Accuracy of two dosimetry software programs for 177Lu radiopharmaceutical therapy using voxel-based patient-specific phantoms

Purpose

Virtual dosimetry using voxel-based patient-specific phantoms and Monte Carlo (MC) simulations offer the advantage of having a gold standard against which absorbed doses may be benchmarked to establish the dosimetry accuracy. Furthermore, these reference values assist in investigating the accuracy of the absorbed dose methodologies from different software programs. Therefore, this study aimed to compare the accuracy of the absorbed doses computed using LundADose and OLINDA/EXM 1.0.

Methods

The accuracy was based on ¹⁷⁷Lu-DOTATATE distributions of three voxel-based phantoms. SPECT projection images were simulated for 1, 24, 96, and 168 h post-administration and reconstructed with LundADose using 3D OS-EM reconstruction. Mono-exponential curves were fitted to the bio-kinetic data for the kidneys, liver, spleen, and tumours resulting in SPECT time-integrated activity (SPECT-TIA). The SPECT-TIA were used to compute mean absorbed doses using LundADose (LND-D_SPECT) and OLINDA (OLINDA-D_SPECT) for the organs. Pre-defined true activity images, were used to obtain TRUE-TIA and, together with full MC simulations, computed the true doses (MC-D_True). The dosimetry accuracy was assessed by comparing LND-D_SPECT and OLINDA-D_SPECT to MC-D_True.

Results

Overall, the results presented an overestimation of the mean absorbed dose by LND-D_SPECT compared to the MC-D_True with a dosimetry accuracy ≤6.6%. This was attributed to spill-out activity from the reconstructed LND-D_SPECT, resulting in a higher dose contribution than the MC-D_True. There was a general underestimation (<8.1%) of OLINDA-D_SPECT compared to MC-D_True attributed to the geometrical difference in shape between the voxel-based phantoms and the OLINDA models. Furthermore, OLINDA-D_SPECT considers self-doses while MC-D_True reflects self-doses plus cross-doses.

Conclusion

The better than 10% accuracy suggests that the mean dose values obtained with LND-D_SPECT and OLINDA-D_SPECT approximate the true values. The mean absorbed doses of the two software programs, and the gold standard were comparable. This work shall be of use for optimising ¹⁷⁷Lu dosimetry for clinical applications.

Estimation of Absorbed Doses of Indigenously Produced "Direct-route" Lutetium-177-Labeled DOTA-TATE PRRT in Normal Organs and Tumor Lesions in Patients of Metastatic Neuroendocrine Tumors: Comparison with No-Carrier-Added [177Lu]Lu-DOTA-TATE and the Trend with Multiple Cycles

