Dosimetry of yttrium-labelled radiopharmaceuticals for internal therapy: 86Y or 90Y imaging?

Nuclear‐medicine probes: where we are and where we are going

Nuclear medicine probes turned into the key for the identification and precise location of sentinel lymph nodes and other occult lesions (i.e., tumors) by using the systemic administration of radiotracers. Intraoperative nuclear probes are key in the surgical management of some malignancies as well as in the determination of positive surgical margins, thus reducing the extent and potential surgery morbidity.

Depending on their application, nuclear probes are classified into two main categories, namely, counting and imaging. Although counting probes present a simple design, are handheld (to be moved rapidly), and provide only acoustic signals when detecting radiation, imaging probes, also known as cameras, are more hardware‐complex and also able to provide images but at the cost of an increased intervention time as displacing the camera has to be done slowly.

This review article begins with an introductory section to highlight the relevance of nuclear‐based probes and their components as well as the main differences between ionization‐ (semiconductor) and scintillation‐based probes. Then, the most significant performance parameters of the probe are reviewed (i.e., sensitivity, contrast, count rate capabilities, shielding, energy, and spatial resolution), as well as the different types of probes based on the target radiation nature, namely: gamma (γ), beta (β) (positron and electron), and Cherenkov. Various available intraoperative nuclear probes are finally compared in terms of performance to discuss the state‐of‐the‐art of nuclear medicine probes.

The manuscript concludes by discussing the ideal probe design and the aspects to be considered when selecting nuclear‐medicine probes.

Treatment of Neuroendocrine Neoplasms with Radiolabeled Peptides-Where Are We Now

Peptide receptor radionuclide therapy (PRRT) has been one of the most successful and exciting examples of theranostics in nuclear medicine in recent decades and is now firmly embedded in many treatment algorithms for unresectable or metastatic neuroendocrine neoplasms (NENs) worldwide. It is widely considered to be an effective treatment for well- or moderately differentiated neoplasms, which express high levels of somatostatin receptors that can be selectively targeted. This review article outlines the scientific basis of PRRT in treatment of NENs and describes its discovery dating back to the early 1990s. Early treatments utilizing Indium-111, a γ-emitter, showed promise in reduction in tumor size and improvement in biochemistry, but were also met with high radiation doses and myelotoxic and nephrotoxic effects. Subsequently, stable conjugation of DOTA-peptides with β-emitting radionuclides, such as Yttrium-90 and Lutetium-177, served as a breakthrough for PRRT and studies highlighted their potential in eliciting progression-free survival and quality of life benefits. This article will also elaborate on the key trials which paved the way for its approval and will discuss therapeutic considerations, such as patient selection and administration technique, to optimize its use.

Positron Emission Intensity in the Decay of 86gY for Use in Dosimetry Studies

The β⁺-emitting radionuclide ^86gY (t_1/2 = 14.7 h) forms a matched-pair with the β⁻-emitting therapeutic radionuclide ⁹⁰Y (t_1/2 = 2.7 d) for theranostic application in medicine. This approach demands a precise knowledge of the positron emission probability of the PET nuclide which was until recently rather uncertain for ^86gY. In this work, an ^86gY source of high radionuclidic purity was prepared and a direct measurement of the positron emission intensity per 100 decay of the parent (hereafter “positron emission intensity”) was performed using high-resolution HPGe detector γ-ray spectroscopy. The electron capture intensity was also determined as an additional check by measuring the K_α and K_β X-rays of energies 14.1 and 15.8 keV, respectively, using a low energy HPGe detector. From those measurements, normalized values of 27.2 ± 2.0% for β⁺-emission and 72.8 ± 2.0% for EC were obtained. These results are in excellent agreement with values recently reported in the literature based on a detailed decay scheme study.

Theragnostics in primary and secondary liver tumors: the need for a personalized approach

Primary and secondary hepatic tumors have a dramatic impact in oncology. Despite many advances in diagnosis and therapy, the management of hepatic malignancies is still challenging, ranging from various loco-regional approaches to system therapies. In this scenario, theragnostic approaches, based on the administration of a radiopharmaceuticals' pair, the first labeled with a radionuclide suitable for the diagnostic phase and the second one bound to radionuclide emitting particles for therapy, is gaining more and more importance. Selective internal radiation therapy (SIRT) with microspheres labeled with ⁹⁰Y or ¹⁶⁶Ho is widely used as a loco-regional treatment for primary and secondary hepatic tumors. While ¹⁶⁶Ho presents both gamma and beta emission and can be therefore considered a real "theragnostic" agent, for ⁹⁰Y-microspheres theragnostic approach is realized at the diagnostic phase through the utilization of macroaggregates of human albumin, labeled with ^99mTc as "biosimilar" agent respect to microspheres. The aim of the present review was to cover theragnostic applications of ⁹⁰Y/¹⁶⁶Ho-labeled microspheres in clinical practice. Furthermore, we report the preliminary data concerning the potential role of some emerging theragnostic biomarkers for hepatocellular carcinoma, such as glypican-3 (GPC3) and prostate specific membrane antigen (PSMA).

Production of a broad palette of positron emitting radioisotopes using a low-energy cyclotron: Towards a new success story in cancer imaging?

Over the last several years, positron emission tomography (PET) has matured as an indispensable component of cancer diagnostics. Owing to the large variability observed among the cancer patients and the need to personalize individual patient's diagnosis and treatment, the need for new positron emitting radioisotopes has continued to grow. This mini review opens with a brief introduction to the criteria for radioisotope selection for PET imaging. Subsequently, positron emitting radioisotopes are categorized as: established, emerging and futuristic, based on the stages of their advancement. The production methodologies and the radiochemical separation procedures for obtaining the important radioisotopes in a form suitable for preparation of radiopharmaceuticals for PET imaging are briefly discussed.

To 1000 Gy and back again: a systematic review on dose-response evaluation in selective internal radiation therapy for primary and secondary liver cancer

Purpose

To systematically review all current evidence into the dose-response relation of yttrium-90 and holmium-166 selective internal radiation therapy (SIRT) in primary and secondary liver cancer.

Methods

A standardized search was performed in PubMed (MEDLINE), Embase, and the Cochrane Library in order to identify all published articles on dose-response evaluation in SIRT. In order to limit the results, all articles that investigated SIRT in combination with other therapy modalities (such as chemotherapy) were excluded.

Results

A total of 3038 records were identified of which 487 were screened based on the full text. Ultimately, 37 studies were included for narrative analysis. Meta-analysis could not be performed due to the large heterogeneity in study and reporting designs. Out of 37 studies, 30 reported a ‘mean dose threshold’ that needs to be achieved in order to expect a response. This threshold appears to be higher for hepatocellular carcinoma (HCC, 100–250 Gy) than for colorectal cancer metastases (CRC, 40–60 Gy). Reported thresholds tend to be lower for resin microspheres than when glass microspheres are used.

Conclusion

Although the existing evidence demonstrates a dose-response relationship in SIRT for both primary liver tumours and liver metastases, many pieces of the puzzle are still missing, hampering the definition of standardized dose thresholds. Nonetheless, most current evidence points towards a target mean dose of 100–250 Gy for HCC and 40–60 Gy for CRC. The field would greatly benefit from a reporting standard and prospective studies designed to elucidate the dose-response relation in different tumour types.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00259-021-05340-0.

