Biological UV dosimeters in the assessment of the biological hazard from environmental radiation

To determine the impact of environmental UV radiation, biological dosimeters that weight directly the incident UV components of sunlight have been developed, improved and evaluated in the frame of the BIODOS project. Four DNA-based biological dosimeters ((i) phage T7, (ii) uracil thin layer, (iii) spore dosimeter and (iv) DLR-biofilm) have been assessed from the viewpoint of their biological relevance, spectral response and quantification of their biological effectiveness. The biological dosimeters have been validated by comparing their readings with weighted spectroradiometer data, by comparison with other biological doses, as well as with the determined amounts of DNA UV photoproducts. The data presented here demonstrate that the biological dosimeters are potentially reliable field dosimeters for measuring the integrated biologically effective irradiance for DNA damage.     

Evaluation of a high exposure solar UV dosimeter for underwater use

Solar ultraviolet radiation (UV) is known to have a significant effect upon the marine ecosystem. This has been documented by many previous studies using a variety of measurement methods in aquatic environments such as oceans, streams and lakes. Evidence gathered from these investigations has shown that UVB radiation (280-320 nm) can negatively affect numerous aquatic life forms, while UVA radiation (320-400 nm) can both damage and possibly even repair certain types of underwater life. Chemical dosimeters such as polysulphone have been tested to record underwater UV exposures and in turn quantify the relationship between water column depth and dissolved organic carbon levels to the distribution of biologically damaging UV underwater. However, these studies have only been able to intercept UV exposures over relatively short time intervals. This paper reports on the evaluation of a high exposure UV dosimeter for underwater use. The UV dosimeter was fabricated from poly 2,6-dimethyl-1,4-phenylene oxide (PPO) film. This paper presents the dose response, cosine response, exposure additivity and watermarking effect relating to the PPO dosimeter as measured in a controlled underwater environment and will also detail the overnight dark reaction and UVA and visible radiation response of the PPO dosimeter, which can be used for error correction to improve the reliability of the UV data measured by the PPO dosimeters. These results show that this dosimeter has the potential for long-term underwater UV exposure measurements.     

The role of the spectral sensitivity curve in the selection of relevant biological dosimeters for solar UV monitoring

To estimate the risk of enhanced UV-B radiation due to stratospheric ozone depletion, phage T7 and uracil thin-layer biological dosimeters have been developed, which weight the UV irradiance according to induced DNA damage. To study the molecular basis of the biological effects observed after UV irradiation, the spectral sensitivity curves of the two dosimeters and induction of the two major DNA photoproducts, cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts ((6-4)PDs), in phage T7 have been determined for polychromatic UV sources. CPDs and (6-4)PDs are determined by lesion-specific monoclonal antibodies in an immunodotblot assay. Phage T7 and uracil biological dosimeters together with a Robertson-Berger (RB) meter have been used for monitoring environmental radiation from the polar region to the equator. The biologically effective dose (BED) established with the three different dosimeters increases according to the changes in the solar angle and ozone column, but the degree of the change differs significantly. The results can be explained based on the different spectral sensitivities of the dosimeters. A possible method for determining the trend of the increase in the biological risk due to ozone depletion is suggested.     

Influence of spectral and angular sensitivity on the readout of biological dosimeters

Biological systems used as biological dosimeters can possess different angular sensitivities from the detectors usually used in physical devices. A simple experimental setup has been developed and used to measure the angular sensitivity of uracil thin-layer biological dosimeters. Results of angular sensitivity measurements for uracil thin-layer dosimeters are presented using a Xe arc lamp as the UV source. According to the experiments described here, uracil thin-layer dosimeters show a cosine-type angular dependence. In several indoor experiments broadband UV meters are used to control the applied dose rate from a given artificial UV source. The experimental setup has been designed and used to verify experimentally the importance of spectral and angular sensitivity differences of biological and physical UV meters applied in biological experiments. Model calculations for two different irradiation systems, using different geometrical arrangements of artificial UV sources, are also presented. For these arrangements relative dose rates that could be measured with dosimeters of arbitrary spectral, but different angular sensitivity have been calculated.     

