MIB Guides: Preclinical Radiopharmaceutical Dosimetry

Preclinical dosimetry is essential for guiding the design of animal radiopharmaceutical biodistribution, imaging, and therapy experiments, evaluating efficacy and/or toxicities in such experiments, ensuring compliance with ethical standards for animal research, and, perhaps most importantly, providing reasonable initial estimates of normal-organ doses in humans, required for clinical translation of new radiopharmaceuticals. This MIB Guide provides a basic protocol for obtaining preclinical dosimetry estimates with organ-level dosimetry software.

MIRD Pamphlet No. 28, Part 2: Comparative Evaluation of MIRDcalc Dosimetry Software Across a Compendium of Diagnostic Radiopharmaceuticals

Radiopharmaceutical dosimetry is usually estimated via organ-level MIRD schema-style formalisms, which form the computational basis for commonly used clinical and research dosimetry software. Recently, MIRDcalc internal dosimetry software was developed to provide a freely available organ-level dosimetry solution that incorporates up-to-date models of human anatomy, addresses uncertainty in radiopharmaceutical biokinetics and patient organ masses, and offers a 1-screen user interface as well as quality assurance tools. The present work describes the validation of MIRDcalc and, secondarily, provides a compendium of radiopharmaceutical dose coefficients obtained with MIRDcalc. Biokinetic data for about 70 currently and historically used radiopharmaceuticals were obtained from the International Commission on Radiological Protection (ICRP) publication 128 radiopharmaceutical data compendium. Absorbed dose and effective dose coefficients were derived from the biokinetic datasets using MIRDcalc, IDAC-Dose, and OLINDA software. The dose coefficients obtained with MIRDcalc were systematically compared against the other software-derived dose coefficients and those originally presented in ICRP publication 128. Dose coefficients computed with MIRDcalc and IDAC-Dose showed excellent overall agreement. The dose coefficients derived from other software and the dose coefficients promulgated in ICRP publication 128 both were in reasonable agreement with the dose coefficients computed with MIRDcalc. Future work should expand the scope of the validation to include personalized dosimetry calculations.

MIRD Pamphlet No. 28, Part 1: MIRDcalc-A Software Tool for Medical Internal Radiation Dosimetry

Medical internal radiation dosimetry constitutes a fundamental aspect of diagnosis, treatment, optimization, and safety in nuclear medicine. The MIRD committee of the Society of Nuclear Medicine and Medical Imaging developed a new computational tool to support organ-level and suborgan tissue dosimetry (MIRDcalc, version 1). Based on a standard Excel spreadsheet platform, MIRDcalc provides enhanced capabilities to facilitate radiopharmaceutical internal dosimetry. This new computational tool implements the well-established MIRD schema for internal dosimetry. The spreadsheet incorporates a significantly enhanced database comprising details for 333 radionuclides, 12 phantom reference models (International Commission on Radiological Protection), 81 source regions, and 48 target regions, along with the ability to interpolate between models for patient-specific dosimetry. The software also includes sphere models of various composition for tumor dosimetry. MIRDcalc offers several noteworthy features for organ-level dosimetry, including modeling of blood source regions and dynamic source regions defined by user input, integration of tumor tissues, error propagation, quality control checks, batch processing, and report-preparation capabilities. MIRDcalc implements an immediate, easy-to-use single-screen interface. The MIRDcalc software is available for free download (www.mirdsoft.org) and has been approved by the Society of Nuclear Medicine and Molecular Imaging.

A Realistic Multiregion Mouse Kidney Dosimetry Model to Support the Preclinical Evaluation of Potential Nephrotoxicity of Radiopharmaceutical Therapy

