Radium-223 dichloride in clinical practice: a review

Advancements in the development of radiopharmaceuticals for nuclear medicine applications in the treatment of bone metastases

Bone metastases are a painful and complex condition that overwhelmingly impacts the prognosis and quality of life of cancer patients. Over the years, nuclear medicine has made remarkable progress in the diagnosis and management of bone metastases. This review aims to provide a comprehensive overview of the recent advancements in nuclear medicine for the diagnosis and management of bone metastases. Furthermore, the review explores the role of targeted radiopharmaceuticals in nuclear medicine for bone metastases, focusing on radiolabeled molecules that are designed to selectively target biomarkers associated with bone metastases, including osteocytes, osteoblasts, and metastatic cells. The applications of radionuclide-based therapies, such as strontium-89 (Sr-89) and radium-223 (Ra-223), are also discussed. This review also highlights the potential of theranostic approaches for bone metastases, enabling personalized treatment strategies based on individual patient characteristics. Importantly, the clinical applications and outcomes of nuclear medicine in osseous metastatic disease are discussed. This includes the assessment of treatment response, predictive and prognostic value of imaging biomarkers, and the impact of nuclear medicine on patient management and outcomes. The review identifies current challenges and future perspectives on the role of nuclear medicine in treating bone metastases. It addresses limitations in imaging resolution, radiotracer availability, radiation safety, and the need for standardized protocols. The review concludes by emphasizing the need for further research and advancements in imaging technology, radiopharmaceutical development, and integration of nuclear medicine with other treatment modalities. In summary, advancements in nuclear medicine have significantly improved the diagnosis and management of osseous metastatic disease and future developements in the integration of innovative imaging modalities, targeted radiopharmaceuticals, radionuclide production, theranostic approaches, and advanced image analysis techniques hold great promise in improving patient outcomes and enhancing personalized care for individuals with bone metastases.

Using VARSKIN+v1.2 to estimate dose from direct skin contamination with radionuclides 223 Ra, 212 Pb and 225 Ac; considerations for Nuclear Medicine staff and associated Personal Protective Equipment (PPE)

OBJECTIVE

To calculate depth-weighted doses for 223 Ra, 212 Pb and 225 Ac for the skin sites of trunk, arms/legs, face, wrist, back of hand, fingertip, back and side of fingers using VARSKIN+v1.2.

METHODS

Published depth distribution histograms of the basal cells were used with dose averaging in VARSKIN+v1.2. A density correction factor was applied for the 1 g/cc within VARSKIN. Results were compared to the regulatory 70 µm depth and to average depth values for the skin sites.

RESULTS

223 Ra has no alpha component at the regulatory 70 µm. This dose is exceeded by the depth-weighted dose rates for all sites (except the fingertip) with factors ×74 (back of finger) to x3600 (trunk). 212 Pb and 225 Ac have alpha contributions at 70 µm. . For 212 Pb, this dose value is greater by over ×2 than the depth-weighted dose rate for the wrist, back of hand, and finger sites, and underestimates dose rates for the other sites. For 225 Ac, the 70µm dose rate is exceeded by the depth-weighted dose rates for the trunk, face, arms/legs by factors of ×4-10. Using fixed depth values, the depth-weighted dose rates are larger for all sites except the fingertip. The skin dose is also calculated for biological half-lives of 1, 3 and 6 h. Using the depth-weighted dose rates and a 3 h biological half-life, the activity for 500 mSv is in the range 9-177 Bq for the trunk, face, arms/legs, wrist and hand for all three radionuclides.

CONCLUSION

For alpha-emitting radionuclides a depth-weighted calculation gives more representative dose values. The very low activity values for 500 mSv skin dose to be exceeded have implications for appropriate staff PPE and training.

Radiometals in Imaging and Therapy: Highlighting Two Decades of Research

The present article highlights the important progress made in the last two decades in the fields of molecular imaging and radionuclide therapy. Advancements in radiometal-based positron emission tomography, single photon emission computerized tomography, and radionuclide therapy are illustrated in terms of their production routes and ease of radiolabeling. Applications in clinical diagnostic and radionuclide therapy are considered, including human studies under clinical trials; their current stages of clinical translations and findings are summarized. Because the metalloid astatine is used for imaging and radionuclide therapy, it is included in this review. In regard to radionuclide therapy, both beta-minus (β-) and alpha (α)-emitting radionuclides are discussed by highlighting their production routes, targeted radiopharmaceuticals, and current clinical translation stage.