UV dosimeters based on neotetrazolium chloride

A novel UV dosimeter is described comprising a tetrazolium dye, neotetrazolium chloride (NTC), dissolved in a film of polymer, polyvinyl alcohol (PVA). The dosimeter is pale yellow/colourless in the absence of UV light, and turns red upon exposure to UV light. The spectral characteristics of a typical UV dosimeter film and the mechanism through which the colour change occurs are detailed. The NTC UV dosimeter films exhibit a response to UV light that is related to the intensity and duration of UV exposure, the level of dye present in the films and the thickness of the films themselves. The response of the dosimeter is temperature independent over the range 20–40 °C and, like most UV dosimeters, exhibits a cosine-like response dependence upon irradiance angle. The introduction of a layer of a UV-screening compound which slows the rate at which the dosimeter responds to UVR enables the dosimeter response to be tailored to different UV doses. The possible use of these novel dosimeters to measure solar UV exposure dose is discussed.     

A PERSONAL DOSIMETER FOR BIOLOGICALLY EFFECTIVE SOLAR UV-B RADIATION

Abstract— The production and optical properties are described of a polymer film suitable for use as a personal dosimeter for biologically effective solar UV-B radiation. The dosimeter only responds to UVR at wavelengths less than 315 nm and is potentially suited for longterm studies of the UV doses received by human subjects.     

Optimizing the sensitivity and radiological properties of the PRESAGE® dosimeter using metal compounds

The aim of this study is to investigate the radiation-modifying effects of incorporating commercially available bismuth-, tin- and zinc-based compounds in the composition of the PRESAGE^® dosimeter, and the feasibility of employing such compounds for radiation dose enhancement. Furthermore, we demonstrate that metal compounds can be included in the formulation to yield water-equivalent PRESAGE^® dosimeters with enhanced dose response. Various concentrations of the metal compounds were added to a newly developed PRESAGE^® formulation and the resulting dosimeters were irradiated with 100 kV and 6 MV photon beams. A comparison between sensitivity and radiological properties of the PRESAGE^® dosimeters with and without the addition of metal compounds was carried out. Optical density changes of the dosimeters before and after irradiation were measured using a spectrophotometer. In general, when metal compounds were incorporated in the composition of the PRESAGE^® dosimeter, the sensitivity of the dosimeters to radiation dose increased depending on the type and concentration of the metal compound, with the bismuth compound showing the highest dose enhancement factor. In addition, these metal compounds were also shown to improve the retention of the post-response absorption value of the PRESAGE^® dosimeter over a period of 2 weeks. Thus, incorporating 1–3 mM (ca. 0.2 wt%) of any of the three investigated metal compounds in the composition of the PRESAGE^® dosimeter is found to be an efficient way to enhance the sensitivity of the dosimeter to radiation dose and stabilize its post-response for longer times. Furthermore, the addition of small amounts of the metal compounds also accelerates the polymerization of the PRESAGE^® dosimeter precursors, significantly reducing the fabrication time. Finally, a novel water-equivalent PRESAGE^® dosimeter formula optimized with metal compounds is proposed for clinical use in both kilovoltage and megavoltage radiotherapy dosimetry.     

Spore Film Dosimeters Are Feasible for UV Dose Monitoring During Heliotherapy

The objective of the study was to compare Bacillus subtilis spore film dosimeters with a Robertson Berger UV meter (RB meter) and diary records for assessing personal UV-B doses during a 13-day heliotherapy (HT) for atopic dermatitis (AD). In addition, the relationship between the personal UV-B dose and change in serum 25-hydroxyvitamin D (25(OH)D) was studied. Altogether 21 adult patients with AD completed the study arranged in the Canary Islands, either in January or March 2005. The spore film dosimeters were used throughout the day during the HT. Serum 25(OH)D was analyzed using radioimmunoassay. The mean personal UV-B dose measured with the dosimeters was 75 SED in January and 131 SED in March. The respective results gained from the RB meter combined with diary records were 63 SED and 119 SED showing a close correlation with the dosimeter results. Serum 25(OH)D concentration increased by 9.7 nmol L⁻¹ in January and by 26.0 7 nmol L⁻¹ in March. The increase in serum 25(OH)D correlated with the UV-B dose received. The patients complied well to use the dosimeters. We conclude spore films to be a feasible and reliable personal UV dosimeter in vivo in field conditions.     