Suborgan absorbed dose estimates in mouse kidneys are crucial to support preclinical nephrotoxicity analyses of α- and β-particle-emitting radioligands exhibiting a heterogeneous activity distribution in the kidneys. This is, however, limited by the scarcity of reference dose factors (S values) available in the literature for specific mouse kidney tissues. Methods: A computational multiregion model of a mouse kidney based on high-resolution MRI data from a healthy mouse kidney was developed. The model was used to calculate S values for 5 kidney tissues (cortex, outer and inner stripes of outer medulla, inner medulla, and papilla and pelvis) for a wide range of β- or α-emitting radionuclides (45 in total) of interest for radiopharmaceutical therapy, using Monte Carlo calculations. Additionally, regional S values were applied for a ¹³¹I-labeled single-domain antibody fragment with predominant retention in the outer stripe of the renal outer medulla. Results: The heterogeneous activity distribution in kidneys of considered α- and low- to medium-energy β-emitters considerably affected the absorbed dose estimation in specific suborgan regions. The suborgan tissue doses resulting from the nonuniform distribution of the ¹³¹I-labeled antibody fragment largely deviated (from -40% to 57%) from the mean kidney dose resulting from an assumed uniform activity distribution throughout the whole kidney. The absorbed dose in the renal outer stripe was about 2.0 times higher than in the cortex and in the inner stripe and about 2.6 times higher than in inner tissues. Conclusion: The use of kidney regional S values allows a more realistic estimation of the absorbed dose in different renal tissues from therapeutic radioligands with a heterogeneous uptake in the kidneys. This constitutes an improvement from the simplistic (less accurate) renal dose estimates assuming a uniform distribution of activity throughout kidney tissues. Such improvement in dosimetry is expected to support preclinical studies essential for a better understanding of nephrotoxicity in humans. The dosimetric database has added value in the development of new molecular vectors for radiopharmaceutical therapy.

Fetal Dose from PET and CT in Pregnant Patients

When pregnancy is discovered during or after a diagnostic examination, the physician or the patient may request an estimate of the radiation dose received by the fetus as per guidelines and standard operating procedures. This study provided the imaging community with dose estimates to the fetus from PET/CT with protocols that are adapted to University of Michigan low-dose protocols for patients known to be pregnant. Methods: There were 9 patients analyzed with data for the first, second, and third trimesters, the availability of which is quite rare. These images were used to calculate the size-specific dose estimate (SSDE) from the CT scan portion and the SUV and ¹⁸F-FDG uptake dose from the PET scan portion using the MIRD formulation. The fetal dose estimates were tested for correlation with each of the following independent measures: gestational age, fetal volume, average water-equivalent diameter of the patient along the length of the fetus, SSDE, SUV, and percentage of dose from ¹⁸F-FDG. Stepwise multiple linear regression analysis was performed to assess the partial correlation of each variable. To our knowledge, this was the first study to determine fetal doses from CT and PET images. Results: Fetal self-doses from ¹⁸F for the first, second, and third trimesters were 2.18 mGy (single data point), 0.74-1.82 mGy, and 0.017-0.0017 mGy, respectively. The combined SSDE and fetal self-dose ranged from 1.2 to 8.2 mGy. These types of images from pregnant patients are rare. Conclusion: Our data indicate that the fetal radiation exposure from ¹⁸F-FDG PET and CT performed, when medically necessary, on pregnant women with cancer is low. All efforts should be made to minimize fetal radiation exposure by modifying the protocol.

Internal dosimetry studies of 177Lu-BBN-GABA-DOTA, as a cancer therapy agent, in human tissues based on animal data

The goal of using radiopharmaceuticals for therapeutic purposes is twofold: first, the most damage to cancer cells and, second, the most negligible dose transfers to healthy tissues. As ¹⁷⁷Lu has the potential to cure a wide range of malignancies due to its varied range of beta energies, ¹⁷⁷Lu-BBN-GABA-DOTA has been developed for therapeutic applications. In addition, ¹⁷⁷Lu-BBN-GABA-DOTA can be over-expressed on gastrin-releasing peptide (GRP) receptors of the prostate, breast, small cell lung cancer, gastric, and colon tumors. The purpose of this study was to calculate the amount of dose absorption in human body organs using medical internal radiation dose (MIRD) and GATE code methods, after animal injection. In this study, the amount of absorbed dose in different organs (spleen, kidney, Lung, Pancreas, Heart, Adrenal, Intestine, Stomach, and Liver) were calculated for 1-MBq accumulation of ¹⁷⁷Lu-BBN-GABA-DOTA in source organs (spleen, kidney, Lung, Pancreas, Heart, Adrenal, Intestine, Stomach, and Liver) using Monte Carlo Simulation (GATE code) with Zubal phantom. Moreover, compared with MIRD method, the results of the simulation showed considerable consistency. It was estimated that a 1-MBq administration of ¹⁷⁷Lu-BBN-GABA-DOTA to the human body would result in an absorbed dose of 1.07E-02 mGy and 4.97E-02 (MIRD method) and 1.26E-02 mGy and 5.19E-02 (Gate code) in the Pancreas and adrenal 120 h after injection, respectively. The highest and lowest percentage differences between MIRD and Gate results are related to the Pancreas and spleen, respectively. Finally, the results showed that there is a good agreement between MIRD method and Gate code simulation for absorbed dose estimation.

