External dose rates to comforters from nuclear medicine patients: a detailed computational approach

SCK•CEN Mentor

Struelens Lara, lstruele@sckcen.be, +32 (0)14 33 28 85

Expert group

Research in Dosimetric Applications

SCK•CEN Co-mentor

Lombardo Pasquale , plombard@sckcen.be , +32 (0)14 33 28 54

Introduction

In nuclear medicine, patients are injected with radiopharmaceuticals for diagnostic or radiotherapeutic procedures. In order to ensure adequate radiation protection of the medical staff and the public, it is necessary to consider the impact of the radiation emitted by the patient, for example, when he/she is guided in the hospital or he/she will leave the hospital after the procedure. Such exposures may occur unknowingly to members of the public or knowingly to people who comfort the patients after the procedure, such as relatives and friends.

Currently there are a limited number of studies on the assessment of potential external dose to comforters, carers and family. Most studies were performed for diagnostic procedures, where the patient is injected with Tc-99m or F-18. In case of therapeutic procedures, data can be found for I-131 therapy to treat thyroid cancer or hyperthyroidism. Although for diagnostic studies, in general, the studies indicate no need of any restrictions before a patient can be released from the hospital, the issue is still in debate. For example, the EMA (European Medicines Agency) recommends to avoid close contact with children or pregnant women for 24h after injection in case of Tc-99m procedures.

If guidelines exist, they are mainly related to I-131 therapy. In any case, all information available on the protection of carers and comforters of nuclear medicine patients, both for diagnostic and therapeutic procedures, is based on dose rate measurements in a single point at a certain distance from the patient and measured on several time points after injection. To assess the exposure level and possible risk to comforters, these dose rate measurements are combined with assumed specific occupancy scenario’s, describing how long carers/comforters are in close contact with a nuclear medicine patient over time. Because a nuclear medicine patient is a physically large radiation source, reducing that source to a dose rate in a single point is prone to large errors, especially at short distances from that patient.

However, the growing number of patients treated and the diversity of radiopharmaceuticals used to diagnose, treat and follow-up patients, stimulates to evaluate risks related to comforters of nuclear medicine patients. In this study, the external dose rates to comforters, carers and other persons, will be evaluated through a more advanced and detailed computational approach.

Objective

The aim of the study is to use the more advanced computational approach to, on one hand be able to confirm the current approach that no restrictions are needed for diagnostic procedures. On the other hand, to be able to formulate guidelines for existing and emerging therapies in nuclear medicine. 

The computational approach will consist of computational anthropomorphic models both for the patient and the comforter and the biokinetics of the radiopharmaceutical in the different source organs (how the radionuclide is distributed in the different organs over time) will be considered from published data.  At first instance, the calculations will be performed for Tc-99m, F-18 and I-131 procedures as most of the data is available for these procedures, which is useful for benchmarking the Monte Carlo calculations that will be performed, using the MCNP code.

A gradual approach will be used in terms of complexity:

  1. Calculation of the dose rate in a point, in terms of the ambient dose equivalent H*(10) at certain distances from the patient model. These results will be benchmarked against H*(10) measurements in literature (literature study already performed) or newly acquired data (in the framework of EURADOS activities) to validate the computational approach.
  2. Calculation of time-dependent absorbed dose rates in the organs of the comforter’s computational model by considering an easy exposure scenario, for example where the 2 computational models (patient and comforter) are standing straight and in front of each other.
  3. Calculation of time-dependent absorbed dose rates in the organs of the comforter’s computational model by considering complex close-contact scenario’s, for example an adult sitting next to a nuclear medicine patient, an adult NM patient carrying or feeding a child, etc. This approach will need the use of deformable computational phantoms. In the SCK•CEN research group on dosimetric applications a lot of experience is available on the development and use of flexible computational phantoms. 

These more accurate organ dose assessments will lead to a more precise estimation of the dose-risk relation for comforters of nuclear medicine patients. Those outcomes can be used to derive new/updated guidelines for comforters and carers and the computational approach will provide a validated methodology in view of new radionuclides that come into clinical practice.

The study implies thus performing many Monte Carlo calculations using the MCNP code on the available computer cluster of SCK•CEN. The use of complex voxel geometries with MCNP is not straightforward and very computer intensive. As a side project, the student will work on the optimisation of this type of calculations by comparing the speed of different versions of MCNP to obtain reasonable computation time for this project but also other projects running in the group.

The minimum diploma level of the candidate needs to be

Professional bachelor , Academic bachelor

The candidate needs to have a background in

Physics , interested to work with computers and perform computer simulations (no programming background is required)