Bone analogue phantoms: redefining standards in patient specific MRT dosimetry

Molecular Radiotherapy (MRT) is a relatively common procedure in counties with developed healthcare systems. In this
procedure, a labelled radioisotope is administered to the body in order to irradiate and kill tumour cells whilst sparing the
surrounding healthy organ tissue. In the UK alone, there are some 200 departments performing over 11000 MRTs annually
and ~200,000 therapies in some 28 EU countries.

In a recent development towards personalised healthcare, a new EU directive 2013/59 was introduced which requires that
all Member states performing any form of radiotherapeutics (including MRT) must provide dosimetry treatment planning for
each patient by 6th February 2018. Although this may sound like an obvious situation, MRT has in fact been used clinically
for around 75 years with no fully established dosimetry practice for calculating the absorbed dose delivered to tumour
targets or to organs at risk. Even though the general steps have been agreed, there still exists a wide variation in the
current acquisition, quality and treatment of images used to determine dose. As a result, treatment protocols have often
evolved locally, based on experience with a relatively small numbers of patients. Although such patients would all have
received similar administered activities, the actual dose received to particular organs could have large variations.

As a consequence of the complexities involved, the application of radionuclide dosimetry has been restricted to those
academic groups with the facilities to develop in-house techniques. Very few therapy centres currently can validate dose
calculations to a known level of accuracy and only a few academic therapy centres can perform MRT Monte Carlo (MC)
calculations. Our group, established between The University of Manchester and The Christie, has developed the ability to
deliver this within a very large MRT practice. We were recently selected to lead the EU work on validating dose calculations from simulated patient phantoms and physical 3D printed phantoms in the EMPIR MRTDosimetry project (2016-19). The
project will provide a standardised European framework for clinical implementation of MRT dose planning. In our approach,
developed with an STFC Mini-IPS grant, 3D-printed patient analogues (phantoms) are constructed based on patient CT
images. This novel technique has clear potential to provide the foundation of a clinical service to provide a basis for
improved activity quantification to all clinical centres and MRT patients in the UK.

We are uniquely positioned to deliver this work, having access to a large data base of MRT patient data at The Christie.
Working with these data, we can provide the foundation for establishing a future national clinical service. The Christie has
the experience in both MRT dosimetry research and in providing training and support for a national clinical service
(PET/CT) required to provide a MRT dosimetry service. In addition our collaboration has strong links with industry, in
particular Hermes Medical Solutions Ltd, a leading provider of nuclear medicine workstation software. By developing a
comprehensive validation methodology for clinical dosimetry systems, and thereby demonstrating that the HERMES
dosimetry system meets this standard, our collaboration will be able to provide a de-facto validation standard for clinical
dosimetry systems and a market leading package. These links provide a pathway to distribute the techniques to the wider
EU and international nuclear medicine market. In turn, this improves patient outcomes by allowing modification of therapy
based on disease response and also benefits the healthcare provider by maximising outcome for the same or reduced
resource.