Standardisation and decay data of 177Lu and 188Re

Activity standardisation of 177Lu

177Lu decays through low-energy β-- and γ-emissions in addition to conversion and Auger electrons. To support the use of this radiopharmaceutical in Switzerland, a 177Lu solution was standardised using the β-γ coincidence technique, as well as the TDCR method. The solution had no 177mLu impurity. Primary coincidence measurements, with plastic scintillators for beta detection, were carried out using both analogue and digital electronics. TDCR measurements using only defocusing were also made. Monte Carlo calculations were used to compute the detection efficiency. The coincidence measurements with both analogue and digital electronics are compatible within one standard uncertainty, but they are lower than (and discrepant with) the TDCR measurements. An ampoule of this solution was submitted to the BIPM as a contribution to the Système International de Référence.

Estimation of relative biological effectiveness of 225Ac compared to 177Lu during [225Ac]Ac-PSMA and [177Lu]Lu-PSMA radiopharmaceutical therapy using TOPAS/TOPAS-nBio/MEDRAS

AIM

Over recent years, [225Ac]Ac-PSMA and [177Lu]Lu-PSMA radiopharmaceutical therapy have evolved as a promising treatment option for advanced prostate cancer. Especially for alpha particle emitter treatments, there is still a need for improving dosimetry, which requires accurate values of relative biological effectiveness (RBE). To achieve that, consideration of DNA damages in the cell nucleus and knowledge of the energy deposition in the location of the DNA at the nanometer scale are required. Monte Carlo particle track structure simulations provide access to interactions at this level. The aim of this study was to estimate the RBE of 225Ac compared to 177Lu. The initial damage distribution after radionuclide decay and the residual damage after DNA repair were considered.

METHODS

This study employed the TOol for PArtcile Simulation (TOPAS) based on the Geant4 simulation toolkit. Simulation of the nuclear DNA and damage scoring were performed using the TOPAS-nBio extension of TOPAS. DNA repair was modeled utilizing the Python-based program MEDRAS (Mechanistic DNA Repair and Survival). Five different cell geometries of equal volume and two radionuclide internalization assumptions as well as two cell arrangement scenarios were investigated. The radionuclide activity (number of source points) was adopted based on SPECT images of patients undergoing the above-mentioned therapies.

RESULTS

Based on the simulated dose-effect curves, the RBE of 225Ac compared to 177Lu was determined in a wide range of absorbed doses to the nucleus. In the case of spherical geometry, 3D cell arrangement and full radionuclide internalization, the RBE based on the initial damage had a constant value of approximately 2.14. Accounting for damage repair resulted in RBE values ranging between 9.38 and 1.46 for 225Ac absorbed doses to the nucleus between 0 and 50 Gy, respectively.

CONCLUSION

In this work, the consideration of DNA repair of the damage from [225Ac]Ac-PSMA and [177Lu]Lu-PSMA revealed a dose dependency of the RBE. Hence, this work suggested that DNA repair is an important aspect to understand response to different radiation qualities.

Simple model for estimation of absorbed dose by organs and tumors after PRRT from a single SPECT/CT study

Background

Following each cycle of peptide receptor radionuclide therapy (PRRT), absorbed doses by tumors and normal organs are typically calculated from three quantitative single-photon emission computed tomography (SPECT)/computed tomography (CT) studies acquired at t₁ = 24 h, t₂ = 96 h, t₃ = 168 h after the first cycle of treatment and from a single study at t₁ after the subsequent cycles. In the present study, we have assessed the feasibility of a single SPECT/CT study after each PRRT cycle using a trained multiple linear regression (MLR) model for absorbed dose calculation and have evaluated its impact on patient management. Quantitative [¹⁷⁷Lu]-DOTA-TATE SPECT/CT data after PRRT of seventy-two consecutive metastatic neuroendocrine tumors patients were retrospectively evaluated. A set of 40 consecutive studies was used to train the MLR model. The two independent variables of the model included the time of imaging after administration of the treatment and the radiopharmaceutical activity concentration in a given  organ/tumor. The dependent variable was the dose absorbed by the organ/tumor obtained with the standard protocol. For bone marrow dosimetry, the independent variables included the time of imaging, and the blood and remainder of the body activity concentration. The model was evaluated in 32 consecutive patients. Absorbed doses were assessed for kidneys, bone marrow, liver, spleen and tumor sites.