Preparation and In Vitro Evaluation of Neutron-Activated, Theranostic Samarium-153-Labeled Microspheres for Transarterial Radioembolization of Hepatocellular Carcinoma and Liver Metastasis

Introduction: Transarterial radioembolization (TARE) has been proven as an effective treatment for unresectable liver tumor. In this study, neutron activated, ¹⁵³Sm-labeled microspheres were developed as an alternative to ⁹⁰Y-labeled microspheres for hepatic radioembolization. ¹⁵³Sm has a theranostic advantage as it emits both therapeutic beta and diagnostic gamma radiations simultaneously, in comparison to the pure beta emitter, ⁹⁰Y. Methods: Negatively charged acrylic microspheres were labeled with ¹⁵²Sm ions through electrostatic interactions. In another formulation, the Sm-labeled microsphere was treated with sodium carbonate solution to form the insoluble ¹⁵²Sm carbonate (¹⁵²SmC) salt within the porous structures of the microspheres. Both formulations were neutron-activated in a research reactor. Physicochemical characterization, gamma spectrometry, and radiolabel stability tests were carried out to study the performance and stability of the microspheres. Results: The Sm- and SmC-labeled microspheres remained spherical and smooth, with a mean size of 35 µm before and after neutron activation. Fourier transform infrared (FTIR) spectroscopy indicated that the functional groups of the microspheres remained unaffected after neutron activation. The ¹⁵³Sm- and ¹⁵³SmC-labeled microspheres achieved activity of 2.53 ± 0.08 and 2.40 ± 0.13 GBq·g⁻¹, respectively, immediate after 6 h neutron activation in the neutron flux of 2.0 × 10¹² n·cm⁻²·s⁻¹. Energy-dispersive X-ray (EDX) and gamma spectrometry showed that no elemental and radioactive impurities were present in the microspheres after neutron activation. The retention efficiency of ¹⁵³Sm in the ¹⁵³SmC-labeled microspheres was excellent (~99% in distilled water and saline; ~97% in human blood plasma), which was higher than the ¹⁵³Sm-labeled microspheres (~95% and ~85%, respectively). Conclusion: ¹⁵³SmC-labeled microspheres have demonstrated excellent properties for potential application as theranostic agents for hepatic radioembolization.

Radiometals for imaging and theranostics, current production, and future perspectives

The aim of this review is to make the reader familiar with currently available radiometals, their production modes, capacities, and quality concerns related to their medical use, as well as new emerging radiometals and irradiation technologies from the perspective of their diagnostic and theranostic applications. Production methods of ¹⁷⁷ Lu serve as an example of various issues related to the production yield, specific activity, radionuclidic and chemical purity, and production economy. Other radiometals that are currently used or explored for potential medical applications, with particular focus on their theranostic value, are discussed. Using radiometals for diagnostic imaging and therapy is on the rise. The high demand for radiometals for medical use prompts investigations towards using alternative irradiation reactions, while using existing nuclear reactors and accelerator facilities. This review discusses these production capacities and what is necessary to cover the growing demand for theranostic nuclides.

90 Y SPECT/CT quantitative study and comparison of uptake with pretreatment 99 m Tc-MAA SPECT/CT in radiomicrosphere therapy

INTRODUCTION

Yttrium-90 (90 Y) microsphere post-treatment imaging reflects the true distribution characteristics of microspheres in the tumor and liver compartments. However, due to its decay spectra profile lacking a pronounced photopeak, the bremsstrahlung imaging for 90 Y has inherent limitations. The absorbed dose calculations for 90 Y microspheres radiomicrosphere therapy (RMT) sustain a limitation due to the poor quality of 90 Y imaging. The aim of this study was to develop quantitative methods to improve the post-treatment 90 Y bremsstrahlung single photon emission tomography (SPECT)/computed tomography (CT) image analysis for dosimetric purposes and to perform a quantitative comparison with the 99m Tc-MAA SPECT/CT images, which is used for theranostics purposes for liver and tumor dosimetry.

METHODS

Pre and post-treatment SPECT/CT data of patients who underwent RMT for primary or metastatic liver cancer were acquired. A Jasczak phantom with eight spherical inserts of various sizes was used to obtain optimal iteration number for the contrast recovery algorithm for improving 90 Y bremsstrahlung SPECT/CT images. Comparison of uptake on 99m Tc-MAA and 90 Y microsphere SPECT/CT images was assessed using tumor to healthy liver ratios (TLRs). The voxel dosimetry technique was used to estimate absorbed doses. Absorbed doses within the tumor and healthy part of the liver were also investigated for correlation with administered activity.

RESULTS

Improvement in CNR and contrast recovery coefficients on patient and phantom 90 Y bremsstrahlung SPECT/CT images respectively were achieved. The 99m Tc-MAA and 90 Y microspheres SPECT/CT images showed significant uptake correlation (r = 0.9, P = 0.05) with mean TLR of 9.4 ± 9.2 and 5.0 ± 2.2, respectively. The correlation between the administered activity and tumor absorbed dose was weak (r = 0.5, P > 0.05), however, healthy liver absorbed dose increased with administered activity (r = 0.8, P = 0.0).

CONCLUSIONS

This study demonstrated correlation in mean TLR between 99m Tc-MAA and 90 Y microsphere SPECT/CT.

Theranostics in neuroendocrine tumours: somatostatin receptor imaging and therapy

Theranostics and its principles: pre-treatment selection of patients who are most likely to benefit from treatment by the use of a related, specific diagnostic test are integral to the treatment of patients with neuroendocrine tumours (NETs). This is due to NETs' important, but variable, somatostatin receptor (SSTR) expression, their heterogeneity and variation in site of primary and rate of progression. Only patients whose tumours have sufficient expression of SSTRs will benefit from SSTR-based radionuclide therapy and demonstrating this expression prior to therapy is essential. This article provides a relevant overview of NETs and the multiple facets of SSTR based theranostics, including imaging and therapy radionuclides; clinical efficacy and toxicity; patient selection and treatment and finally emerging radiopharmaceuticals and newer clinical applications.

Inter-comparison of quantitative imaging of lutetium-177 (177Lu) in European hospitals

BACKGROUND

This inter-comparison exercise was performed to demonstrate the variability of quantitative SPECT/CT imaging for lutetium-177 (177Lu) in current clinical practice. Our aim was to assess the feasibility of using international inter-comparison exercises as a means to ensure consistency between clinical sites whilst enabling the sites to use their own choice of quantitative imaging protocols, specific to their systems. Dual-compartment concentric spherical sources of accurately known activity concentrations were prepared and sent to seven European clinical sites. The site staff were not aware of the true volumes or activity within the sources-they performed SPECT/CT imaging of the source, positioned within a water-filled phantom, using their own choice of parameters and reported their estimate of the activities within the source.

RESULTS

The volumes reported by the participants for the inner section of the source were all within 29% of the true value and within 60% of the true value for the outer section. The activities reported by the participants for the inner section of the source were all within 20% of the true value, whilst those reported for the outer section were up to 83% different to the true value.

CONCLUSIONS

A variety of calibration and segmentation methods were used by the participants for this exercise which demonstrated the variability of quantitative imaging across clinical sites. This paper presents a method to assess consistency between sites using different calibration and segmentation methods.

