Heavy-ions shielding data for hadrontherapy application with Monte Carlo methods.

In hadrontherapy centers, ion beams are accelerated by a cyclotron or synchrotron through electric and magnetic fields and, once the treatment energy is reached, ions interact with the patient. The interaction of the beam with magnets, other elements of particle accelerator or with the patient generates secondary radiation and the calculation for the design of the shielding is required. A first assessment of the shielding, generally made by concrete, can be performed by using Monte Carlo simulations, in which neutron yields and the ambient dose equivalent, H*(10), spatial distribution are obtained. The aim of this work is to evaluate, with a Monte Carlo approach, ambient dose equivalent values at various concrete depths generated by the secondary radiation. Simulations are performed considering helium, lithium, carbon, oxygen and iron primary beams. For existing facilities that already accelerates carbon ion, an equivalent carbon ratio is introduced to estimate the ion currents to get, in a given point, the same ambient dose equivalent as a carbon ion. Numerical results have been obtained simulating an ion beam that impinges on a thick iron or international commission on radiation units and measurements (ICRU) tissue, respectively, representing magnets and patient. The secondary radiation is transported through a large concrete shielding where ambient dose equivalent values are calculated as function of concrete thickness.

Soil radioactivity in the highest volcanic region of Northern Andes.

This work studied the spatial pattern of four natural radionuclides (226Ra, 228Ra, 228Th and 40K) as well as one artificial one (137Cs) in soils in the Chimborazo province (Ecuador), which belongs to the North Andes of South America. Soil samples were collected considering the Ecuador geological map. Statistical analyses showed that activity concentrations of 226Ra, 228Ra, 228Th do not exceed the worldwide average, while one geological unit exceeds the worldwide average for 40K. These high activity concentrations are attributed to radionuclide accumulation in plutonic and metamorphic rocks and also in ash resulting from eruptions of the Sangay volcano. The inverse distance weighted interpolation method was used to develop corresponding radioactivity maps where the highest activity concentrations are in the central-east of the studied area. In addition, a distribution pattern of 226Ra and 40K is observed in the geologies influenced by the presence of Chimborazo, Igualata, Tungurahua and Altar volcanoes. Spearman's nonparametric test shows positive correlations suggesting the presence of very homogeneous lithologies and that volcanic activities can influence the distribution of radionuclides in our environment. In seven of the samples, 137Cs was detected.

A tri-modal tissue-equivalent anthropomorphic phantom for PET, CT and multi-parametric MRI radiomics.

PURPOSE: Radiomics has emerged as an advanced image processing methodology to define quantitative imaging biomarkers for prognosis and prediction of treatment response and outcome. The development of quantitative imaging biomarkers requires careful analysis to define their accuracy, stability and reproducibility through phantom measurements. Few efforts were devoted to develop realistic anthropomorphic phantoms. In this work, we developed a multimodality image phantom suitable for PET, CT and multiparametric MRI imaging. METHODS: A tissue-equivalent gel-based mixture was designed and tested for compatibility with different imaging modalities. Calibration measurements allowed to assess gel composition to simulate PET, CT and MRI contrasts of oncological lesions. The characterized gel mixture was used to create realistic synthetic lesions (e.g. lesions with irregular shape and non-uniform image contrast), to be inserted in a standard anthropomorphic phantom. In order to show phantom usefulness, issues related to accuracy, stability and reproducibility of radiomic biomarkers were addressed as proofs-of-concept. RESULTS: The procedure for gel preparation was straightforward and the characterized gel mixture allowed to mime simultaneously oncological lesion contrast in CT, PET and MRI imaging. Proofs-of-concept studies suggested that phantom measurements can be customized for specific clinical situations and radiomic protocols. CONCLUSIONS: We developed a strategy to manufacture an anthropomorphic, tissue-equivalent, multimodal phantom to be customized on specific radiomics protocols, for addressing specific methodological issues both in mono and multicentric studies.

Response of the environmental thermal neutron flux to earthquakes.

