Intercomparison of clinical dosimetry approaches in molecular radiotherapy by Monte-Carlo simulation
Why DosiTest ?
Molecular radiotherapy (MRT) consists in destructing tumour targets by radiolabelled vectors. This nuclear medicine specialty is being considered with increasing interest for example via the success achieved in the treatment of non-Hodgkin lymphomas by radioimmunotherapy and more recently in the treatment of neuroendocrine tumours by Peptide Receptor Radionuclide Therapy (PRRT) with 177Lu-labeled peptides, and more.
One of the keys of MRT optimization relies on the personalisation of absorbed doses delivered to the patient: this is required to ascertain that irradiation is focused on tumour cells while keeping surrounding healthy tissue irradiation at an acceptable – non-toxic – level.
Absorbed dose evaluation
Absorbed dose evaluation in MRT requires the localization of injected radioactive sources by scintigraphic imaging, both in space (within the patient) and time (pharmacokinetics). Besides, absorbed dose calculation must be carried out with regards to propagating media, emitted radiations and their interactions within the patient.
Global clinical dosimetry accuracy relies on the accuracy of each of these steps. The current situation is that of a wide heterogeneity of implemented dosimetric approaches.
This can be explained as MRT is covering a range of treatments involving various vectors and isotopes. This has consequences on the methodology required to assess activity distribution, pharmacokinetics and absorbed dose calculation. In addition, the resources available (both human and technological/methodological) are highly variable from one centre to another.
As a consequence there is no reference, standardized dosimetric protocol to date.
Clinical dosimetry workflow
A major limit to the development of standardised protocols is the difficulty to evaluate the accuracy of the complete chain that leads from scintigraphic acquisition to absorbed dose calculation. Even though it may be possible to validate experimentally some aspects of image quantification via test objects, the absorbed dose within a patient’s tissues cannot be experimentally evaluated in situ.
The project DosiTest aims at evaluating the impact of the various steps that contribute to the realization of a dosimetric study, by means of a virtual multicentric intercomparison based on Monte-Carlo modelling.