Monte Carlo simulation and radiometric characterization of proton irradiated [18O]H₂O for the treatment of the waste streams originated from [18F]FDG synthesis process

Experimental and Monte Carlo characterization of radionuclidic impurities originated from proton irradiation of [18O]H2O in a modern medical cyclotron

In this work we present a characterization of the radionuclidic impurities originated by proton irradiation of enriched water [¹⁸O]H₂O in a medical cyclotron through Monte Carlo simulations and experimental measurements. A set of standard samples of enriched water loaded in the cyclotron target cell have been irradiated at 30 μA proton current for 1 h each and, after an appropriate cooling time, measured by HPGe gamma spectrometry. In this way it was possible to study the direct release of radionuclidic impurities from target components as well as the release as a function of target ageing. Previously to experimental measurements, Monte Carlo calculations with the PHITS Code have been carried out to estimate the radionuclides generated within the target components (in particular Havar^® foil) with the aim to identify the nuclides expected to be found in the irradiated water due to cell-to-water transmission mechanisms. Comparison between simulations data and experimental measurements by gamma spectrometry showed that only a very small amount of the radionuclides produced in the target window are released in the enriched water through corrosion/erosion effects, while the release decreases with increasing aging of the target.

Validating production of PET radionuclides in solid and liquid targets: Comparing Geant4 predictions with FLUKA and measurements

The Monte Carlo toolkit Geant4 is used to simulate the production of a number of positron emitting radionuclides: ¹³N, ¹⁸F, ⁴⁴Sc, ⁵²Mn, ⁵⁵Co ⁶¹Cu, ⁶⁸Ga, ⁸⁶Y, ⁸⁹Zr and ⁹⁴Tc, which have been produced using a 13MeV medical cyclotron. The results are compared to previous simulations with the Monte Carlo code FLUKA and experimental measurements. The comparison shows variable degrees of agreement for different isotopes. The mean absolute deviation of Monte Carlo results from experiments was 1.4±1.6 for FLUKA and 0.7±0.5 for Geant4 using TENDL cross sections with QGSP-BIC-AllHP physics. Both agree well within the large error, which is due to the uncertainties present in both experimentally determined and theoretical reaction cross sections. Overall, Geant4 has been confirmed as a tool to simulate radionuclide production at low proton energy.

Radioactive by-products of a self-shielded cyclotron and the liquid target system for F-18 routine production

Routine production of F-18 radionuclide using proton beams accelerated in a cyclotron could potentially generate residual radioisotopes in the cyclotron vicinity which eventually become major safety concerns over radiation exposure to the workers. In this investigation, a typical 11-MeV proton, self-shielded cyclotron has been assessed for its residual radiation sources in the cyclotron's shielding, tank/chamber, cave wall as well as target system. Using a portable gamma ray spectroscopy system, the radiation measurement in the cyclotron environment has been carried out. Experimental results indicate that relatively long-lived radioisotopes such as Mn-54, Zn-65 and Eu-152 are detected in the inner and outer surface of the cyclotron shielding respectively while Mn-54 spectrum is observed around the cyclotron chamber. Weak intensity of Eu-152 radioisotope is again spotted in the inner and outer surface of the cyclotron cave wall. Angular distribution measurement of the Eu-152 shows that the intensity slightly drops with increasing observation angle relative to the proton beam incoming angle. In the target system, gamma rays from Co-56, Mn-52, Co-60, Mn-54, Ag-110 m are identified. TALYS-calculated nuclear cross-section data are used to study the origins of the radioactive by-products.

A Review of NIST Primary Activity Standards for (18)F: 1982 to 2013

The new NIST activity standardization for (18)F, described in 2014 in Applied Radiation and Isotopes (v. 85, p. 77), differs from results obtained between 1998 and 2008 by 4 %. The new results are considered to be very reliable; they are based on a battery of robust primary measurement techniques and bring the NIST standard into accord with other national metrology institutes. This paper reviews all ten (18)F activity standardizations performed at NIST from 1982 to 2013, with a focus on experimental variables that might account for discrepancies. We have identified many possible sources of measurement bias and eliminated most of them, but we have not adequately accounted for the 1998-2008 results.

Quantification of the activity of tritium produced during the routine synthesis of (18)F fluorodeoxyglucose for positron emission tomography

Gamma emitting radioactive by-products generated during the cyclotron irradiation of (18)O labelled water by protons to produce (18)FDG (fluorodeoxyglucose) for positron emission tomography are well characterised. However, the production of tritium ((3)H) through the (18)O(p,t)(16)O nuclear reaction has not been investigated in detail. The aim of this study was to measure tritium activity produced during a large number of (18)FDG production runs in order to obtain a better perspective on its impact on radioactive waste management, particularly as regards storage and disposal. Tritium was assayed by liquid scintillation counting in recovered (18)O water from 24 separate production runs. The mean (SD) values of activity and activity concentration were 170 (20) kBq and 81 (8) kBq ml(-1) respectively. Both quantities were positively correlated with the activity of (18)F. Tritium was detected in much lower concentration in water used to rinse the target vessel. The activity of tritium is such that it is exempt from regulatory control and may be combined with bulk non-active waste for disposal as Very Low Level Waste. However, variations in the irradiation conditions or the procedures for the collection of recovered water might result in its classification as Low Level Waste, necessitating a more complex disposal regime.