A New Radiopharmaceutical 225 Ac-DOTA-IBA in the Treatment of a Case of Bone Metastases

ABSTRACT

α-Emitter 225 Ac has been considered a candidate for targeted α-therapy. DOTA-IBA is new a precursor targeting bone metastasis. It can be used for radionuclide labeling with 225 Ac. We present a case with refractory bone pain for bone metastasis, who demonstrated an excellent therapy response after 1 cycle of 225 Ac-DOTA-IBA therapy. Moreover, the patient did not have any observable adverse effects.

Preparation, Characterization, and Preliminary Imaging Study of [188Re]Re-Ibandronate as a Novel Theranostic Radiopharmaceutical for Bone Metastasis

Background

Bone is a common site of metastasis from a malignant tumor. Several radiopharmaceuticals are available to relieve bone pain in patients with cancer. However, every radiopharmaceutical has its own disadvantages, and there is still a need to investigate easily accessible and high bone affinity radiopharmaceuticals. Ibandronate (IBA) and ¹⁸⁸Re were used for radiolabeling to develop and evaluate a novel type of bone-seeking radiopharmaceutical.

Methods

The preparation conditions of [¹⁸⁸Re]Re-IBA were investigated, and thin-layer chromatography was used to analyze radiochemical purity. The stability, plasma protein binding rate, lipid-water distribution coefficient, safety and biodistribution in normal mice, and bone imaging of [¹⁸⁸Re]Re-IBA in New Zealand rabbits were studied. In addition, the nude mice model of bone metastasis was established, and biodistribution and imaging characteristics of [¹⁸⁸Re]Re-IBA in these nude mice were studied.

Results

[¹⁸⁸Re]Re-IBA was successfully prepared with radiochemical purity >95%. The optimum preparation conditions were as follows: IBA, 0.8–1.4 mg; ascorbic acid, 0.2–0.5 mg; stannous chloride, 0.14–0.18 mg; potassium perrhenate, 0.005 mg; and [¹⁸⁸Re]ReO₄⁻ activity, 18.5–296 MBq, reacted for 30 min at 95°C with pH = 2. [¹⁸⁸Re]Re-IBA demonstrated good stability, high plasma protein binding rate, good hydrophilicity, and low toxicity. The biodistribution and bone imaging in normal animals showed rapid blood clearance, high bone uptake, low uptake in the solid organs and soft tissue, and high contrast during imaging. The biodistribution and imaging of bone metastasis in nude mice showed that [¹⁸⁸Re]Re-IBA has higher uptake in bone metastasis lesions than normal bone.

Conclusions

Our study encompassed the successful preparation of [¹⁸⁸Re]Re-IBA, a novel bone-seeking radiopharmaceutical, and confirmed it has potential in the treatment of bone metastasis and monitoring through imaging.

Single-Photon Emission Computed Tomography/Computed Tomography Image-Based Radiomics for Discriminating Vertebral Bone Metastases From Benign Bone Lesions in Patients With Tumors

Purpose: The purpose of this study was to investigate the feasibility of Single-Photon Emission Computed Tomography/Computed Tomography (SPECT/CT) image-based radiomics in differentiating bone metastases from benign bone lesions in patients with tumors. Methods: A total of 192 lesions from 132 patients (134 in the training group, 58 in the validation group) diagnosed with vertebral bone metastases or benign bone lesions were enrolled. All images were evaluated and diagnosed independently by two physicians with more than 20 years of diagnostic experience for qualitative classification, the images were imported into MaZda software in Bitmap (BMP) format for feature extraction. All radiomics features were selected by least absolute shrinkage and selection operator (LASSO) regression and 10-fold cross-validation algorithms after the process of normalization and correlation analysis. Based on these selected features, two models were established: The CT model and SPECT model (radiomics features were derived from CT and SPECT images, respectively). In addition, a combination model (ComModel) combined CT and SPECT features was developed in order to better evaluate the predictive performance of radiomics models. Subsequently, the diagnostic performance between each model was separately evaluated by a confusion matrix. Results: There were 12, 13, and 18 features contained within the CT, SPECT, and ComModel, respectively. The constructed radiomics models based on SPECT/CT images to discriminate between bone metastases and benign bone lesions not only had high diagnostic efficacy in the training group (AUC of 0.894, 0.914, 0.951 for CT model, SPECT model, and ComModel, respectively), but also performed well in the validation group (AUC; 0.844, 0.871, 0.926). The AUC value of the human experts was 0.849 and 0.839 in the training and validation groups, respectively. Furthermore, both SPECT model and ComModel show higher classification performance than human experts in the training group (P = 0.021 and P = 0.001, respectively) and the validation group (P = 0.037 and P = 0.007, respectively). All models showed better diagnostic accuracy than human experts in the training group and the validation group. Conclusion: Radiomics derived from SPECT/CT images could effectively discriminate between bone metastases and benign bone lesions. This technique may be a new non-invasive way to help prevent unnecessary delays in diagnosis and a potential contribution in disease staging and treatment planning.

