALITY ASSURANCE METHODOLOGY IN SMALL FIELD IRRADIATION. Brazilian Journal of Oncology 2019; 15.
DOI: 10.1055/s-0044-1798209