Dosimetry of nuclear medical imaging: current practices and new modalities

Radiation dosimetry is a multi-disciplinary activity of theory, experiment and numerical evaluations, which involves physics, biology, statistics, instrumentation and computer modeling. Of primary interest are biological effects either for the harm they cause to living organisms or otherwise. As biological effects are consequences of chemical transformations, which in turn are due to ionization phenomena, the dosimetry relies on the number of ions created. In the context of medical imaging, the interest is mainly on photon interactions with matter. For practical assessment of dose deposits, great strides have been made in terms of the transducer development, speeds of data processing thanks to technological innovations of the latter half of the 20th century and they continue to evolve. The ever increasing computational power and the activities of high energy physics communities also contributed vastly to the dosimetric evaluations. In this regard, the Monte Carlo simulation codes based on the electron -gamma-showers are worth noting. In the last few decades, MCNP, EGS and the GEANT based GATE are now widely used with precisions and details unimaginable a few decades ago. Despite all these developments, the dosimetry is still missing an important ingredient. The dosimetry's ultimate aim is to assess the biological risk to the patient. However, physical instruments cannot access it. My talk will highlight these developments and suggest a possible path to achieve accurate estimates of physicochemical phenomena for dose due to various species of radiations of use in medical imaging. (author)