Radiation Calibration Laboratory Research Articles

Testing the NASA BioSentinel Pixel Dosimeter Using Gamma-ray and Neutron Sources at the LLNL Calibration Lab.

The objective of this paper is to evaluate the accuracy of the NASA BioSentinel Pixel Dosimeter (BPD) using gamma-ray and neutron sources in a standard calibration lab. The dosimeter tested here is the ground-based version of the BPD that will be onboard the BioSentinel mission. The BPD was exposed to radiation from 60Co, 137Cs, and 252Cf at selected distances (dose rates) at the Lawrence Livermore National Laboratory (LLNL) Radiation Calibration Laboratory (RCL), and the results were compared with NIST traceable benchmark values. It is recognized that these sources are not analogs for the space environment but do provide direct comparisons between BPD response and well characterized calibration lab values. For gamma rays, the BPD measured absorbed dose agrees to ≤ 3.8% compared with RCL benchmark values. For neutrons, the results show that the BPD is insensitive, i.e., the BPD detected only the gamma-ray dose component from 252Cf. The LET spectra obtained for gamma rays from 60Co and 252Cf are consistent with expectations for these gamma-ray energies, but the LET spectrum from the 137Cs gamma rays differs substantially. The potential causes for this difference are the high dose rate from 137Cs and the lower secondary electron energy produced by 137Cs gamma rays. However, neither of these results in errors in the absorbed dose. Based on comparisons with NIST-traceable standards, it is evident that the BPD can measure absorbed dose accurately from low LET charged particles. The sensor's insensitivity to neutrons is unlikely to be a limitation for the BioSentinel mission due to the expected low secondary neutron fluence.

A thermal neutron source for the CERN radiation Calibration Laboratory

This work presents the design, construction and experimental characterisation of a lightweight and low-cost thermal neutron assembly, to be used with the existing Am–Be source irradiator of CERN radiation Calibration Laboratory (Cal Lab). The assembly consists of a cylindrical moderator (18 cm diameter, 25.5 cm height and 5.5 kg weight) and an optional reflector box (5 cm thick walls, 20 kg weight). The moderator is tailored to fit on the Am–Be source in its irradiation position, while the box encloses the detector under test during the irradiation. The exposure volume delimited by the box is 30 × 30 × 30 cm3. The thermal neutron fluence at the exposure location, i.e., 30 cm from the source, was optimized by FLUKA Monte Carlo (MC) simulations. The simulations were validated with measurements performed with a bare 3He proportional counter. The thermal neutron fluence at the nominal irradiation position is 7.43 × 102 cm−2s−1 with the cylindrical moderator only, and 5.75 × 103 cm−2s−1 with the cylinder and the reflector box, with the detector placed at the centre of the box. The thermal neutron fluence inside the box is rather uniform (variation <5%).

PERFORMANCE OF HANDHELD NAI(TL) SPECTROMETERS AS DOSIMETERS BY LABORATORY AND FIELD DOSE RATE MEASUREMENTS.

In the framework of the IAEA Coordinated Research Project (CRP) J02012 on 'Advancing Radiation Detection Equipment for Detecting Nuclear and Other Radioactive Material Out of Regulatory Control', the properties of two commercial instruments (1) InSpector 1000 analyzer (Canberra), with a 2″×2″ NaI(Tl) scintillator and (2) RIIDEYE M-G3 analyzer (Thermo Scientific), with a 3″×3″ NaI(Tl) scintillator, were evaluated as dosimeters by laboratory and field measurements. In the Ionizing Radiation Calibration Laboratory (IRCL) of the Greek Atomic Energy Commission, the NaI(Tl) spectrometers were tested in order to measure Ambient gamma Dose Equivalent Rate (ADER). The NaI(Tl) scintillators were irradiated in a homogeneous field with 662 keV photons with different ADER values from 0.17 to 100μSv h-1 at 0° incidence (irradiation field perpendicular to the detector's front window) and at 90° incidence. For each irradiation, the measured ADER by the spectrometers and the 'true' ADER values (provided by the IRCL) were compared. In addition, the angular dependence (0-359°) of the ADER response of the spectrometers was studied with a 152Eu source placed at 1, 2 and 3m from the spectrometers. The ADER dependence as function of the distance from the 152Eu source (at 0° incidence) measured by the two detectors was compared with the theoretical one. In the field studies, ADER was measured by the spectrometers at seven locations belonging to the Greek Early Warning System Network (which is based on Reuter-Stokes ionization chambers). These locations have different ADER values ranging from 20 to 120 nSv h-1. In these locations, gamma ADER were also deduced (1) by in situ gamma spectrometry measurements with portable Germanium HPGe detectors and (2) by the Reuter-Stokes ionization chambers (by subtraction of the cosmic radiation). Gamma dose measurements were also performed with the InSpector 1000 and RIIDEYE M-G3 detectors in 25 locations (beaches) of Northern Greece and compared with the ADER values deduced by sand sample analysis with gamma spectroscopy. Beaches with sand are good candidates for such type of measurements since they are commonly flat and in principle the natural radionuclides are homogenously distributed.

