Comparison of two different types of LiF:Mg,Cu,P thermoluminescent dosimeters for detection of beta rays (beta-TLDs) from 90Sr/90Y, 85Kr and 147Pm sources

Safety injections of nuclear medicine radiotracers: towards a new modality for a real-time detection of extravasation events and 18F-FDG SUV data correction

BACKGROUND

¹⁸F-FDG PET/CT imaging allows to study oncological patients and their relative diagnosis through the standardised uptake value (SUV) evaluation. During radiopharmaceutical injection, an extravasation event may occur, making the SUV value less accurate and possibly leading to severe tissue damage. The study aimed to propose a new technique to monitor and manage these events, to provide an early evaluation and correction to the estimated SUV value through a SUV correction coefficient.

METHODS

A cohort of 70 patients undergoing ¹⁸F- FDG PET/CT examinations was enrolled. Two portable detectors were secured on the patients' arms. The dose-rate (DR) time curves on the injected DRⁱⁿ and contralateral DR^con arm were acquired during the first 10 min of injection. Such data were processed to calculate the parameters Δpⁱⁿ_NOR = (DRⁱⁿ_max- DRⁱⁿ_mean)/DRⁱⁿ_max and ΔR_t = (DRⁱⁿ(t) - DR^con(t)), where DRⁱⁿ_max is the maximum DR value, DRⁱⁿ_mean is the average DR value in the injected arm. OLINDA software allowed dosimetric estimation of the dose in the extravasation region. The estimated residual activity in the extravasation site allowed the evaluation of the SUV's correction value and to define an SUV correction coefficient.

RESULTS

Four cases of extravasations were identified for which ΔR_t [(390 ± 26) µSv/h], while ΔR_t [(150 ± 22) µSv/h] for abnormal and ΔR_t [(24 ± 11) µSv/h] for normal cases. The Δpⁱⁿ_NOR showed an average value of (0.44 ± 0.05) for extravasation cases and an average value of (0.91 ± 0.06) and (0.77 ± 0.23) in normal and abnormal classes, respectively. The percentage of SUV reduction (SUV_%CR) ranges between 0.3% and 6%. The calculated self-tissue dose values range from 0.027 to 0.573 Gy, according to the segmentation modality. A similar correlation between the inverse of Δpⁱⁿ_NOR and the normalised ΔR_t with the SUV correction coefficient was found.

CONCLUSIONS

The proposed metrics allowed to characterised the extravasation events in the first few minutes after the injection, providing an early SUV correction when necessary. We also assume that the characterisation of the DR-time curve of the injection arm is sufficient for the detection of extravasation events. Further validation of these hypotheses and key metrics is recommended in larger cohorts.

Response evaluation of two commercial thermoluminescence dosimeters (TLDs) against different parameters

Objectives

It is essential to study the dosimetric performance and reliability of personal dosimeters. This study examines and compares the responses of two commercial thermoluminescence dosimeters (TLDs), the TLD-100 and the MTS-N.

Methods

We compared the two TLDs to various parameters such as energy dependence, linearity, homogeneity, reproducibility, light sensitivity (zero point), angular dependence, and temperature effects using the IEC 61066 standard.

Results

The results acquired showed that both TLD materials show linear behavior as indicated by the quality of the fit. In addition, the angular dependence results for both detectors show that all dose responses are within the range of acceptable values. However, the TLD-100 outperformed the MTS-N in terms of light sensitivity reproducibility for all detectors together, while the MTS-N outperforms the TLD-100 for each detector independently and that showed TLD-100 has more stability than MTS-N. The MTS-N shows better batch homogeneity (10.84%) than TLD-100 (13.65%). The effect of temperature in signal loss was clearer at higher temperature 65°C and it was however below ±30%.

Conclusions

The overall results for dosimetric properties determined in terms of dose equivalents for all combinations of detectors are satisfactory. The MTS-N cards have better results in the energy dependence, angular dependency, batch homogeneity and less signal fading, whereas the TLD-100 cards are less sensitive to light and more reproducible.

Advances in knowledge

Although previous studies showed several types of comparisons between TLDs, they have used limited parameters and different data analysis. This study has dealt with more comprehensive characterization methods and examinations combining TLD-100 and MTS-N cards.

Development of the Composite Thermoluminescent Detectors Based on the Single Crystalline Films and Crystals of Perovskite Compounds

This work is dedicated to the development of new types of composite thermoluminescent detectors based on the single crystalline films of Ce-doped GdAlO₃ perovskite and Mn-doped YAlO₃ and (Lu_0.8Y_0.2)AlO₃:Mn perovskites as well as Ce and Pr-doped YAlO₃ single crystal substrates. These detectors were obtained using the Liquid Phase Epitaxy growth method from the melt solution based on the PbO-B₂O₃ fluxes. Such composite detectors can by applied for the simultaneous registration of different components of mixed ionization fluxes using the differences between the thermoluminescent glow curves, recorded from the film and crystal parts of epitaxial structures. For creation of the new composite detectors, we considered using, for the film and crystal components of epitaxial structures (i) the different perovskite matrixes doped with the same type of activator or (ii) the same perovskite host with various types of activators. The thermoluminescent properties of the different types of epitaxial structures based on the abovementioned films and crystal substrates were examined in the conditions of β-particles and X-ray excitation with aim of determination of the optimal combination of perovskites for composite detectors. It was shown that, among the structures with all the studied compositions, the best properties for the simultaneous thermoluminescent detection of α- and X-rays were the GdAlO₃:Ce film/YAlO₃:Ce crystal epitaxial structure.