Attenuation of Biologically Effective UV Radiation in Tropical Atlantic Waters Measured with a Biochemical DNA Dosimeter

Abstract— A biochemical dosimeter was developed to study the attenuation of biologically effective UV radiation in marine tropical waters. Small quartz vials were used containing a solution of DNA molecules; the vials were incubated at discrete water depths. Subsequently, DNA damage was determined in these samples, using an antibody directed against thymine dimers followed by chemiluminescent detection. Measurements of DNA damage were compared with calculated biologically effective doses, as derived from spectroradiometer measurements. The biodosimeter was found to be a reliable and easy tool to determine levels of harmful UV radiation in marine waters. The highest attenuation coefficient (1.60 m^-l) measured with the biochemical dosimeter was found in eutrophic waters, at a coastal station off Curabcao, Netherlands Antilles. At the other stations attenuation coefficients ranged from 0.18 m^-1 in central Atlantic waters to 0.43 m^-1 close to the Curapcao coast line. Latter results indicate that biologically effective UV radiation may easily reach ecologically significant depths, e.g. coral reef communities.     

Optical waveguide dosimetry for gamma-radiation in the dose range 10-1 − 104 Gy

Two types of liquid-core optical waveguide (OWG) dosimeters are commercially available for dosimetry in the irradiation of foods and other products. “Opti-chromic” type FWT-70-40M has a useful range of about 10-10⁴ Gy and type FWT-70–83M about 10²−10⁴ Gy. 5 Within the limits of random uncertainty of the reading of the absorbed dose (±5%, 1σ), the response to γ-radiation is independent of dose rate over the range 10^-1−10⁴ Gy/h, when measured at the peak of the spectrum [absorption band maximum (600 nm wavelength)]. The response curve is linear with dose up to ≈10³ Gy, but is non-linear at higher doses, where the readings are made away from the absorption peak (656nm). Both dosimeter types when measured at 600 nm are temperature dependent over the temperatures ranges of -40 to 60°C during irradiation. The dosimeters cannot be used when exposed to temperatures > 60°C because of bubble formation and loss of light propagation. At doses < 10³ Gy (at600 nm), the dosimeters are stable (in terms of dose readings) for several months following irradiation, but at doses ≈ 10⁴ kGy (at 656 nm), they show a gradual absorbance increase (error in dose interpretation), over post-irradiation storage periods longer than 1 month. A special, sensitive OWG dosimeter (50-cm coil), designed for doses down to 10^-1 Gy, shows a linear response up to at least 15 Gy, a temperature dependence of response only at temperatures below ≈ 20°C, and no dose-rate dependence.     

Personal solar UV exposure measurements employing modified polysulphone with an extended dynamic range

Polysulphone dosimeters using a simple to use filter have been developed and tested to provide an extended dynamic measurement range of personal solar UV exposures over an extended period (3 to 6 days). At a Southern Hemisphere subtropical site (27.6 degrees S, 151.9 degrees E), the dynamic range of the filtered polysulphone allowed measurements of erythemal exposures to approximately 100 minimum erythemal dose (MED) for a change in optical absorbance at 330 nm (deltaA330) of 0.35. In comparison, unfiltered polysulphone dosimeters were exposed to approximately 8 MED for the same deltaA330. The error associated with the use of the filtered polysulphone dosimeters is of the order of +/-15%, compared with +/-10% of the unfiltered variety. The developed filtered polysulphone dosimeter system allowed the measurement of erythemal UV exposures over 3 to 6 days at a subtropical site without the need to replace the dosimeters because of saturation. The results show that longer-term measurement programs of personal solar UV have been made more feasible with the use of these polysulphone dosimeters with an extended dynamic range compared with unfiltered polysulphone dosimeters.     

Natural indoor gamma background in Coonoor environment of South India

Indoor natural radiation dose existing in dwellings of Coonoor have been estimated using thermoluminescent dosimeters. TLDs are displayed in indoors and are replaced after three-month period. The seasonal averages of the dose rate and the annual effective dose equivalent are calculated from the measured results. Geographical and seasonal variations as well as the differences between indoor to outdoor dose rates have also been studied. Very good correlation exists between the indoor dose rates measured by TLD and environmental radiation dosimeter with correlation coefficient of 0.91. The annual effective dose equivalent to the Coonoor population due to indoor gamma radiation was estimated to be 970 mSv/y for the period of 1997–1998.     