An Analysis for Therapeutic Doses of Patients with Neuroendocrine Tumor Treated with Lutetium-177-DOTATATE

Background: The aim of this study is to clarify the critical organs that limit treatment scheme and also evaluate the validity of currently used critical organ threshold values in neuroendocrine tumor (NET) patients, receiving peptide receptor radionuclide therapy (PRRT) with Lutetium-177 (¹⁷⁷Lu)-DOTATATE. Thirty-six NET patients (ages 16-73 years) who received ¹⁷⁷Lu-DOTATATE treatment were evaluated retrospectively in this study. Dosimetric calculations were made using medical internal radionuclide dose method. For calculation of organ doses, Internal Dose Assessment at Organ Level/Exponential Modelling 1.1 software program was used. Follow-up data were used to determine the organ failure. Results: A total of 141 cycles and mean of 3.91 (±1.33) cycles were applied to the patients. A mean of 691 mCi (±257 mCi) ¹⁷⁷Lu-DOTATATE infusion in total and a dose between 70 and 200 mCi per treatment was applied to patients. Seven of 36 patients reached 23 Gy renal dose limit. In these patients, although kidney doses were between 23 and 29 Gy, there was no diminution in renal functions during follow-up. Two of 36 patients reached total bone marrow dose of 2 Gy limit. Bone marrow suppression did not develop in these patients. Conclusion: The critical organs that seem to affect the treatment scheme in PRRT with ¹⁷⁷Lu-DOTATATE are kidney and bone marrow. Although there are established threshold levels, derived from radiotherapy experience, more studies are needed to clarify these dose limits in systemic radionuclide therapies such as PRRT.

A thermoluminescent method for the evaluation of the 131I effective half-life in the thyroid when treating Graves' disease

When planning treatment for Graves' disease with ¹³¹I, the effective half-life (T_eff) should be estimated individually as it depends on biological characteristics such as iodine uptake and excretion, which differ from an individual to another (Berg et al. 1996). All the methods to quantify T_eff described in the literature are quite complex and are difficult to be used in clinical routine. With the aim of optimizing this process, a simplified method is proposed here to evaluate T_eff of ¹³¹I during treatment of Graves' disease. The present study suggests improving the method of determining T_eff based on thermoluminescence dosimetry. This involves implementing a new method and includes reduction of TLD (Thermoluminescent Dosimeter) measurements. The proposed method was validated on patients with Graves' disease. The radiation dose delivered to the patients was determined using the MIRD (Medical Internal Radiation Dosimetry) formalism. The relative difference between T_eff obtained based on seven measurement intervals at [0-24 h, 24-48 h, 48-72 h, 72-96 h, 96-120 h, 120-144 h, 144-168 h] and based on three measurement intervals at [0-24 h, 72-96 h, 144-168 h] and [0-24 h, 120-144 h, 144-168 h] was 1.9% and 3.81%, respectively. Comparison of doses obtained based on a general T_eff and on a personalized T_eff gave a statistically significant difference with a correlation coefficient R²of 0.44. The T_eff obtained from just three measurements was found to be sufficiently accurate and easily applicable. The results obtained demonstrate the need to determine and use personalized T_eff values instead of using a fixed value of 7 days.