The origin and reduction of spurious extrahepatic counts observed in 90Y non-TOF PET imaging post radioembolization

Our literature survey revealed a physical effect unknown to the nuclear medicine community, i.e. internal bremsstrahlung emission, and also the existence of long energy resolution tails in crystal scintillation. None of these effects has ever been modelled in PET Monte Carlo (MC) simulations. This study investigates whether these two effects could be at the origin of two unexplained observations in ⁹⁰Y imaging by PET: the increasing tails in the radial profile of true coincidences, and the presence of spurious extrahepatic counts post radioembolization in non-TOF PET and their absence in TOF PET. These spurious extrahepatic counts hamper the microsphere delivery check in liver radioembolization. An acquisition of a ³²P vial was performed on a GSO PET system. This is the ideal setup to study the impact of bremsstrahlung x-rays on the true coincidence rate when no positron emission and no crystal radioactivity are present. A MC simulation of the acquisition was performed using Gate-Geant4. MC simulations of non-TOF PET and TOF-PET imaging of a synthetic ⁹⁰Y human liver radioembolization phantom were also performed. Internal bremsstrahlung and long energy resolution tails inclusion in MC simulations quantitatively predict the increasing tails in the radial profile. In addition, internal bremsstrahlung explains the discrepancy previously observed in bremsstrahlung SPECT between the measure of the ⁹⁰Y bremsstrahlung spectrum and its simulation with Gate-Geant4. However the spurious extrahepatic counts in non-TOF PET mainly result from the failure of conventional random correction methods in such low count rate studies and poor robustness versus emission-transmission inconsistency. A novel proposed random correction method succeeds in cleaning the spurious extrahepatic counts in non-TOF PET. Two physical effects not considered up to now in nuclear medicine were identified to be at the origin of the unusual ⁹⁰Y true coincidences radial profile. TOF reconstruction removing of the spurious extrahepatic counts was theoretically explained by a better robustness against emission-transmission inconsistency. A novel random correction method was proposed to overcome the issue in non-TOF PET. Further studies are needed to assess the novel random correction method robustness.

Dual-Nuclide Radiopharmaceuticals for Positron Emission Tomography Based Dosimetry in Radiotherapy

Improvement of the accuracy of dosimetry in radionuclide therapy has the potential to increase patient safety and therapeutic outcomes. Although positron emission tomography (PET) is ideally suited for acquisition of dosimetric data because PET is inherently quantitative and offers high sensitivity and spatial resolution, it is not directly applicable for this purpose because common therapeutic radionuclides lack the necessary positron emission. This work reports on the synthesis of dual-nuclide labeled radiopharmaceuticals with therapeutic and PET functionality, which are based on common and widely available metal radionuclides. Dual-chelator conjugates, featuring interlinked cyclen- and triazacyclononane-based polyphosphinates DOTPI and TRAP, allow for strictly regioselective complexation of therapeutic (e.g., 177 Lu, 90 Y, or 213 Bi) and PET (e.g., 68 Ga) radiometals in the same molecular framework by exploiting the orthogonal metal ion selectivity of these chelators (DOTPI: large cations, such as lanthanide(III) ions; TRAP: small trivalent ions, such as GaIII ). Such DOTPI-TRAP conjugates were decorated with 3 Gly-urea-Lys (KuE) motifs for targeting prostate-specific membrane antigen (PSMA), employing Cu-catalyzed (CuAAC) as well as strain-promoted (SPAAC) click chemistry. These were labeled with 177 Lu or 213 Bi and 68 Ga and used for in vivo imaging of LNCaP (human prostate carcinoma) tumor xenografts in SCID mice by PET, thus proving practical applicability of the concept.

Clinical History of the Theranostic Radionuclide Approach to Neuroendocrine Tumors and Other Types of Cancer: Historical Review Based on an Interview of Eric P. Krenning by Rachel Levine

In nuclear medicine, the term theranostics describes the combination of therapy and diagnostic imaging. In practice, this concept dates back more than 50 years; however, among the most successful examples of theranostics are peptide receptor scintigraphy and peptide receptor radionuclide therapy of neuroendocrine tumors. The development of these modalities through the radiolabeling of somatostatin analogs with various radionuclides has led to a revolution in patient management and established a foundation for expansion of the theranostic principle into other oncology indications. This article provides a review of the evolution and development of the theranostic radionuclide approach to the management of neuroendocrine tumors, as described by the inventor of this technique, Eric P. Krenning, in an interview with Rachel Levine.

The Beginning and Development of the Theranostic Approach in Nuclear Medicine, as Exemplified by the Radionuclide Pair 86Y and 90Y

In the context of radiopharmacy and molecular imaging, the concept of theranostics entails a therapy-accompanying diagnosis with the aim of a patient-specific treatment. Using the adequate diagnostic radiopharmaceutical, the disease and the state of the disease are verified for an individual patient. The other way around, it verifies that the radiopharmaceutical in hand represents a target-specific and selective molecule: the "best one" for that individual patient. Transforming diagnostic imaging into quantitative dosimetric information, the optimum radioactivity (expressed in maximum radiation dose to the target tissue and tolerable dose to healthy organs) of the adequate radiotherapeutical is applied to that individual patient. This theranostic approach in nuclear medicine is traced back to the first use of the radionuclide pair 86Y/90Y, which allowed a combination of PET and internal radiotherapy. Whereas the β-emitting therapeutic radionuclide 90Y (t½ = 2.7 d) had been available for a long time via the 90Sr/90Y generator system, the β⁺ emitter 86Y (t½ = 14.7 h) had to be developed for medical application. A brief outline of the various aspects of radiochemical and nuclear development work (nuclear data, cyclotron irradiation, chemical processing, quality control, etc.) is given. In parallel, the paper discusses the methodology introduced to quantify molecular imaging of 86Y-labelled compounds in terms of multiple and long-term PET recordings. It highlights the ultimate goal of radiotheranostics, namely to extract the radiation dose of the analogue 90Y-labelled compound in terms of mGy or mSv per MBq 90Y injected. Finally, the current and possible future development of theranostic approaches based on different PET and therapy nuclides is discussed.

Internal dosimetry for radioembolization therapy with Yttrium-90 microspheres

The absorbed doses in the liver and adjacent viscera in Yttrium‐90 radioembolization therapy for metastatic liver lesions are not well‐documented. We sought for a clinically practical way to determine the dosimetry of this advent treatment. Six different female XCAT BMIs and seven different male XCAT BMIs were generated. Using Monte Carlo GATE code simulation, the total of 100MBq ⁹⁰Y was deposited uniformly in the source organ, liver. Self‐irradiation and absorbed doses in lung, kidney and bone marrow were calculated. The mean energy of Yittrium‐90 (i.e., 0.937 MeV) was used. The S‐values and equivalent doses in target organs were estimated. The dose absorbed in the liver was between 84 and 53 Gy and below the target of 80 to 150 Gy. The absorbed dose in the bone marrow, lungs, and kidneys are very low and below 0.1 , 0.4, and 0.5 Gy respectively. Our study indicates that larger activities than the conventional dose of 3 GBq may be both required and safe. Further confirmations in clinical settings are needed.

Cerenkov luminescence imaging: physics principles and potential applications in biomedical sciences

Cerenkov luminescence imaging (CLI) is a novel imaging modality to study charged particles with optical methods by detecting the Cerenkov luminescence produced in tissue. This paper first describes the physical processes that govern the production and transport in tissue of Cerenkov luminescence. The detectors used for CLI and their most relevant specifications to optimize the acquisition of the Cerenkov signal are then presented, and CLI is compared with the other optical imaging modalities sharing the same data acquisition and processing methods. Finally, the scientific work related to CLI and the applications for which CLI has been proposed are reviewed. The paper ends with some considerations about further perspectives for this novel imaging modality.