Some new results were obtained by the array of EN-detectors (Electron and Neutron detectors) developed in the frame of the PRISMA (PRImary Spectrum Measurement Array) project for Extensive Air Showers detection. Our EN-detectors running both on the Earth surface and underground are continuously measuring the environmental thermal neutron flux. Neutrons are partially produced by radioactive gas radon and its daughter decays through (α,n)-reactions in soil close to the detectors. Then neutrons thermalize in media and, being in equilibrium with it, they are sensitive to many geo-dynamic phenomena including earthquakes. In this work the EN-detectors were measuring the variations of an environmental neutron flux in Tibet (30.11 N, 90.53 E, 4300 m a.s.l) at a distance of ∼600 km from the collision zone of the Asian-Indian plates subduction zone (Nepal region). We have observed some anomalies in the dynamics of the neutron flux around the time of the catastrophic earthquakes of magnitude M = 7.8 happened in Gorkha (Nepal) on 25.04.2015 followed by a series of aftershocks of M > 6. The use of nuclear physics methods can provide novel results in geophysics and this work demonstrates the sensitivity of the environmental thermal neutron flux to changes in tense-deformed crust conditions caused by earthquakes with epicentral distances greater than 500 km.

Are physicians aware enough of patient radiation protection? Results from a survey among physicians of Pavia District- Italy.

BACKGROUND: Radiological practices are the first anthropic sources of ionizing radiation exposure of the population. However, a review of recent publications underlines inadequate doctors' knowledge about doses imparted in medical practices and about patient protection that might explain unnecessary radiological prescriptions. We investigated the knowledge of the physicians of Pavia District (Italy) on the risk of radiation exposure. METHODS: A cross sectional study was performed involving the Medical Association of Pavia District. Data were collected with a self-administered questionnaire, available on-line with private login and password. RESULTS: Four hundred nineteen physicians fulfilled the questionnaire; 48% of participants reported training about radiation protection. The average percentage of correct answers on the knowledge on ionizing radiation was 62.29%, with a significantly higher result between radiologist. Around 5 and 13% of the responders do not know that, respectively, ultrasonography and magnetic resonance do not expose patients to ionizing radiations. Only 5% of the physicians properly identified the cancer risk rate associated to abdomen computed tomography. CONCLUSIONS: The findings show a quite good level of the general knowledge about ionizing radiations, higher that reported in literature. Nevertheless, we believe the usefulness of training on the risk linked to radiation exposure in medicine for physicians employed in every area.

[Theory and testing of an accident risk assessment system based on prior experience]. / Teorizzazione e sperimentazione di un metodo di valutazione del rischio infortunio sulla base di eventi pregressi.

OBJECTIVES: to improve the "National Project: Integrated investigations for an indepth analysis of cases of Fatal Accidents", a project which, on one hand, is too open to interpretation of events, while, on the other, does not offer the possibility to analyse external factors which are often at the basis of accidents in the workplace. METHODS: identification and weighting criteria regarding causes of accident have been established and correlated by means of a specific algorithm, with the aim of making them numerically measurable. This has made it possible to use them as indicators to identify lines of priority in prevention planning. The theoretical model has been tested in an analysis of 35 work accidents which occurred in a firm in Mantova. RESULTS: the model has been evaluated in comparison to the analysis which was previously used to examine cases of work-related accidents and it has proved to be more efficient in the move towards establishing preventative action at the beginning of a chain of events. CONCLUSIONS: While maintaining the "Learning from mistakes" model, the method here proposed represents an extension and an implementation of previous practices. It is an effective operative method for companies, offering both a qualitative and quantitative analysis of work-related accidents with a view to their prevention.

[Judgment of fitness for work in employees with a history of malignant neoplastic disease and exposed to ionizing radiations: evaluation criteria and their application in a case-series study]. / Il giudizio di idoneità al rischio da esposizione a radiazioni ionizzanti nei lavoratori con pregressa patologia neoplastica: criteri di valutazione e analisi di una casistica.

