Personal dosimetry of workers without a physical dosemeter using computational methods

Monitoring the individual exposure of workers constitutes an integral part of any radiation
protection program. Individual monitoring of exposed workers to external ionizing radiation
is essential in order to ensure safe and satisfactory working conditions; demonstrate
compliance with dose limits and the application of the ALARA principle. At present,
personal dosimetry is typically performed by issuing staff with physical dosimeters. These
physical measurement devices are part of routine practice, but still have many limitations,
both from a practical and from a metrological point of view. The results are usually known
only after some delay (30-60 days) with passive dosimeters. In addition, performing precise
and reliable personal dose measurements in all types of workplaces is quite difficult. There
are issues with compliance and multiple dosimeters can be mixed up or worn incorrectly.
The number and positioning of individual dosimeters is becoming more complex with the
new focus on eye lens dosimetry. Also, the uncertainties with the present dosimeters are
not negligible. An uncertainty factor of 2 is accepted as good practice for low doses and
for neutron fields in particular the uncertainties are even higher. On the other hand, computational
techniques are evolving rapidly. In the past, simplified mathematical phantoms
were used, while now very detailed voxel and mesh phantoms are available. In addition,
with increasing computational power, such calculations can be performed faster and faster.
The objective of this thesis work is to improve occupational dosimetry by an innovative approach:
the development of a computational dosimetry application based on Monte-Carlo
(MC) simulations without the use of physical dosimeters. This is done using a combination
of (i) monitoring of the position of workers in real time and (ii) the spatial radiation field,
including its energy and angular distribution. With this input, the doses of the workers
can be simulated or calculated. The methodology was applied and validated for two situations
where improvements in dosimetry are urgently needed: neutron and interventional
radiology workplaces. Human motion tracking system was developed to monitor worker’s
movements. The movement of the worker is then used to animate an anthropomorphic flexible
computational phantom. As regards interventional radiology workplaces, the required
information and data sources have been identified. In particular, for the calculations the
most reliable way to gather the required information is from the Radiation Dose Structured
Report (RDSR). For neutron fields, the radiation field map of the workplace can be based
on analytical calculations or more advanced MC calculations. This proposed methodology
for personal dosimetry for workers is very innovative and challenging. It explores a
new direction in personal dosimetry and, as such, adds value to the radiation protection
community and regulatory system. In addition, the proposed approach can be used for
ALARA optimization, as well as for education and training activities.