Absolute, Reference, and Relative Dosimetry in Radiotherapy

The correct estimation of the dose to be delivered to a patient is strongly dependent on a correct dosimetry procedure. To achieve this purpose, it must ensure that the measurement results represent the best possible value reported with its typical uncertainties, and the results must be comparable with other institutions. The International Metrological Network fundamentally seeks to standardize the processes and the methodologies among the various laboratories in the world. The concept and structure of the various levels of laboratories can be defined as primary or secondary standards laboratories. The absolute dosimetry refers to the measurement of a quantity with an instrument of the highest metrological quality, which allows its determination in accordance with its definition, usually carried out in Primary Laboratories. The main quantities of interest for the absolute dosimetry are exposure, air kerma, and absorbed dose to air and to water. This entire chain of measurements and formalism must consider the specific physical conditions of the interaction processes between the radiation beam with the detector in the measurement processes, aiming to ensure the least possible uncertainty in the dose delivered to the patient.