Uncertainty Estimation in Intensity-Modulated Radiotherapy Absolute Dosimetry Verification
- Radiofisica. Hospital Universitario Virgen Macarena, Sevilla (Spain) and Departamento de Fisiologia Medica y Biofisica, Facultad de Medicina, Universidad de Sevilla, Sevilla (Spain)
- Abt Medizinische Physik in der Strahlentherapie, Deutsches Krebsforschungszentrum, Heidelberg (Germany)
- Departamento de Fisica de Particulas, Facultade de fisica, Universidade de Santiago de Compostela, Santiago de Compostela (Spain)
- Nuclear Data Section, International Atomic Energy Agency, Vienna (Austria)
- Fisica Sanitaria, Arcispedale S. Maria Nuova, Reggio Emilia (Italy)
- Radiofisica. Hospital Universitario Virgen Macarena, Sevilla (Spain)
Purpose: Intensity-modulated radiotherapy (IMRT) represents an important method for improving RT. The IMRT relative dosimetry checks are well established; however, open questions remain in reference dosimetry with ionization chambers (ICs). The main problem is the departure of the measurement conditions from the reference ones; thus, additional uncertainty is introduced into the dose determination. The goal of this study was to assess this effect systematically. Methods and Materials: Monte Carlo calculations and dosimetric measurements with five different detectors were performed for a number of representative IMRT cases, covering both step-and-shoot and dynamic delivery. Results: Using ICs with volumes of about 0.125 cm{sup 3} or less, good agreement was observed among the detectors in most of the situations studied. These results also agreed well with the Monte Carlo-calculated nonreference correction factors (c factors). Additionally, we found a general correlation between the IC position relative to a segment and the derived correction factor c, which can be used to estimate the expected overall uncertainty of the treatment. Conclusion: The increase of the reference dose relative standard uncertainty measured with ICs introduced by nonreference conditions when verifying an entire IMRT plan is about 1-1.5%, provided that appropriate small-volume chambers are used. The overall standard uncertainty of the measured IMRT dose amounts to about 2.3%, including the 0.5% of reproducibility and 1.5% of uncertainty associated with the beam calibration factor. Solid state detectors and large-volume chambers are not well suited to IMRT verification dosimetry because of the greater uncertainties. An action level of 5% is appropriate for IMRT verification. Greater discrepancies should lead to a review of the dosimetric procedure, including visual inspection of treatment segments and energy fluence.
- OSTI ID:
- 20951646
- Journal Information:
- International Journal of Radiation Oncology, Biology and Physics, Vol. 68, Issue 1; Other Information: DOI: 10.1016/j.ijrobp.2006.11.056; PII: S0360-3016(06)03655-8; Copyright (c) 2007 Elsevier Science B.V., Amsterdam, Netherlands, All rights reserved; Country of input: International Atomic Energy Agency (IAEA); ISSN 0360-3016
- Country of Publication:
- United States
- Language:
- English
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