Characterization of the energy distribution of neutrons generated by 5 MeV protons on a thick beryllium target at different emission angles

Neutron energy spectra at different emission angles, between 0° and 120° from the Be(p,xn) reaction generated by a beryllium thick-target bombarded with 5 MeV protons, have been measured at the Legnaro Laboratories (LNL) of the Italian National Institute for Nuclear Physics research (INFN). A new and quite compact recoil-proton spectrometer, based on a monolithic silicon telescope, coupled to a polyethylene converter, was efficiently used with respect to the traditional Time-of-Flight (TOF) technique. The measured distributions of recoil-protons were processed through an iterative unfolding algorithm in order to determine the neutron energy spectra at all the angles accounted for. The neutron energy spectrum measured at 0° resulted to be in good agreement with the only one so far available at the requested energy and measured years ago with TOF technique. Moreover, the results obtained at different emission angles resulted to be consistent with detailed past measurements performed at 4 MeV protons at the same angles by TOF techniques.     

Design of a beam shaping assembly and preliminary modelling of a treatment room for accelerator-based BNCT at CNEA

This work reports on the characterisation of a neutron beam shaping assembly (BSA) prototype and on the preliminary modelling of a treatment room for BNCT within the framework of a research programme for the development and construction of an accelerator-based BNCT irradiation facility in Buenos Aires, Argentina. The BSA prototype constructed has been characterised by means of MCNP simulations as well as a set of experimental measurements performed at the Tandar accelerator at the National Atomic Energy Commission of Argentina.     

Applicability of the Be(d,n)B reaction to AB-BNCT skin and deep tumor treatment

In the range of low bombarding energies (less than about 1.5 MeV) the ⁹Be(d,n)¹⁰B reaction produces neutron spectra that can be moderated depending on the choice of the target thickness and the deuteron bombarding energy. In this work, a Monte Carlo simulation study to determine the capability of this reaction to deliver enough dose to efficiently control both skin and deep seated tumors has been performed by means of MCNP calculations using eight optimized ⁹Be targets.     

Optimisation study of α-cyclotron production of At-211/Po-211g for high-LET metabolic radiotherapy purposes

The production of no-carrier-added (NCA) α-emitter ²¹¹At/^211gPo radionuclides for high-LET targeted radiotherapy and immunoradiotherapy, through the ²⁰⁹Bi(α,2n) reaction, together with the required wet radiochemistry and radioanalytical quality controls carried out at LASA is described, through dedicated irradiation experiments at the MC-40 cyclotron of JRC-Ispra. The amount of both the γ-emitter ²¹⁰At and its long half-lived α-emitting daughter ²¹⁰Po is optimised and minimised by appropriate choice of energy and energy loss of α particle beam. The measured excitation functions for production of the main radioisotopic impurity ²¹⁰At→²¹⁰Po are compared with theoretical predictions from model calculations performed at ENEA.     

Selenium-72 formation via Br(p,x) induced by 100 MeV Protons: Steps towards a novel Se/As generator system

Selenium-72 production by the proton bombardment of a natural NaBr target has been successfully demonstrated at the Los Alamos National Laboratory Isotope Production Facility (LANL-IPF). Arsenic-72 (half life 26 h) is a medium-lived positron emitting radionuclide with the major advantage of being formed as the daughter of another “generator” radioisotope (Se-72, 8.5 d). A ⁷²Se/⁷²As generator would be the preferred mechanism for clinical utilization of ⁷²As for positron emission tomography (PET). No portable ⁷²Se/⁷²As generator system has been demonstrated for convenient, repeated ⁷²As elution (“milking”). In this work, we describe ⁷²Se production and recovery from irradiated NaBr targets using a 100 MeV proton beam. We also introduce an ⁷²As generator principle based on ⁷²Se chelation followed by liquid-liquid extraction, which will be transferred to a solid-phase sorption/elution system.     

Reversible defect of 123I-15-(p-iodophenyl)-9-(R,S)-methylpentadecanoic acid indicates residual viability within infarct-related area

To evaluate the relationship between the reversible defect of 123I-15-(p-iodophenyl)-9-(R,S)-methylpentadecanoic acid (9MPA) and residual viability within an infarct-related area, we performed resting single photon emission computed tomography (SPECT) with 9MPA and positron emission tomography (PET) with 18F-deoxyglucose (FDG) and 13N-ammonia (NH3) in 7 patients with prior myocardial infarction. 9MPA-SPECT was obtained 2 min (early) and 50 min (delayed) after tracer injection. Tomographic images of the left ventricle were divided into 13 segments to correlate the regional uptake of each tracer. Residual viability within an infarct-related segment was confirmed by NH3- and FDG-PET. Twenty-six infarct-related segments, confirmed by NH3-PET, showed reduced uptake of 9MPA on early images. In these 26 segments, 6 showed reversible defect of 9MPA and 20 showed fixed defect on delayed images. Residual viability was present in all segments exhibiting reversible 9MPA defect and 7 segments (35%) exhibiting fixed defect (p < 0.05). The sensitivity, specificity and accuracy of reversible 9MPA defect for the detection of myocardial viability were 46%, 100%, and 73%, respectively. Myocardial clearance of 9MPA was significantly slower in non-viable segments than in ischemic but viable segments (4.9+/-5.1% vs. 10.1+/-5.3%; p < 0.05). These data suggest that a reversible 9MPA defect indicates residual viability within the infarct-related area.     