Functional recovery after macula involving retinal detachment and its correlation with preoperative biomarkers in optical coherence tomography

To introduce an ETDRS grid-based classification for macula involving retinal detachment (MIRD) with or without center (foveal) involvement and to identify biomarkers in preoperative optical coherence tomography (OCT) associated with a favorable postoperative functional outcome in eyes with center involving retinal detachment (CIRD). One hundred and two eyes of 102 consecutive patients (f/m: 35/67) with primary rhegmatogenous retinal detachment, preoperative evidence of MIRD (perifoveal involvement of ≤ 6.0 mm), and successful retinal surgery were included in this retrospective cohort study. Eyes were assigned to 5 grades of MIRD (G1–G5), based on the extent of detachment in the ETDRS grid. Eyes with a detached foveal status (CIRD) were assigned to G4 or G5. In CIRD, the following OCT biomarkers were quantified and correlated with mean BCVA (logMAR) at 3 months postsurgery, using univariate and multivariable regression models: grade of detachment, extent of intraretinal edema, height of foveal detachment, subretinal folds, and epiretinal membrane. Forty-one of 102 eyes (40.2%) presented with an attached foveal status, defined as either outer (G1: 11.8%) or inner (G2: 18.6%) macular involvement or fovea-threatening MIRD (G3: 9.8%). Sixty-one eyes (59.8%) showed CIRD (G4 or G5). Eyes with CIRD had significantly worse postoperative BCVA than eyes without foveal involvement (0.355 logMAR vs. 0.138 logMAR, p<0.001). If CIRD was limited to three outer ETDRS quadrants (G4), mean BCVA was better compared to CIRD involving all four ETDRS quadrants (G5) (0.254 logMAR vs. 0.522 logMAR, p<0.001). Reading ability (BCVA ≤ 0.4 logMAR) was restored in 97.6% of eyes with G1–G3 compared to 86.9% of eyes with G4 (p=0.072) and 52.4% of eyes with G5 (p<0.001). In multivariable regression analysis of eyes with CIRD, a lower grade of detachment (G4 vs. G5: p<0.05) and lower extent of cystoid edema (focal/none vs. wide: p<0.001) were both associated with better postoperative function. The functional outcome after MIRD may be worse in the presence of foveal involvement (CIRD), but a lower grade of detachment and the absence of intraretinal edema can predict a good recovery in spite of CIRD.

Clinical implementation of PLANET® Dose for dosimetric assessment after [177Lu]Lu-DOTA-TATE: comparison with Dosimetry Toolkit® and OLINDA/EXM® V1.0

Background

The aim of this study was to compare a commercial dosimetry workstation (PLANET® Dose) and the dosimetry approach (GE Dosimetry Toolkit® and OLINDA/EXM® V1.0) currently used in our department for quantification of the absorbed dose (AD) to organs at risk after peptide receptor radionuclide therapy with [¹⁷⁷Lu]Lu-DOTA-TATE.

Methods

An evaluation on phantom was performed to determine the SPECT calibration factor variations over time and to compare the Time Integrated Activity Coefficients (TIACs) obtained with the two approaches. Then, dosimetry was carried out with the two tools in 21 patients with neuroendocrine tumours after the first and second injection of 7.2 ± 0.2 GBq of [¹⁷⁷Lu]Lu-DOTA-TATE (40 dosimetry analyses with each software). SPECT/CT images were acquired at 4 h, 24 h, 72 h and 192 h post-injection and were reconstructed using the Xeleris software (General Electric). The liver, spleen and kidneys masses and TIACs were determined using Dosimetry Toolkit® (DTK) and PLANET® Dose. The ADs were calculated using OLINDA/EXM® V1.0 and the Local Deposition Method (LDM) or Dose voxel-Kernel convolution (DK) on PLANET® Dose.

Results

With the phantom, the 3D calibration factors showed a slight variation (0.8% and 3.3%) over time, and TIACs of 225.19 h and 217.52 h were obtained with DTK and PLANET® Dose, respectively. In patients, the root mean square deviation value was 8.9% for the organ masses, 8.1% for the TIACs, and 9.1% and 7.8% for the ADs calculated with LDM and DK, respectively. The Lin’s concordance correlation coefficient was 0.99 and the Bland–Altman plot analysis estimated that the AD value difference between methods ranged from − 0.75 to 0.49 Gy, from − 0.20 to 0.64 Gy, and from − 0.43 to 1.03 Gy for 95% of the 40 liver, kidneys and spleen dosimetry analyses. The dosimetry method had a minor influence on AD differences compared with the image registration and organ segmentation steps.

