A NEW DOSE DETERMINATION METHOD FOR HP(3) AND DP LENS FOR BETA REFERENCE RADIATION QUALITIES.

For the purpose of obtaining the smaller uncertainties for Hp(3) and Dp lens in 90Sr/90Y beta reference fields, a new dose determination method based on the Monte-Carlo simulation was proposed. The conversion coefficients from the absorbed dose in air, at the reference point of the extrapolation ionisation chamber, Dair, det to Hp(3; α) and the conversion factors from Dair, det to Dp lens(α) were calculated with EGSnrc, respectively, for the irradiation angles from 0° to 60°. Compared with the dose determination method in International Organization for Standardization (ISO) 6980 standard, the uncertainty reductions of 7.7-52.8% for Hp(3; α) and 7.9-55.0% for Dp lens(α) were achieved, respectively. In addition, for the conversion coefficients from the reference absorbed dose DR to Hp(3; α), the calculations were performed for more irradiation conditions, which are not included in the current ISO 6980 standard. For the calculations of the conversion factors from DR to Dp lens(α), the eye and head phantoms with Chinese characteristics were utilised, which makes the conversion factors more suitable for use in China.

Intercomparison of Geant4 low energy electromagnetic models in 90Y dosimetry.

This work shows the comparison between Geant4 low energy electromagnetic physics lists G4EmLi-vermorePhysics, G4EmPenelopePhysics, G4EmLowEPPhysics, and G4EmDNAPhysics_option2 when simulating the energy deposition of low mono-energetic electrons and ß- emitted from 90Y isotope. The simulation time and influence of production cut were considered. In the sense of balance between the accuracy and computer resource, G4EmPenelopePhysics can be proposed as the best physics model for our future Treatment Planning System (TPS) for treating liver cancer using 90Y microsphere radioembolization therapy.

EXPOSURE INHOMOGENEITY FROM 241AM AND 90SR/90Y SOURCES IN TERMS OF THE EYE LENS MONITORING IN THE NUCLEAR FACILITIES.

This article highlights the issues of exposure inhomogeneity that are relative to eye lens monitoring for low-energy photons from 241Am and beta-rays from 90Sr/90Y including a personal protective equipment because eye lens exposure has been concerned more than before due to the proposed reduction of relevant dose limit. These nuclides are common and concerned sources in the nuclear industry. Our previous study presented a quantitative estimation of exposure inhomogeneity, which was applied to simple but typical exposure situations. For the present study, exposure inhomogeneity of 241Am was approximately within a factor of 1.6, implying a more homogeneous situation than expected. Regarding 90Sr/90Y exposure, estimation from both Hp(10) and Hp(0.07) on trunk would lead to an over- or underestimation by a factor of more than 10. In contrast, Hp(3) measurement on trunk will improve by up to a factor of 2. With respect to the personal protective equipment, lead apron and protective glasses are effective for the 60-keV photons for both anterior-posterior and rotational irradiations, while a full-face respirator can reduce the eye lens dose by approximately 17% for 90Sr/90Y betas. As a whole, this study demonstrated that the effect of protective equipment could be effectively incorporated into the homogeneity evaluation.

Evaluation of different methods for measuring 89Sr and 90Sr: Measurement uncertainty for the different methods as a function of the activity ratio.

In case of a radiological emergency situation involving e.g. fission of uranium or plutonium, analysis of radioactive strontium will be of importance. The primary radionuclides of interest are 90Sr, its progeny 90Y and 89Sr. A few days following an event, 89Sr will be the predominant radioisotope of strontium. Most methods found in the literature are valid and applicable when measuring 90Sr, but when samples contain both 89Sr/90Sr interference problematics arise. How these interferences are dealt with will have an effect on the uncertainty of the 90Sr determination. This work aims at evaluating three measurement approaches, all mentioned in the literature, with respect to the measurement uncertainty when determining 90Sr in an emergency preparedness situation and to propose a suitable measurement strategy.