Prompt gamma emissions in the reaction for neutrons around the 1.45 eV absorption resonance

The relative intensities of different gamma emissions produced after the reaction ¹¹⁵In(n,γ)¹¹⁶In were analyzed for the particular case of incident neutron energies around the 1.45 eV indium absorption resonance. For this purpose, a pulsed neutron source in combination with the time-of-flight method for selecting the incident neutron energy range was employed. For neutrons around the mentioned absorption resonance the prompt gamma spectrum was extended to energies below 273 keV, and the intensities of gamma emissions not reported in the literature for epithermal neutrons were determined.     

The Clinical Usefulness of 18F-FDG PET/CT for the Evaluation of Lymph Node Metastasis in Periorbital Malignancies

Objective

The aim of this study was to assess the clinical role of ¹⁸F-FDG PET/CT for the evaluation of lymph node metastasis in periorbital malignancies, compared with CT alone.

Materials and Methods

We analyzed eighteen PET/CT and CT scans in 15 patients with biopsy-proven periorbital malignancies. We compared the diagnostic capabilities of PET/CT and CT with regard to nodal metastasis by level-by-level analysis and by N staging prediction. The reference standards were surgical pathology (n = 7) from dissected lymph node specimens and the results from radiological follow-up (n = 11, mean 20.5 months; range 10-52 months). Moreover, any changes in patient care as prompted by PET/CT were recorded and compared with treatment planning for CT alone.

Results

PET/CT had a sensitivity of 100%, while CT had a sensitivity of 57% (p = 0.03) for nodal metastasis by level-by-level analysis. PET/CT had a specificity of 97%, positive predictive value of 93%, negative predictive value of 100%, and diagnostic accuracy of 98%, while the CT values for these same parameters were 97%, 89%, 82%, and 84%, respectively. PET/CT correctly predicted N staging with an accuracy of 100%, while CT was only 83% accurate (p = 0.01). Regarding the impact on patient care, the extent of surgery for regional lymph nodes and the treatment decision were modified by PET/CT in 39% of patients.

Conclusion

PET/CT could provide useful information in the management of regional lymph node metastases in patients with periorbital malignancies.     

The Contribution of the Nuclear Reaction 1H(n, γ)2D to the Yield of DNA Single Strand Breaks in Cultured Mammalian Cells Irradiated by Thermal Neutrons

Summary

The yield of single strand breaks (ssb) in DNA of the HeLa S-3 cells after thermal neutron irradiation was examined using the alkaline sucrose gradient method. The contribution of the ¹H(n, γ)²D reaction to the yield of ssb was determined by substituting D₂O for H₂O in the irradiated medium. Calculation shows that when cells are irradiated in the H₂O medium, the per cent contribution of the contaminating γ-rays, the nuclear reaction ¹H(n, γ)²D and the other nuclear reactions is 31, 44 and 25 per cent respectively assuming additivity of effects. The estimated number of ssb induced by the nuclear reaction ¹H(n, γ)²D was at least 4·4 times greater than that by ⁶⁰Co γ-rays at the same absorbed dose. Two possible interpretations are discussed to explain the high efficiency of the ¹H(n, γ)²D reaction for ssb induction.     

Value of <Emphasis Type="Italic">O</Emphasis>-(2-[<Superscript>18</Superscript>F]fluoroethyl)-<Emphasis Type="SmallCaps">l</Emphasis>-tyrosine PET for the diagnosis of recurrent glioma

Purpose The prognosis of patients with recurrent gliomas depends on reliable and early diagnosis of tumour recurrence after initial therapy. In this context, magnetic resonance imaging (MRI) and computed tomography (CT) often fail to differentiate between radiation- and tumour-induced contrast enhancement. Furthermore, absence of contrast enhancement, or even of ¹⁸F-fluorodeoxyglucose uptake in PET, does not exclude recurrence. The aim of this study was to establish the diagnostic value of O-(2-[¹⁸F]fluoroethyl)-l-tyrosine (FET) PET in recurrent gliomas.Methods Fifty-three patients with glioma (primary grading: 27=WHO grade IV, 16=grade III, 9=grade II, 1=grade I) and clinically suspected recurrence underwent FET PET scans 4–180 months after different treatment modalities. For semiquantitative evaluation, maximal SUV (SUV_max) and mean SUV within 80% and 70% isocontour thresholds (SUV₈₀/SUV₇₀) were evaluated and the respective ratios to the background (BG) were calculated. PET results were correlated with MRI/CT, clinical follow-up or biopsy findings.Results All patients presented with FET uptake, of varying intensity, in the area of the primary tumour after initial therapy. In the 42 patients with confirmed recurrence, there was additional distinct focal FET uptake with significantly higher values compared with those in the 11 patients without clinical signs of recurrence and showing only low and homogeneous FET uptake at the margins of the resection cavity. With respect to tumour grading, there was a slight but non-significant increase from WHO II (SUV_max/BG: 2.53±0.28) to WHO III (SUV_max/BG: 2.84±0.49) and WHO IV (SUV_max/BG: 3.55±1.07) recurrence.Conclusion FET PET reliably distinguishes between post-therapeutic benign lesions and tumour recurrence after initial treatment of low- and high-grade gliomas.     

The 4.438 MeV gamma to neutron ratio for the Am–Be neutron source

An accurate measurement of the 4.438 MeV $\gamma$-ray to total neutron ratio, namely $R=S_{\gamma }/S_n$, for a Chinese-made Am–Be neutron source is described. The neutron strength of the source relative to a previously standardized source was determined by the manganese bath technique. The $\gamma$-rays spectra of the source were measured using a $\varnothing 75\times 75$ mm NaI(Tl) detector. The background induced by neutrons and the absolute full energy peak efficiency of the detector were calculated using the MCNP code. The experimental ratio so obtained agrees well with the calculated value. A synthetic evaluated and recommended value of $R=0.575\pm 4.8\%$ was given. We conclude that the experimental R-value appears an important characteristic for an Am–Be source.