Effectiveness of radiolabelled somatostatin analogues (90Y-DOTATOC and 177Lu-DOTATATE) in patients with metastatic neuroendocrine tumours: a single centre experience in Mexico

OBJECTIVE

To determine the effectiveness of therapy with the radiolabelled somatostatin analogues, ⁹⁰Y-DOTATOC and ¹⁷⁷Lu-DOTATATE, in the treatment of metastatic neuroendocrine tumours with progression to first-line treatment.

MATERIAL AND METHODS

A study was conducted on 30 patients diagnosed with neuroendocrine tumours (gastroenteropancreatic, bronchopulmonary, MEN2A, MEN2B, phaeochromocytoma, and paraganglioma) with metastatic disease diagnosed by the pathology department, with progression to first-line treatment, and recruited from December 2014 to February 2016. Efficacy was analysed using computed tomography (CT) according RECIST 1.1 criteria, and the molecular changes using the SUVmax of PET/CT with ⁶⁸Ga-DOTATOC. Safety was carried out with a renal scan with ^99mTc-MAG3.

RESULTS

The 30 patients received a total of 49 cycles ⁹⁰Y-DOTATOC (21 doses) and ¹⁷⁷ Lu-DOTATATE (28 doses), with a mean of 1.5 cycles per patient. Of these, 17 (56.7%) showed a partial morphological response, 22 (73.3%) molecular and biochemical response, and 23 (76.6%) clinical response. One patient died during the median follow-up of 13 months. The median overall survival from diagnosis was 54 months (95% CI; 31.18-76.81), and median progression-free survival was 32 months (95% CI; 15.00-48.99).

CONCLUSION

Therapy with ⁹⁰Y-DOTATOC and ¹⁷⁷Lu-DOTATATE is a promising therapy for patients with well and moderately differentiated neuroendocrine tumours. The efficacy is better the larger the number of cycles administered, inversely proportional to the number of metastases (<10), and is associated with the level of uptake according to the SUVmax by the metastases, regardless of metabolically active tumour volume.

A comparative evaluation of the chelators H4octapa and CHX-A″-DTPA with the therapeutic radiometal (90)Y

OBJECTIVES

To compare the radiolabeling performance, stability, and practical efficacy of the chelators CHX-A″-DTPA and H4octapa with the therapeutic radiometal (90)Y.

METHODS

The bifunctional chelators p-SCN-Bn-H4octapa and p-SCN-Bn-CHX-A″-DTPA were conjugated to the HER2-targeting antibody trastuzumab. The resulting immunoconjugates were radiolabeled with (90)Y to compare radiolabeling efficiency, in vitro and in vivo stability, and in vivo performance in a murine model of ovarian cancer.

RESULTS

High radiochemical yields (>95%) were obtained with (90)Y-CHX-A″-DTPA-trastuzumab and (90)Y-octapa-trastuzumab after 15min at room temperature. Both (90)Y-CHX-A″-DTPA-trastuzumab and (90)Y-octapa-trastuzumab exhibited excellent in vitro and in vivo stability. Furthermore, the radioimmunoconjugates displayed high tumoral uptake values (42.3±4.0%ID/g for (90)Y-CHX-A″-DTPA-trastuzumab and 30.1±7.4%ID/g for (90)Y-octapa-trastuzumab at 72h post-injection) in mice bearing HER2-expressing SKOV3 ovarian cancer xenografts. Finally, (90)Y radioimmunotherapy studies performed in tumor-bearing mice demonstrated that (90)Y-CHX-A″-DTPA-trastuzumab and (90)Y-octapa-trastuzumab are equally effective therapeutic agents, as treatment with both radioimmunoconjugates yielded substantially decreased tumor growth compared to controls.

CONCLUSIONS

Ultimately, this work demonstrates that the acyclic chelators CHX-A″-DTPA and H4octapa have comparable radiolabeling, stability, and in vivo performance, making them both suitable choices for applications requiring (90)Y.

The significance of bremsstrahlung SPECT/CT after yttrium-90 radioembolization treatment in the prediction of extrahepatic side effects

Purpose Unwanted deposition of 90Y microspheres in organs other than the liver during radioembolization of liver tumours may cause severe side effects such as duodenal ulcer. The aim of this study was to evaluate the significance of posttherapy bremsstrahlung (BS) SPECT/CT images of the liver in comparison to planar and SPECT images in the prediction of radioembolization-induced extrahepatic side effects.Methods A total of 188 radioembolization procedures were performed in 123 patients (50 women, 73 men) over a 2-year period. Planar, whole-body and BS SPECT/CT imaging were performed 24 h after treatment as a part of therapy work-up.Any focally increased extrahepatic accumulation was evaluated as suspicious. Clinical follow-up and gastroduodenoscopy served as reference standards. The studies were reviewed to evaluate whether BS SPECT/CT imaging was of benefit.Results In the light of anatomic data obtained from SPECT/CT, apparent extrahepatic BS in 43% of planar and in 52% of SPECT images proved to be in the liver and hence false positive.The results of planar scintigraphy could not be analysed further since 12 images were not assessable due to high scatter artefacts. On the basis of the gastrointestinal (GI)complications and the results of gastroduodenoscopy, true positive,true-negative, false-positive and false-negative results of BS SPECT and SPECT/CT imaging in the prediction of GI ulcers were determined. The sensitivity, specificity, positive and negative predictive values and the accuracy of SPECT and SPECT/CT in the prediction of GI ulcers were 13%, 88%, 8%,92% and 82%, and 87%, 100%, 100%, 99% and 99%,respectively.Conclusion Despite the low quality of BS images, BSSPECT/CT can be used as a reliable method to confirm the safe distribution of 90Y microspheres and in the prediction of GI side effects.

Cherenkov luminescence measurements with digital silicon photomultipliers: a feasibility study

Background

A feasibility study was done to assess the capability of digital silicon photomultipliers to measure the Cherenkov luminescence emitted by a β source. Cherenkov luminescence imaging (CLI) is possible with a charge coupled device (CCD) based technology, but a stand-alone technique for quantitative activity measurements based on Cherenkov luminescence has not yet been developed. Silicon photomultipliers (SiPMs) are photon counting devices with a fast impulse response and can potentially be used to quantify β-emitting radiotracer distributions by CLI.

Methods

In this study, a Philips digital photon counting (PDPC) silicon photomultiplier detector was evaluated for measuring Cherenkov luminescence. The PDPC detector is a matrix of avalanche photodiodes, which were read one at a time in a dark count map (DCM) measurement mode (much like a CCD). This reduces the device active area but allows the information from a single avalanche photodiode to be preserved, which is not possible with analog SiPMs. An algorithm to reject the noisiest photodiodes and to correct the measured count rate for the dark current was developed.

Results

The results show that, in DCM mode and at (10–13) °C, the PDPC has a dynamic response to different levels of Cherenkov luminescence emitted by a β source and transmitted through an opaque medium. This suggests the potential for this approach to provide quantitative activity measurements. Interestingly, the potential use of the PDPC in DCM mode for direct imaging of Cherenkov luminescence, as a opposed to a scalar measurement device, was also apparent.

Conclusions

We showed that a PDPC tile in DCM mode is able to detect and image a β source through its Cherenkov radiation emission. The detector’s dynamic response to different levels of radiation suggests its potential quantitative capabilities, and the DCM mode allows imaging with a better spatial resolution than the conventional event-triggered mode. Finally, the same acquisition procedure and data processing could be employed also for other low light levels applications, such as bioluminescence.

