how to illuminate the inside of our body with particle accelerators

The historical motivation for the large particle accelerators created in the 20th century was initially centered in the field of basic science, but today their applications have expanded to improve the daily lives of mankind. These include aspects as varied as food preservation, water purification, the manufacture of semiconductors, the creation of biomolecules, the construction of new polymeric materials and, above all, medicine and pharmacology.

Nuclear medicine uses atoms of the same element whose nuclei have a different number of neutrons, called isotopes or radioisotopes if they also emit a particle.

These radioisotopes have been manufactured over the past decades for various medical uses such as therapy and computerized imaging. The most common computerized imaging technique using radioisotopes is called SPECT (Single photon emission computed tomography), through the isotope Technetium-99m (99mTc), which emits photons (gamma rays).

This drug basically consists of a micro-lantern that illuminates the human body. The SPECT scanner, thanks to a camera sensitive to these photons, revolves around the patient and captures complete images that a computer classifies into sections. The production of 99mTc has been carried out for decades in nuclear reactors using the decay of molybdenum 99 and during the last decade also via proton accelerators which the IAEA (International Atomic Energy Agency) proposes to use .

One of the most useful in practice medical diagnostic visualization techniques is called PET (Positron emission tomography). Although PET is still used less than the previous SPECT – partly due to its relatively high cost – it has improved and its use is much wider in medicine, since the image obtained generates a much better resolution . For this reason, his interest has extended in recent years to different specializations of nuclear medicine.

Imaging the new PET using various radiopharmaceuticals is therefore a research area of ​​extraordinary importance for today’s biomedicine.

Radiopharmaceuticals for PET

Various short-lived positron emitters are of primary importance for medical diagnosis by means of PET. Some of the radioisotopes that can be made using low-energy accelerators are fluorine-18, oxygen-15, nitrogen-13, and carbon-11 (18F, 15O, 13N, and 11C, respectively).

Since positrons are the antimatter of electrons, these radiopharmaceuticals emit positrons which, colliding with electrons in the patient’s body, generate photons which create an image. This is processed by computer so medical personnel can see and diagnose.

These drugs behave like nano lanterns which allow high resolution images to diagnose multiple pathologies.

A logistical challenge

Fluorine-18 is one of the most widely used isotopes in many hospitals. It can be made externally, as it has a short but long enough half-life (about 110 minutes), to be able to be sent to the medical center from the outside.

Even so, external shipping requires many more doses of high radioactive activity to be manufactured, as some of them decay and deactivate during transport hours. Overall therefore, the current external manufacture of radiopharmaceuticals requires excesses in economic, energy, radioactive and speed terms. The effectiveness of these broadcasts can be improved by locally manufacturing personalized pharmaceutical doses in the hospital itself.

Oxygen, nitrogen and carbon are very important elements, as they make up the cells of the human body and can be used to label a wide variety of useful pharmaceutical compounds.

However, the short half-life of its isotopes (between two and twenty minutes) requires local manufacture within the hospital itself. This implies the impossibility of its medical use unless it is manufactured immediately and without the need for transport.

There is a lot of interest in these other radiopharmaceuticals for PET, which are still little used in medicine. In particular, the great interest in 11C, which can replace ordinary 12C in any molecule in the human body, is very noticeable.

In this case of the Carbon 11 radioisotope, one can imagine that the nano-lantern which illuminates the PET images exhausts its battery in a few minutes and that after having worked it disappears without needing to be removed.

The local manufacture of all kinds of PET radiopharmaceuticals is therefore an important applicability for biomedicine. The local and tailor-made manufacture of these promising isotopes using compact accelerators would allow their real medical use.

Accelerators for radiopharmaceutical production

The most common means of manufacturing radiopharmaceuticals are nuclear reactors or particle accelerators. The most common means today is the use of cyclotrons, which have been in use for several decades.

These devices are heavy and bulky, often accelerating protons to energies of tens of MeV (Mega Electron Volts) in medical applications. Its cost of manufacture and operation, maintenance and energy expenditure is high and prevents hospitals from generalizing its use.

Linear accelerators (LINear ACcelerator, LINAC), in particular a new compact generation, have several advantages over traditional cyclotrons.

Firstly, linacs have lower beam losses than cyclotrons because the latter, due to their circular nature, are subject at all times to the centripetal Lorentz force which radiates the photons tangentially and the beam loses lumen. ‘energy.

Second, the new generation of Linacs is much more compact, economical, light and undemanding, both in terms of energy expenditure and radioactive protection.

Thanks to these numerous advantages, this type of accelerator becomes an excellent alternative for producing radiopharmaceuticals in the hospital, even at low proton energy.

Linac 7 Project

Linac 7 is a project consisting of a new generation proton linear accelerator entirely conceived, designed and built in the Particle Beam Laboratory (IZPILab-Beam Laboratory) of the University of the Basque Country UPV/EHU, and of which many components are currently in operation.

One of the most important health applications designed under this project is the production of drugs of various types, locally around large clinical centers. The dimensions and characteristics of the accelerator can service a hospital in an in-house laboratory or even allow it to be shipped on a small truck to share an on-demand radiopharmaceutical manufacturing schedule across multiple medical facilities upon request.

There is a lot of interest in Europe in the use of different particle accelerator options for the production of medical radioisotopes. In particular, the European Commission promotes the ARIES Consortium (Research and innovation accelerator for European science and society), whose report, published on June 22, 2020, describes the current state of the manufacture of medical radioisotopes with accelerators and expresses very precisely the scientific, medical and industrial interest in the development of new Linacs for PET.

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