INTRODUCTION: The increase in working age has many epidemiological consequences, one of which is an increased incidence of neoplastic diseases among the working population. Therefore it is more frequent than in the past that the Approved Physician ("Autorizzato" according to Italian legislation) have to judge working fitness in employees suffering from cancer and at the same time exposed to ionizing sources. AIMS: In this study we give suggestions for the decision if a worker, who have previously suffered from malignant tumors, is ready to go or not to go back to work. METHODS: Though we believe in the preventive theory of the linear correlation without threshold for stochastic effects ("Linear No Threshold" LNT), we considered data from the literature that highlight how very low doses of radiation exposure do not increase the risk of stochastic effects and how the potential occupational exposure to low doses does not introduce a significant additional risk of cancer in subjects with a history of malignant tumor. RESULTS: We identify "objective" elements of judgment related to the neoplastic disease of the worker and his activity, but we emphasize the importance of the psychological condition of the worker, as well as his professional interest and his career opportunities. CONCLUSIONS: The criteria we recommend were applied to a group of workers suffering from cancer and with different working activities at risk of exposure to ionizing radiations. The evaluation process is a first rational approach to the assessment of their suitability in worker suffering from neoplastic disease, with the need for custom handling for each individual.

The BIANCA model/code of radiation-induced cell death: application to human cells exposed to different radiation types.

This paper presents a biophysical model of radiation-induced cell death, implemented as a Monte Carlo code called BIophysical ANalysis of Cell death and chromosome Aberrations (BIANCA), based on the assumption that some chromosome aberrations (dicentrics, rings, and large deletions, called ''lethal aberrations'') lead to clonogenic inactivation. In turn, chromosome aberrations are assumed to derive from clustered, and thus severe, DNA lesions (called ''cluster lesions,'' or CL) interacting at the micrometer scale; the CL yield and the threshold distance governing CL interaction are the only model parameters. After a pilot study on V79 hamster cells exposed to protons and carbon ions, in the present work the model was extended and applied to AG1522 human cells exposed to photons, He ions, and heavier ions including carbon and neon. The agreement with experimental survival data taken from the literature supported the assumptions. In particular, the inactivation of AG1522 cells was explained by lethal aberrations not only for X-rays, as already reported by others, but also for the aforementioned radiation types. Furthermore, the results are consistent with the hypothesis that the critical initial lesions leading to cell death are DNA cluster lesions having yields in the order of *2 CL Gy-1 cell-1 at low LET and*20 CL Gy-1 cell-1 at high LET, and that the processing of these lesions is modulated by proximity effects at the micrometer scale related to interphase chromatin organization. The model was then applied to calculate the fraction of inactivated cells, as well as the yields of lethal aberrations and cluster lesions, as a function of LET; the results showed a maximum around 130 keV/lm, and such maximum was much higher for cluster lesions and lethal aberrations than for cell inactivation.

A model of radiation-induced cell killing: insights into mechanisms and applications for hadron therapy.

A mechanism-based, two-parameter biophysical model of cell killing was developed with the aim of elucidating the mechanisms underlying radiation-induced cell death and predicting cell killing by different radiation types, including protons and carbon ions at energies and doses of interest for cancer therapy. The model assumed that certain chromosome aberrations (dicentrics, rings and large deletions, called "lethal aberrations") lead to clonogenic inactivation, and that aberrations derive from µm-scale misrejoining of chromatin fragments, which in turn are produced by "dirty" double-strand breaks called "cluster lesions" (CLs). The average numbers of CLs per Gy per cell were left as a semi-free parameter and the threshold distance for chromatin-fragment rejoining was defined the second parameter. The model was "translated" into Monte Carlo code and provided simulated survival curves, which were compared with survival data on V79 cells exposed to protons, carbon ions and X rays. The agreement was good between simulations and survival data and supported the assumptions of the model at least for doses up to a few Gy. Dicentrics, rings and large deletions were found to be lethal not only for AG1522 cells exposed to X rays, as already reported by others, but also for V79 cells exposed to protons and carbon ions of different energies. Furthermore, the derived CL yields suggest that the critical DNA lesions leading to clonogenic inactivation are more complex than "clean" DSBs. After initial validation, the model was applied to characterize the particle and LET dependence of proton and carbon cell killing. Consistent with the proton data, the predicted fraction of inactivated cells after 2 Gy protons was 40-50% below 7.7 keV/µm, increased by a factor ∼1.6 between 7.7-30.5 keV/µm, and decreased by a factor ∼1.1 between 30.5-34.6 keV/µm. These LET values correspond to proton energies below a few MeV, which are always present in the distal region of hadron therapy spread-out Bragg peaks (SOBP). Consistent with the carbon data, the predicted fraction of inactivated cells after 2 Gy carbon was 40-50% between 13.7-32.4 keV/µm, it increased by a factor ∼1.7 between 32.4-153.5 keV/µm, and decreased by a factor ∼1.1 between 153.5-339.1 keV/µm. Finally, we applied the model to predict cell death at different depths along a carbon SOBP used for preclinical experiments at HIMAC in Chiba, Japan. The predicted fraction of inactivated cells was found to be roughly constant (less than 10%) along the SOBP, suggesting that this approach may be applied to predict cell killing of therapeutic carbon beams and that, more generally, dicentrics, rings and deletions at the first mitosis may be regarded as a biological dose for these beams. This study advanced our understanding of the mechanisms of radiation-induced cell death and characterized the particle and LET dependence of proton and carbon cell killing along a carbon SOBP. The model does not use RBE values, which can be a source of uncertainty. More generally, this model is a mechanism-based tool that in minutes can predict cell inactivation by protons or carbon ions of a given energy and dose, based on an experimental photon curve and in principle, a single (experimental) survival point for the considered ion type and energy.

