Use of short-lived positron emitters for in-beam and real-time ß+ range monitoring in proton therapy.

AIM: The purpose of this work is to evaluate the precision with which the GEANT4 toolkit simulates the production of ß+ emitters relevant for in-beam and real-time PET in proton therapy. BACKGROUND: An important evolution in proton therapy is the implementation of in-beam and real-time verification of the range of protons by measuring the correlation between the activity of ß+ and dose deposition. For that purpose, it is important that the simulation of the various ß+ emitters be sufficiently realistic, in particular for the 12N short-lived emitter that is required for efficient in-beam and real-time monitoring. METHODS: The GEANT4 toolkit was used to simulate positron emitter production for a proton beam of 55 MeV in a cubic PMMA target and results are compared to experimental data. RESULTS: The three ß+ emitters with the highest production rates in the experimental data (11C, 15O and 12N) are also those with the highest production rate in the simulation. Production rates differ by 8% to 174%. For the 12N isotope, the ß+ spatial distribution in the simulation shows major deviations from the data. The effect of the long range (of the order of 20 mm) of the ß+ originating from 12N is also shown and discussed. CONCLUSIONS: At first order, the GEANT4 simulation of the ß+ activity presents significant deviations from the data. The need for precise cross-section measurements versus energy below 30 MeV is of first priority in order to evaluate the feasibility of in-beam and real-time PET.

In-beam quality assurance using induced ß(+) activity in hadrontherapy: a preliminary physical requirements study using Geant4.

Light and heavy ions particle therapy, mainly by means of protons and carbon ions, represents an advantageous treatment modality for deep-seated and/or radioresistant tumours. An in-beam quality assurance principle is based on the detection of secondary particles induced by nuclear fragmentations between projectile and target nuclei. Three different strategies are currently under investigation: prompt γ rays imaging, proton interaction vertex imaging and in-beam positron emission tomography. Geant4 simulations have been performed first in order to assess the accuracy of some hadronic models to reproduce experimental data. Two different kinds of data have been considered: ß(+)-emitting isotopes and prompt γ-ray production rates. On the one hand simulations reproduce experimental ß(+) emitting isotopes production rates to an accuracy of 24%. Moreover simulated ß(+) emitting nuclei production rate as a function of depth reproduce well the peak-to-plateau ratio of experimental data. On the other hand by tuning the tolerance factor of the photon evaporation model available in Geant4, we reduce significantly prompt γ-ray production rates until a very good agreement is reached with experimental data. Then we have estimated the total amount of induced annihilation photons and prompt γ rays for a simple treatment plan of ∼1 physical Gy in a homogenous equivalent soft tissue tumour (6 cm depth, 4 cm radius and 2 cm wide). The average annihilation photons emitted during a 45 s irradiation in a 4 π solid angle are ∼2 × 10(6) annihilation photon pairs and 10(8) single prompt γ whose energy ranges from a few keV to 10 MeV.

First results on angular distributions of thermal dileptons in nuclear collisions.

The NA60 experiment at the CERN Super Proton Synchrotron has studied dimuon production in 158A GeV In-In collisions. The strong excess of pairs above the known sources found in the complete mass region 0.2

Evidence for radial flow of thermal dileptons in high-energy nuclear collisions.

The NA60 experiment at the CERN SPS has studied low-mass dimuon production in 158A GeV In-In collisions. An excess of pairs above the known meson decays has been reported before. We now present precision results on the associated transverse momentum spectra. The slope parameter Teff extracted from the spectra rises with dimuon mass up to the rho, followed by a sudden decline above. While the initial rise is consistent with the expectations for radial flow of a hadronic decay source, the decline signals a transition to an emission source with much smaller flow. This may well represent the first direct evidence for thermal radiation of partonic origin in nuclear collisions.

J/psi production in Indium-Indium collisions at 158 GeV/nucleon.

The NA60 experiment studies muon pair production at the CERN Super Proton Synchrotron. In this Letter we report on a precision measurement of J/psi in In-In collisions. We have studied the J/psi centrality distribution, and we have compared it with the one expected if absorption in cold nuclear matter were the only active suppression mechanism. For collisions involving more than approximately 80 participant nucleons, we find that an extra suppression is present. This result is in qualitative agreement with previous Pb-Pb measurements by the NA50 experiment, but no theoretical explanation is presently able to coherently describe both results.

First measurement of the rho spectral function in high-energy nuclear collisions.

We report on a precision measurement of low-mass muon pairs in 158 AGeV indium-indium collisions at the CERN SPS. A significant excess of pairs is observed above the yield expected from neutral meson decays. The unprecedented sample size of 360,000 dimuons and the good mass resolution of about 2% allow us to isolate the excess by subtraction of the decay sources. The shape of the resulting mass spectrum is consistent with a dominant contribution from pi+pi- -->rho -->mu+mu- annihilation. The associated space-time averaged spectral function shows a strong broadening, but essentially no shift in mass. This may rule out theoretical models linking hadron masses directly to the chiral condensate.