Results

There was no difference in management decisions, whether PRRT can be safely continued or not because unsafe absorbed dose to risk organs between the standard and the MLR model-based protocol using a single SPECT/CT study performed at t₃ = 168 h after the first cycle and at t₁ = 24 h after the subsequent cycles. Cumulative absorbed doses were obtained with mean relative differences of − 0.5% ± 5.4%, 1.6% ± 15.1%, − 6.2% ± 7.3%, − 5.5% ± 5.8% and 2.9% ± 12.7% for kidneys, bone marrow, liver, spleen and tumors, respectively (Pearson’s r correlation coefficient 0.99, 0.91, 0.99, 0.99 and 0.97, respectively).

Conclusion

Dosimetry calculations using a MLR model with a single SPECT/CT study are in good agreement with the standard protocol, while avoiding the use of dosimetry software and enabling improved patient comfort and reduced scanner and staff time.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-021-00409-z.

Dosimetry after peptide receptor radionuclide therapy: impact of reduced number of post-treatment studies on absorbed dose calculation and on patient management

Background

After each cycle of [¹⁷⁷Lu]-DOTA-TATE peptide receptor radionuclide therapy (PRRT) dosimetry is performed to enable precise calculation of the radiation-absorbed dose to tumors and normal organs. Absorbed doses are routinely calculated from three quantitative single-photon emission computed tomography (SPECT) studies corrected by computed tomography (CT) acquired at t₁ = 24 h, t₂ = 96 h, and t₃ = 168 h after the first cycle of treatment. After following cycles, a single SPECT/CT study is performed. The aim of the present study is to assess the feasibility of a “two time point” quantitative SPECT/CT protocol after the first PRRT cycle and its impact on patient management.

Quantitative SPECT/CT data of 25 consecutive patients with metastatic neuroendocrine tumors after PRRT were retrospectively analyzed. Radiation-absorbed doses calculated using the standard protocol with three SPECT/CT studies acquired at (t₁, t₂, t₃) were compared to those obtained from three different “two time point” protocols with SPECT/CT studies performed at (t₁, t₂), (t₁, t₃), or (t₂, t₃).

Results

The best agreement for the cumulative doses absorbed by the kidneys, bone marrow, liver, spleen, and tumors with the conventional protocol was obtained with the (t₁, t₃) protocol with mean relative differences of − 1.0% ± 2.4%, 0.4% ± 3.1%, − 0.9% ± 4.0%, − 0.8% ± 1.1%, and − 0.5% ± 2.0%, respectively, and correlation coefficients of r = 0.99 for all.

In all patients, there was no difference in the management decision of whether or not to stop PRRT because of unsafe absorbed dose to risk organs using either the standard protocol or the (t₁, t₃) protocol.

Conclusion

These preliminary results demonstrate that dosimetry calculations using two quantitative SPECT/CT studies acquired at 24 and 168 h after the first PRRT cycle are feasible and are in good agreement with the standard imaging protocol with no change in patient management decisions, while enabling improved patient comfort and reduced scanner and staff time.

Preliminary Studies of 177Lu-Diethylenetriamine Penta-Acetic Acid-Deoxyglucose in Hepatic Tumor-Bearing Mice

