Efficacy and safety of 177Lu-PSMA radionuclide treatment in patients with diffuse bone marrow involvement: A multicenter retrospective study

e17543

Background: 177Lu-labelled prostate-specific membrane antigen (LuPSMA) radionuclide therapy of metastatic castration-resistant prostate cancer (mCRPC) is currently under investigation in phase III trial (VISION). However, patients with diffuse bone involvement, diagnosed with a superscan by bone scintigraphy at baseline, were excluded due to lack of efficacy and safety data. We therefore aimed to investigate the feasibility of LuPSMA in patients with diffuse bone marrow involvement on baseline PSMA-targeted PET/CT. Methods: Patients with progressive mCRPC treated with LuPSMA at six centers in Germany, USA and Australia were considered for inclusion.Eligible patients had 50% or greater bone involvement of the axial skeleton on the baseline PSMA PET. The primary endpoints were PSA response (PCWG3), toxicity (CTCAE v4.02), and overall survival (OS). Secondary endpoints included quality of life (assessed with Brief Pain Inventory-Short Form questionnaires) and radiological response (as measured by CT using RECIST 1.1). Results: 43 of 352 (12%) screened patients met inclusion criteria and were retrospectively analyzed. Median baseline PSA was 1000 (IQR 431-2151) ng/ml. PSA decline ≥50% was achieved in 26/43 (65%) patients, while median PSA progression-free survival was 4.8 (95%CI 2.4–7.1) mo. 15/42 (36%) evaluable patients exhibited pain progression with a median time-to-pain progression of 8.3 (95%CI 5.4–11.3) mo. After a median follow-up of 18.9 mo, median OS was 11.6 (95%CI 8.8-14.3) mo. Objective response in nodal or visceral disease was reported in 7/18 (39%) patients with evaluable target lesions on CT. Grade 3/4 anemia, thrombocytopenia and neutropenia occurred in 9/43 (21%), 10/43 (23%) and 3/43 (8%) patients, respectively. Of note, all patients had grade 1 anemia at baseline, with a median hemoglobin of 9.6 g/dl. 2/43 (5%) patients experienced an adverse event that required a reduction to the LuPSMA activity beginning with the third cycle. Conclusions: Patients with diffuse bone marrow involvement demonstrate similar LuPSMA efficacy and safety when compared to phase II evidence. Acceptable safety outcomes do not support exclusion of patients with a superscan from future LuPSMA treatment protocols.

Early Prostate-Specific Antigen Changes and Clinical Outcome After 177Lu-PSMA Radionuclide Treatment in Patients with Metastatic Castration-Resistant Prostate Cancer

Prostate-specific antigen (PSA) is widely used to monitor treatment response in patients with metastatic castration-resistant prostate cancer. However, PSA measurements are considered only after 12 wk of treatment. We aimed to evaluate the prognostic value of early PSA changes after ¹⁷⁷Lu-labeled prostate-specific membrane antigen (¹⁷⁷Lu-PSMA) radionuclide treatment in metastatic castration-resistant prostate cancer patients. Methods: Men who were treated with ¹⁷⁷Lu-PSMA under a compassionate-access program at our institution and had available PSA values at baseline and at 6 wk after treatment initiation were included in this retrospective analysis. Patients were assigned to 3 groups on the basis of PSA changes: response (≥30% decline), progression (≥25% increase), and stable (<30% decline and <25% increase). The coprimary endpoints were overall survival and imaging-based progression-free survival. The secondary endpoints were PSA changes at 12 wk and PSA flare-up. Results: We identified 124 eligible patients with PSA values at 6 wk. A greater than or equal to 30% decline in PSA at 6 wk was associated with longer overall survival (median, 16.7 mo; 95% CI, 14.4-19.0) than stable PSA (median, 11.8 mo; 95% CI, 8.6-15.1) (P = 0.007) or PSA progression (median, 6.5 mo; 95% CI, 5.2-7.8) (P < 0.001). Patients with a greater than or equal to 30% decline in PSA at 6 wk also had a lower risk of imaging-based progression than patients with stable PSA (hazard ratio, 0.60; 95% CI, 0.38-0.94) (P = 0.02), whereas patients with PSA progression had a higher risk of imaging-based progression than patients with stable PSA (hazard ratio, 3.18; 95% CI, 1.95-5.21) (P < 0.001). The percentage changes in PSA at 6 and 12 wk were highly associated (r = 0.90; P < 0.001). Of 31 patients who experienced early PSA progression at 6 wk, 29 (94%) showed biochemical progression at 12 wk. Overall, only 1 (3%) of 36 patients with PSA progression at 6 wk achieved any PSA decline at 12 wk (1% of the entire cohort). The limitations of the study included its retrospective nature and the single-center experience. Conclusion: PSA changes at 6 wk after ¹⁷⁷Lu-PSMA initiation are an early indicator of long-term clinical outcome. Patients with PSA progression after 6 wk of treatment could benefit from a very early decision to switch treatment. PSA flare-up during ¹⁷⁷Lu-PSMA treatment is very uncommon. Prospective studies are now warranted to validate our findings and potentially inform clinicians earlier on the effectiveness of ¹⁷⁷Lu-PSMA.