Occupational radiation exposure assessment during the management of [68Ga]Ga-DOTA-TOC

Background

Since it was first approved in Europe in 2016, the gallium-68 (⁶⁸Ga) radiopharmaceutical [⁶⁸Ga]Ga-DOTA-TOC has been widely used for imaging of somatostatin receptor (SSTR) positive tumours using positron emission tomography–computed tomography (PET/CT). Significant patient benefits have been reported, so its use is rapidly increasing. However, few studies have been published regarding occupational doses to nuclear medicine personnel handling this radiopharmaceutical, despite its manual usage at low distances from the skin and the beta-emission decay scheme, which may result in an increased absorbed dose to their hands. In this context, this study aims to analyse the occupational exposure during the administration of [⁶⁸Ga]Ga-DOTA-TOC for PET/CT imaging. For this purpose, extremity, eye lens and whole-body dosimetry in terms of Hp(0.07), Hp(3) and Hp(10), respectively, was conducted on six workers with both thermoluminescent dosimeters, and personal electronic dosimeters.

Results

The non-dominant hand is more exposed to radiation than the dominant hand, with the thumb and the index fingertip being the most exposed sites on this hand. Qualitative analysis showed that when no shielding is used during injection, doses increase significantly more in the dominant than in the non-dominant hand, so the use of shielding is strongly recommended. While wrist dosimeters may significantly underestimate doses to the hands, placing a ring dosimeter at the base of the ring or middle finger of the non-dominant hand may give a valuable estimation of maximum doses to the hands if at least a correction factor of 5 is applied. Personal equivalent doses for the eyes did not result in measurable values (i.e., above the lowest detection limit) for almost all workers. The extrapolated annual dose estimations showed that there is compliance with the annual dose limits during management of [⁶⁸Ga]Ga-DOTA-TOC for diagnostics with PET in the hospital included in this study.

Conclusions

Imaging with [⁶⁸Ga]Ga-DOTA-TOC is a safe process for the workers performing the administration of the radiopharmaceutical, including intravenous injection to the patient and the pre- and post-activity control, as it is highly unlikely that annual dose limits will be exceeded if good working practices and shielding are used.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-022-00505-8.

Composite Detectors Based on Single-Crystalline Films and Single Crystals of Garnet Compounds

This manuscript summarizes recent results on the development of composite luminescent materials based on the single-crystalline films and single crystals of simple and mixed garnet compounds obtained by the liquid-phase epitaxy growth method. Such composite materials can be applied as scintillating and thermoluminescent (TL) detectors for radiation monitoring of mixed ionization fluxes, as well as scintillation screens in the microimaging techniques. The film and crystal parts of composite detectors were fabricated from efficient scintillation/TL materials based on Ce³⁺-, Pr³⁺-, and Sc³⁺-doped Lu₃Al₅O₁₂ garnets, as well as Ce³⁺-doped Gd_3−xA_xAl_5−yGa_yO₁₂ mixed garnets, where A = Lu or Tb; x = 0–1; y = 2–3 with significantly different scintillation decay or positions of the main peaks in their TL glow curves. This work also summarizes the results of optical study of films, crystals, and epitaxial structures of these garnet compounds using absorption, cathodoluminescence, and photoluminescence. The scintillation and TL properties of the developed materials under α- and β-particles and γ-quanta excitations were studied as well. The most efficient variants of the composite scintillation and TL detectors for monitoring of composition of mixed beams of ionizing radiation were selected based on the results of this complex study.

Skin dose saving of the staff in 90Y/177Lu peptide receptor radionuclide therapy with the automatic dose dispenser

OBJECTIVE

When handling Y-labelled and Lu-labelled radiopharmaceuticals, skin exposure is mainly due to β-particles. This study aimed to investigate the equivalent dose saving of the staff when changing from an essentially manual radiolabelling procedure to an automatic dose dispenser (ADD).

MATERIALS AND METHODS

The chemist and physician were asked to wear thermoluminescence dosimeters on their fingertips to evaluate the quantity of Hp(0.07) on the skin. Data collected were divided into two groups: before introducing ADD (no ADD) and after introducing ADD.

RESULTS

For the chemist, the mean values (95th percentile) of Hp(0.07) for no ADD and ADD are 0.030 (0.099) and 0.019 (0.076) mSv/GBq, respectively, for Y, and 0.022 (0.037) and 0.007 (0.023) mSv/GBq, respectively, for Lu. The reduction for ADD was significant (t-test with P<0.05) for both isotopes. The relative differences before and after ADD collected for every finger were treated using the Wilcoxon test, proving a significantly higher reduction in extremity dose to each fingertip for Lu than for Y (P<0.05). For the medical staff, the mean values of Hp(0.07) (95th percentile) for no ADD and ADD are 0.021 (0.0762) and 0.0143 (0.0565) mSv/GBq, respectively, for Y, and 0.0011 (0.00196) and 0.0009 (0.00263) mSv/GBq, respectively, for Lu. The t-test provided a P-value less than 0.05 for both isotopes, making the difference between ADD and no ADD significant.

CONCLUSION

ADD positively affects the dose saving of the chemist in handling both isotopes. For the medical staff not directly involved with the introduction of the ADD system, the analysis shows a learning curve of the workers over a 5-year period. Specific devices and procedures allow staff skin dose to be limited.

Application of whole-body personal TL dosemeters in mixed field beta-gamma radiation

Application of whole-body personal TL dosemeters based on a high-sensitivity LiF:Mg,Cu,P (MCP-N) in mixed field beta-gamma radiation has been characterised. The measurements were carried out with (90)Sr/(90)Y, (85)Kr and (137)Cs point sources to calculate the energy response and linearity of the TLD response in a dose range of 0.1-30 mSv. From the result, calibration curves were obtained, enabling the readout of individual dose equivalent Hp(10) from gamma radiation and Hp(0.07) from beta radiation in mixed field beta-gamma. Limitation of the methodology and its application are presented and discussed.