Electronic supplementary material

The online version of this article (doi:10.1186/s40658-015-0134-z) contains supplementary material, which is available to authorized users.

Application and Dosimetric Requirements for Gallium-68-labeled Somatostatin Analogues in Targeted Radionuclide Therapy for Gastroenteropancreatic Neuroendocrine Tumors

Neuroendocrine tumors (NETs) are associated with variable prognosis, with grade 1 and 2 NETs having more favorable outcomes than grade 3. Patients with gastroenteropancreatic (GEP)-NET need individualized interdisciplinary evaluations and treatment. New treatment options have become available with significant improvements in progression-free survival. Peptide receptor radionuclide therapy (PRRT) using (90)Y or (177)Lu-labeled somatostatin analogues (SSTa) has also shown promise in the treatment of advanced progressive NETs. (68)Ga-1,4,7,10-tetraazacyclodecane-1,4,7,10-tetraacetic acid (DOTA)-SSTa can be used as companion imaging agents to assist in radionuclide therapy selection. (68)Ga-DOTA-SSTa PET/computed tomography might also provide information for prognosis, tumor response assessment to PRRT, and internal dosimetry.

Advances in SPECT for Optimizing the Liver Tumors Radioembolization Using Yttrium-90 Microspheres

Radioembolization (RE) with Yttrium-90 ((90)Y) microspheres is an effective treatment for unresectable liver tumors. The activity of the microspheres to be administered should be calculated based on the type of microspheres. Technetium-99m macroaggregated albumin ((99m)Tc-MAA) single photon emission computed tomography/computed tomography (SPECT/CT) is a reliable assessment before RE to ensure the safe delivery of microspheres into the target. (90)Y bremsstrahlung SPECT imaging as a posttherapeutic assessment approach enables the reliable determination of absorbed dose, which is indispensable for the verification of treatment efficacy. This article intends to provide a review of the methods of optimizing (90)Y bremsstrahlung SPECT imaging to improve the treatment efficacy of liver tumor RE using (90)Y microspheres.

PET/CT-Based Dosimetry in 90Y-Microsphere Selective Internal Radiation Therapy: Single Cohort Comparison With Pretreatment Planning on (99m)Tc-MAA Imaging and Correlation With Treatment Efficacy

⁹⁰Y PET/CT can be acquired after ⁹⁰Y-microsphere selective radiation internal therapy (SIRT) to describe radioactivity distribution. We performed dosimetry using ⁹⁰Y-microsphere PET/CT data to evaluate treatment efficacy and appropriateness of activity planning from (99m)Tc-MAA scan and SPECT/CT. Twenty-three patients with liver malignancy were included in the study. (99m)Tc-MAA was injected during planning angiography and whole body (99m)Tc-MAA scan and liver SPECT/CT were acquired. After SIRT using ⁹⁰Y-resin microsphere, ⁹⁰Y-microsphere PET/CT was acquired. A partition model (PM) using 4 compartments (tumor, intarget normal liver, out-target normal liver, and lung) was adopted, and absorbed dose to each compartment was calculated based on measurements from (99m)Tc-MAA SPECT/CT and ⁹⁰Y-microsphere PET/CT, respectively, to be compared with each other. Progression-free survival (PFS) was evaluated in terms of tumor absorbed doses calculated by (99m)Tc-MAA SPECT/CT and ⁹⁰Y-microsphere PET/CT results. Lung shunt fraction was overestimated on (99m)Tc-MAA scan compared with ⁹⁰Y-microsphere PET/CT (0.060 ± 0.037 vs. 0.018 ± 0.026, P < 0.01). Tumor absorbed dose exhibited a close correlation between the results from (99m)Tc-MAA SPECT/CT and ⁹⁰Y-microsphere PET/CT (r = 0.64, P < 0.01), although the result from (99m)Tc-MAA SPECT/CT was significantly lower than that from ⁹⁰Y-microsphere PET/CT (135.4 ± 64.2 Gy vs. 185.0 ± 87.8 Gy, P < 0.01). Absorbed dose to in-target normal liver was overestimated on (99m)Tc-MAA SPECT/CT compared with PET/CT (62.6 ± 38.2 Gy vs. 45.2 ± 32.0 Gy, P = 0.02). Absorbed dose to out-target normal liver did not differ between (99m)Tc-MAA SPECT/CT and ⁹⁰Y-microsphere PET/CT (P = 0.49). Patients with tumor absorbed dose >200 Gy on ⁹⁰Y-microsphere PET/CT had longer PFS than those with tumor absorbed dose ≤200 Gy (286 ± 56 days vs. 92 ± 20 days, P = 0.046). Tumor absorbed dose calculated by (99m)Tc-MAA SPECT/CT was not a significant predictor for PFS. Activity planning based on (99m)Tc-MAA scan and SPECT/CT can be effectively used as a conservative method. Post-SIRT dosimetry based on ⁹⁰Y-microsphere PET/CT is an effective method to predict treatment efficacy.

Theranostic Imaging of Yttrium-90

This paper overviews Yttrium-90 ((90)Y) as a theranostic and nuclear medicine imaging of (90)Y radioactivity with bremsstrahlung imaging and positron emission tomography. In addition, detection and optical imaging of (90)Y radioactivity using Cerenkov luminescence will also be reviewed. Methods and approaches for qualitative and quantitative (90)Y imaging will be briefly discussed. Although challenges remain for (90)Y imaging, continued clinical demand for predictive imaging response assessment and target/nontarget dosimetry will drive research and technical innovation to provide greater clinical utility of (90)Y as a theranostic agent.

A review of 3D image-based dosimetry, technical considerations and emerging perspectives in 90Y microsphere therapy

Yttrium-90 radioembolization (⁹⁰Y-RE) is a well-established therapy for the treatment of hepatocellular carcinoma (HCC) and also of metastatic liver deposits from other malignancies. Nuclear Medicine and Cath Lab diagnostic imaging takes a pivotal role in the success of the treatment, and in order to fully exploit the efficacy of the technique and provide reliable quantitative dosimetry that are related to clinical endpoints in the era of personalized medicine, technical challenges in imaging need to be overcome. In this paper, the extensive literature of current ⁹⁰Y-RE techniques and challenges facing it in terms of quantification and dosimetry are reviewed, with a focus on the current generation of 3D dosimetry techniques. Finally, new emerging techniques are reviewed which seek to overcome these challenges, such as high-resolution imaging, novel surgical procedures and the use of other radiopharmaceuticals for therapy and pre-therapeutic planning.

Yttrium-based therapy for neuroendocrine tumors

Peptide receptor radionuclide therapy with (90)Y-peptides is generally well tolerated. Acute side effects are usually mild; some are related to the coadministration of amino acids and others to the radiopeptide itself. Chronic and permanent effects on target organs, particularly kidneys and bone marrow, are generally mild if necessary precautions are taken. The potential risk to kidney and red marrow limits the amount of radioactivity that may be administered. However, when tumor masses are irradiated with adequate doses, volume reduction may be observed. (90)Y-octreotide has been the most used radiopeptide in the first 8 to 10 years of experience.