Multicentric analytical comparability study of programmed death-ligand 1 expression on tumor-infiltrating immune cells and tumor cells in urothelial bladder cancer using four clinically developed immunohistochemistry assays

Programmed death-ligand 1 (PD-L1) expression on tumor cells (TC) or tumor-infiltrating immune cells (IC) correlated in several studies with PD-L1/programmed death-1 (PD-1) checkpoint inhibitor efficacy. Since June 2018, a positive PD-L1 status is required for atezolizumab or pembrolizumab treatment of patients with advanced or metastasized urothelial bladder cancer, who are ineligible for cisplatin-containing therapy. We examined technical comparability and inter-reader agreement of four clinically developed PD-L1 assays in locally advanced disease. Archived, formalin-fixed, paraffin-embedded sections from 30 patients (73.3% cystectomies, 26.7% transurethral resections) were stained by PD-L1 immunohistochemistry using VENTANA SP142, VENTANA SP263, DAKO 22C3, and DAKO 28-8 at two sites per manufacturers’ protocols and scored blinded at five sites for PD-L1 expression on IC (% per tumor area) and TC (%). Small, non-significant inter-assay differences were observed for IC. For TC, SP142 showed significantly lower staining percentages. Pairwise comparisons revealed − 0.3 to 1.6% differences in adjusted means between assays for IC, and for TC, − 10.5 to − 7.8% (SP142 versus others) and − 1.9 to 2.7% (other comparisons). Inter-reader and inter-assay agreement was moderate to high for both IC and TC. Allocation to binary cutoffs (1%, 5%, 10%) showed substantial to high Kappa agreement scores (0.440–0.923) for IC and TC between assays for each reader. This first multicenter study, with five independent readers blinded with respect to the assay used, suggests that all four currently clinically relevant assays are analytically similar for evaluation of PD-L1-stained IC and three (SP263, 22C3, and 28-8) for PD-L1-stained TC. Inter-observer agreement for trained readers in scoring of both IC and TC positivity was generally high.

Early Experience of Rechallenge 177Lu-PSMA Radioligand Therapy After an Initial Good Response in Patients with Advanced Prostate Cancer

Our aim was to retrospectively evaluate the feasibility of rechallenge ¹⁷⁷Lu-prostate-specific membrane antigen (¹⁷⁷Lu-PSMA) radioligand therapy. Methods: Rechallenge radioligand therapy was defined as subsequent treatment with ¹⁷⁷Lu-PSMA after initial exposure with an excellent response followed by progression. Biochemical, radiographic, clinical antitumor response, and adverse events were analyzed. Prostate-specific antigen (PSA) progression-free survival (PFS) and overall survival were calculated. Results: Eight patients underwent a median of 2 (range: 1-4) cycles of rechallenge with ¹⁷⁷Lu-PSMA for imaging and therapy. A maximum PSA decrease of 50% was achieved in 3 patients (37.5%). Radiographic response was favorable in 3 patients, whereas 4 exhibited progressive disease. Eastern Cooperative Oncology Group performance status was stable during therapy in all patients. No grade 4 toxicity was noticed, and grade 3 toxicity occurred in 3 patients (37.5%). The median PSA-PFS and overall survival were 3.2 mo (95% confidence interval, 2.6-3.7 mo) and 14.0 mo (95% confidence interval, 6.2-21.8 mo), respectively. Conclusion: In a small patient cohort with an initial excellent response, ¹⁷⁷Lu-PSMA rechallenge is still active, with lower efficacy and higher toxicity.