Objective: The purpose of this study was to explore the potential use of ¹⁷⁷Lu-diethylenetriamine penta-acetic acid-deoxyglucose (¹⁷⁷Lu-DTPA-DG) as a radiopharmaceutical for hepatic tumor treatment. Methods: Lutetium-177 (¹⁷⁷Lu) was labeled with DTPA-DG by adding 2 mCi ¹⁷⁷LuCl₃ to 0.05 mg DTPA-DG (pH 5-6) at room temperature for 1 h. The quality of the¹⁷⁷Lu-DTPA-DG solutions was determined by thin-layer chromatography and high-performance liquid chromatography. Cellular uptake studies with ¹⁸F-fluorodeoxyglucose (FDG), ¹⁷⁷Lu-DTPA-DG and ¹⁷⁷Lu-DTPA and a blocking study with 1.0 mg d-glucose were performed. Biodistribution, imaging, and radiotherapy studies of ¹⁷⁷Lu-DTPA-DG were performed with the SMMC-7721 model. Results: ¹⁷⁷Lu-DTPA-DG had a high radiochemical purity (>97%). The cellular uptake of ¹⁷⁷Lu-DTPA-DG was much higher than that of the ¹⁷⁷Lu-DTPA. The biodistribution of ¹⁷⁷Lu-DTPA-DG demonstrated that the complex accumulated in the tumor with high tumor/blood and tumor/muscle ratios. The tumors in mice in the ¹⁷⁷Lu-DTPA-DG group clearly displayed the high uptake of ¹⁷⁷Lu-DTPA-DG. After radiotherapy with ¹⁷⁷Lu-DTPA-DG, tumor growth decreased, and the overall survival was longer than that in the ¹⁷⁷LuCl₃ group (268.58 ± 17.96 mm³ vs. 507.43 ± 55.72 mm³, p = 0.002) and the normal saline group (268.58 ± 17.96 mm³ vs. 483.68 ± 27.51 mm³, p < 0.05). Conclusions: This preliminary study suggests that ¹⁷⁷Lu-DTPA-DG has the potential to become a liver radiopharmaceutical agent and should be further investigated.

Predictive power of the post-treatment scans after the initial or first two courses of [177Lu]-DOTA-TATE

BACKGROUND

The aim of this study was to evaluate the predictive power of the absorbed dose to kidneys after the first course of treatment with [¹⁷⁷Lu]-DOTA-TATE for neuroendocrine tumors (NETs) on the cumulative kidney absorbed dose after 3 or 4 cycles of treatment. Post-treatment scans (PTS) are acquired after each cycle of peptide receptor radionuclide therapy (PRRT) with [¹⁷⁷Lu]-DOTA-TATE for personalized radiation dosimetry in order to ensure a cumulative absorbed dose to kidneys under a safety threshold of 25 Gy. One hundred eighty-seven patients who completed treatment with [¹⁷⁷Lu]-DOTA-TATE and underwent PTS for dosimetry calculation were included in this retrospective study. The correlation between the cumulative absorbed dose to kidneys after the completion of treatment and the absorbed dose after the first cycle(s) was studied. Multilinear regression analysis was done to predict the cumulative absorbed dose to the kidneys of the subsequent cycles, and an algorithm for the follow up of kidney absorbed dose is proposed.

RESULTS

Patients whose absorbed dose to kidneys after the first cycle of treatment is below 5.6 Gy can receive four cycles of treatment with a cumulative dose less than 25 Gy (p < 0.1). For the other patients, the cumulative absorbed dose after 3 or 4 cycles of treatment can be predicted after the second cycle of treatment to allow for an early decision regarding the number of cycles that may be given.

CONCLUSIONS

The follow up of kidney absorbed dose after PRRT can be simplified with the algorithm presented in this study, reducing by one-third the number of post-treatment scans and reducing hospitalization time for more than half of the treatment cycles.

A dosimetry procedure for organs-at-risk in 177Lu peptide receptor radionuclide therapy of patients with neuroendocrine tumours

PURPOSE

Peptide receptor radionuclide therapy with ¹⁷⁷Lu-DOTATATE has become a standard treatment modality in neuroendocrine tumours (NETs). No consensus has yet been reached however regarding the absorbed dose threshold for lesion response, the absorbed dose limit to organs-at-risk, and the optimal fractionation and activity to be administered. This is partly due to a lack of uniform and comparable dosimetry protocols. The present article details the development of an organ-at-risk dosimetry procedure, which could be implemented and used routinely in a clinical context.

