An analytic model to calculate Voxel S-Values for 177^{177}Lu

Objective: $^{177}$Lu is one of the most employed isotopes in targeted radionuclide therapies and theranostics, and 3D internal dosimetry for such procedures has great importance. Voxel S-Values (VSVs) approach is widely used for this purpose, but VSVs are available for a limited number of voxel dimensions. The aim of this work is to develop an analytic model for the calculation of $^{177}$Lu-VSVs in any cubic voxelized geometry of practical interest. Approach: Monte Carlo (MC) simulations were implemented with the toolkit GAMOS to evaluate VSVs in voxelized geometries of soft tissue from a source of $^{177}$Lu homogeneously distributed in the central voxel. Nine geometric setups, containing 15x15x15 cubic voxels of sides l ranging from 2 mm to 6 mm, in steps of 0.5 mm, were considered. For each l, the VSVs computed as a function of the "normalized radius", Rn = R/l (with R = distance from the center of the source voxel), were fitted with a parametric function. The dependencies of the parameters as a function of l were then fitted with appropriate functions, in order to implement the model for deducing $^{177}$Lu-VSVs for any l within the aforementioned range. Main results: The MC-derived VSVs were satisfactorily compared with literature data for validation, and the VSVs computed with the analytic model agree with the MC ones within 2\% for Rn $\leq$ 2 and within 6\% for Rn > 2. Significance: The proposed model enables the easy and fast calculation, with a simple spreadsheet, of $^{177}$Lu-VSVs in any cubic voxelized geometry of practical interest, avoiding the necessity of implementing ad-hoc MC simulations to estimate VSVs for specific voxel dimensions not available in literature data.Comment: 16 pages, 7 figures, first round review in "Biomedical Physics & Engineering Express

18^{18}F-PSMA-1007 salivary gland dosimetry: Comparison between different methods for dose calculation and assessment of inter- and intra-patient variability

Dosimetry of salivary glands (SGs) is usually implemented using simplified calculation approaches and approximated geometries. Our aims were to compare different dosimetry methods to calculate SGs absorbed doses (ADs) following 18F-PSMA-1007 injection, and to assess the AD variation across patients and single SG components. Five patients with prostate cancer recurrence underwent PET/CT acquisitions of the head and neck, 0.5, 2 and 4 hours after 18F-PSMA-1007 injection. Parotid and submandibular glands were segmented on CT to derive SGs volumes and masses, while PETs were used to derive Time-Integrated Activity Coefficients. Average ADs to single SG components or total SG (tSG) were calculated with the following methods: i) direct Monte Carlo (MC) simulation with GATE/GEANT4; ii) spherical model (SM) of OLINDA/EXM 2.1, adopting either patient-specific or standard ICRP89 organ masses (SMstd); iii) ellipsoidal model (EM); iv) MIRD approach with organ S-factors from OLINDA/EXM 2.1 and OpenDose collaboration, with or without contribution from cross irradiation originating outside the SGs. The maximum percent AD difference across SG components ({\delta}max) and across patients ({\Delta}max) were calculated. Compared to MC, ADs to single SG components were significantly underestimated by all methods (average relative differences between -14.5% and -30.4%). Using MC, SM and EM, {\delta}max were never below 25% (up to 113%). {\delta}max up to 702% were obtained with SMstd. Concerning tSG, results within 10% of the MC were obtained only if cross irradiation from the remainder of the body or from the remainder of the head was accounted for. The {\Delta}max ranged between 58% and 78% across patients. Specific masses of single SG components should always be considered given their large intra- and inter- patient variability.Comment: 33 pages, 3 figures, sumbitted to "Physics in Medicine & Biology

Study of an electron linac driven x-ray radio-tomographic system response as a function of the electron beam current

At the Dipartimento di Fisica, Universita di Messina, a high energy X-ray radio-tomographc system driven by a 5 MeV electron linac, has been recently assembled. It has been tested and has already provided good results in inspecting heavy materials. In order to achieve good radiographic results, especially when inspecting heavy or thick materials, an enhancement of the X-ray dose at the sample position can be required and most of times this is associated to an enhancement of the grey level in the acquired image, according to a linear function. Nevertheless, in the hypothesis to work at the maximum magnetron power, a variation of the X-ray dose, obtained changing the electron beam current, is associated to a variation of the electron beam energy. As a consequence, the X- ray energy spectrum varies thus influencing the response of the radio-tomographic system. This does not allow a linear correspondence between the X-ray fluence (or the electron beam current) and the image grey level. By means of MCNP-4C2 simulations, the influence of electron beam energy variations on the produced bremsstrahlung spectrum has been studied and the theoretical results seems to be confirmed by the preliminary experimental ones

A new method for the determination of very small Γγ partial widths

We present a new method for the measurement of very small Γγ partial width that is important for the synthesis of elements in astrophysics. The method is based on the simultaneous detection of scattered beam, residual nucleus and decay γ rays. This method is optimized for the use of the CHIMERA detector at LNS. Experimental details are described

A new method for the determination of very small Γ γ

We present a new method for the measurement of very small Γγ partial width that is important for the synthesis of elements in astrophysics. The method is based on the simultaneous detection of scattered beam, residual nucleus and decay γ rays. This method is optimized for the use of the CHIMERA detector at LNS. Experimental details are described