Influence of the exposure time in the area monitors at radiodiagnostic

Area monitoring ensures radiation exposure at an acceptable level, which must be lower than the legal limit. Experimental measurements were taken in an ionizing radiation calibration laboratory. The specified reference radiation to radiation protection N80 was used. Five area monitors were used. The ranges of dose rate inaccuracy measured in rate mode for times ≤ 2 and ≥ 3s were from 10 to 48% and from 1 to 15%, respectively. The inaccuracy ranges measured in integrated mode for times ≤ 2 and ≥ 3s were from 4 to 8% and from 0 to 22%, respectively.

TEMPORAL DEPENDENCE OF THE RADIATION MONITORING INSTRUMENTS FOR AREA MONITORING USED AT RADIODIAGNOSTIC AND INTERVENTION FACILITIES.

Area monitoring is a fundamental test at radiodiagnostic facilities to maintain an acceptable level of radiation exposure for employees and members of the public. Experimental measurements were taken in an ionising radiation calibration laboratory. Four area monitor instruments were used. Dose and dose rate measurements were measured in integrated and rate operating modes. The results show that precautions are necessary where the area monitor uses exposure times of ≤2 s. When taking measurements in rate mode for times ≤2 s, the area monitors evaluated show a tendency to underestimate dose rate, the inaccuracy was 41 %, and varied between 34 and 45 % for different energies. It is highly recommendable to work in integrated mode, inaccuracy varied from 2 to 35 %. For measurements taken with exposure times of ≥3 s, the average inaccuracy was 15 % and the range was between 2 and 41 %.

Evaluation of surface dose outside the treatment area for five breast cancer irradiation modalities using thermo-luminescent dosimeters

Purpose: To measure and compare the surface dose outside the treatment area at six different points of interest (POIs) for five different breast cancer radiation treatment modalities by using thermo-luminescent dosimeters (TLDs). This experiment will evaluate the magnitude of the dose due to scatter and leakage radiation at different areas outside the target on a patient that could potentially lead, in the long term, to radiation induced secondary malignancies. Methods: TLD-100 were calibrated according to the University of Wisconsin Radiation Calibration Laboratory protocol and then used for dose measurements at selected POIs namely sternum, lower abdomen, contralateral breast, thyroid, shoulder, and eye. Twenty five breast cancer patients and the following modalities were included in this study: Strut-adjusted volume implant (SAVI), mammosite multi-lumen (ML), Accuboost, electron boost and photon boost. The surface doses in all patients were measured in a single fraction. The delivered target doses were normalized to 200 cGy. Finally, breast quadrant analysis was performed. Results: The maximum average dose for each POI was as follows: Sternum 6.51 cGy (SD 2.93), lower abdomen 4.50 cGy (SD 2.63), contralateral breast 8.52 cGy (SD 3.86), thyroid 5.50 cGy (SD 2.75), shoulder 5.58 cGy (SD 2.77), and eye 2.65 cGy (SD 0.68). The highest POI dose of 15.84 cGy was found in contralateral breast. Conclusion: The measured surface dose at each POI varies with the modality of treatment. The surface doses show a strong correlation to the tumor bed location in the breast quadrant. The SAVI, electron boost, and photon boost modalities had delivered smaller surface dose at POIs than the Accuboost and Mammosite ML modalities. While the measured doses fall within the low range, its significance in producing second malignancies would require a large cohort of patients and a longer follow up.

Photon beam audits for radiation therapy clinics: a pilot mailed dosemeter study in Turkey

A thermoluminescent dosemeter (TLD) mailed dose audit programme was performed at five radiotherapy clinics in Turkey. The intercomparison was organised by the University of Wisconsin Radiation Calibration Laboratory (UWRCL), which was responsible for the technical aspects of the study including reference irradiations, distribution, collection and evaluation. The purpose of these audits was to perform an independent dosimetry check of the radiation beams using TLDs sent by mail. Acrylic holders, each with five TLD chips inside and instructions for their irradiation to specified absorbed dose to water of 2 Gy, were mailed to all participating clinics. TLD irradiations were performed with a 6 MV linear accelerator and (60)Co photon beams. The deviations from the TL readings of UWRCL were calculated. Discrepancies inside the limits of ±5 % between the participant-stated dose, and the TLD-measured dose were considered acceptable. One out of 10 beams checked was outside this limit, with a difference of 5.8 %.

