Radiation dosimetry: Where do we stand and where do we go from here?

Abstract

Radiation dosimetry is an important discipline in most areas of Radiation Medicine (radiotherapy, radiodiagnostics and nuclear medicine) and in Radiation Protection. In the extremes is, on the one hand, radiotherapy where modern dose escalation requires optimization of the dose delivered so that the highest levels can be achieved with minimum complications and morbidity, in consistency with what some call AHARA: as high as reasonably achievable. The other extreme is radiodiagnostics, where again there is a need for optimizing patient dose delivery to the lowest level which allows a clinically useful image: the old concept of ALARA. These optimization processes, intrinsic to the clinical procedure, form part of the quality management process which establishes standards of good practice and includes protecting patients by “doing the right thing”. Since decades, radiotherapy dosimetry has leaded the developments on harmonization and accuracy. Dosimetry protocols and codes of practice worldwide have lead to a situation where practically the same terminology is shared by all scientists, from the hospital to the standards laboratory. The accuracy reached for dosimetry in the so-called reference conditions (beam or source calibration) has also reached unprecedented levels and most clinical institutions today achieve results compatible with reasonable levels of uncertainty or minor discrepancies. Research during the last years has mostly been focused on verifying, both experimentally and with Monte Carlo simulations, that recommended parameters and quantities are accurate within their stated uncertainties. Reference conditions in radiotherapy dosimetry are robust and well established. But what happens when we departure from reference conditions, when direct patient dose calculations are involved?. Some of the existing dosimetry audits in Europe and USA show that too many large errors are being found. These are the situations that should concern us now and where research should be focused. A similar development in the dosimetry of diagnostic radiology and nuclear medicine has not existed. So many different terms have been developed by single authors that it is difficult to realize when they refer to the same quantity and conditions. A major effort has been accomplished recently with the publication of the new ICRU report 74 on patient dosimetry for diagnostic rays, where for the first time it is stressed that there is a need for harmonization of quantities and terminology in the field. Developed in synchronization with the ICRU report, a soon to be published code of practice for diagnostic radiology dosimetry has been prepared by the IAEA so that the two international reports complement each other and provide a framework of harmonization which without doubt will improve dramatically the overall status of the dosimetry in this field.