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Updated: Jul 15, 2026
06:20
Irradiator Commissioning and Dosimetry for Assessment of LQ α and β Parameters, Radiation Dosing Schema, and in vivo Dose Deposition
Published on: March 11, 2021
Uncertainty estimation in intensity-modulated radiotherapy absolute dosimetry verification.
Francisco Sánchez-Doblado1, Günther H Hartmann, Javier Pena
1Radiofísica, Hospital Universitario Virgen Macarena, Sevilla, Spain. paco@us.es
Summary
Small ionization chambers (ICs) provide accurate intensity-modulated radiotherapy (IMRT) dosimetry, with nonreference conditions adding 1-1.5% uncertainty. Overall IMRT dose uncertainty is approximately 2.3% using appropriate ICs.
Area of Science:
- Medical Physics
- Radiation Oncology
Background:
- Intensity-modulated radiotherapy (IMRT) is a crucial technique for improving radiation therapy (RT).
- While relative dosimetry checks for IMRT are established, reference dosimetry using ionization chambers (ICs) faces challenges due to measurement conditions deviating from reference standards, introducing uncertainty.
- This study systematically assesses the impact of these nonreference conditions on dose determination.
Purpose of the Study:
- To systematically evaluate the effect of nonreference conditions on reference dosimetry in intensity-modulated radiotherapy (IMRT).
- To determine the additional uncertainty introduced by these deviations when using ionization chambers (ICs).
Main Methods:
- Conducted Monte Carlo simulations and dosimetric measurements using five different detectors.
- Investigated representative IMRT cases, encompassing both step-and-shoot and dynamic delivery techniques.
- Analyzed the agreement between detectors and Monte Carlo-calculated nonreference correction factors (c factors).
Main Results:
- Small-volume ionization chambers (approx. 0.125 cm³ or less) showed good agreement among detectors in most IMRT scenarios.
- Results aligned well with Monte Carlo-derived nonreference correction factors (c factors).
- A correlation was found between IC position relative to treatment segments and the derived c factor, useful for estimating overall treatment uncertainty.
Conclusions:
- Nonreference conditions increase the relative standard uncertainty of reference dose measurements with ICs in IMRT by approximately 1-1.5% when using small-volume chambers.
- The total standard uncertainty for measured IMRT dose is about 2.3%, including reproducibility and beam calibration uncertainties.
- Solid-state detectors and large-volume chambers are less suitable for IMRT verification due to higher uncertainties; an action level of 5% is recommended for IMRT verification.
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