한국의학물리학회지:의학물리 (Progress in Medical Physics)

  • 제31권4호
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  • Pages.145-152
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  • 2020
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  • 2508-4445(pISSN)
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  • 2508-4453(eISSN)
한국의학물리학회 (Korean Society of Medical Physics)
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High-Dose-Rate Electron-Beam Dosimetry Using an Advanced Markus Chamber with Improved Ion-Recombination Corrections

  • Jeong, Dong Hyeok (Research center, Dongnam Institute of Radiological and Medical Sciences) ;
  • Lee, Manwoo (Research center, Dongnam Institute of Radiological and Medical Sciences) ;
  • Lim, Heuijin (Research center, Dongnam Institute of Radiological and Medical Sciences) ;
  • Kang, Sang Koo (Research center, Dongnam Institute of Radiological and Medical Sciences) ;
  • Jang, Kyoung Won (Research center, Dongnam Institute of Radiological and Medical Sciences)
  • 투고 : 2020.08.19
  • 심사 : 2020.10.23
  • 발행 : 2020.12.31
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초록

Purpose: In ionization-chamber dosimetry for high-dose-rate electron beams-above 20 mGy/pulse-the ion-recombination correction methods recommended by the International Atomic Energy Agency (IAEA) and the American Association of Physicists in Medicine (AAPM) are not appropriate, because they overestimate the correction factor. In this study, we suggest a practical ion-recombination correction method, based on Boag's improved model, and apply it to reference dosimetry for electron beams of about 100 mGy/pulse generated from an electron linear accelerator (LINAC). Methods: This study employed a theoretical model of the ion-collection efficiency developed by Boag and physical parameters used by Laitano et al. We recalculated the ion-recombination correction factors using two-voltage analysis and obtained an empirical fitting formula to represent the results. Next, we compared the calculated correction factors with published results for the same calculation conditions. Additionally, we performed dosimetry for electron beams from a 6 MeV electron LINAC using an Advanced Markus® ionization chamber to determine the reference dose in water at the source-to-surface distance (SSD)=100 cm, using the correction factors obtained in this study. Results: The values of the correction factors obtained in this work are in good agreement with the published data. The measured dose-per-pulse for electron beams at the depth of maximum dose for SSD=100 cm was 115 mGy/pulse, with a standard uncertainty of 2.4%. In contrast, the ks values determined using the IAEA and AAPM methods are, respectively, 8.9% and 8.2% higher than our results. Conclusions: The new method based on Boag's improved model provides a practical method of determining the ion-recombination correction factors for high dose-per-pulse radiation beams up to about 120 mGy/pulse. This method can be applied to electron beams with even higher dose-per-pulse, subject to independent verification.

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과제정보

The study was supported by the Dongnam Institute of Radiological and Medical Sciences (DIRAMS) grant funded by the Korea government (MSIT) (No. 50498-2020).

참고문헌

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