Quantitative and qualitative assessment of Yttrium-90 PET/CT imaging

Yttrium-90 is known to have a low positron emission decay of 32 ppm that may allow for personalized dosimetry of liver cancer therapy with ⁹⁰Y labeled microspheres. The aim of this work was to image and quantify ⁹⁰Y so that accurate predictions of the absorbed dose can be made. The measurements were performed within the QUEST study (University of Sydney, and Sirtex Medical, Australia). A NEMA IEC body phantom containing 6 fillable spheres (10–37 mm ∅) was used to measure the ⁹⁰Y distribution with a Biograph mCT PET/CT (Siemens, Erlangen, Germany) with time-of-flight (TOF) acquisition. A sphere to background ratio of 8∶1, with a total ⁹⁰Y activity of 3 GBq was used. Measurements were performed for one week (0, 3, 5 and 7 d). he acquisition protocol consisted of 30 min-2 bed positions and 120 min-single bed position. mages were reconstructed with 3D ordered subset expectation maximization (OSEM) and point spread function (PSF) for iteration numbers of 1–12 with 21 (TOF) and 24 (non-TOF) subsets and CT based attenuation and scatter correction. Convergence of algorithms and activity recovery was assessed based on regions-of-interest (ROI) analysis of the background (100 voxels), spheres (4 voxels) and the central low density insert (25 voxels). For the largest sphere, the recovery coefficient (RC) values for the 30 min –2-bed position, 30 min-single bed and 120 min-single bed were 1.12±0.20, 1.14±0.13, 0.97±0.07 respectively. For the smaller diameter spheres, the PSF algorithm with TOF and single bed acquisition provided a comparatively better activity recovery. Quantification of Y-90 using Biograph mCT PET/CT is possible with a reasonable accuracy, the limitations being the size of the lesion and the activity concentration present. At this stage, based on our study, it seems advantageous to use different protocols depending on the size of the lesion.

Positron Emission Tomography (PET) in Oncology

Since its introduction in the early nineties as a promising functional imaging technique in the management of neoplastic disorders, FDG-PET, and subsequently FDG-PET/CT, has become a cornerstone in several oncologic procedures such as tumor staging and restaging, treatment efficacy assessment during or after treatment end and radiotherapy planning. Moreover, the continuous technological progress of image generation and the introduction of sophisticated software to use PET scan as a biomarker paved the way to calculate new prognostic markers such as the metabolic tumor volume (MTV) and the total amount of tumor glycolysis (TLG). FDG-PET/CT proved more sensitive than contrast-enhanced CT scan in staging of several type of lymphoma or in detecting widespread tumor dissemination in several solid cancers, such as breast, lung, colon, ovary and head and neck carcinoma. As a consequence the stage of patients was upgraded, with a change of treatment in 10%-15% of them. One of the most evident advantages of FDG-PET was its ability to detect, very early during treatment, significant changes in glucose metabolism or even complete shutoff of the neoplastic cell metabolism as a surrogate of tumor chemosensitivity assessment. This could enable clinicians to detect much earlier the effectiveness of a given antineoplastic treatment, as compared to the traditional radiological detection of tumor shrinkage, which usually takes time and occurs much later.

A simple method for estimating dose delivered to hepatocellular carcinoma after yttrium-90 glass-based radioembolization therapy: preliminary results of a proof of concept study

PURPOSE

To investigate a simple semiquantitative method to estimate yttrium-90 ((90)Y) dose delivered with radioembolization to infiltrative hepatocellular carcinoma (HCC).

MATERIALS AND METHODS

In a prospective study, patients with infiltrative HCC and portal vein thrombosis (PVT) underwent glass-based (90)Y radioembolization including technetium-99m macroaggregated albumin ((99m)Tc-MAA) hepatopulmonary shunt study before therapy and bremsstrahlung single photon emission computed tomography (SPECT)/computed tomography (CT) after (90)Y radioembolization. Baseline magnetic resonance imaging was coregistered with (99m)Tc-MAA and bremsstrahlung SPECT/CT imaging separately. Unit tumor activity ((90)Y radioactivity delivered to each cubic centimeter of tumor) was estimated based on a lobar infusion approach. Correlation between proportions of (99m)Tc-MAA and (90)Y delivered to the tumor was investigated. Survival analysis was performed using Kaplan-Meier estimations.

RESULTS

(90)Y therapy was administered in 18 consecutive patients (median age, 55.3 y; mean tumor volume, 588 cm(3)). Higher intratumoral (90)Y dose predicted prolonged survival, with 13.2-month median survival in patients with HCC and mean (90)Y dose of ≥ 100 Gy versus 4.6-month median survival for other patients (P < .001). Of administered (90)Y dose, 51.9% was delivered to the targeted tumors compared with 74.1% of (99m)Tc-MAA with linear correlation between biodistribution of (99m)Tc-MAA and (90)Y observed (Pearson r = 0.774, P < .001).

CONCLUSIONS

The findings in this study suggest that approximately 50% of administered (90)Y dose is taken up by targeted infiltrative HCC with PVT. Intratumoral (90)Y dose ≥ 100 Gy in unresectable infiltrative HCC via a lobar intraarterial approach is a positive prognostic factor for survival.

Optimal design of anger camera for bremsstrahlung imaging: monte carlo evaluation

A conventional Anger camera is not adapted to bremsstrahlung imaging and, as a result, even using a reduced energy acquisition window, geometric x-rays represent <15% of the recorded events. This increases noise, limits the contrast, and reduces the quantification accuracy. Monte Carlo (MC) simulations of energy spectra showed that a camera based on a 30-mm-thick BGO crystal and equipped with a high energy pinhole collimator is well-adapted to bremsstrahlung imaging. The total scatter contamination is reduced by a factor 10 versus a conventional NaI camera equipped with a high energy parallel hole collimator enabling acquisition using an extended energy window ranging from 50 to 350 keV. By using the recorded event energy in the reconstruction method, shorter acquisition time and reduced orbit range will be usable allowing the design of a simplified mobile gantry. This is more convenient for use in a busy catheterization room. After injecting a safe activity, a fast single photon emission computed tomography could be performed without moving the catheter tip in order to assess the liver dosimetry and estimate the additional safe activity that could still be injected. Further long running time MC simulations of realistic acquisitions will allow assessing the quantification capability of such system. Simultaneously, a dedicated bremsstrahlung prototype camera reusing PMT–BGO blocks coming from a retired PET system is currently under design for further evaluation.

Radiolabeled Cetuximab Conjugates for EGFR Targeted Cancer Diagnostics and Therapy

The epidermal growth factor receptor (EGFR) has evolved over years into a main molecular target for the treatment of different cancer entities. In this regard, the anti-EGFR antibody cetuximab has been approved alone or in combination with: (a) chemotherapy for treatment of colorectal and head and neck squamous cell carcinoma and (b) with external radiotherapy for treatment of head and neck squamous cell carcinoma. The conjugation of radionuclides to cetuximab in combination with the specific targeting properties of this antibody might increase its therapeutic efficiency. This review article gives an overview of the preclinical studies that have been performed with radiolabeled cetuximab for imaging and/or treatment of different tumor models. A particularly promising approach seems to be the treatment with therapeutic radionuclide-labeled cetuximab in combination with external radiotherapy. Present data support an important impact of the tumor micromilieu on treatment response that needs to be further validated in patients. Another important challenge is the reduction of nonspecific uptake of the radioactive substance in metabolic organs like liver and radiosensitive organs like bone marrow and kidneys. Overall, the integration of diagnosis, treatment and monitoring as a theranostic approach appears to be a promising strategy for improvement of individualized cancer treatment.

