Faktor Koreksi Ionization Chamber pada Dosimetri Berkas Elektron: Kualitas Berkas, Polaritas, dan Rekombinasi Ion di Berbagai Kondisi Pengukuran
DOI:
https://doi.org/10.35895/rf.v6i2.101Keywords:
Ultra-high dose rate, FLASH radiotherapy, dose per pulse, small-field dosimetry, ionization chamber designAbstract
Ionization chamber dosimetry in electron beam radiotherapy required accurate correction for beam quality, polarity effects, and ion recombination. This review examined current evidence on these correction factors under conventional, high dose rate electron, ultra-high dose rate, extended source-to-surface distance, and small-field conditions, with emphasis on recent updates to international electron dosimetry formalisms. Updated Monte Carlo calculations for the beam quality correction factor produced values approximately 0.5% lower than older protocol tabulations, while multicenter experimental data showed that inter-institutional variability remained within the ±2% clinical tolerance. For the polarity correction factor, dose per pulse, electrode spacing, field size, and cable geometry were identified as the main determinants, with cable irradiation producing large apparent polarity corrections in large-field and high dose rate electron beams. For the ion recombination correction factor, conventional two-voltage analysis was reliable only up to approximately 10 mGy per pulse; above this range, empirical logistic models provided more accurate correction estimates. Sub-millimeter electrode spacing and high electric field strength were the most important chamber design parameters for ultra-high dose rate dosimetry. Overall, correction factor uncertainties remained controlled under conventional reference conditions but increased substantially under high dose-per-pulse and non-reference geometries, which current protocols did not adequately cover. These findings supported the need for dedicated dosimetry protocols for high dose rate electron, ultra-high dose rate, extended source-to-surface distance, and small-field electron beam modalities.
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