SU‐FF‐T‐276: Utilization of Conebeam CT to Accurately Assess TLD Placement for In‐Vivo Dosimetry

Purpose: Assessing the predicted dose at the thermoluminescent dosimeter (TLD) location is one of difficulties when utilizing in‐vivo TLD dosimetry. Accurate dose prediction at the exact TLD location increases confidence in the measured TLD results. Method and Materials: Prior to localization and treatment, TLDs are placed according to physician's direction. A conebeam CT (CBCT) image set, in treatment position and encompassing all TLD locations, is obtained. The patient's treatment is delivered and the TLDs are sent for analysis (University of Wisconsin, Radiation Calibration Laboratory). The acquired CBCT image set is imported into the Eclipse treatment planning computer and the data set is rigidly fused with the initial treatment planning simulation CT data set. The TLDs are visible on the CBCT data set, allowing for visualization of the TLD location on initial planning CT which contains the calculated dose distribution. The calculated dose at the exact location of the TLD is obtained for comparison to the measured TLDs. Thus, the calculated dose at the exact TLD position is obtained for comparison to the measured TLD results. From 2008 – 2009, three patients underwent treatment for scalp lesions, resulting in twelve TLD measurements from the above described technique. Results: All TLD results were corrected for contribution from the CBCT acquisition. The percentage agreement of measured vs. predicted TLD doses was 0.2 ± 7.5 %. Conclusion: These results indicate that CBCT can be used to predict the dose at the exact TLD location during treatment within 10%. Additionally, CBCT removes uncertainty in TLD location on the patient at the time of exposure.

Calibration, performance and type testing of personal dosemeters used in ionising-radiation applications in Greece

Active Personal Dosemeters (APDs) are widely used in real-time personal dosimetry. Their performance, operational characteristics and limitations, as well as their calibration should be routinely checked to assure satisfactory operation and safe use. This study summarises the results of such type tests and calibrations performed in almost 4750 dosemeters at Ionising Radiation Calibration Laboratory (HIRCL) of Greek Atomic Energy Commission (GAEC). About 13.8% of the pencil type and 4.3% of the electronic dosemeters were found to be out of limits of acceptable performance. For the pencil type dosemeters, the mean calibration factor (CF+/-SD) for high- and low-dose categories was found to be 1.014+/-0.102 (range 0.793-1.458) and 0.995+/-0.059 (range 0.794-1.311), respectively. Of these >85% of them had reproducibility better than 90%, while <1% showed remarkable non-linearity and approximately 10% of them failed to retain the dose reading within the limits after 24 h. For the electronic dosemeters, the mean CF was 1.034+/-0.046 (range 0.967-1.238). The majority of them showed good reproducibility and linearity results while, after irradiation, the dose readings were not shifted through time. The energy response varies with the dosemeter type, reaching in one dosemeter type down to 50%. Both electronic and pencil did not showed electronic equilibrium problems.

Scattered Neutron Calibration Fields of KAERI

Some scattered neutron fields for the calibration of personal dosemeters and survey meters used for radiation protection purpose were constructed in the Radiation Calibration Laboratory (RCL) of Korea Atomic Energy Research Institute (KAERI). The radionuclide sources of 252Cf and 241AmBe were used for producing the neutron calibration fields with not so much different method recommended by ISO. The calibration points of interest were behind the shadow objects and the concrete wall in the irradiation room. In order to characterize the neutron calibration fields at the point of test, the spectral neutron fluence rate was determined by means of the Bonner Multi-sphere Spectrometry System (BMSS) and the measured spectra unfolded using the BUNKI code. This paper shows the dosimetric data available for calibration and the feasibility of use as the Realistic Neutron Calibration Fields (RNCF) of KAERI.

Determination of Neutron Room Scattering Corrections in RCL's Calibration Facility at KAERI

Neutron room scattering corrections that should be made when neutron detectors are calibrated with a D 2 O moderated 252 Cf neutron source in the centre of a calibration room are considered. Such room scattering corrections are dependent on specific neutron source type, detector type, calibration distance, and calibration room configuration. Room scattering corrections for the responses of thermoluminescence dosemeter and two different types of spherical detectors to a neutron source in the Radiation Calibration Laboratory (RCL) neutron calibration facility at the Korea Atomic Energy Research Institute (KAERI) were experimentally determined and are presented. The measured room scattering results are then compared with theoretical results calculated by predicting room scattering effects in terms of parameters related to the specific configuration. Agreement between measured and calculated scattering correction is generally about 10% for three kinds of detectors in the calibration facility.

Neutron Spectral Measurements at ORNL

Bonner multisphere spectrometry was used to measure the neutron spectra at several representative working fields at the Transuranium Processing Plant of the Oak Ridge National Laboratory (ORNL). The spectrum of an uncommon calibration source in use at the ORNL's Radiation Calibration Laboratory, a 252Cf moderated by a 15 cm radius polyethylene sphere, was also measured using the same multisphere technique. Thorough calibration of the spectrometer system was first made. The spectral measurements are presented and the results are discussed in detail.