Background: Lutetium-177-labeled somatostatin analogue, [¹⁷⁷Lu]Lu-DOTA-TATE is most commonly used across the world for peptide receptor radionuclide therapy (PRRT) of neuroendocrine tumors (NETs). The primary objective of this study was to estimate the absorbed doses in organs and tumor lesions in NET patients treated with indigenously produced "direct-route" [¹⁷⁷Lu]Lu-labeled DOTA-TATE and impact of multiple treatment cycles on absorbed doses, and compare with those treated with no-carrier-added [¹⁷⁷Lu]Lu-labeled DOTA-TATE. Materials and Methods: Sixty patients of NET were enrolled in this prospective study. These patients received up to 6 cycles of PRRT with [¹⁷⁷Lu]Lu-DOTA-TATE (total 232 cycles) at 10- to 12-week intervals between the two successive therapy cycles. The patients were administered 5.55-7.4 GBq (150-200 mCi) of [¹⁷⁷Lu]Lu-DOTA-TATE in 100 mL of normal saline over a period of 30 min. Postadministration whole-body planar scintigraphy were acquired at five time points 0.5 (prevoid), 2, 12, 24, and 72 h (postvoid) and one SPECT scan at 24 h (postvoid). Number of disintegrations was determined from time-activity curves generated by drawing regions of interests (ROIs) on the images. Tumor masses were derived from computed tomography (CT) data. The absorbed doses for normal organs and tumor lesions were calculated using OLINDA 2.1.1 software. The same were also estimated in a group of 22 patients who were treated with no-carrier-added [¹⁷⁷Lu]Lu-labeled DOTA-TATE. Results: The mean absorbed organ doses (mean ± SD) in Gy/GBq received by normal organs were as follows: kidneys 0.64 ± 0.21, liver 0.10 ± 0.05, spleen 0.88 ± 0.35, bone marrow 0.04 ± 0.02, urinary bladder 0.26 ± 0.06, heart wall 0.04 ± 0.02, and whole-body 0.06 ± 0.02. Tumor dosimetry was performed in a total of 410 tumor lesions, the mean absorbed dose to the tumor lesions was 4.79 ± 4.23 Gy/GBq. Large variations were observed in absorbed doses received by these lesions (range: 0.15-21.26 Gy/GBq). With no-carrier-added [¹⁷⁷Lu]Lu-DOTA-TATE, the mean absorbed organ doses (mean ± SD) in Gy/GBq received by normal organs were as follows: kidneys 0.76 ± 0.16, liver 0.10 ± 0.05, spleen 1.14 ± 0.31, bone marrow 0.05 ± 0.02, urinary bladder 0.27 ± 0.05, heart wall 0.06 ± 0.02, whole-body 0.07 ± 0.02, and tumor dose 5.87 ± 5.74. Conclusions: There was no statistically significant difference in the dosimetry data of patients treated with no-carrier-added (indirect route) [¹⁷⁷Lu]Lu-labeled DOTA-TATE and the dosimetry data of patients treated with [¹⁷⁷Lu]Lu-labeled with DOTA-TATE formulated using ¹⁷⁷Lu produced through "Direct-route" and were comparable with the data reported.

Assessment of absorbed dose for Zr-89, Sm-153 and Lu-177 medical radioisotopes: IDAC-Dose2.1 and OLINDA experience

OBJECTIVE

In this article, IDAC-Dose2.1 and OLINDA computer codes are compared as they are the most widely used software tools for internal dosimetry assessment at the present time. OLINDA/EXM personal computer code was created as a replacement for the widely used MIRDOSE3.1 code. IDAC-Dose2.1 was developed based on the ICRP specific absorbed fractions and computational framework of internal dose assessment given for reference adults in ICRP Publication 133. IDAC uses cumulated activities per administered activity in hours and calculates the absorbed dose and the effective dose. The program calculates the dose in the Eckerman stylized family phantoms. It is useful in standardizing and automating internal dose calculations, assessing doses in clinical trials with radiopharmaceuticals, making theoretic calculations for existing pharmaceuticals, teaching, and other purposes.

METHODS

To produce such a comparison, the results of this work were compared with available published data in the literature on radiopharmaceuticals. Radiopharmaceuticals with ⁸⁹Zr, ¹⁵³Sm, ¹⁷⁷Lu radionuclides are used as the basis for the comparison. ⁸⁹Zr, ¹⁵³Sm, ¹⁷⁷Lu radionuclides are regarded as the future of radiopharmaceutical treatment. For ⁸⁹Zr, two different labelled carriers, Zr-89_cMAb U36 and Zr-89 Panitumumab, were used on patients.

RESULTS

The results show a clear difference in terms of absorbed dose of the Zr-89 radiopharmaceuticals for red bone marrow when calculated by IDAC-Dose2.1 (0.76 mGy/MBq), while the estimated absorbed dose in literature results is 0.07 mGy/MBq and 0.14 mGy/MBq when the calculation is done by OLINDA program. In the case of ¹⁷⁷Lu-EDTMP, the absorbed dose in red bone marrow is in reasonable agreement (0.63 mGy/MBq and 0.8 mGy/MBq for IDAC-Dose2.1 and OLINDA, respectively). A significant difference was found for the absorbed dose in the bone surface, which was almost twice as high for OLINDA (2.1 mGy/MBq for IDAC-Dose2.1 and 5.4 mGy/MBq for OLINDA). In some direct cases, the calculated absorbed dose in the urinary bladder wall with OLINDA is ten times higher compared to WinAct (which was utilized to calculate the total activity in the organs and tissues) and IDAC 2.1. These results are considered key to greater accuracy in internal dose calculation.