177Lu-EDTMP for Metastatic Bone Pain Palliation: A Systematic Review and Meta-Analysis

Purpose: Painful metastatic bone involvement is common in advanced stages of many cancers. Between available radionuclides for bone pain palliation, no consensus has been reached on lutetium ethylenediaminetetramethylene phosphonate (¹⁷⁷Lu-EDTMP) administration in this milieu. The aim of this study is to evaluate the treatment efficacy, safety profile, and toxicities of ¹⁷⁷Lu-EDTMP in patients with metastatic bone involvement, according to the published literature. Methods: A comprehensive literature search of PubMed/MEDLINE, Scopus, and Google Scholar databases was carried out to retrieve pertinent articles published until January 2019, concerning the clinical efficacy and safety of ¹⁷⁷Lu-EDTMP for bone pain palliative purposes. Results: Eight studies (172 patients) were included. This analysis revealed statistically significant effect of ¹⁷⁷Lu-EDTMP therapy on the visual analog score (4.84% (95% CI: 3.88-5.81; p < 0.001), bone palliative pain response (84%, 95% CI: 75%-90%; p < 0.001), and Karnofsky performance status (21%, 95% CI: 18%-24%; p < 0.001) overall (as well as in the high-dose and low-dose subgroups). Complete palliative pain response to treatment was observed in 32% (95% CI: 16%-53%) of patients receiving ¹⁷⁷Lu-EDTMP. Anemia was found to be the most common hematologic toxicity imposed by this therapeutic approach (grade I/II anemia in 24% (95% CI: 14%-38%; p < 0.001) and grade III/IV anemia in 19% (95% CI: 12%-28%; p < 0.001)). Conclusions: ¹⁷⁷Lu-EDTMP seems to have comparable efficacy and safety profile as that of the frequently administered radiopharmaceuticals for bone palliation. Therefore, this agent can be a good option for bone pain palliative purposes, in case of limited access to other bone palliative radiopharmaceuticals.

Targeted Palliative Radionuclide Therapy for Metastatic Bone Pain

Bone metastasis develops in multiple malignancies with a wide range of incidence. The presence of multiple bone metastases, leading to a multitude of complications and poorer prognosis. The corresponding refractory bone pain is still a challenging issue managed through multidisciplinary approaches to enhance the quality of life. Radiopharmaceuticals are mainly used in the latest courses of the disease. Bone-pain palliation with easy-to-administer radionuclides offers advantages, including simultaneous treatment of multiple metastatic foci, the repeatability and also the combination with other therapies. Several β¯- and α-emitters as well as pharmaceuticals, from the very first [⁸⁹Sr]strontium-dichloride to recently introduced [²²³Ra]radium-dichloride, are investigated to identify an optimum agent. In addition, the combination of bone-seeking radiopharmaceuticals with chemotherapy or radiotherapy has been employed to enhance the outcome. Radiopharmaceuticals demonstrate an acceptable response rate in pain relief. Nevertheless, survival benefits have been documented in only a limited number of studies. In this review, we provide an overview of bone-seeking radiopharmaceuticals used for bone-pain palliation, their effectiveness and toxicity, as well as the results of the combination with other therapies. Bone-pain palliation with radiopharmaceuticals has been employed for eight decades. However, there are still new aspects yet to be established.