Analysis of radioactive strontium-90 in food by Cerenkov liquid scintillation counting.

A simple liquid scintillation counting method using DGA/TRU resins for removal of matrix/radiometric interferences, Cerenkov counting for measuring 90Y, and EDXRF for quantifying Y recovery was validated for analyzing 90Sr in various foods. Analysis of samples containing energetic ß emitters required using TRU resin to avoid false detection and positive bias. Additional 34% increase in Y recovery was obtained by stirring the resin while eluting Y with H2C2O4. The method showed acceptable accuracy (±10%), precision (10%), and detectability (~0.09Bqkg-1).

Calibration setting numbers for dose calibrators for the PET isotopes (52)Mn, (64)Cu, (76)Br, (86)Y, (89)Zr, (124)I.

For PET radionuclides, the radioactivity of a sample can be conveniently measured by a dose calibrator. These devices depend on a "calibration setting number", but many recommended settings from manuals were interpolated based on standard sources of other radionuclide(s). We conducted HPGe gamma-ray spectroscopy, resulting in a reference for determining settings in two types of vessels containing one of several PET radionuclides. Our results reiterate the notion that in-house, experimental calibrations are recommended for different radionuclides and vessels.

Robustness of plastic scintillation microspheres in the continuous measurement of different river waters.

Plastic scintillation microspheres (PSm) represent one of the most promising options for monitoring alpha and beta radioactivity in river water. For that reason, a study of the stability of PSm packed into a cell against the continuous flow of river water with different degrees of turbidity was performed over a period of 100h. The results showed that the volume of the cell became stable after 15h of pumping and continued to be stable throughout the 100h of the experiment. During this period of time, the detection efficiency of the PSm, in terms of efficiency*volume, presented mean values of 0.75(3)% for (3)H and 272(11)% for (90)Sr/(90)Y. No dependence on flow time or river water type was observed. The background was also constant for 100h and for the different water types, although (222)Rn should be removed from the water beforehand to prevent its accumulation in the PSm. Since PSm did not present any degradation throughout the whole experiment, PSm can undoubtedly be used for monitoring radioactivity with low reagent consumption, low waste generation and low maintenance costs.

Method for rapid screening analysis of Sr-90 in edible plant samples collected near Fukushima, Japan.

A screening method for measuring (90)Sr in edible plant samples by focusing on (90)Y in equilibrium with (90)Sr is reported. (90)Y was extracted from samples with acid, co-precipitated with iron hydroxide, and precipitated with oxalic acid. The dissolved oxalate precipitate was loaded on an extraction chromatography resin, and the (90)Y-enriched eluate was analyzed by Cherenkov counting with a TDCR liquid scintillation counter. (90)Sr ((90)Y) concentration was determined in plant samples collected near the damaged Fukushima Daiichi Nuclear Power Plants with this method.

Calculation of Coincidence Summing Correction Factors for an HPGe detector using GEANT4.

The aim of this paper was to calculate the True Coincidence Summing Correction Factors (TSCFs) for an HPGe coaxial detector in order to correct the summing effect as a result of the presence of (88)Y and (60)Co in a multigamma source used to obtain a calibration efficiency curve. Results were obtained for three volumetric sources using the Monte Carlo toolkit, GEANT4. The first part of this paper deals with modeling the detector in order to obtain a simulated full energy peak efficiency curve. A quantitative comparison between the measured and simulated values was made across the entire energy range under study. The True Summing Correction Factors were calculated for (88)Y and (60)Co using the full peak efficiencies obtained with GEANT4. This methodology was subsequently applied to (134)Cs, and presented a complex decay scheme.

Collimator and energy window optimization for 9°Y bremsstrahlung SPECT imaging: A SIMIND Monte Carlo study.

