This report addresses uncertainties pertaining to brachytherapy source dosimetry. The ISO Guide to the Expression of Uncertainty in Measurement (GUM) and the NIST Technical Note 1297 are taken as reference standards for uncertainty formalism. Uncertainties in measuring or estimating brachytherapy dose distributions using Monte Carlo methods are provided with discussion of the components intrinsic to the overall dosimetric assessment. Uncertainties provided are based on published observations and cited when available. The topic of uncertainty is addressed in detail. The uncertainty propagation from the primary calibration standard through transfer to the clinic for air-kerma strength is covered first. Uncertainties in each of the brachytherapy dosimetry parameters of the TG-43 formalism are then explored, ending with transfer to the clinic and recommended approaches. For LDR and HDR low-energy and high-energy brachytherapy sources, a k = 1 combined dosimetric uncertainty of about 5% is estimated which is consistent with prior literature estimates. Recommendations are provided for the source manufacturer, treatment planning systems, dosimetry investigator and the medical physicist. These recommendations include the use of the GUM, a requirement of constancy of manufacturer source design, dosimetry investigator guidelines, provision of the lowest uncertainty for the treatment dosimetry for the patient, and the establishment of an action level for dosimetric uncertainty. These recommendations reflect the guidance of the AAPM and the ESTRO for its members, and may also be used as guidance to vendors and regulatory agencies in developing good manufacturing practices for sources used in routine clinical treatments.
Citation: Medical Physics
Pub Type: Journals
brachytherapy, dosimetry, uncertainty, standards