Human biodistribution and dosimetry of [11C]-UCB-J, a PET radiotracer for imaging synaptic density

RATIONALE

[¹¹C]-UCB-J is an emerging tool for the noninvasive measurement of synaptic vesicle density in vivo. Here, we report human biodistribution and dosimetry estimates derived from sequential whole-body PET using two versions of the OLINDA dosimetry program.

METHODS

Sequential whole-body PET scans were performed in 3 healthy subjects for 2 h after injection of 254 ± 77 MBq [¹¹C]-UCB-J. Volumes of interest were drawn over relevant source organs to generate time-activity curves and calculate time-integrated activity coefficients, with effective dose coefficients calculated using OLINDA 2.1 and compared to values derived from OLINDA 1.1 and those recently reported in the literature.

RESULTS

[¹¹C]-UCB-J administration was safe and showed mixed renal and hepatobiliary clearance, with largest organ absorbed dose coefficients for the urinary bladder wall and small intestine (21.7 and 23.5 μGy/MBq, respectively). The average (±SD) effective dose coefficient was 5.4 ± 0.7 and 5.1 ± 0.8 μSv/MBq for OLINDA versions 1.1 and 2.1 respectively. Doses were lower than previously reported in the literature using either software version.

CONCLUSIONS

A single IV administration of 370 MBq [¹¹C]-UCB-J corresponds to an effective dose of less than 2.0 mSv, enabling multiple PET examinations to be carried out in the same subject.

TRIAL REGISTRATION

EudraCT number: 2016-001190-32. Registered 16 March 2016, no URL available for phase 1 trials.

Preclinical Incorporation Dosimetry of [18F]FACH-A Novel 18F-Labeled MCT1/MCT4 Lactate Transporter Inhibitor for Imaging Cancer Metabolism with PET

Overexpression of monocarboxylate transporters (MCTs) has been shown for a variety of human cancers (e.g., colon, brain, breast, and kidney) and inhibition resulted in intracellular lactate accumulation, acidosis, and cell death. Thus, MCTs are promising targets to investigate tumor cancer metabolism with positron emission tomography (PET). Here, the organ doses (ODs) and the effective dose (ED) of the first 18F-labeled MCT1/MCT4 inhibitor were estimated in juvenile pigs. Whole-body dosimetry was performed in three piglets (age: ~6 weeks, weight: ~13-15 kg). The animals were anesthetized and subjected to sequential hybrid Positron Emission Tomography and Computed Tomography (PET/CT) up to 5 h after an intravenous (iv) injection of 156 ± 54 MBq [18F]FACH. All relevant organs were defined by volumes of interest. Exponential curves were fitted to the time-activity data. Time and mass scales were adapted to the human order of magnitude and the ODs calculated using the ICRP 89 adult male phantom with OLINDA 2.1. The ED was calculated using tissue weighting factors as published in Publication 103 of the International Commission of Radiation Protection (ICRP103). The highest organ dose was received by the urinary bladder (62.6 ± 28.9 µSv/MBq), followed by the gall bladder (50.4 ± 37.5 µSv/MBq) and the pancreas (30.5 ± 27.3 µSv/MBq). The highest contribution to the ED was by the urinary bladder (2.5 ± 1.1 µSv/MBq), followed by the red marrow (1.7 ± 0.3 µSv/MBq) and the stomach (1.3 ± 0.4 µSv/MBq). According to this preclinical analysis, the ED to humans is 12.4 µSv/MBq when applying the ICRP103 tissue weighting factors. Taking into account that preclinical dosimetry underestimates the dose to humans by up to 40%, the conversion factor applied for estimation of the ED to humans would rise to 20.6 µSv/MBq. In this case, the ED to humans upon an iv application of ~300 MBq [18F]FACH would be about 6.2 mSv. This risk assessment encourages the translation of [18F]FACH into clinical study phases and the further investigation of its potential as a clinical tool for cancer imaging with PET.