Investigation of dopant effect on some TL dosimeters containing boron

Effective atomic numbers, effective electron densities for photon mass energy absorption and kerma values of soft tissue and some thermoluminescence dosimeter containing boron are calculated in the energy range from 1 keV to 20 MeV. It is investigated that the variation of effective atomic numbers, effective electron densities and kerma with energy. The TL dosimeters studied are compared with the soft tissue for calculated values. In addition, dopant effect on the effective atomic numbers and electron densities for photon mass energy absorption and kerma values of the TL dosimeter containing boron is presented. Effect of the concentrations of the element H on effective electron density of the soft tissue is discussed.     

Optimization of the sensitivity and stability of the PRESAGE™ dosimeter using trihalomethane radical initiators

The aim of this study is to investigate the effect of trihalomethane radical initiators on the radiological properties, radiation dose sensitivity and post response photo-stability of the PRESAGE dosimeter. Different PRESAGE dosimeters containing 50 and 100 mM of iodoform (CHI₃), bromoform (CHBr₃) or chloroform (CHCl₃) radical initiators where fabricated and irradiated with 6 MV photons for a range of radiation doses from 0 to 30 Gy. A comparison between sensitivity and radiological properties of the PRESAGE dosimeters with the different radical initiators was carried out. Optical density changes of the dosimeters before and after irradiation were measured using a spectrophotometer. The incorporation of different radical initiators in the composition of the PRESAGE dosimeter resulted in variation of the radiation dose sensitivity and radiological properties of the dosimeters depending on the type and concentration of the radical initiator used, with iodoform showing the highest dose-response slope followed by bromoform and chloroform. However, at 100 mM iodoform, the effective atomic number was significantly higher than water (Z_eff=16). This enhancement in dose-response was found to be directly related to the carbon–halogen bond dissociation energy and to the radiological properties of each individual radical initiator used in this study. Furthermore, the post-response stability of the PRESAGE dosimeters over two weeks remained stable regardless of the trihalomethane radical initiator employed, with negligible change in the post-response stability and linearity of the PRESAGE dosimeters.     

A new label dosimetry system

A new label dosimeter which changes its color by large radiation doses has been developed. The green color of the unirradiated dosimeter gradually turns to brown then to red at high doses. The label dosimeter was prepared with a peal-off paper backing, allowing it to stick by self-adhesion to a product box. Three types of dosimeters having different sensitivities to radiation doses were prepared. Correlations were established between absorbed doses and color scale or the green/red axis of the irradiated dosimeters, using a micro color unit equipped with a data station. The data were analyzed to determine the reproducibility of the reflectance measured from the label dosimeters exposed to different doses of γ radiation. These dosimeters showed great stability on extended storage before and after irradiation.Detailed measurements of absorbed dose extremes (D_min and D_max) in product boxes, processed in the Egypt Mega Gamma I radiation processing facility, were obtained using these dosimeters. These dosimeters are currently available in large quantities and are inexpensive, which makes them suitable for routine high-dose applications in radiation processing of materials.     

Validation of phage T7 biological dosimeter by quantitative polymerase chain reaction using short and long segments of phage T7 DNA

Phage T7 can be used as a biological dosimeter; its reading, the biologically effective dose (BED), is proportional to the inactivation rate |ln (n/n0)|. For the measurement of DNA damage in phage T7 dosimeter, a quantitative polymerase chain reaction (QPCR) methodology has been developed using 555 and 3826 bp fragments of phage T7 DNA. Both optimized reactions are so robust that an equally good amplification was obtained when intact phage T7 was used in the reaction mixture. In the biologically relevant dose range a good correlation was obtained between the BED of the phage T7 dosimeter and the amount of ultraviolet (UV) photoproducts determined by QPCR with both fragments under the effect of five various UV sources. A significant decrease in the yield of photoproducts was detected by QPCR in isolated T7 DNA and in heated phage compared with intraphage DNA with all irradiation sources. Because the yield of photoproducts was the same in B, C and A conformational states of T7 DNA, a possible explanation for modulation of photoproduct frequency in intraphage T7 DNA is that the presence of bound phage proteins induces an alteration in DNA structure that can result in increased induction of photoproducts.     

