What can primary standards do for you?

Full text: In virtually all fields of high-level technology enormous advances have been achieved by continuously perfecting the methodologies. As a result we are offered completely new products or products with a performance which not too long ago had been judged as utterly unrealisable. One impressive example is the enormous increase in circuit density of electronic devices realised over the last two decades or so. This progress was achieved by uniting forces of many disciplines successfully. In this context metrology, the science of measurement plays an indisputably vital role. Without the development of a rugged dimensional metrology chain down to the sub-micron regime the development experienced in electronic circuitry could not have taken place. Also in other fields of metrology, many national laboratories have actively endeavoured to develop primary standards tailored to the needs of the end user. This process applies to the full extent and may be even especially to the field of dosimetry of ionising radiation. Traditionally, metrology institutes provide calibrations for reference conditions that were largely selected by themselves. For performing external radiotherapy the user is provided with a 60Co-calibration in spite of the fact that he uses in the overwhelming majority of cases fields produced by linear accelerators. By what could be termed a change of paradigm, metrology institutes attempt increasingly to provide standards well matched to clinical needs. The driving forces behind this development are at least two-fold: The ever increasing sophistication of diagnostic and therapeutic methods, like e.g. IMRT to name just one, requires both new measurement techniques and reduced measurement uncertainties in order to realize fully the advantages of new radiological procedures. Secondly, new technical developments appear on the market, demanding for completely new kinds of dose measurements. An example of this kind are miniature x-ray tubes for brachytherapy. With the main emphasis on radiotherapy an overview will be given on the efforts undertaken by metrology institutes in order to supply the medical physicist in the clinic with dosimetric tools suitable and adequate for the complete range of current radiological procedures