Treatment efficacy of radioembolization using Yttrium-90 ((90)Y) microspheres is assessed by the (90)Y bremsstrahlung single photon emission computed tomography (SPECT) imaging following radioembolization. The radioisotopic image has the potential of providing reliable activity map of (90)Y microspheres distribution. One of the main reasons of the poor image quality in (90)Y bremsstrahlung SPECT imaging is the continuous and broad energy spectrum of the related bremsstrahlung photons. Furthermore, collimator geometry plays an impressive role in the spatial resolution, sensitivity and image contrast. Due to the relatively poor quality of the (90)Y bremsstrahlung SPECT images, we intend to optimize the medium-energy (ME) parallel-hole collimator and energy window. The Siemens e.cam gamma camera equipped with a ME collimator and a voxelized phantom was simulated by the SImulating Medical Imaging Nuclear Detectors (SIMIND) program. We used the SIMIND Monte Carlo program to generate the (90)Y bremsstrahlung SPECT projection of the digital Jaszczak phantom. The phantom consist of the six hot spheres ranging from 9.5 to 31.8mm in diameter, which are used to evaluate the image contrast. In order to assess the effect of the energy window on the image contrast, three energy windows ranging from 60 to 160 KeV, 160 to 400 KeV, and 60 to 400 KeV were set on a (90)Y bremsstrahlung spectrum. As well, the effect of the hole diameter of a ME collimator on the image contrast and bremsstrahlung spectrum were investigated. For the fixed collimator and septa thickness values (3.28 cm and 1.14 mm, respectively), a hole diameter range (2.35-3.3mm) was chosen based on the appropriate balance between the spatial resolution and sensitivity. The optimal energy window for (90)Y bremsstrahlung SPECT imaging was extended energy window from 60 to 400 KeV. Besides, The optimal value of the hole diameter of ME collimator was obtained 3.3mm. Geometry of the ME parallel-hole collimator and energy window are indeed important indicators of the image quality in (90)Y bremsstrahlung imaging. The obtained optimal ME collimator and optimal energy window have the potential to improve the image contrast of (90)Y bremsstrahlung images. Subsequently, high quality (90)Y bremsstrahlung images can provide reliable estimate of the (90)Y microsphere activity distribution after radioembolization.

Comparison of (90)Y activity measurements in nuclear medicine in Germany.

In 2014, PTB and the company Eckert & Ziegler organized a national comparison exercise to determine the activity of a (90)Y solution. One aim of the comparison was to assess the measurement capability of hospitals and medical practices in Germany. P6-type vials were filled with aliquots of a radioactive (90)Y solution and then sent to 19 participants who were asked to measure the activity in the ampoules as well as in their own standard geometry using syringes. Most of the submitted results have a deviation of less than ±10% from the PTB reference activity when measured in the P6-type vials. The spread is somewhat larger when measured in a syringe geometry. The comparison revealed that some participants have difficulties in applying decay corrections and only a few participants were capable of estimating realistic measurement uncertainties.

Standardisation of (90)Y and determination of calibration factors for (90)Y microspheres (resin) for the NPL secondary ionisation chamber and a Capintec CRC-25R.

The use of (90)Y resin microspheres (SIR-Spheres® microspheres) in Nuclear Medicine has dramatically increased in recent years due to its favourable outcome in the treatment of liver cancer and liver metastases (Rajekar et al., 2011). The measurement of administered activity before and residual activity after treatment in radionuclide calibrators is required to determine total activity delivered to the patient. In comparison with External Beam Radiotherapy (EBRT) where administered doses are often know to within ±5%, the actual administered activity in nuclear medicine procedures may only be known to within ±20% and subsequent dose calculations can result in even larger uncertainties (Fenwick et al., 2009). It is a well-recognised issue that ion chambers are instruments that are sensitive to the measurement geometry and matrix of a source, in particular for pure beta or low energy (<100keV) x-ray emitters (Gadd et al., 2006). This paper presents new calibration factors for NPL secondary standard ionisation chamber system (Vinten 671) and a Capintec CRC-25R radionuclide calibrator along with a discussion of the measurement problems associated with this radionuclide and matrix. Calibration of the NPL secondary standard system for this measurement matrix will enable NPL to provide standards for the Nuclear Medicine community and consequently increase the measurement capability.