Construction of spectral sensitivity function using polychromatic UV sources.

A procedure is presented for constructing the spectral sensitivity functions of biological dosimeters, using five polychromatic UV sources possessing different emission spectra. Phage T7 and uracil biological dosimeters have been used for measuring the dose rates of the lamps. Their spectral sensitivity functions consisting of two exponential terms have been constructed. The parameters of the spectral sensitivity functions have been determined by comparing the directly measured and calculated dose-rate values. The parameters of the sensitivity function are accepted as correct values when the deviation of the measured and calculated values is a minimum. Based on the deviations between the constructed and the experimentally determined spectral sensitivities with monochromatic sources, the differences between the measured and calculated results are interpreted. The importance of the correct spectral sensitivity data is demonstrated through the effectiveness spectra of a TL 01 lamp for phage T7 killing, uracil dimerization and erythema induction.     

Erythemal Ultraviolet Exposure in Two Groups of Outdoor Workers in Valencia, Spain

UVexposure is considered to be one of the most important risk factors in skin cancers, mainly in outdoor occupational activities. Outdoor workers receive regular and significant solar UV erythemal radiation (UVER). To quantify the UVER exposure of certain groups of workers, dosimeters are used to measure the biologically effective UV radiation received in the course of their daily work. Two groups of outdoor workers, composed of gardeners and lifeguards, were measured for UVER exposure using sensitive spore-film filter-type personal dosimeters (Viospor). The study took place in Valencia, Spain, in June and July 2008, and involved one group of four gardeners and another of five beach lifeguards for a period of 4 and 6 days, respectively. The gardeners' mean UV exposure was 4.13 ± 0.60 SED day⁻¹, where 1 SED is defined as effective 100 J m⁻² when weighted with the CIE erythemal response function, whereas the lifeguards received 11.43 ± 2.15 SED day⁻¹. The mean exposure ratio (ER) relative to ambient of gardeners was 0.09 ± 0.01 and for lifeguards was 0.27 ± 0.05. ER is defined as the ratio between the personal dose on a selected anatomical site and the corresponding ambient dose on a horizontal plane during the same exposure period. The lifeguards received the highest UVER exposure, although both groups had measured UVER exposure in excess of occupational guidelines, indicating that protective measures are necessary.     

Effects of humidity and light on dosimetric properties of clear polymethylmethacrylate

Effects of humidity and light conditions /fluoroscent light, sunlight and diffuse sunlight/ on the response of 2 mm thick clear polymethylmethacrylate /PMMA/ dosimeter during irradiation and during postirradiation storage were determined spectrophotometrically at 305 and 314 nm. The results showed that irradiation of dosimeters at 12–97% relative humidity did not result in any change in the response upto 2 weeks of post-irradiation storage. However, there is some decrease in the response at higher humidities />76%/ for longer storage time. Post-irradiation storage and dosimeters at constant relative humidity conditions between 35 and 97% had no effect on the response up-to 3 weeks. Post-irradiation storage at lower relative humidity /12%/ showed some decrease in the response for longer periods. The response of dosimeter is not very sensitive to short time exposure to diffuse sunlight and fluorescent light. However, a significant increase in the optical density was observed during exposure of dosimeters to direct sunlight.     

Polymer Gel Dosimeters with Increased Solubility: A Preliminary Investigation of the NMR and Optical Dose-Response Using Different Crosslinkers and Co-Solvents

Summary: The potential of ten different crosslinkers was investigated, with the aim of improving the performance of polymer gel dosimeters used for detecting radiation dose distributions generated by cancer radiation therapy equipment. Unfortunately, none of the candidate crosslinkers was shown to be more effective than N,N′-methylene-bisacrylamide, the standard crosslinker used in polymer gel dosimetry applications. Two co-solvents, glycerol and isopropanol, were used to increase the solubility of N,N′-methylene-bisacrylamide crosslinker in polymer gel dosimeter recipes. Using isopropanol, the crosslinker solubility increased from approximately from 3 to 10% by weight, enabling the manufacture of polymer gel dosimeters with much higher levels of crosslinking than was previously possible. The new dosimeter recipes can be imaged effectively using nuclear magnetic resonance and optical techniques, and may be suitable for read-out using x-ray CT (Computed Tomography).