Activity Measurement of (44)Sc and Calibration of Activity Measurement Instruments on Production Sites and Clinics

⁴⁴Sc is a promising radionuclide for positron emission tomography (PET) in nuclear medicine. As a part of the implementation of a production site for ⁴⁴Sc, precise knowledge of the activity of the product is necessary. At the Paul Scherrer Institute (PSI) and the University of Bern (UniBE), ⁴⁴Sc is produced by enriched ⁴⁴CaO-target irradiation with a cyclotron. The two sites use different techniques for activity measurement, namely a dose calibrator at the PSI and a gamma-ray spectrometry system at UniBE and PSI. In this work, the ⁴⁴Sc was produced at the PSI, and samples of the product were prepared in dedicated containers for onsite measurements at PSI, UniBE, and the Institute of Radiation Physics (IRA) in Lausanne for precise activity measurement using primary techniques and for the calibration of the reference ionization chambers. An accuracy of 1% was obtained for the activity measurement, allowing for a precise calibration of the dose calibrator and gamma-ray spectrometry of the two production sites. Each production site now has the capability of measuring ⁴⁴Sc activity with an accuracy of 2%.

Multicenter Study of Quantitative SPECT: Reproducibility of 99mTc Quantitation Using a Conjugated-Gradient Minimization Reconstruction Algorithm

This multicenter study aimed to determine the reproducibility of quantitative SPECT images reconstructed using a commercially available method of ordered-subset conjugate-gradient minimization. Methods: A common cylindric phantom containing a 100 kBq/mL concentration of ^99mTc-pertechnetate solution in a volume of 7 L was scanned under standard imaging conditions at 6 institutions using the local clinical protocol of each. Interinstitutional variation among the quantitative SPECT images was evaluated using the coefficient of variation. Dose calibrator accuracy was also investigated by measuring the same lot of commercially available ^99mTc vials at each institution. Results: The respective radioactivity concentrations under standard and clinical conditions ranged from 95.71 ± 0.60 (mean ± SD) to 108.35 ± 0.36 kBq/mL and from 96.78 ± 0.64 to 108.49 ± 0.11 kBq/mL, respectively. Interinstitutional variation in radioactivity concentration was 4.20%. The bias in the radioactivity concentrations in SPECT images was associated with the accuracy of the dose calibrator at each institution. Conclusion: The reproducibility of the commercially available quantitative SPECT reconstruction method is high and comparable to that of PET, for comparatively large (∼7 L), homogeneous objects.

Comparison of 99mTc Injected Activity with Prescribed Activity in Four Types of Nuclear Medicine Exams

BACKGROUND

99mTc is a radioactive isotope that is obtained by eluting a 99Mo/99mTc generator. (PINSTECH, Islamabad) and used for radionuclide scanning.

OBJECTIVES

The objective of this work is to study the uncertainties in 99mTc activity that exist due to time delay between injection preparation and administration to patients, during the process of gamma camera scanning.

METHODS

Lead canisters were used for storing elution vials and dose calibrator for measuring 99mTc activity in mCi. The activity of preparing 99mTc injection and its administration to patients were compared with the prescribed values of activity recommended in the Society of Nuclear Medicine procedure guidelines.

RESULTS

This study showed that uncertainty in the activity existed in one thyroid patient, 38 bone patients, 5 renal patients and 45 cardiac patients.

CONCLUSION

This uncertainty in activity exists due to time delay between injection preparation and administration to patients, as well as due to residual radionuclide that is not injected into patients and remains in the syringe.

[Administration Accuracy of Automated Infusion Device for PET Using Improved Disposable Kit]

PURPOSE

The AI-300 automated infusion device (Sumitomo Heavy Industries, Ltd., Tokyo, Japan) is subject to administration error as a function of smaller volumes of ¹⁸F-FDG dispensed via a three-way cock supplied with a disposable kit. The present study aimed to validate the administration accuracy of the AI-300 using an improved disposable kit for quantitative positron emission tomography (PET) assessment.

METHODS

We determined administration accuracy between the improved and previous disposable kits by measuring variations in dispensed volumes and radioactive concentrations of ¹⁸F-FDG according to the criteria of the Japanese Society of Nuclear Medicine. A reference value was generated by measuring radioactivity using a standard dose calibrator.

RESULTS

The values obtained using the previous kit deviated from the reference values by a maximum of -10.6%, and the deviation depended on dispensed volumes of ¹⁸F-FDG<0.25 mL. In contrast, the values were relatively stable when using the improved kit with dispensed ¹⁸F-FDG volumes < 0.25 mL. Variations in radioactive concentrations were relatively stable using the improved kit, whereas that of the previous kit was slightly unstable at high radioactive concentrations.

CONCLUSION

The administration accuracy of the AI-300 using the previous kit varied considerably according to smaller dispensed volumes, but the improved kit might alleviate this problem. The present results indicated that the improved disposal kit should be immediately implemented to eliminate uncertainty surrounding quantitative PET findings.

An update on 'dose calibrator' settings for nuclides used in nuclear medicine

BACKGROUND

Most clinical measurements of radioactivity, whether for therapeutic or imaging nuclides, rely on commercial re-entrant ionization chambers ('dose calibrators'). The National Institute of Standards and Technology (NIST) maintains a battery of representative calibrators and works to link calibration settings ('dial settings') to primary radioactivity standards. Here, we provide a summary of NIST-determined dial settings for 22 radionuclides.

METHODS

We collected previously published dial settings and determined some new ones using either the calibration curve method or the dialing-in approach.

RESULTS

The dial settings with their uncertainties are collected in a comprehensive table.