Radiochemical aspects of alpha emitting radionuclides for medical application

The use of α-emitting radionuclides in targeted alpha therapy (TAT) holds great potential for treatment of human diseases, such as cancer, due to the short pathlength and high potency of the α particle, which can localize damage to targeted cells while minimizing effects to healthy surrounding tissues. In this review several potential α-emitting radionuclides having emission properties applicable to TAT are discussed from a radiochemical point of view. Overviews of production, radiochemical separation and chelation aspects relative to developing TAT radiopharmaceuticals are provided for the α-emitting radionuclides (and their generator systems) 211At, 224Ra/212Pb/212Bi, 225Ac/213Bi, 227Th/223Ra, 230U/226Th, 149Tb and 255Fm.

223Ra-dichloride therapy of bone metastasis: optimization of SPECT images for quantification

BACKGROUND

223Ra imaging is crucial to evaluate the successfulness of the therapy of bone metastasis of castration-resistant prostate cancer (CRPC). The goals of this study were to establish a quantitative tomographic 223Ra imaging protocol with clinically achievable conditions, as well as to investigate its usefulness and limitations. We performed several experiments using the Infinia Hawkeye 4 gamma camera (GE) and physical phantoms in order to assess the optimal image acquisition and reconstruction parameters, such as the windows setting, as well as the iteration number and filter of the reconstruction algorithm. Then, based on the MIRD pamphlet 23, we used a NEMA phantom and an anthropomorphic TORSO® phantom to calibrate the gamma camera and investigate the accuracy of quantification.

RESULTS

Experiences showed that the 85 keV ± 20%, 154 keV ± 10%, and 270 keV ± 10% energy windows are the most suitable for 223Ra imaging. The study with the NEMA phantom showed that the OSEM algorithm with 2 iterations, 10 subsets, and the Butterworth filter offered the best compromise between contrast and noise. Moreover, the calibration factors for different sphere sizes (26.5 ml, 11.5 ml, and 5.6 ml) were constant for 223Ra concentrations ranging between 6.5 and 22.8 kBq/ml. The values found are 73.7 cts/s/MBq, 43.8 cts/s/MBq, and 43.4 cts/s/MBq for 26.5 ml, 11.5 ml, and 5.6 ml sphere, respectively. For concentration lower than 6.5 kBq/ml, the calibration factors exhibited greater variability pointing out the limitations of SPECT/CT imaging for quantification. By the use of a TORSO® phantom, we simulated several tumors to normal tissue ratios as close as possible to clinical conditions. Using the calibration factors obtained with the NEMA phantom, for 223Ra concentrations higher than 8 kBq/ml, we were able to quantify the activity with an error inferior to 18.8% in a 5.6 ml lesion.

CONCLUSIONS

Absolute quantitative 223Ra SPECT imaging appears feasible once the dimension of the target is determined. Further evaluation should be needed to apply the calibration factor-based quantitation to clinical 223Ra SPECT/CT imaging. This will open the possibility for patient-specific 223Ra treatment planning and therapeutic outcome prediction in patients.

Can bone scans guide therapy with radium-223 dichloride for prostate cancer bone metastases?

BACKGROUND

Radium-223 dichloride (Ra-223 Xofigo) has recently been approved as an addition to the host of available therapies in the USA as a treatment option for metastatic castrate-resistant prostate cancer (mCRPC) with bone metastases. This study describes our initial experience in patients treated with Ra-223 dichloride. It attempts to optimize patients' selection for the best outcome from Ra-223 dichloride therapy.

METHODS

Consecutive patients who were referred for treatment with Ra-223 dichloride were prospectively followed. Patients' demographics, functional status per the Eastern Cooperative Oncology Group (ECOG) performance score, pain level per the numeric rating score (NRS), prostate-specific antigen (PSA), creatinine, and hematological values were compared at baseline and at the end of therapy. Patients also had a bone scan before starting therapy and at the end of therapy. Patients were divided into the favorable response (FR) group if their pain and/or functional status improved and the unfavorable response (UR) group if they did not improve, deteriorated, or deceased. Bone scan findings before and after Ra-223 dichloride therapy were compared in both the FR and UR groups.