MONTE CARLO SIMULATION OF THE BREMSSTRAHLUNG RADIATION FOR THE MEASUREMENT OF AN INTERNAL CONTAMINATION WITH PURE-BETA EMITTERS IN VIVO.

Rapid measurement techniques are required for a large-scale emergency monitoring of people. In vivo measurement of the bremsstrahlung radiation produced by incorporated pure-beta emitters can offer a rapid technique for the determination of such radionuclides in the human body. This work presents a method for the calibration of spectrometers, based on the use of UPh-02T (so-called IGOR) phantom and specific (90)Sr/(90)Y sources, which can account for recent as well as previous contaminations. The process of the whole- and partial-body counter calibration in combination with application of a Monte Carlo code offers readily extension also to other pure-beta emitters and various exposure scenarios.

CALIBRATION OF THERMOLUMINESCENCE AND FILM DOSEMETERS FOR SKIN DOSES FROM HIGH-ACTIVITY MICROPARTICLES.

The use of EXT-RAD™ extremity TLDs and radiochromic film to measure doses from primarily beta-emitting microparticles is discussed. Specific calibration techniques have been developed, using both Monte Carlo modelling and experiments. Results for a (90)Sr/(90)Y microparticle are presented to illustrate the general techniques and to demonstrate reasonable agreement between the dosimetry methods.

DOSE MEASUREMENTS TO THE LENS IN NUCLEAR MEDICINE AND IN FLUOROSCOPY-GUIDED INTERVENTIONAL PROCEDURES: ANALYSIS OF THE RESULTS AND ASSESSMENT OF THE EFFECTIVENESS OF PROTECTIVE EYEWEAR ANTI-X.

The new limit of 20 mSv to the lens raises the need for further assessment of the equivalent dose to the lens for nuclear medicine and interventional radiology operators. (a) A measurement campaign was performed in nuclear medicine, (b) a routine monitoring was organised in interventional procedures and (c) the effectiveness of protective eyewear was assessed. In nuclear medicine, for photon fields, the adequacy of Hp(0.07) of dosemeter worn on the trunk is confirmed; with (90)Y, the annual values of Hp(3) measured in therapeutic session are <5 mSv. In interventional procedures, routine monitoring of the dose to the lens must be maintained where the values of Hp(0.07) dosemeter worn on the trunk are higher than one-third of the new limits. The measures carried out have shown that the attenuation factor mean of the protective glasses is equal to ∼4 (range 1.7-11.4).

Intrahepatic Activity Distribution in Radioembolization with Yttrium-90-Labeled Resin Microspheres Using the Body Surface Area Method--A Less than Perfect Model.

PURPOSE: To retrospectively assess the influence of the parameters of the body surface area (BSA) method in hepatic radioembolization using yttrium-90-labeled microspheres on the determination of the prescribed activity. MATERIALS AND METHODS: Data from 283 consecutive patients treated with radioembolization (BSA method) were included. For interindividual comparisons, activity concentrations (ACs; MBq/mL) were calculated for each liver. The impact of the BSA method parameters was assessed by analysis of variance and pairwise t test with Bonferroni-Holm correction. RESULTS: Prescribed activity was 1.01-2.71 GBq, with BSA, liver volume (LV), tumor burden, and the liver-lung shunt reduction factor (LLS RF) being significant contributing factors to the AC (all P < .0001, analysis of variance). BSA and LV correlated only moderately (ρ = 0.46, P < .0001). Compared with base activity defined by the BSA (median = 1.67 GBq; range, 1.20-2.32 GBq), the activity contribution of tumor burden was small (median = 150 MBq; range, 3-800 MBq). Resulting activities were reduced according to LLS RF by 20% in 12.4% and by 40% in 3.5% of patients. AC was significantly (up to 56%) lower in association with larger LV than in small LV (LV < 1,500 mL vs ≥ 2,500 mL, P < .0001). CONCLUSIONS: In the BSA model, BSA and LV showed only a moderate correlation, resulting in a significantly lower AC in patients with larger livers. Tumor burden percentage contributed little to the prescribed activity because the BSA model did not account for actual LVs and tumor volumes. These inaccuracies may potentially result in underdosage in patients with larger livers, especially if further LLS RF needs to be applied.