METHODS

Forty-seven patients with NETs underwent ¹⁷⁷Lu-DOTATATE therapy. Three SPECT/CT images were acquired at 4, 24 and 144-192 h post-injection. Three blood samples were obtained together with the SPECT/CT acquisitions and 2 additional samples were obtained around 30 min and 1 h post-injection. A bi-exponential fit was used to compute the source organ time-integrated activity coefficients. Coefficients were introduced into OLINDA/EXM software to compute organ-at-risk absorbed doses. Median values for all patients were computed for absorbed dose coefficient D/A₀ and for late effective half-life T_1/2eff for kidneys, spleen and red marrow.

RESULTS

Dosimetry resulted in a median[interquartile range] of 0.78[0.35], 1.07[0.58] and 0.028[0.010] Gy/GBq for D/A₀ and of 55[9], 71[9] and 52[18] h for T_1/2eff for kidneys, spleen and red marrow respectively.

CONCLUSIONS

A dosimetry procedure for organs-at-risk in ¹⁷⁷Lu-DOTATATE therapy based on serial SPECT/CT images and blood samples can be implemented routinely in a clinical context with limited patient burden. The results obtained were in accordance with those of other centres.

Reducing the number of CTs performed to monitor personalized dosimetry during peptide receptor radionuclide therapy (PRRT)

Background

Peptide receptor radionuclide therapy (PRRT) with [¹⁷⁷Lu]-DOTA-TATE is an effective treatment of neuroendocrine tumors (NETs). After each cycle of treatment, patient dosimetry evaluates the radiation dose to the risk organs, kidneys, and bone marrow, the most radiosensitive tissues. Absorbed doses are calculated from the radioactivity in the blood and from single photon emission computed tomography (SPECT) images corrected by computed tomography (CT) acquired after each course of treatment. The aim of this work is to assess whether the dosimetry along all treatment cycles can be calculated using a single CT. We hypothesize that the absorbed doses to the risk organs calculated with a single CT will be accurate enough to correctly manage the patients, i.e., whether or not to continue PRRT.

Twenty-four patients diagnosed with metastatic NETs undergoing PRRT with [¹⁷⁷Lu]-DOTA-TATE were retrospectively included in this study. We compared radiation doses to the kidneys and bone marrow using two protocols. In the “classical” one, dosimetry is calculated based on a SPECT and a CT after each treatment cycle. In the new protocol, dosimetry is calculated based on a SPECT study after each cycle but with the first acquired CT for all cycles.

Results

The decision whether or not to stop PRRT because of unsafe absorbed dose to the risk organs would have been the same had the classical or the new protocol been used. The agreement between the cumulative doses to the kidneys and bone marrow obtained from the two protocols was excellent with Pearson’s correlation coefficients r = 0.95 and r = 0.99 (P < 0.0001) and mean relative differences of 5.30 ± 6.20% and 0.48 ± 4.88%, respectively.

Conclusions

Dosimetry calculations for a given patient can be done using a single CT registered to serial SPECTs. This new protocol reduces the need for a hybrid camera in the follow-up of patients receiving [¹⁷⁷Lu]-DOTA-TATE.

Accuracy and precision assessment for activity quantification in individualized dosimetry of 177Lu-DOTATATE therapy

Background

In order to obtain a reliable ¹⁷⁷Lu-DOTATATE therapy dosimetry, it is crucial to acquire accurate and precise activity measurements with the radionuclide calibrator, the SPECT/CT camera, and the NaI(Tl) well counter. The aim of this study was to determine, in a clinical context, the accuracy and the precision of their activity quantification over a range of activities and time.

Ninety-three ¹⁷⁷Lu sources from the manufacturer were measured in the radionuclide calibrator over 2.5 years to evaluate its calibration accuracy and precision compared to the manufacturer’s value. A NEMA 2012/IEC 2008 phantom was filled with a ¹⁷⁷Lu activity concentration sphere-to-background ratio of five. It was acquired with the SPECT/CT camera to determine the reconstruction parameters offering the best compromise between partial volume effect and signal-to-noise ratio. The calibration factor was computed accordingly. The calibration quality was monitored over 2.5 years with 33 phantom acquisitions with activities ranging from 7040 to 0.6 MBq. Home-made sources were used to calibrate the well counter. Its reliability was evaluated with activities ranging from 150 to 0.2 kBq measured 34 times over 2.5 years.