Conclusions

The ADs to organs at risk obtained with the new workstation PLANET® Dose are concordant with those calculated with the currently used software and in agreement with the literature. These results validate the use of PLANET® Dose in clinical routine for patient dosimetry after targeted radiotherapy with [¹⁷⁷Lu]Lu-DOTA-TATE.

Internal dosimetry studies of 170Tm-EDTMP complex, as a bone pain palliation agent, in human tissues based on animal data

Radiopharmaceuticals with therapeutic applications are designed to deliver high doses of radiation to target organs with minimizing unwanted radiation to healthy tissues. Owing to the potential of targeted radiotherapy to treat a wide range of malignancies, ¹⁷⁰Tm -EDTMP was developed for possible therapeutic applications. This study describes absorbed dose prediction of ¹⁷⁰Tm-EDTMP in human organs after animal injection which is determined via medical internal radiation dose (MIRD) and MCNP-4C code methods. It was estimated that a 1-MBq administration of ¹⁷⁰Tm-EDTMP into the human body would result in an absorbed dose of 37.9 mGy (MIRD method) and 38.02 mGy (MCNP-4C code) in the bone surface after 60 days post injection. Highest and lowest difference between MIRD and MCNP results are for lung and bone surface respectively. Finally, the results show that there is a good agreement between MIRD method and MCNP-4C simulation code for absorbed dose estimation.

203/212Pb Theranostic Radiopharmaceuticals for Image-guided Radionuclide Therapy for Cancer

Receptor-targeted image-guided Radionuclide Therapy (TRT) is increasingly recognized as a promising approach to cancer treatment. In particular, the potential for clinical translation of receptor-targeted alpha-particle therapy is receiving considerable attention as an approach that can improve outcomes for cancer patients. Higher Linear-energy Transfer (LET) of alpha-particles (compared to beta particles) for this purpose results in an increased incidence of double-strand DNA breaks and improved-localized cancer-cell damage. Recent clinical studies provide compelling evidence that alpha-TRT has the potential to deliver a significantly more potent anti-cancer effect compared with beta-TRT. Generator-produced 212Pb (which decays to alpha emitters 212Bi and 212Po) is a particularly promising radionuclide for receptor-targeted alpha-particle therapy. A second attractive feature that distinguishes 212Pb alpha-TRT from other available radionuclides is the possibility to employ elementallymatched isotope 203Pb as an imaging surrogate in place of the therapeutic radionuclide. As direct non-invasive measurement of alpha-particle emissions cannot be conducted using current medical scanner technology, the imaging surrogate allows for a pharmacologically-inactive determination of the pharmacokinetics and biodistribution of TRT candidate ligands in advance of treatment. Thus, elementally-matched 203Pb labeled radiopharmaceuticals can be used to identify patients who may benefit from 212Pb alpha-TRT and apply appropriate dosimetry and treatment planning in advance of the therapy. In this review, we provide a brief history on the use of these isotopes for cancer therapy; describe the decay and chemical characteristics of 203/212Pb for their use in cancer theranostics and methodologies applied for production and purification of these isotopes for radiopharmaceutical production. In addition, a medical physics and dosimetry perspective is provided that highlights the potential of 212Pb for alpha-TRT and the expected safety for 203Pb surrogate imaging. Recent and current preclinical and clinical studies are presented. The sum of the findings herein and observations presented provide evidence that the 203Pb/212Pb theranostic pair has a promising future for use in radiopharmaceutical theranostic therapies for cancer.