Simulation of the dose rate per activity of beta-emitting radionuclides.

The dose rate per activity was simulated for 10 beta-emitting radionuclides and for different activity distributions (point source, areal sources and a semi-infinite volume source). The results are given for 7 different distances from the source (from 0.01 to 2 m) for both contributions: the beta- and electron-emission, and the X- and gamma-emission. Data are provided for both operational quantities and organ doses: Hp(0.07), Hp(3), Hp(10), Hskin and Hlens. Finally, a software applicaton to interpolate the dose rate per activity due to the beta-emission of arbitrary radionuclides is presented and a simple superposition of these data and of gamma-ray dose constants to calculate the total dose rate is described.

Determination of radiostrontium in milk samples by ultra-low-level liquid scintillation counting: a validated approach.

Strontium-90 is a hazardous radionuclide derived from nuclear fission processes, and it decays emitting high-energy beta-particles forming yttrium-90. It may be easily absorbed in humans through several food supply chains, since it is chemically similar to some important biological elements such as potassium and calcium. In this work an analytical method for the determination of radiostrontium in milk by liquid scintillation counting was developed in order to obtain a precise quantification at low activity concentration levels. Moreover, a full validative approach was applied to confirm method reliability. Good analytical performance was obtained by developing an in-house validation model according to Regulation 882/2004/EC and Decision 657/2002/EC with a good selectivity, a decision threshold and detection limit corresponding to 0.003 and 0.006 Bq l⁻¹ (α = ß = 0.05) respectively, a repeatability value, expressed as CV%, equal to 13%, a mean recovery value equal to 102.5% and a measurement uncertainty equal to 11.5%. Strontium and yttrium chemical yields were determined by a reliable analytical method by inductively coupled mass spectrometry, assuring a suitable correction of final result. The results of the method validation, combined with a quality control assurance, performed on a reference material, demonstrated that the procedure represents a substantial improvement in the determination of 9°Sr relating to accurate confirmation analyses.

Comparison of 9°Y and ¹77Lu measurement capability in UK and European hospitals.

Comparison exercises involving (90)Y and (177)Lu were performed during 2009 and 2012, respectively, to assess the measurement capability of hospitals in the UK and Europe. The results from the measurement of a typical liquid solution of (90)Y show that only 40% of participants could measure the solution to within 5% of the certificated value and that a significant -6% bias was present due to the use of non-standard geometries for the calibration of equipment. The results from the measurement of a standard liquid solution of (177)Lu show that 81% of participants could measure to within 5% of the certificated value and in fact 65% of these results were within 2% of the certificated value, showing administered activities can be far more accurately measured for (177)Lu than for (90)Y and that (177)Lu has a far smaller geometry dependence. These studies were performed to identify specific measurement issues in the user community and to identify areas where future research should be focused. In addition to this the work allows the participants to adjust measurement practice and identify key measurement issues.

Development of anthropomorphic hand phantoms for personal dosimetry in 90Y-Zevalin preparation and patient delivering.

Anthropomorphic tissue-equivalent hand phantoms were achieved to measure the extremity dose involved in Zevalin (90)Y-labelling and patient delivering procedure for radioimmunotherapy treatment of non-Hodgkin lymphoma. The extremity doses to hands and wrists of operators were measured by using thermoluminescent detectors mounted on the developed phantoms. Measurements of chest- and lens-equivalent doses performed on a Rando phantom are also reported.