Can a ToF-PET photon attenuation reconstruction test stopping-power estimations in proton therapy? A phantom study.

Objective. The aim of the phantom study was to validate and to improve the computed tomography (CT) images used for the dose computation in proton therapy. It was tested, if the joint reconstruction of activity and attenuation images of time-of-flight PET (ToF-PET) scans could improve the estimation of the proton stopping-power.Approach. The attenuation images, i.e. CT images with 511 keV gamma-rays (γCTs), were jointly reconstructed with activity maps from ToF-PET scans. Theß+activity was produced with FDG and in a separate experiment with proton-induced radioactivation. The phantoms contained slabs of tissue substitutes. The use of theγCTs for the prediction of the beam stopping in proton therapy was based on a linear relationship between theγ-ray attenuation, the electron density, and the stopping-power of fast protons.Main results. The FDG based experiment showed sufficient linearity to detect a bias of bony tissue in the heuristic look-up table, which maps between x-ray CT images and proton stopping-power.γCTs can be used for dose computation, if the electron density of one type of tissue is provided as a scaling factor. A possible limitation is imposed by the spatial resolution, which is inferior by a factor of 2.5 compared to the one of the x-ray CT.γCTs can also be derived from off-line, ToF-PET scans subsequent to the application of a proton field with a hypofractionated dose level.Significance. γCTs are a viable tool to support the estimation of proton stopping with radiotracer-based ToF-PET data from diagnosis or staging. This could be of higher potential relevance in MRI-guided proton therapy.γCTs could form an alternative approach to make use of in-beam or off-line PET scans of proton-inducedß+activity with possible clinical limitations due to the low number of coincidence counts.

Why the preclinical imaging field needs nuclear medicine technologists and radiographers?

INTRODUCTION: Preclinical imaging is still seen as a new field, and its recognition as a specific topic occurring only about 20 years ago. Nuclear medicine technologists (NMTs) and radiographers' skills covering technical, anatomical and clinical fields can be highly beneficial to preclinical imaging research centres: many tasks and knowledge are complementary between clinics and preclinical laboratories. Our goal is to reach a consensus on the required set of competencies needed to translate the work of NMTs and radiographers from the clinic to the preclinical laboratory, particularly in regard to multimodal imaging. PRECLINICAL IMAGING ENVIRONMENT: Currently, all imaging modalities used in clinical routine (ultrasound, CT, MRI, PET, SPECT, radiographs) are available, using specific architectures allowing for the spatial resolution and sensitivity needed for small rodents (which are the most commonly used species in research). Ideally, a preclinical laboratory should produce images/examinations at a high throughput in order to meet the statistical expectations of the studies (while respecting the 3R principles for animal research) and the care and welfare of each individual. To reach the quality and throughput expectations of such an organization, specific qualified professionals are needed to complete the scientific/research staff. WHERE NMTS AND RADIOGRAPHERS FIT IN: The increasing use of preclinical imaging requires professionals who can put imaging procedures into action, ensuring a significant success throughput. NMTs and radiographers have a variety of skills that work well within a preclinical laboratory, with the ability to perform the following tasks independently: animal preparation, positioning, monitoring and anaesthesia recovery, acquisition parameter programming, archiving and data processing, device quality controls, surface cleaning and disinfection, radioactive and biological waste management, radiation safety for users, use of hot lab equipment and auxiliary equipment, injected products and material management. In light of the current European Qualification Framework, a set of skills, knowledge and competencies were defined to cover the whole set of duties and tasks deliverable to an NMT or radiographer working in a preclinical laboratory. One of the key responsibilities of the NMT or radiographer is related to compliance on animal care and welfare when undertaking any animal procedures, including imaging. CONCLUSION: We believe that NMTs and radiographers' skills match perfectly with the requirements of a preclinical imaging lab, and that they could be considered a keystone of such an organization in the future. Moreover, some evidence has also shown that an experienced NMT or radiographer in this sector can take on roles as research investigators.