RESULTS

Twenty patients were treated with Ra-223 dichloride. Twelve patients had innumerable bone metastases, three patients had super scans, and three patients had two to seven bone lesions. Two patients were lost to follow-up after the first injection. There were eight patients in the FR group and 10 patients in the UR group. Patients with UR had mean ECOG and NRS pain scores of 1.3 and 5.0 versus 0.8 and 4.4 in the FR group. The mean PSA and creatinine levels in the UR group were 445.2 ng/mL and 1.2 mg/dL versus 22.7 ng/mL and 1.1 mg/dL in the FR group. The mean hemoglobin, platelets, and absolute neutrophil values were 11.2 g/dL, 314.9 K/cmm, and 7.3 K/cmm in the UR group versus 11.6 g/dL, 207.0 K/cmm, and 6.2 K/cmm in the FR group. Seven of the eight patients with FR had a bone scan at the end of therapy showing improvement in five patients, a mixed response in one patient, and progression in another patient. Five patients in the UR group completed five or six injections and had bone scans showing flare of bone metastases in three patients, progression in one patient, and improvement in the fifth patient. Three patients in the UR group died after the first or second injections. Two of these patients had baseline super scans and the third one had widespread bone metastases.

CONCLUSION

mCRPC patients with lower PSA levels at baseline and fewer bone lesions are more likely to respond favorably to Ra-223 dichloride therapy.

Targeted and Nontargeted α-Particle Therapies

α-Particle irradiation of cancerous tissue is increasingly recognized as a potent therapeutic option. We briefly review the physics, radiobiology, and dosimetry of α-particle emitters, as well as the distinguishing features that make them unique for radiopharmaceutical therapy. We also review the emerging clinical role of α-particle therapy in managing cancer and recent studies on in vitro and preclinical α-particle therapy delivered by antibodies, other small molecules, and nanometer-sized particles. In addition to their unique radiopharmaceutical characteristics, the increased availability and improved radiochemistry of α-particle radionuclides have contributed to the growing recent interest in α-particle radiotherapy. Targeted therapy strategies have presented novel possibilities for the use of α-particles in the treatment of cancer. Clinical experience has already demonstrated the safe and effective use of α-particle emitters as potent tumor-selective drugs for the treatment of leukemia and metastatic disease.

Current status of theranostics in prostate cancer

The aim of this review is to report on the current status of prostate-specific membrane antigen (PSMA)-directed theranostics in prostate cancer (PC) patients. The value of 68Ga-PSMA-directed PET imaging as a diagnostic procedure for primary and recurrent PC as well as the role of evolving PSMA radioligand therapy (PRLT) in castration-resistant (CR)PC is assessed. The most eminent data from mostly retrospective studies currently available on theranostics of prostate cancer are discussed. The current knowledge on 68Ga-PSMA PET/CT implicates that primary staging with PET/CT is meaningful in patients with high-risk PC and that the combination with pelvic multi parametric (mp)MR (or PET/mpMR) reaches the highest impact on patient management. There may be a place for 68Ga-PSMA PET/CT in intermediate-risk PC patients as well, however, only a few data are available at the moment. In secondary staging for local recurrence, 68Ga-PSMA PET/mpMR is superior to PET/CT, whereas for distant recurrence, PET/CT has equivalent results and is faster and cheaper compared to PET/mpMR. 68Ga-PSMA PET/CT is superior to 18F / 11Choline PET/CT in primary staging as well as in secondary staging. In patients with biochemical relapse, PET/CT positivity is directly associated with prostate-specific antigen (PSA) increase and amounts to roughly 50% when PSA is raised to ≤0.5 ng/ml and to ≥90% above 1 ng/ml. Significant clinical results have so far been achieved with the subsequent use of radiolabeled PSMA ligands in the treatment of CRPC. Accumulated activities of 30 to 50 GBq of 177Lu-PSMA ligands seem to be clinically safe with biochemical response and PERCIST/RECIST response in around 75% of patients along with xerostomia in 5-10% of patients as the only notable side effect. On the basis of the current literature, we conclude that PSMA-directed theranostics do have a major clinical impact in diagnosis and therapy of PC patients. We recommend that 68Ga-PSMA PET/CT should be performed in primary staging together with pelvic mpMR in high-risk patients and in all patients for secondary staging, and that PSMA-directed therapy is a potent strategy in CRPC patients when other treatment options have failed. The combination of PSMA-directed therapy with existing therapy modalities (such as 223Ra-chloride or androgen deprivation therapy) has to be explored, and prospective clinical multicenter trials with theranostics are warranted.