Evaluation of the production capabilities of 18F, 11C, 13N and 15O PET isotopes at the PET-cyclotron-radiochemistry site of Messina University

The production of 18F, 11C, 13N, and 15O positron emitting radionuclides for PET imaging is usually accomplished in Nuclear Medicine Departments through direct nuclear reactions induced by protons accelerated by compact medical cyclotrons on liquid or gaseous targets. Messina University has funded the construction of a PET-cyclotron-radio-chemistry plant at the Messina University Hospital, equipped with a 11 MeV self-shielded cyclotron. We estimated the expected production yields of these nuclides, accounting for target thickness, production of other radioactive nuclides, and time effects on the irradiated target purity. To this aim, both TALYS code (v. 1.8) and an analytical approach based on EXFOR experimental data were used. The general agreement between the two approaches, and with the available literature data, allows to assess the expected yields at the End of Bombardment, and relative target purities, to be used for further radiopharmaceutical preparation steps

Internal Bremsstrahlung emission during 32P decay

The aim of this work is to experimentally investigate the role of Internal Bremsstrahlung (IB) in the decay of 32P, a pure beta-emitter with end-point energy of 1.71 MeV and half-life of 14.28 days. IB is a continuous electromagnetic radiation occurring in beta-decay, that had been widely studied in the past years. Its contribution, even if appreciable, is neglected in Monte Carlo (MC) simulation as well as in dosimetric and radiation protection calculations.Ionization current measurements were carried out using a well ionization chamber and compared with MC simulations, performed in the GAMOS (GEANT4-based Architecture for Medicine-Oriented Simulations) framework. Two experimental data sets of 32P IB spectra, taken from the literature, were used to model the IB photon spectral distribution and to include IB emission as an additional source term in MC calculation.Without IB, MC simulations underestimate up to about -18% the measured exposure, whereas the inclusion of IB according to either of the two spectra lead to differences of +2% or +8%. Consequently, the IB process is relevant for high-energy pure beta-emitters such as 32P, and its contribution should be considered in all the dosimetric and radioprotection calculations

A novel α-amylase-lipase formulation as anti-staling agent in durum wheat bread

The aim of this work has been to evaluate the anti-staling effect exerted by a novel a-amylase-lipase enzyme formulation on durum wheat bread, in comparison with four different commercial amylase preparations and with control without added enzymes. Bread-making trials were carried out at industrial level. Sliced bread, packed under modified atmosphere, was analyzed for texture profile, moisture content, and water activity during 90 days. Crumb sections were submitted to environmental scanning electron microscopy at the end of the storage period. The a-amylase-lipase enzyme preparation showed synergistic interactions in preventing staling. In particular, bread added of these two enzymes in mixture was always softer and more chewable than either control or samples added of other enzymes. Moreover, a-amylase-lipase exhibited the most marked effect in slowing down both hardening and chewiness changes during time. Starting from 7 days of storage, both water activity and moisture content of bread added of a-amylase-lipase were higher than in control. Starting from 68 days the moisture content of aamylase-lipase-added bread became lower than that of other enzyme-added breads, and at the end of storage also water activity was significantly lower. Pore morphology of a-amylase-lipase-added bread appeared markedly different from that of control bread

Patient dose in image guided radiotherapy: Monte Carlo study of the CBCT dose contribution

Image Guided RadioTherapy (IGRT) is a technique whose diffusion is growing thanks to the well-recognized gain in accuracy of dose delivery. However, multiple Cone Beam Computed Tomography (CBCT) scans add dose to patients, and its contribution has to be assessed and minimized. Aim of our work was to evaluate, through Monte Carlo simulations, organ doses in IGRT due to CBCT and therapeutic MV irradiation in head-neck, thorax and pelvis districts. We developed a Monte Carlo simulation in GAMOS (Geant4-based Architecture for Medicine-Oriented Simulations), reproducing an Elekta Synergy medical linac operating at 6 and 10 MV photon energy, and we set up a scalable anthropomorphic model. After a validation by comparison with the experimental quality indexes, we evaluated the average doses to all organs and tissues belonging to the model for the three cases of irradiated district. Scattered radiation in therapy is larger than that diffused by CBCT by one to two orders of magnitude

Isospin effects on reaction dynamics at Fermi energies

The study of nuclei properties and of collision dynamics is a very active research field whose result have implications in different domains as for example astrophysics. The present and future facilities delivering radioactive ion beams with high intensity allow to extend these studies in the region far from the stability valley. New insight has thus been found on the effects of neutron richness on reaction mechanisms as well as on nuclear structure and nuclear matter properties, as for instance, the role of symmetry energy term of the nuclear Equation of State. The presence of diverse reaction products demands for highly performing and very specialized devices, also able to disentangle among different mechanisms, from fast dynamical processes to statistical emission from equilibrated sources. Numerous studies of the effects of N/Z ratio on fusion and associated processes can be found at different energies, together with many examples of the influence of neutron richness on the reaction time scale and the competition between equilibrated and prompt processes. A survey of very recent findings obtained with the CHIMERA and FARCOS devices is presented