Results

For the radionuclide calibrator, median [interquartile range] for the error on activity measurement was −0.99 [1.31] %. The optimal SPECT reconstruction parameters were obtained with 16 iterations, 16 subsets and a 12-mm Gaussian post-filter. The calibration factor was 9.87 cps/MBq with an error of −1.05 [2.12] %. The well counter was calibrated with 31.5 cps/kBq, and the error was evaluated to −12.89 [16.55] %.

Conclusions

The accuracy and the precision of activity quantification using dedicated quality control were found to be sufficient for use in dosimetry implemented in clinical routine. The proposed methodology could be implemented in other centres to obtain reproducible ¹⁷⁷Lu-based treatment dosimetry.

Quantitative SPECT/CT Imaging of (177)Lu with In Vivo Validation in Patients Undergoing Peptide Receptor Radionuclide Therapy

PURPOSE

The purpose of this study is to extend an established SPECT/CT quantitation protocol to (177)Lu and validate it in vivo using urine samples, thus providing a basis for 3D dosimetry of (177)Lu radiotherapy and improvement over current planar methods which improperly account for anatomical variations, attenuation, and overlapping organs.

PROCEDURES

In our quantitation protocol, counts in images reconstructed using an ordered subset-expectation maximization algorithm are converted to kilobecquerels per milliliter using a calibration factor derived from a phantom experiment. While varying reconstruction parameters, we tracked the ratio of image to true activity concentration (recovery coefficient, RC) in hot spheres and a noise measure in a homogeneous region. The optimal parameter set was selected as the point where recovery in the largest three spheres (16, 8, and 4 ml) stagnated, while the noise continued to increase. Urine samples were collected following 12 SPECT/CT acquisitions of patients undergoing [(177)Lu]DOTATATE therapy, and activity concentrations were measured in a well counter. Data was reconstructed using parameters chosen in the phantom experiment, and estimated activity concentration from the images was compared to the urine values to derive RCs.

RESULTS

In phantom data, our chosen parameter set yielded RCs in 16, 8, and 4 ml spheres of 80.0, 74.1, and 64.5 %, respectively. For patients, the mean bladder RC was 96.1 ± 13.2% (range, 80.6-122.4 %), with a 95 % confidence interval between 88.6 and 103.6 %. The mean error of SPECT/CT concentrations was 10.1 ± 8.3% (range, -19.4-22.4 %).

CONCLUSIONS

Our results show that quantitative (177)Lu SPECT/CT in vivo is feasible but could benefit from improved reconstruction methods. Quantifying bladder activity is analogous to determining the amount of activity in the kidneys, an important task in dosimetry, and our results provide a useful benchmark for future efforts.

(177)Lu: DDEP Evaluation of the decay scheme for an emerging radiopharmaceutical

A new decay scheme evaluation using the DDEP methodology for (177)Lu is presented. Recently measured half-life measurements have been incorporated, as well as newly available γ-ray emission probabilities. For the first time, a thorough investigation has been made of the γ-ray multipolarities. The complete data tables and detailed evaluator comments are available through the DDEP website.

Tumour targeting with radiometals for diagnosis and therapy

Use of radiometals in nuclear oncology is a rapidly growing field and encompasses a broad spectrum of radiotracers for imaging via PET (positron emission tomography) or SPECT (single-photon emission computed tomography) and therapy via α, β(-), or Auger electron emission. This feature article opens with a brief introduction to the imaging and therapy modalities exploited in nuclear medicine, followed by a discussion of the multi-component strategy used in radiopharmaceutical development, known as the bifunctional chelate (BFC) method. The modular assembly is dissected into its individual components and each is discussed separately. The concepts and knowledge unique to metal-based designs are outlined, giving insight into how these radiopharmaceuticals are evaluated for use in vivo. Imaging nuclides (64)Cu, (68)Ga, (86)Y, (89)Zr, and (111)In, and therapeutic nuclides (90)Y, (177)Lu, (225)Ac, (213)Bi, (188)Re, and (212)Pb will be the focus herein. Finally, key examples have been extracted from the literature to give the reader a sense of breadth of the field.