Evaluation of [18F]FNM biodistribution and dosimetry based on whole-body PET imaging of rats

INTRODUCTION

The aim of this work was to study the biodistribution, metabolism and radiation dosimetry of rats injected with [¹⁸F]FNM using PET/CT images. This novel radiotracer targeting NMDA receptor has potential for investigation for neurological and psychiatric diseases.

METHODS

Free fraction and stability in fresh human plasma were determined in vitro. PET/CT was performed on anesthetized rats. Organs were identified and 3D volumes of interest (VOIs) were manually drawn on the CT in the center of each organ. Time activity curves (TACs) were created with these VOIs, enabling the calculation of residence times. To confirm these values, ex vivo measurements of organs were performed. Plasma and urine were also collected to study in vivo metabolism. Data was extrapolated to humans, effective doses were estimated using ICRP-60 and ICRP-89 dosimetric models and absorbed doses were estimated using OLINDA/EXM V1.0 and OLINDA/EXM V2.0 (which use weighting factors from ICRP-103 to do the calculations).

RESULTS

The [¹⁸F]FNM was stable in human plasma and the diffusible free fraction was 53%. As with memantine, this tracer is poorly metabolized in vivo. Ex vivo distributions validated PET/CT data as well as demonstrating a decrease of radiotracer uptake in the brain due to anesthesia. Total effective dose was around 6.11 μSv/MBq and 4.65 μSv/MBq for female and male human dosimetric models, respectively.

CONCLUSIONS

This study shows that the presented compound exhibits stability in plasma and plasma protein binding very similar to memantine. Its dosimetry shows that it is suitable for use in humans due to a low total effective dose compared to other PET radiotracers.

A multi species evaluation of the radiation dosimetry of [11C]erlotinib, the radiolabeled analog of a clinically utilized tyrosine kinase inhibitor

INTRODUCTION

Erlotinib is a tyrosine kinase inhibitor prescribed for non-small cell lung cancer (NSCLC) patients bearing epidermal growth factor receptor mutations in the kinase domain. The objectives of this study were to (1) establish a human dosimetry profile of [¹¹C]erlotinib and (2) assess the consistency of calculated equivalent dose across species using the same dosimetry model.

METHODS

Subjects examined in this multi-species study included: a stage IIIa NSCLC patient, 3 rhesus macaque monkeys, a landrace pig, and 4 athymic nude-Fox1nu mice. [¹¹C]erlotinib PET data of the whole body were acquired dynamically for up to 120min. Regions of interest (ROIs) were manually drawn to extract PET time activity curves (TACs) from identifiable organs. TACs were used to calculate time-integrated activity coefficients (residence times) in each ROI, which were then used to calculate the equivalent dose in OLINDA. Subject data were used to predict the equivalent dose to the organs of a 73.7kg human male.

RESULTS

In three of four species, the liver was identified as the organ receiving the highest equivalent dose (critical organ). The mean equivalent doses per unit of injected activity to the liver based on human, monkey, and mouse data were 29.4μSv/MBq, 17.4±6.0μSv/MBq, and 5.27±0.25μSv/MBq, respectively. The critical organ based on the pig data was the gallbladder wall (20.4μSv/MBq) but the liver received a nearly identical equivalent dose (19.5μSv/MBq).

CONCLUSIONS

(1) When designing PET studies using [¹¹C]erlotinib, the liver should be considered the critical organ. (2) In organs receiving the greatest equivalent dose, mouse data underestimated the dose in comparison to larger species. However, the effective dose of [¹¹C]erlotinib to the whole body of a 73.7kg man was predicted with good consistency based on mice (3.14±0.05μSv/MBq) or the larger species (3.46±0.25μSv/MBq).