CONCLUSION

In general, current manufacturer-provided calibration settings give activities that agree with National Institute of Standards and Technology standards to within a few percent.

Comparison of 3 Devices for Automated Infusion of Positron-Emitting Radiotracers

The administration accuracy and precision of an automated infusion device for positron-emitting radiotracers are directly associated with bias and variance in the SUVs of ¹⁸F-FDG PET/CT. Therefore, the accuracy of such devices must be confirmed and calibrated at locations in which they are used. The present study aimed to validate the administration accuracy of 3 automated infusion devices for quantitative PET assessment. Methods: Temporal variations as well as variations in radioactive concentrations and dispensed volumes of ¹⁸F-FDG were determined for the M-130, AI-300, and UG-05 automated infusion devices. The total-test dispensed volumes were 25, 20, and 18.5 mL, respectively. A reference value was generated by measuring amounts of radioactivity using a standard dose calibrator. Administration accuracy was validated according to the criteria of the Japanese Society of Nuclear Medicine. Results: The temporal variation in the M-130 and UG-05 for a specified 185 MBq was relatively stable, in the range of -1.60%-0.92% and 1.16%-5.35%, respectively, whereas that in the AI-300 was -0.55%-8.68%. For the M-130 and UG-05 devices, the difference between measured and reference value was in the range of -5%-5%. The values measured by the AI-300 deviated from the reference values by a maximum of 30%, which depends on radioactive concentration and dispensed volume of ¹⁸F-FDG. Conclusion: The administration accuracy of the AI-300 varied considerably under different conditions, but a software update might somewhat improve this. Our findings indicate that dispensed volumes of ¹⁸F-FDG should be carefully considered when the radioactive concentration is high. Administration accuracy should be regularly confirmed at each location to maintain the quality of quantitative PET assessment. The present study provides useful information about how to confirm the administration accuracy of automated infusion devices.

[Effects of Different Containers on Radioactivity Measurements using a Dose Calibrator with Special Reference to 111In and 123I]

Low-energy characteristic x-rays emitted by ¹¹¹In and ¹²³I sources are easily absorbed by the containers of the sources, affecting radioactivity measurements using a dose calibrator. We examined the effects of different containers on the estimated activities. The radioactivities of ¹¹¹In, ¹²³I, ²⁰¹Tl, and ^99mTc were measured in containers frequently employed in clinical practice in Japan. The ¹¹¹In measurements were performed in the vials A and B of the ¹¹¹In-pentetreotide preparation kit and in the plastic syringe. The activities of ¹²³I-metaiodobenzylguanidine and ²⁰¹Tl chloride were measured in the prefilled glass syringes and plastic syringes. The milking vial, vial A, vial B, and plastic syringe were used to assay ^99mTc. For ¹¹¹In and ¹²³I, measurements were performed with and without a copper filter. The filter was inserted into the well of the dose calibrator to absorb low-energy x-rays. The relative estimate was defined as the ratio of the activity estimated with the dose calibrator to the standard activity. The estimated activities varied greatly depending on the container when ¹¹¹In and ¹²³I sources were assayed without the copper filter. The relative estimates of ¹¹¹In were 0.908, 1.072, and 1.373 in the vial A, vial B, and plastic syringe, respectively. The relative estimates of ¹²³I were 1.052 and 1.352 in the glass syringe and plastic syringe, respectively. Use of the copper filter eliminated the container-dependence in ¹¹¹In and ¹²³I measurements. Container-dependence was demonstrated in neither ²⁰¹Tl nor ^99mTc measurements. The activities of ¹¹¹In and ¹²³I estimated with a dose calibrator differ greatly among the containers. Accurate estimation may be attained using the container-specific correction factor or using the copper filter.

Deviation in the predefined calibration factors of the dose calibrators and the associated inaccuracy in the radioactivity measurements of beta-gamma emitters

Aim:

To determine whether the predefined calibration factors of the dose calibrators can provide accurate radioactivity measurements of beta-gamma emitters used in routine therapeutic nuclear medicine procedures.

Materials and Methods:

Two models of dose calibrators were used in the present study for radioactivity measurements of ¹⁵³Sm ethylenediamine-N, N, N’, N’-tetrakis methylene phosphonic acid (EDTMP) and ¹⁷⁷Lu (EDTMP). A known (precalibrated) activity of each of the two beta emitters received by us from our National Supplier for administration to the patients with extensive bony metastases for bone pain palliation, was used for experiments.

Results:

When we used the manufacturers’ provided dial setting of 450 × 10, each of the dose calibrators underestimated the radioactivity of ¹⁷⁷Lu by about 9.0%. Dial settings of 403 × 10 and 408 × 10 for ¹⁷⁷Lu on CRC-15R and CRC-ultra dose calibrators respectively were calculated experimentally using an iterative approach. The radioactivity measurements made at these settings provided an excellent agreement with the specified values. Likewise, a dial setting of 230 for each of the two dose calibrators was calculated for ¹⁵³Sm, which provided a good agreement between the experimentally derived radioactivity values and the certified values. A deviation of ± 5.0% was observed when radioactivity of ¹⁷⁷Lu and ¹⁵³Sm was measured over a wide range (4.0 MBq to 2.1 GBq) for time intervals equivalent to 4.5 half-lives of each of the two radionuclides. A deviation of ± 5% was observed when radioactivity was counted in different dilution volumes and in syringes of varying size.

Conclusion:

These variations could lead to a cumulative error of about 20.0% toward the inaccuracy in the radioactivity measurements of the beta-gamma emitters and thus predefined calibration factors of the dose calibrators may require experimental re-setting of these parameters and periodic checking to provide accurate radioactivity estimates of beta-gamma emitters in a given clinical setting.