Activation of dosimeters used in qa of medical linear accelerators

This paper presents the first results of a project intended to investigate γ-radiation activity induced in dosimeters used in clinical practice during routine quality assurance of high-energy photon beams emitted by electron linear accelerators. Two aspects of the activation via photonuclear reactions (X,n) of therapeutic beam and subsequent capture of secondary neutrons (n,γ) are under considerations: the influence of activation on intrinsic background of the dosimeters and exposure of dosimetrists who operate this equipment. The activation of several types of ionization chambers as well as the silicon diodes was studied after long-time exposure (10 000 MUs) of the 15 MV photon beam (Elekta Synergy). Photon fluxes obtained from spectra of γ-rays registered by HPGe spectrometer were subsequently converted to equivalent doses using appropriate coefficients. The main contribution to the induced activity comes from the neutron capture process on Al, Mn and Cu, therefore it decays quite fast with the half-lives of the order of 15 minutes. Nevertheless, the activation of chlorine was also observed. The estimated equivalent doses to skin and eye lens were in the range 0.19 – 0.62 μSv/min. However, no influence on intrinsic background signal of all studied dosimeters was observed. The preliminary results indicate that induced radioactivity of dosimeters is strongly influenced by therapeutic beam quality and neutron source strength of particular linac. This dependence will be studied deeper in order to quantify it more precisely

Effects of low-dose ionizing radiation on α,β-globulins solutions studied by DSC

An attempt has been made to detect the effect of a small dose of ionizing radiation on the course of a,b-globulin thermal denaturation in aqueous solutions. Doses of 0.1 and 1.8 Gy have been delivered using c-rays emitted by 60Co isotope while doses of 10 and 100 Gy have been supplied by X-rays produced by linear accelerator. The highest dose has visibly changed DSC curve of protein solution while the changes due to lower doses are hardly detectable. Although very weak, the irradiation effect found has been dose dependent. The results suggest that the influence of ionizing radiation on globulins solution is bigger when the dose rate is lower at given dose. The opposite direction of differences between irradiated and control samples for fresh and stored protein solutions suggests various characters of changes in initial and later period of sample aging. This may be an important reason for difficulties in an investigation of the effect of ionizing radiation on protein solution, especially for low doses delivered very slowly

Gamma Radiation in the Vicinity of the Entrance to Linac Radiotherapy Room

Radiotherapy using high-energy photon beams (10–20 MV) is accompanied by the production of secondary neutron radiation via (γ/X,n) reactions. These interactions as well as subsequent neutron capture are the source of induced gamma radioactivity. When studied with standard range of spectrometric systems, only decay gamma radiation is usually registered, whereas a significant part of radiation—prompt gammas—is omitted, what might result in a significant underestimation of occupational risk for therapists in the vicinity of the door to the treatment room during therapeutic beam emission. Presented study has shown the main components of gamma radiation field in this localization investigated with the use of high-purity germanium spectrometry. Among them, prompt gamma radiation in light elements of concrete and in metal construction of the door, as well as 477.6 and 2224.6 keV photons emitted by neutron absorbing layers, contributes the most. Effective dose values depend on thickness of the door as well as on neutron production by particular linac and are within the range of 1.8–56.2 μSv/h. Standard environmental radiometry could underestimate these values by about 60% due to low efficiency for high-energy photon counting

Assessing Boreal Peat Fire Severity and Vulnerability of Peatlands to Early Season Wildland Fire

Globally peatlands store large amounts of carbon belowground with 80% distributed in boreal regions of the northern hemisphere. Climate warming and drying of the boreal region has been documented as affecting fire regimes, with increased fire frequency, severity and extent. While much research is dedicated to assessing changes in boreal uplands, few research efforts are focused on the vulnerability of boreal peatlands to wildfire. In this case study, an integration of field data collection, land cover mapping of peatland types and Landsat-based fire severity mapping was conducted for four early season (May to mid-June) wildfires where peatlands are abundant in northeastern Alberta Canada. The goal was to better understand if peatlands burn more or less preferentially than uplands in fires and how severely the organic soil layers (peat) of different peatland ecotypes burn. The focus was on early season wildfires because they dominated the research area in the decade of study. To do this, a novel Landsat-5 metric was developed to retrieve fire severity of the organic surface layer. Spatial comparisons and statistical analysis showed that proportionally bogs are more likely to burn in early season Alberta wildfires than other ecosystem types, even fire-prone upland conifer. Although for a small sample, we found that when fire weather conditions for the duff layers are severe, the fens of this study appear to become more susceptible to burning. In addition, overall bogs experienced greater severity of burn to the peat layers than fens. Due to the small sample size of peat loss from fire in uplands and limited geographic area of this case study, we were unable to assess if bogs are burning more severely than uplands. Further analysis and Landsat algorithm development for organic soil fire severity in peatlands and uplands are needed to more fully understand trends in belowground consumption for wildfires of all seasons and boreal ecotypes

Measurements of doses from photon beam irradiation and scattered neutrons in an anthropomorphic phantom model of prostate cancer: A comparison between 3DCRT, IMRT and tomotherapy