Matching chelators to radiometals for radiopharmaceuticals

Radiometals comprise many useful radioactive isotopes of various metallic elements. When properly harnessed, these have valuable emission properties that can be used for diagnostic imaging techniques, such as single photon emission computed tomography (SPECT, e.g.(67)Ga, (99m)Tc, (111)In, (177)Lu) and positron emission tomography (PET, e.g.(68)Ga, (64)Cu, (44)Sc, (86)Y, (89)Zr), as well as therapeutic applications (e.g.(47)Sc, (114m)In, (177)Lu, (90)Y, (212/213)Bi, (212)Pb, (225)Ac, (186/188)Re). A fundamental critical component of a radiometal-based radiopharmaceutical is the chelator, the ligand system that binds the radiometal ion in a tight stable coordination complex so that it can be properly directed to a desirable molecular target in vivo. This article is a guide for selecting the optimal match between chelator and radiometal for use in these systems. The article briefly introduces a selection of relevant and high impact radiometals, and their potential utility to the fields of radiochemistry, nuclear medicine, and molecular imaging. A description of radiometal-based radiopharmaceuticals is provided, and several key design considerations are discussed. The experimental methods by which chelators are assessed for their suitability with a variety of radiometal ions is explained, and a large selection of the most common and most promising chelators are evaluated and discussed for their potential use with a variety of radiometals. Comprehensive tables have been assembled to provide a convenient and accessible overview of the field of radiometal chelating agents.

In vivo dosimetry based on SPECT and MR imaging of 166Ho-microspheres for treatment of liver malignancies

(166)Ho-poly(l-lactic acid) microspheres allow for quantitative imaging with MR imaging or SPECT for microsphere biodistribution assessment after radioembolization. The purpose of this study was to evaluate SPECT- and MR imaging-based dosimetry in the first patients treated with (166)Ho radioembolization.

METHODS

Fifteen patients with unresectable, chemorefractory liver metastases of any origin were enrolled in this phase 1 study and were treated with (166)Ho radioembolization according to a dose escalation protocol (20-80 Gy). The contours of all liver segments and all discernible tumors were manually delineated on T2-weighted posttreatment MR images and registered to the posttreatment SPECT images (n = 9) or SPECT/CT images (n = 6) and MR imaging-based R2* maps (n = 14). Dosimetry was based on SPECT (n = 15) and MR imaging (n = 9) for all volumes of interest, tumor-to-nontumor (T/N) activity concentration ratios were calculated, and correlation and agreement of MR imaging- and SPECT-based measurements were evaluated.

RESULTS

The median overall T/N ratio was 1.4 based on SPECT (range, 0.9-2.8) and 1.4 based on MR imaging (range, 1.1-3.1). In 6 of 15 patients (40%), all tumors had received an activity concentration equal to or higher than the normal liver (T/N ratio ≥ 1). Analysis of SPECT and MR imaging measurements for dose to liver segments yielded a high correlation (R(2) = 0.91) and a moderate agreement (mean bias, 3.7 Gy; 95% limits of agreement, -11.2 to 18.7).

CONCLUSION

With the use of (166)Ho-microspheres, in vivo dosimetry is feasible on the basis of both SPECT and MR imaging, which enables personalized treatment by selective targeting of inadequately treated tumors.

Relevance of PET for pretherapeutic prediction of doses in peptide receptor radionuclide therapy

Personalized dosimetry in radionuclide therapy has gained much attention in recent years. This attention has also an impact on peptide receptor radionuclide therapy (PRRT). This article reviews the PET-based imaging techniques that can be used for pretherapeutic prediction of doses in PRRT. More specifically the usage of (86)Y, (90)Y, (68)Ga, and (44)Sc are discussed: their characteristics for PET acquisition, the available peptides for labeling, the specifics of the imaging protocols, and the experiences gained from phantom and clinical studies. These techniques are evaluated with regard to their usefulness for dosimetry predictions in PRRT, and future perspectives are discussed.

Post-radioembolization yttrium-90 PET/CT - part 1: diagnostic reporting

Background

Yttrium-90 (⁹⁰Y) positron emission tomography with integrated computed tomography (PET/CT) represents a technological leap from ⁹⁰Y bremsstrahlung single-photon emission computed tomography with integrated computed tomography (SPECT/CT) by coincidence imaging of low abundance internal pair production. Encouraged by favorable early experiences, we implemented post-radioembolization ⁹⁰Y PET/CT as an adjunct to ⁹⁰Y bremsstrahlung SPECT/CT in diagnostic reporting.

Methods

This is a retrospective review of all paired ⁹⁰Y PET/CT and ⁹⁰Y bremsstrahlung SPECT/CT scans over a 1-year period. We compared image resolution, ability to confirm technical success, detection of non-target activity, and providing conclusive information about ⁹⁰Y activity within targeted tumor vascular thrombosis. ⁹⁰Y resin microspheres were used. ⁹⁰Y PET/CT was performed on a conventional time-of-flight lutetium-yttrium-oxyorthosilicate scanner with minor modifications to acquisition and reconstruction parameters. Specific findings on ⁹⁰Y PET/CT were corroborated by ⁹⁰Y bremsstrahlung SPECT/CT, ^99mTc macroaggregated albumin SPECT/CT, follow-up diagnostic imaging or review of clinical records.

Results

Diagnostic reporting recommendations were developed from our collective experience across 44 paired scans. Emphasis on the continuity of care improved overall diagnostic accuracy and reporting confidence of the operator. With proper technique, the presence of background noise did not pose a problem for diagnostic reporting. A counter-intuitive but effective technique of detecting non-target activity is proposed, based on the pattern of activity and its relation to underlying anatomy, instead of its visual intensity. In a sub-analysis of 23 patients with a median follow-up of 5.4 months, ⁹⁰Y PET/CT consistently outperformed ⁹⁰Y bremsstrahlung SPECT/CT in all aspects of qualitative analysis, including assessment for non-target activity and tumor vascular thrombosis. Parts of viscera closely adjacent to the liver remain challenging for non-target activity detection, compounded by a tendency for mis-registration.

Conclusions

Adherence to proper diagnostic reporting technique and emphasis on continuity of care are vital to the clinical utility of post-radioembolization ⁹⁰Y PET/CT. ⁹⁰Y PET/CT is superior to ⁹⁰Y bremsstrahlung SPECT/CT for the assessment of target and non-target activity.

The joint IAEA, EANM, and SNMMI practical guidance on peptide receptor radionuclide therapy (PRRNT) in neuroendocrine tumours

Peptide receptor radionuclide therapy (PRRNT) is a molecularly targeted radiation therapy involving the systemic administration of a radiolabelled peptide designed to target with high affinity and specificity receptors overexpressed on tumours. PRRNT employing the radiotagged somatostatin receptor agonists (90)Y-DOTATOC ([(90)Y-DOTA(0),Tyr(3)]-octreotide) or (177)Lu-DOTATATE ([(177)Lu-DOTA(0),Tyr(3),Thr(8)]-octreotide or [(177)Lu-DOTA(0),Tyr(3)]-octreotate) have been successfully used for the past 15 years to target metastatic or inoperable neuroendocrine tumours expressing the somatostatin receptor subtype 2. Accumulated evidence from clinical experience indicates that these tumours can be subjected to a high absorbed dose which leads to partial or complete objective responses in up to 30 % of treated patients. Survival analyses indicate that patients presenting with high tumour receptor expression at study entry and receiving (177)Lu-DOTATATE or (90)Y-DOTATOC treatment show significantly higher objective responses, leading to longer survival and improved quality of life. Side effects of PRRNT are typically seen in the kidneys and bone marrow. These, however, are usually mild provided adequate protective measures are undertaken. Despite the large body of evidence regarding efficacy and clinical safety, PRRNT is still considered an investigational treatment and its implementation must comply with national legislation, and ethical guidelines concerning human therapeutic investigations. This guidance was formulated based on recent literature and leading experts' opinions. It covers the rationale, indications and contraindications for PRRNT, assessment of treatment response and patient follow-up. This document is aimed at guiding nuclear medicine specialists in selecting likely candidates to receive PRRNT and to deliver the treatment in a safe and effective manner. This document is largely based on the book published through a joint international effort under the auspices of the Nuclear Medicine Section of the International Atomic Energy Agency.