Dosimetry-Based Consideration on Remission and Relapse after Therapy with 223Ra-Dichloride in Castration-Resistant Prostate Cancer (CRPC) with Bone Metastases. A Case Report

Here, we present the case of a 64-year-old male patient diagnosed with castration-resistant prostate cancer (CRPC) with bone metastasis, treated with abiraterone prednisone/prednisolone in combination with ²²³Ra-dichloride therapy, who had remission and a subsequent relapse of bone metastasis on repeated bone scans after therapy. We also discuss the possibility of continuing the ²²³Ra-dichloride therapy over the six planned administrations by administering other cycles at the same dose or at higher doses, if shown to be devoid of a significant increase in side effects, based on dosimetry considerations.

Skeletal standardized uptake values obtained by quantitative SPECT/CT as an osteoblastic biomarker for the discrimination of active bone metastasis in prostate cancer

Purpose

To investigate the improvement of prognostication of active bone metastatic burden by discriminating bone metastases from degenerative changes in hot foci, using skeletal standardized uptake values (SUVs) by quantitative bone single photon emission tomography/computed tomography (SPECT/CT) in patients with prostate cancer.

Methods

We investigated 170 patients with prostate cancer who underwent skeletal quantitative SPECT/CT using ^99mTc-methylene-diphosphonate (MDP), through conjugate gradient reconstruction with tissue zoning, attenuation, and scatter corrections applied, called as CGZAS reconstruction, in a retrospective cohort study. The maximum, peak, and average SUVs (SUVmax, SUVpeak, and SUVave, respectively) were obtained for visually normal thoracic (T; n = 100) and lumbar (L; n = 140) vertebral bodies as controls, as well as for bone metastases (n = 126) and degenerative changes (n = 114) as hot foci. They were also correlated with age, body-weight, height, biochemistry data, and extent of disease (EOD). Discrimination accuracy of the SUVs for bone metastases in hot foci was evaluated by a patient-based and lesion-based receiver-operator characteristic curve (ROC) analysis.

Results

The skeletal SUVmax was 7.58 ± 2.42 for T, 8.12 ± 12.24 for L, 16.73 ± 6.74 for degenerative changes, and 40.90 ± 33.46 for bone metastases. The SUVs of the bone metastasis group were significantly (p < 0.001) greater than of the other three groups. With disease extent, serum alkaline phosphatase and prostate specific antigen were increased, while SUVs for bone metastases were decreased in EOD grade 4. In ROC analyses for bone metastases by skeletal SUVs demonstrating the diagnostic accuracy of skeletal SUVs for discriminating bone metastasis from degenerative changes in hot foci, area under curves were 0.840, 0.817, and 0.845 in patient-based mode, and 0.932, 0.920, and 0.930 in lesion-based mode.

Conclusions

The skeletal SUVs by ^99mTc-MDP SPECT/CT for active bone metastases were greater than those for degenerative changes in patients with prostate cancer, with a feasible discrimination accuracy in the hot foci. Therefore, skeletal SUVs, especially SUVmax, in quantitative bone SPECT/CT may be helpful indices for the prognostication of bone metastatic burden, improving discrimination of active bone osteoblastic metastases in patients with prostate cancer from frequently coexisting degenerative changes.

The potential of 223Ra and 18F-fluoride imaging to predict bone lesion response to treatment with 223Ra-dichloride in castration-resistant prostate cancer

PURPOSE

The aims of this study were to calculate bone lesion absorbed doses resulting from a weight-based administration of 223Ra-dichloride, to assess the relationship between those doses and corresponding 18F-fluoride uptake and to assess the potential of quantitative 18F-fluoride imaging to predict response to treatment.

METHODS

Five patients received two intravenous injections of 223Ra-dichloride, 6 weeks apart, at 110 kBq/kg whole-body weight. The biodistribution of 223Ra in metastatic lesions as a function of time after administration as well as associated lesion dosimetry were determined from serial 223Ra scans. PET/CT imaging using 18F-fluoride was performed prior to the first treatment (baseline), and at week 6 immediately before the second treatment and at week 12 after baseline.