Voxel-Based Dosimetry of Iron Oxide Nanoparticle-Conjugated 177Lu-Labeled Folic Acid Using SPECT/CT Imaging of Mice

Several radiolabeled folic acid conjugates have been developed for targeted imaging and therapy. However, the therapeutic concept with radiolabeled folate conjugates has not yet been applied to clinical applications owing to the high renal absorbed dose. The effectiveness of targeted radionuclide therapy (TRT) depends primarily on the absorbed dose rate and on the total absorbed dose delivered to the tumor and to normal tissue. Owing to various limitations associated with organ level dosimetry, voxel-based dosimetry has become essential for the assessment of a more  accurate absorbed dose during TRT. In this study, we synthesized iron oxide nanoparticle (IONP)-conjugated radiolabeled folate (¹⁷⁷Lu-IONP-Folate) and performed voxel-based dosimetry using SPECT/CT images of normal mice through direct Geant4 application for emission tomography (GATE) Monte Carlo (MC) simulation. We also prepared ¹⁷⁷Lu-Folate and ¹⁷⁷Lu-IONPs for the comparison of absorbed doses with that of ¹⁷⁷Lu-IONP-Folate. In addition, we calculated the mean absorbed dose at the organ-level using the medical internal radiation dose (MIRD) schema. The radioactivities of all three radiotracers were mainly accumulated in the liver and kidneys immediately after injection. For the kidneys, the voxel-based absorbed doses obtained with ¹⁷⁷Lu-IONP-Folate, ¹⁷⁷Lu-Folate, and ¹⁷⁷Lu-IONPs were 1.01 ± 0.17, 2.46 ± 0.50, and 0.52 ± 0.08 Gy/MBq, respectively. The renal absorbed dose decreased significantly (∼half) when ¹⁷⁷Lu-IONP-Folate was used compared with when the ¹⁷⁷Lu-Folate only was used. The mean absorbed dose values obtained at organ-level using the MIRD schema were comparable to voxel-based absorbed doses estimated with GATE MC. The voxel-based absorbed dose values obtained in this study of individualized activity show that the renal absorbed dose could be reduced to almost half with ¹⁷⁷Lu-IONP-Folate. Therefore, ¹⁷⁷Lu-IONP-Folate could be clinically applicable in the TRT of folate receptor-positive cancers in a personalized manner when using the voxel-based dosimetry method.

Y90 Radioembolization Dosimetry: Concepts for the Interventional Radiologist

Transarterial radioembolization (TARE) with beta particle emitting microspheres via Yttrium-90 decay has become a fundamental component of the contemporary Interventional Oncology practice. TARE continues to advance as a result of increased utilization, clinical study, technological improvements, and evolving applications. To maximize TARE safety and efficacy, a core understanding of dosimetry is essential. The intent of this overview is to provide the reader with a general survey of radiation physics and biology, device differentiation, patient selection, anatomic assessment, activity administration models, and procedural techniques involved with TARE dosimetry.

Comparison of Accuracy in Calculation of Absorbed Dose to Patients Following Bone Scan with (99m)Tc-Marked Diphosphonates by Two Different Background Correction Methods

To improve the accuracy of the activity quantification and the image quality in scintigraphy, scatter correction is a vital procedure. The aim of this study is to compare the accuracy in calculation of absorbed dose to patients following bone scan with (99m)Tc-marked diphosphonates ((99m)Tc-MDP) by two different methods of background correction in conjugate view method. This study involved 22 patients referring to the Nuclear Medicine Center of Shahid Chamran Hospital, Isfahan, Iran. After the injection of (99m)Tc-MDP, whole-body images from patients were acquired at 10, 60, 90, and 180 min. Organ activities were calculated using the conjugate view method by Buijs and conventional background correction. Finally, the absorbed dose was calculated using the Medical Internal Radiation Dosimetry (MIRD) technique. The results of this study showed that the absorbed dose per unit of injected activity (rad/mCi) ± standard deviation for pelvis bone, bladder, and kidneys by Buijs method was 0.19 ± 0.05, 0.08 ± 0.01, and 0.03 ± 0.01 and by conventional method was 0.13 ± 0.04, 0.08 ± 0.01, and 0.024 ± 0.01, respectively. This showed that Buijs background correction method had a high accuracy compared to conventional method for the estimated absorbed dose of bone and kidneys whereas, for the bladder, its accuracy was low.

Dosimetric analysis of (123)I, (125)I and (131)I in thyroid follicle models

Background

Radioiodine is routinely used or proposed for diagnostic and therapeutic purposes: ¹²³I, ¹²⁵I and ¹³¹I for diagnostics and ¹²⁵I and ¹³¹I for therapy. When radioiodine-labelled pharmaceuticals are administered to the body, radioiodide might be released into the circulation and taken up by the thyroid gland, which may then be an organ at risk. The aim of this study was to compare dosimetric properties for ¹²³I, ¹²⁵I and ¹³¹I in previously developed thyroid models for man, rat and mouse.

