What is Dose and What is Not and Which is the Available Information for Personalized Dosimetry

Biological effects induced by exposure to radiation made evident the need for an accurate dosimetry from the early days of X-ray use in medicine. Later the scientific interest turned also to the estimation of risks of radiation-induced cancer and genetic effects. Various dosimetric quantities have been used in diagnostic radiology and sometimes confusion is caused because the same name is used for different quantities. The question arises: what is patient dose and what is not?

It’s common practice to indicate the dose received by a patient in radiology using the dosimetric indexes defined for the different imaging modalities. However, dosimetric indexes are a useful tool for practices optimization and comparison, but certainly they don’t describe patient dose.

To accurately estimate patient dose there is the need to collect a lot of information concerning patient characteristics and irradiation events in order to obtain organ or tissue dose.

Nowadays, thanks to the digital technology used in medical imaging, various ways of collecting these data are available. The information is communicated using specific standards (i.e. DICOM), such as the non-image information object definitions. These objects are carrying information about equipment output and do not provide any information on patient dose. Although they can include some of the information needed to estimate patient dose, unfortunately this information is not complete. Moreover some more recent modality (e.g. CBCT) are not covered by the present standard. For this reason the DICOM WG-28 (Physics Strategy) is currently working on a revision of the RDSR to include the missing information.

Furthermore none of these objects includes a template for patient-specific dose data to be recorded after estimation. For this reason a new DICOM object, the Patient Radiation Dose Structured Report (P-RDSR) has been added to the standard in 2017, in order to include some of the information lacking in the RDSR necessary for estimating patient-specific dose and to provide the archival tool to record the results of any dose estimation as well as the methodology used to achieve this estimate.

DICOM standard is vital to provide a common syntax and semantics for information exchange. Essentially, DICOM provides “tools” and “technologies”. However, DICOM standard alone is insufficient: it may be open to interpretation, and some information remains optional, preventing a common implementation that guarantees interoperability for all the use cases and applications. There is a need for specifications about how to apply the standards to particular real world scenarios. These specifications are provided by IHE (Integrating the Healthcare Enterprise) through the development of the so-called “profiles”.

This talk will review the basic concepts on patient dosimetry as well as the existing DICOM objects and IHE profiles used to monitor patient exposure, highlighting pros and cons and introducing to the future developments.