Perspectives of Nuclear Physics in Europe - European Science ...

4.6 Nuclear Physics Tools and Applications
rays originating from injected γ-emitting radioisotopes
in single-photon emission computerized tomography
(SPECT) or from the annihilation of the positron from
a β + -emitter in positron emission tomography (PET),
although non-radioactive methods (such as nuclear magnetic
resonance) are also very common. Applications
of nuclear sciences to biology and other fields of life
sciences are also extensive. Radiobiology and radioprotection
are very well established scientific disciplines.
Radioisotopes
Radiopharmaceutical production is one of the key features
in the next decade even if we simply consider
the needs for SPECT imaging. The lack in the future of
neutron sources from reactors will result in a reduction
of the production of radioisotopes as 99m Tc, 123 I, 122 I etc.
It is necessary to develop new production methods for
emerging radioisotopes such as 64 Cu, 94m Tc, and 124 I
(using medium and low energy cyclotrons) and radionuclide
generator systems for PET studies ( 68 Ge/ 68 Ga and
82 Sr/ 82 Rb), including development of radiochemical processes
for separation of the radionuclides from irradiated
targets, development of technology for the production
of radionuclide generator systems and development
of appropriate quality assurance and quality control
techniques for the PET radiotracers. Among the shortlived
radioisotopes used in therapy, 90 Y and 188 Re are
attracting great interest, and they should be produced
in situ using radioisotope generators.
Current hot topics in radioisotope production and
use include:
• 99 Mo/ 99 Tc supply and alternative methods for 99 Mo
production;
• innovative β+ emitters for PET imaging;
• metal radionuclides for PET imaging;
• α, β, and conversion-electron emitting radioisotopes
for systemic therapy;
• therapy using radioisotopes coupled to antibodies
and peptides;
• radiotracers in drug development;
• production of isotopes with high specific activity.
Particle therapy
Besides radiotherapy with fast neutrons and boron neutron
capture therapy (BNCT), the term “particle therapy”
is today used mostly for ion beam therapy – i.e. therapy
using protons or heavier ions, particularly carbon at energies
between 200 and 400 MeV/n. According to the most
recent survey of the Particle Therapy Cooperative Group,
25 new accelerator facilities dedicated to cancer therapy
are in planning stage or under construction. The debate
on the cost/benefit ratio for these facilities is ongoing,
and it is dependent on new technologies and on the success
of hypofractionation regimes, which appear already
very promising for treatment of lung cancer. The current
clinical results, although on a limited sample, support
the rationale of the therapy – i.e. that the improved dose
distribution (for charged particles in general) and the
radiobiological characteristics (for heavy ions) do lead to
improved clinical results, especially for tumours localized
in proximity of critical organs, or resistant to conventional
treatments. Although in many cases clinical data
are still not sufficient to draw firm conclusions on the
cost effectiveness of this treatment modality, the lack of
phase-III trials can only be solved building new facilities,
and these new centres should offer the opportunity to
use both protons and heavier ions.
In Europe, protontherapy is established in several centres
and further ones are under construction. As regards
therapy with carbon ions, a pilot project started at GSI in
Germany in 1997 and the new hospital-based centres in
Heidelberg and the forthcoming centres in Italy (CNAO),
in France (ETOILE) and in Austria (Med-AUSTRON) will
treat many patients in the future years. The main innovations
compared to previous experience in USA and
Japan are the active scanning system (as opposite to
passive modulation), the use of a biophysical modeling
in the treatment planning to account for the change in
relative biological effectiveness (RBE), and the online PET
scanning for monitoring of the dose during the treatment.
Spot-scanning provides improved dose distributions, and
reduces the production of secondary particles, particularly
neutrons, which may lead to late side effects.
Most of the clinical experience with ions heavier than
protons is relative to carbon, because for this particle
the RBE is about 1 at the entrance channel, and can be
as high as 3-4 in the Bragg peak. Ions much heavier
than carbon are difficult to use for therapy, first because
the nuclear fragmentation of the projectile unfavorably
modifies the shape of the Bragg curves, and second
because the LET is high already in the entrance channel.
Oxygen (A=16) may be used in special cases, e.g.
for very hypoxic tumours. On the other hand, ions with
2