Advances in immuno-positron emission tomography: antibodies for molecular imaging in oncology

Identification of cancer cell-surface biomarkers and advances in antibody engineering have led to a sharp increase in the development of therapeutic antibodies. These same advances have led to a new generation of radiolabeled antibodies and antibody fragments that can be used as cancer-specific imaging agents, allowing quantitative imaging of cell-surface protein expression in vivo. Immuno-positron emission tomography (immunoPET) imaging with intact antibodies has shown success clinically in diagnosing and staging cancer. Engineered antibody fragments, such as diabodies, minibodies, and single-chain Fv (scFv) -Fc, have been successfully employed for immunoPET imaging of cancer cell-surface biomarkers in preclinical models and are poised to bring same-day imaging into clinical development. ImmunoPET can potentially provide a noninvasive approach for obtaining target-specific information useful for titrating doses for radioimmunotherapy, for patient risk stratification and selection of targeted therapies, for evaluating response to therapy, and for predicting adverse effects, thus contributing to the ongoing development of personalized cancer treatment.

Availability of yttrium-90 from strontium-90: a nuclear medicine perspective

Yttrium-90 (T(½) 64.1 hours, E(βmax)=2.28 MeV) is a pure β⁻ particle emitting radionuclide with well-established applications in targeted therapy. There are several advantages of ⁹⁰Y as a therapeutic radionuclide. It has a suitable physical half-life (∼64 hours) and decays to a stable daughter product ⁹⁰Zr by emission of high-energy β⁻ particles. Yttrium has a relatively simple chemistry and its suitability for forming complexes with a variety of chelating agents is well established. The ⁹⁰Sr/⁹⁰Y generator is an ideal source for the long-term continuous availability of no-carrier-added ⁹⁰Y suitable for the preparation of radiopharmaceuticals for radionuclide therapy. The parent radionuclide ⁹⁰Sr, which is a long-lived fission product, is available in large quantities from spent fuel. Several useful technologies have been developed for the preparation of ⁹⁰Sr/⁹⁰Y generators. There are several well-established radiopharmaceuticals based on monoclonal antibodies, peptides, and particulates labeled with ⁹⁰Y, that are in regular use for the treatment of some forms of primary cancers and arthritis. At present, there are no generators for the elution of ⁹⁰Y that can be set up in a hospital radiopharmacy. The radionuclide is procured from manufacturers and the radiopharmaceuticals are formulated on site. This article reviews the development of ⁹⁰Sr/⁹⁰Y generator and the development of ⁹⁰Y radiopharmaceuticals.

Yttrium-labelled peptides for therapy of NET

Peptide receptor radionuclide therapy (PRRT) consists in the systemic administration of a synthetic peptide, labelled with a suitable beta-emitting radionuclide, able to irradiate tumours and their metastases via the internalization through a specific receptor, overexpressed on the cell membrane. After 15 years of experience, we can state that PRRT with (90)Y-labelled peptides is generally well tolerated. Acute side effects are usually mild, some of which are related to the co-administration of amino acids, such as nausea. Others are related to the radiopeptide, such as fatigue or the exacerbation of an endocrine syndrome, which rarely occurs in functioning tumours. Chronic and permanent effects on target organs, particularly the kidneys and the bone marrow, are generally mild if the necessary precautions are taken. Currently, the potential risk to kidney and red marrow limits the amount of radioactivity that may be administered. However, when tumour masses are irradiated with adequate doses, volume reduction may be observed. (90)Y-octreotide has been the most widely used radiopeptide in the first 8-10 years of experience. Unfortunately, all of the published results derive from different and inhomogeneous phase I/II studies. Hence, a direct comparison is virtually impossible to date. Nevertheless, even with these limitations, objective responses are registered in 10-34% of patients. The optimal timing of (90)Y-DOTATOC in the management of somatostatin receptor (SSTR)-positive tumours and the way in which it should be integrated with other treatments have yet to be defined, and prospective phase II/III trials comparing the efficacy and toxicity of different schemes of (90)Y-DOTATOC administration are still warranted.

Lutetium-labelled peptides for therapy of neuroendocrine tumours

Treatment with radiolabelled somatostatin analogues is a promising new tool in the management of patients with inoperable or metastasized neuroendocrine tumours. Symptomatic improvement may occur with ¹⁷⁷Lu-labelled somatostatin analogues that have been used for peptide receptor radionuclide therapy (PRRT). The results obtained with ¹⁷⁷Lu-[DOTA⁰,Tyr³]octreotate (DOTATATE) are very encouraging in terms of tumour regression. Dosimetry studies with ¹⁷⁷Lu-DOTATATE as well as the limited side effects with additional cycles of ¹⁷⁷Lu-DOTATATE suggest that more cycles of ¹⁷⁷Lu-DOTATATE can be safely given. Also, if kidney-protective agents are used, the side effects of this therapy are few and mild and less than those from the use of ⁹⁰Y-[DOTA⁰,Tyr³]octreotide (DOTATOC). Besides objective tumour responses, the median progression-free survival is more than 40 months. The patients' self-assessed quality of life increases significantly after treatment with ¹⁷⁷Lu-DOTATATE. Lastly, compared to historical controls, there is a benefit in overall survival of several years from the time of diagnosis in patients treated with ¹⁷⁷Lu-DOTATATE. These findings compare favourably with the limited number of alternative therapeutic approaches. If more widespread use of PRRT can be guaranteed, such therapy may well become the therapy of first choice in patients with metastasized or inoperable neuroendocrine tumours.

Hemoglobin level significantly impacts the tumor cell survival fraction in humans after internal radiotherapy

Background

Anemia is usually not taken into account in internal radiotherapy. We investigated whether the hemoglobin (Hb) level could have an impact on the tumor response, as observed in external beam radiotherapy (EBRT).

Methods

Absorbed doses of 25 hepatic metastatic sites in eight patients who underwent a liver selective internal radiotherapy (SIRT) were computed by a 3D convolution of a dose deposition kernel with the ⁹⁰Y time-of-flight positron emission tomography (TOF-PET) images acquired following therapy. Early tumor response was assessed by comparing a follow-up FDG TOF-PET scan with a baseline scan. Hb level was measured on the day of the SIRT procedure.

Results

All patients displayed early tumor response increasing with the tumor-absorbed dose. Significant differences between patients were noted, the response slope correlating with the Hb level. After applying a global fit on all metastases using a tumor radiosensitivity modulated by a Hb enhancement factor (HEF) linearly dependent on the Hb level, a strong correlation (R = 0.96) was observed between the early response and the absorbed dose. Hb level had a major impact on tumor response by modulating HEF by a factor 6.

Conclusions

These results prove the significant impact of Hb level on the tumor response and support the study of methods for correcting tumor hypoxia, such as intensively performed in EBRT. The quantitative analysis of the relationship between tumor doses and early response has the power to allow fast screening of such correction methods in limited patient series. Internal radiotherapy could be more efficient if performed earlier in the therapy line, when the disease- and treatment-related anemia remains limited.