RESULTS

Absorbed doses to metastatic bone lesions ranged from 0.6 Gy to 44.1 Gy. For individual patients, there was an average factor difference of 5.3 (range 2.5-11.0) between the maximum and minimum lesion dose. A relationship between lesion-absorbed doses and serial changes in 18F-fluoride uptake was demonstrated (r2 = 0.52). A log-linear relationship was demonstrated (r2 = 0.77) between baseline measurements of 18F-fluoride uptake prior to 223Ra-dichloride therapy and changes in uptake 12 weeks after the first cycle of therapy. Correlations were also observed between both 223Ra and 18F-fluoride uptake in lesions (r = 0.75) as well as between 223Ra absorbed dose and 18F-fluoride uptake (r = 0.96).

CONCLUSIONS

There is both inter-patient and intra-patient heterogeneity of absorbed dose estimates to metastatic lesions. A relationship between 223Ra lesion absorbed dose and subsequent lesion response was observed. Analysis of this small group of patients suggests that baseline uptake of 18F-fluoride in bone metastases is significantly correlated with corresponding uptake of 223Ra, the associated 223Ra absorbed dose and subsequent lesion response to treatment.

Radium 223 dichloride for prostate cancer treatment

Prostate cancer is the most common malignant disease in men. Several therapeutic agents have been approved during the last 10 years. Among them, radium-223 dichloride (Xofigo^®) is a radioactive isotope that induces irreversible DNA double-strand breaks and consequently tumor cell death. Radium-223 dichloride is a calcium-mimetic agent that specifically targets bone lesions. Radium-223 dichloride has been approved for the treatment of metastatic castration-resistant prostate cancer with symptomatic bone metastases, without known visceral metastases. In this review, first we summarize the interplay between prostate tumor cells and bone microenvironment; then, we discuss radium-223 dichloride mechanism of action and present the results of the available clinical trials and future developments for this new drug.

68Ga-PSMA-11 PET as a Gatekeeper for the Treatment of Metastatic Prostate Cancer with 223Ra: Proof of Concept

We retrospectively evaluated the utility of ⁶⁸Ga-PSMA-11 PET for planning ²²³RaCl₂ therapy of patients with metastatic prostate cancer and its impact on the therapeutic response as determined by prostate-specific antigen (PSA) and alkaline phosphatase (ALP), as well as the correlation of PSA changes with the results of prostate-specific membrane antigen (PSMA) PET follow-up scans. Methods: Sixty-three patients with a median age of 73 y who underwent 307 cycles of therapy with ²²³RaCl₂ were analyzed. In 31 patients, bone scanning and radiologic imaging were performed for pretherapeutic imaging (group 1). In 32 patients, bone scanning and PSMA PET were performed before therapy (group 2). Patients with small lymph node metastases and local recurrence were not excluded from treatment, consistent with current guidelines. PSA and ALP were measured before each treatment cycle and 4 wk after the final cycle. Thirteen patients from group 2, who underwent a second PSMA PET scan as a follow-up, were evaluated to determine the significance of PSA changes as a follow-up marker. Results: In group 1, 4 patients (12.9%) showed a PSA decline, of whom 2 patients and 1 patient showed a PSA decline of more than 30% and more than 50%, respectively. In contrast, in group 2, 14 patients (43.8%) showed a PSA decline, of whom 10 and 8 patients showed a decline of more than 30% and more than 50%, respectively (P = 0.007). Thirty-seven patients had a high ALP level (19 from group 1 and 18 from group 2). Twelve (63.2%) and 16 (88.9%) patients in groups 1 and 2, respectively, showed an ALP decline. This difference was not significant; however, 7 (36%) and 13 (72.2%) patients in groups 1 and 2, respectively, showed an ALP decline of more than 30% (P = 0.04). Considering any ALP decline as a response, no patient with increasing ALP showed a PSA response (P = 0.036). There was a significant correlation between the PSA changes and the therapeutic response according to follow-up PSMA PET. Conclusion: When PSMA PET is used as the gatekeeper in addition to bone scanning, radionuclide therapy with ²²³Ra may be more effective and have more success regarding changes in the PSA. An increase in PSA during therapy cycles occurs because of disease progression.