Introduction. The rapid development of new radiotherapy technologies, such as intensity modulated radiotherapy (IMRT) or tomotherapy, has resulted in the capacity to deliver a more homogenous dose in the target. However, the higher doses associated with these techniques are a reason for concern because they may increase the dose outside the target. In the present study, we compared 3DCRT, IMRT and tomotherapy to assess the doses to organs at risk (OARs) resulting from photon beam irradiation and scattered neutrons. Material and methods. The doses to OARs outside the target were measured in an anthropomorphic Alderson phantom using thermoluminescence detectors (TLD 100) 6Li (7.5%) and 7Li (92.5%). The neutron fluence rate [cm-2·s-1] at chosen points inside the phantom was measured with gold foils (0.5 cm diameter, mean surface density of 0.108 g/cm3). Results. The doses [Gy] delivered to the OARs for 3DCRT, IMRT and tomotherapy respectively, were as follows: thyroid gland (0.62 ± 0.001 vs. 2.88 ± 0.004 vs. 0.58 ± 0.003); lung (0.99 ± 0.003 vs. 4.78 ± 0.006 vs. 0.67 ± 0.003); bladder (80.61 ± 0.054 vs. 53.75 ± 0.070 vs. 34.71 ± 0.059); and testes (4.38 ± 0.017 vs. 6.48 ± 0.013 vs. 4.39 ± 0.020). The neutron dose from 20 MV X-ray beam accounted for 0.5% of the therapeutic dose prescribed in the PTV. The further from the field edge the higher the contribution of this secondary radiation dose (from 8% to ~45%). Conclusion. For tomotherapy, all OARs outside the therapeutic field are well-spared. In contrast, IMRT achieved better sparing than 3DCRT only in the bladder. The photoneutron dose from the use of high-energy X-ray beam constituted a notable portion (0.5%) of the therapeutic dose prescribed to the PTV

Characteristics of natural radioactivity at the Reiche Zeche mine, Germany

Determination of the natural radiation background in underground localizations is necessary to describe them for possible use not only for physics experiments. The characteristics of natural radioactivity at the Reiche Zeche mine is presented and contains results from in-situ measurements, radon concentration in air, and = laboratory analyses of water and rock samples from the investigated localization. The measurements were performed in the Research and Education Mine “Reiche Zeche”, Germany at the depth of 150 m (410 m w.e.)

Mapping mountain peatlands and wet meadows using multi-date, multi-sensor remote sensing in the Cordillera Blanca, Peru

Wetlands (called bofedales in the Andes of Peru) are abundant and important components of many mountain ecosystems across the globe. They provide many benefits including water storage, high quality habitat, pasture, nutrient sinks and transformations, and carbon storage. The remote and rugged setting of mountain wetlands creates challenges for mapping, typically leading to misclassification and underestimates of wetland extent. We used multi-date, multi-sensor radar and optical imagery (Landsat TM/PALSAR/RADARSAT-1/SRTM DEM-TPI) combined with ground truthing for mapping wetlands in Huascarán National Park, Peru. We mapped bofedales into major wetland types: 1) cushion plant peatlands, 2) cushion plant wet meadows, and 3) graminoid wet meadows with an overall accuracy of 92%. A fourth wetland type was found (graminoid peatlands) but was too rare to map accurately, thus it was combined with cushion peatland to form a single peatland class. Total wetland area mapped in the National Park is 38,444 ha, which is 11% of the park area. Peatlands were the most abundant wetland type occupying 6.3% of the park, followed by graminoid wet meadows (3.5%) and cushion wet meadows (1.3%). These maps will serve as the foundation for improved management, including restoration, and estimates of landscape carbon stocks

Lead shielding efficiency from the gamma background measurements in the salt cavern of the Polkowice–Sieroszowice copper mine

The studies of lead shielding efficiency from the gamma background measurements were performed in the salt cavern of the copper mine - a site considered for an underground laboratory. Within the energy range of 50–2700 keV, the measured gamma-ray count rates normalized to the mass of the high-purity detectors germanium crystal are 5.93 and 6.32 s−1kg−1 for the used low-background and portable spectrometers, respectively. The gamma-ray flux of 0.124 (2) cm−2s−1 connected with the natural radioisotopes was observed by the portable HPGe, including 0.026 (1) cm−2s−1 contribution of radon decay products, whereas the photon flux at the spectrum continuum was 0.18 (5) cm−2s−1

Characteristics of natural background radiation in the Polkowice-Sieroszowice mine, Poland

Natural radioactivity in underground locations is the main parameter for the safety of work (occupational hazards) and for the success of experiments in physics or biology requiring unique conditions. The characterization of natural prominence was carried out in the Conceptual Lab development in one of KGHM deep copper mines co‐ordinated by KGHM Cuprum R&D. Natural radioactivity studies were performed and included in situ gamma spectrometry, neutron flux measurements, radon concentration, and alpha and gamma laboratory spectrometry measurements of rock samples. At a depth of 1014.4 m (2941.8 m w.e.) within the anhydrite layer, a neutron flux of 2.0 ± 0.2 × 10−6 cm−2 s−1, a gamma‐ray dose of 0.008 ± 0.001 μSv/h, a photon flux density of 0.64 ± 0.20 cm−2 s−1, and a radon concentration of 6.6 Bq/m3 were determined. Laboratory analyses of 226,228Ra, 40K, and 238,234U concentrations in collected rock samples showed low values. The exceptionally low level of natural radioactivity in the Polkowice‐Sieroszowice mine makes this location a unique place for scientific research