Comparison of Dosimetry Protocols for Electron Beam Radiotherapy Calibrations and Measurement Uncertainties.

Fawzia E M Elbashir,Sitah Alanazi,Mohamed Hassan Eisa,David A Bradley,Abdelmoneim Sulieman,Farouk Habbani,Wassim Ksouri,Ibrahim I Suliman

doi:10.3390/life12010031

Abstract

This paper presents guidelines for the calibration of radiation beams that were issued by the International Atomic Energy Agency (IAEA TRS 398), the American Association of Physicists in Medicine (AAPM TG 51) and the German task group (DIN 6800-2). These protocols are based on the use of an ionization chamber calibrated in terms of absorbed dose to water in a standard laboratory’s reference quality beam, where the previous protocols were based on air kerma standards. This study aims to determine uncertainties in dosimetry for electron beam radiotherapy using internationally established high-energy radiotherapy beam calibration standards. Methods: Dw was determined in 6-, 12- and 18 MeV electron energies under reference conditions using three cylindrical and two plane-parallel ion chambers in concert with the IAEA TRS 398, AAPM TG 51 and DIN 6800-2 absorbed dose protocols. From mean measured Dw values, the ratio TRS 398/TG 51 was found to vary between 0.988 and 1.004, while for the counterpart TRS 398/DIN 6800-2 and TG 51/DIN 6800-2, the variation ranges were 0.991–1.003 and 0.997–1.005, respectively. For the cylindrical chambers, the relative combined uncertainty (k = 1) in absorbed dose measurements was 1.44%, while for the plane-parallel chambers, it ranged from 1.53 to 1.88%. Conclusions: A high degree of consistency was demonstrated among the three protocols. It is suggested that in the use of the presently determined dose conversion factors across the three protocols, dose intercomparisons can be facilitated between radiotherapy centres.

Highlights

Current dosimetry protocols for calibration of clinical high-energy photon beams are based on the standard adoption of absorbed dose to water (Dw) [1,2,3,4]
There is a regular need to reflect upon progress made in seeking improved accuracy, high-precision radiotherapy dosimetry, an important part of which is the comparison of the different protocols that are widely adopted
Results are presented for the Dw measured using three cylindrical and two planeparallel ion chambers in concert with absorbed dose-based protocols

Summary

Introduction

Current dosimetry protocols for calibration of clinical high-energy photon beams are based on the standard adoption of absorbed dose to water (Dw) [1,2,3,4]. Absorbed dose standards allow the use of a more straightforward formalism, providing fewer uncertainties compared to the previous air kerma protocols and a more robust system of primary standards for radiation measurements [5,6]. The desire is to reduce discrepancies in measurements and to assist in dose standardization Following publication of these protocols some 20 years ago, a number of studies have sought to determine differences that might derive from their adoption and to provide insights into the origin of any such differences.

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Methods

Results

Conclusion