Cardiac magnetic resonance imaging: patient safety considerations.

Magnetic Resonance Imaging (MRI) is widely used in medicine. In cardiology, it is used to assess congenital or acquired diseases of the heat: and large vessels. Unless proper precautions are taken, it is generally advisable to avoid using this technique in patients with implanted electronic stimulators, such as pacemakers and defibrillators, on account of the potential risk of inducing electrical currents on the endocardial catheters, since these currents might stimulate the heart at a high frequency, thereby triggering dangerous arrhythmias. In addition to providing some basic information on pacemakers, defibrillators and MRI, and on the possible physical phenomena that may produce harmful effects, the present review examines the indications given in the literature, with particular reference to coronary stents, artificial heart valves and implantable cardiac stimulators.

Laboratory UV exposure: risk assessment and protective measures.

In research laboratories ultraviolet radiation is widely used, particularly in photochemistry and photobiology, as a sterilizing agent and for the characterization of samples. The results of a survey conducted near several university laboratories are presented with the aim of quantifying exposure levels to UV-incoherent radiation and to assess individual risk for researchers and students. It has been shown that exposure is not negligible, especially if safety procedures are neglected and personal protective equipments, described in this study, are not used.

Evaluation of the dose to pediatric patients undergoing micturating cystourethrography examination and optimization of the examination.

PURPOSE: The aim of our work was to estimate the dose to paediatric patients undergoing micturating cystourethrography (MCU), and to optimize those examination procedures that were found to be particularly significant from the point of view of the radiation dose. At the same time it was also decided to evaluate the absorbed dose to the parents, who frequently assist the child during MCU. MATERIALS AND METHODS: The study was carried out on 220 children undergoing micturatig cystourethrography, by measuring in vivo the dose equivalent entering and exiting from the patient with thermoluminescent dosimetry and the KAP (Kerma Area Product). From the latter, the imparted energy and the average absorbed dose to the patients were subsequently calculated. RESULTS: The average absorbed dose was 0.69+/-0.54 mGy, with a variation interval of 0.126-3.110 mGy. A remarkable dispersion of the absorbed dose values was observed, also for subjects of similar size. This indicates that radiation protection of paediatric patients still allows for wide margins of optimization. In fact it was possible to verify that the dose depends not only on the size of the child, but also on his/her degree of cooperation, and on the technical ability of the operator. The latter aspect was estimated by comparing the doses delivered by two different physicians; differences by a factor of 5 were observed. The application of additional filtration of 2 mm of Al (total 5 mm Al) concurred to a dose reduction without significant variations in image quality. The effective dose received by the parents present during the examination was 4+/-7 microSv. CONCLUSIONS: A specific feature of paediatric MCU is not only the amount of radiation dose, often not negligible, but also the remarkable variation of the dose values, even within the same age group. The specialist has an important role in the justification of the examination: the adoption of a specific protocol has allowed reduction of the number of children undergoing MCU. Optimization of the examination requires quality control on the equipment, as well as the adoption of good radiographic techniques and the provision of suitable environments for children. The present study has helped to focus the attention of practitioners on radiation protection and, consequently, to reduce the dose delivered to the children. The effective dose received by the parents showed that their presence can be justified provided that they are adequately protected.