Quantitative (177)Lu SPECT (QSPECT) imaging using a commercially available SPECT/CT system

Purpose: The combination of single photon emission computed tomography (SPECT) and computer tomography (CT) that incorporates iterative reconstruction algorithms with attenuation and scatter correction should facilitate accurate non-invasive quantitative imaging. Quantitative SPECT (QSPECT) may improve diagnostic ability and could be useful for many applications including dosimetry assessment. Using ¹⁷⁷Lu, we developed a QSPECT method using a commercially available SPECT/CT system. Methods: Serial SPECT of ¹⁷⁷Lu sources (89–12,400 MBq) were acquired with multiple contiguous energy windows along with a co-registered CT, and were reconstructed using an iterative algorithm with attenuation and scatter correction. Camera sensitivity (based on reconstructed SPECT count rate) and dead-time (based on wide-energy spectrum count rate) were resolved by non-linear curve fit. Utilizing these parameters, a SPECT dataset can be converted to a QSPECT dataset allowing quantitation in Becquerels per cubic centimetre or standardized uptake value (SUV). Validation QSPECT/CT studies were performed on a ¹⁷⁷Lu cylindrical phantom (7 studies) and on 5 patients (6 studies) who were administered a therapeutic dose of [¹⁷⁷Lu]octreotate. Results: The QSPECT sensitivity was 1.08 × 10⁻⁵± 0.02 × 10⁻⁵ s⁻¹ Bq⁻¹. The paralyzing dead-time constant was 0.78 ± 0.03 µs. The measured total activity with QSPECT deviated from the calibrated activity by 5.6 ± 1.9% and 2.6 ± 1.8%, respectively, in phantom and patients. Dead-time count loss up to 11.7% was observed in patient studies. Conclusion: QSPECT has high accuracy both in our phantom model and in clinical practice following [¹⁷⁷Lu]octreotate therapy. This has the potential to yield more accurate dosimetry estimates than planar imaging and facilitate therapeutic response assessment. Validating this method with other radionuclides could open the way for many other research and clinical applications.

Standardization and measurement of gamma-ray probability per decay of 177Lu

The procedure followed by the Nuclear Metrology Laboratory (LMN), at the Nuclear and Energy Research Institute (IPEN), for the primary standardization of (177)Lu is described. This radionuclide is widely used in radiopharmacy due to its convenient half-life and emitted beta ray energies. The (177)Lu solution was supplied during an international comparison sponsored by BIPM in 2009 and the primary standardization has been accomplished by the 4pibeta-gamma coincidence method using a proportional counter in 4pi geometry coupled with two NaI(Tl) scintillation counters. The beta efficiency was varied by placing Collodion and aluminum absorbers over and under the radioactive source. The (177)Lu calibrated sources were also measured in a previously calibrated HPGe spectrometer, in order to obtain the emission probability per decay for the selected gamma-ray transitions. The experimental extrapolation curves were also compared with Monte Carlo simulations by means of code ESQUEMA developed at the LMN.

Radionuclide metrology in the life sciences: Recent advances and future trends

This paper reviews activities in the field of radionuclide metrology applied to the life sciences between the years 2000 and 2005. The requirements for accuracy and consistency in making radioactivity measurements in radiation medicine, coupled with an increased awareness of the role of measurement standards in quality assurance programmes, has prompted a great deal of research in this area. During the past 5 years, particular emphasis has been on: (1) the development of primary standards for radionuclides, (2) development of secondary/transfer standards, (3) development of radionuclide standards for brachytherapy, and (4) inter-laboratory comparisons at the end-user level. Activities carried out by National Metrology Institutions in these areas are reviewed and a look at future trends is presented.