Methods

Dosimetric calculations were performed using the Monte Carlo code MCNPX 2.6.0 and nuclear decay data from ICRP 107. Only the non-radiative transitions in the decays were considered. The S value was determined for the cell nuclei in species-specific thyroid follicle models for mouse, rat and man for different spatial distributions of radioiodine.

Results

For the species-specific single follicle models with radioiodine homogeneously within the follicle lumen, the highest S value came from ¹³¹I, with the largest contribution from the β particles. When radioiodine was homogeneously distributed within the follicle cells or the follicle cell nucleus, the highest contribution originated from ¹²⁵I, about two times higher than ¹²³I, with the largest contribution from the Auger electrons. The mean absorbed dose calculated for our human thyroid multiple follicle model, assuming homogenous distribution of for ¹²³I, ¹²⁵I, or ¹³¹I within the follicle lumens and follicle cells, was 9%, 18% and 4% higher, respectively, compared with the mean absorbed dose according to Medical Internal Radiation Dose (MIRD) formalism and nuclear decay data. When radioiodine was homogeneously distributed in the follicle lumens, our calculations gave up to 90% lower mean absorbed dose for ¹²⁵I compared to MIRD (20% lower for ¹²³I, and 2% lower for ¹³¹I).

Conclusions

This study clearly demonstrates the importance of using more detailed dosimetric methods and models than MIRD formalism for radioiodine, especially ¹²³I and ¹²⁵I, in the thyroid. For radioiodine homogeneously distributed in the follicle lumens our calculations for the human multiple follicle models gave up to 90% lower mean absorbed dose compared with MIRD formalism.

Outpatient single-session yttrium-90 glass microsphere radioembolization

PURPOSE

To investigate the feasibility of yttrium-90 ((90)Y) glass microsphere radioembolization (including angiography, lung shunt assessment, and treatment) as a single-session, outpatient procedure.

MATERIALS AND METHODS

Between January 2008 and June 2013, 14 patients underwent outpatient, single-session radioembolization with (90)Y glass microspheres. As part of the routine diagnostic work-up, all patients underwent either computed tomography (CT) or magnetic resonance imaging of the liver with three-dimensional analysis and had laboratory results forwarded to our center for confirmation of candidacy before treatment. On treatment day, all patients underwent planning mesenteric angiography with flat panel cone-beam CT imaging. Patients were administered 33-85 MBq of technetium-99m macroaggregated albumin ((99m)Tc-MAA) via a microcatheter positioned in a hepatic artery supplying the tumor of interest. Planar scintigraphy was initiated within 2 hours after the administration of (99m)Tc-MAA and lung shunt fraction was determined. Final dosimetry calculations were performed while the patient was being transferred back from nuclear medicine to interventional radiology.

RESULTS

All patients successfully underwent planning angiography with administration of (99m)Tc-MAA and (90)Y radioembolization as a single-session treatment. There were no reportable or recordable medical events; treatment was carried out to the desired dose in all cases. The mean total procedure time was 2.70 hours ± 0.72 (range, 1.63-3.97 h).

CONCLUSIONS

This study reports a novel proof of concept for performing radioembolization in a single-session setting. By using the described method, time between initial clinical assessments and radioembolization treatment is decreased, and costs are minimized.

MIRD pamphlet No. 24: Guidelines for quantitative 131I SPECT in dosimetry applications

The reliability of radiation dose estimates in internal radionuclide therapy is directly related to the accuracy of activity estimates obtained at each imaging time point. The recently published MIRD pamphlet no. 23 provided a general overview of quantitative SPECT imaging for dosimetry. The present document is the first in a series of isotope-specific guidelines that will follow MIRD 23 and focuses on one of the most commonly used therapeutic radionuclides, (131)I. The purpose of this document is to provide guidance on the development of protocols for quantitative (131)I SPECT in radionuclide therapy applications that require regional (normal organs, lesions) and 3-dimensional dosimetry.