Standardization of radionuclide by β(LS)-γ coincidence counting using the geometry-efficiency variation method

A liquid scintillation counting method consisting of three photomultiplier tubes for beta counters and a NaI(Tl) gamma counter has been developed for the standardization of radionuclides with the beta-gamma coincidence technique. The beta detection efficiency functions are obtained by means of a geometry-variation method developed in the present work; an array of beta detectors is moved uniformly at the same time from a centrally located counting vial to 50 mm. The method has been applied in the standardization of 60Co and 134Cs. Unquenched liquid scintillation samples with nominal count rates from 1000 to 6000 s-1 were prepared. The observed beta detection efficiencies with this method are from 90 to 45% in the case of 60Co, and from 84 to 50% for 134Cs. The output of each beta channel is summed together and compared with gamma data by the coincidence analyzer. The dead time of each counting channel is adjusted to be 20 micros, sufficiently long to suppress the afterpulses in the beta counting channel. The activity of each sample is determined by using the Cox and Isham formula. The obtained results are in good agreement with KRISS certified values.

Absolute counting of 188Re radiopharmaceuticals

The Institute of Nuclear Energy Research (INER) has provided 188Re radiopharmaceuticals for hospitals in Taiwan. To enhance the accuracy of commercial radionuclide calibrators used by radiopharmacies and hospitals, and to ensure that patients receive proper doses of these radiopharmaceuticals, it is very important to standardize this nuclide. The 4pibeta-gamma coincidence counting method was used to standardize the mass activities of 188Re in this study. At the same time, three well type ionization chambers, Centronic IG11-N20, Centronic IG11-A20, and ISOCAL-IV, were calibrated by the standardized solutions of the nuclide. In this research, the calibration figures of ISOCAL-IV for the nuclide were consistent with the results of National Physical Laboratory (NPL, UK). The outcome implied that the results of coincidence counting did mutually agree. On the other hand, the radionuclide calibrator in the radiopharmacy was producing measurement errors of about 20% when using the manufacturers recommended calibration setting: an accurate correction factor has now been determined in this study.

Biodistribution and dosimetry of 177Lu-labeled [DOTA0,Tyr3]octreotate in male nude mice with human small cell lung cancer

In this study the biodistribution of a somatostatin analogue, (177)Lu-[DOTA(0),Tyr(3)]octreotate, was investigated in an animal model, as a possible therapeutic radiopharmaceutical.

METHODS

(177)Lu-[DOTA(0),Tyr(3)]octreotate was injected i.v. into nude mice bearing somatostatin receptor-positive tumors of the human small cell lung cancer (SCLC) cell line NCI-H69. In addition, nontumor bearing mice were injected i.v. with (177)LuCl(3). The activity concentration in tumor and normal tissues was measured and dosimetric estimations for tumor tissue were made.

RESULTS

The tumor had higher activity concentration of (177)Lu-[DOTA(0),Tyr(3)]octreotate compared to all measured normal tissues at all time points. The activity concentration in the tumor tissue was 3.7 %IA/g, 2.1 %IA/g, and 1.2 %IA/g after 24 h, 3 days and 7 days, respectively. The mean absorbed dose to a 1 g tumor was 0.3 Gy/MBq. The highest activity concentration of (177)LuCl(3) was observed in the bone marrow and increased with time.

CONCLUSION

This study shows that (177)Lu-labeled [DOTA(0),Tyr(3)]octreotate has therapeutic potential for SCLC. The study also points out the importance of optimal labeling efficiency since the high bone marrow uptake of free lutetium ions can be controlled by a high peptide-bound fraction.

Half-life measurements with ionization chambers—A study of systematic effects and results

Accurate half-lives have been determined at the Physikalisch-Technische Bundesanstalt (PTB) using ionization-chamber measuring systems to assure the quality of radioactivity standards over the period of their use as detector calibrants or other purposes such as nuclear medicine and environmental monitoring. Some long-lived radionuclides have been measured for up to 28 years: 85Kr, 90Sr, 108Agm, 133Ba, 152Eu, 154Eu, and more recently 65Zn, 106Ru, 109Cd and 137Cs; short-lived radionuclides have also been studied such as: 18F, 67Ga, 81Rb, 99Mo, 99Tcm, 103Pd, 111In, 123I, 131I, 153Sm, 169Er, 177Lu, 186Re, 188Re, 201Tl, 222Rn and 224Ra. Relative uncertainties of half-life values of the order of 5 x 10(-4) were obtained. These values are compared to the results of other measurements and evaluations, and the limiting systematic effects are discussed.