Use of Hepatocytes in Adhesion and Suspension Cultures for Liver Support Bioreactors

Hepatocyte cultivation in bioreactors for hybrid liver support systems is possible under two conditions: attached to a substrate like membranes or microcarriers or in suspension culture. To compare the ammonia metabolism of hepatocytes cultivated under these two conditions, cultures of primary seeded rat hepatocytes were cultivated either attached to collagen coated tissue culture plastic or as a suspension culture.

During the time course of culture, the ability of hepatocytes to reduce the ammonia content of the medium decreased in both adhesion and suspension cultures, though to different extents.

In suspension cultures, ammonia content was reduced from 350 μM to about 100 μM (day 4) and to about 180 μM (day 6). No significant reduction was seen on day 8 of culture. In contrast, hepatocytes attached to collagen coated dishes remained viable and functional for at least 8 days after plating, reducing ammonia content from 350 μM to 70 μM (day 4), 90 μM (day 6) and 180 μM (day 8). The period of useful metabolism of hepatocytes in bioreactors for hybrid liver support systems appears to depend on the culture conditions

Hyperkalemia in patients treated with endoradiotherapy combined with amino acid infusion is associated with severe metabolic acidosis

Background

Amino acid co-infusion for renal protection in endoradiotherapy (ERT) applied as prostate-specific membrane antigen (PSMA)-targeted radioligand therapy (RLT) or peptide receptor radionuclide therapy (PRRT) has been shown to cause severe hyperkalemia. The pathophysiology behind the rapid development of hyperkalemia is not well understood. We hypothesized that the hyperkalemia should be associated with metabolic acidosis.

Results

Twenty-two patients underwent ERT. Prior to the first cycle, excretory kidney function was assessed by mercapto-acetyltriglycine (MAG-3) renal scintigraphy, serum biochemistry, and calculated glomerular filtration rate (eGFR). All patients received co-infusion of the cationic amino acids L-arginine and L-lysine for nephroprotection. Clinical symptoms, electrolytes, and acid-base status were evaluated at baseline and after 4 h.

No patient developed any clinically relevant side effects. At baseline, acid base status and electrolytes were normal in all patients. Excretory kidney function was normal or only mildly impaired in all except two patients with stage 3 renal insufficiency. All patients developed hyperkalemia. Base excess and HCO₃⁻ were significantly lower after 4 h. In parallel, mean pH dropped from 7.36 to 7.29. There was a weak association between calculated (r = − 0.21) as well as MAG-3-derived GFR (r = − 0.32) and the rise in potassium after 4 h.

Conclusion

Amino acid co-infusion during ERT leads to severe metabolic acidosis which induces hyperkalemia by potassium hydrogen exchange. This novel finding implies that commercially available bicarbonate solutions might be an easy therapeutic option to correct metabolic acidosis rapidly.

Electronic supplementary material

The online version of this article (10.1186/s13550-018-0370-z) contains supplementary material, which is available to authorized users.

Clinical experience with 100 consecutive patients treated with Lu-177-labeled PSMA-I&T radioligand therapy for metastatic castration-resistant prostate cancer

206

Background: To report our clinical experience with 177Lutetium-labeled prostate-specific membrane antigen-ligand (177Lu-PSMA-I&T) for systemic radioligand therapy in 100 consecutive patients with metastatic castration-resistant prostate cancer (mCRPC). Methods: All patients were treated under a review board-approved compassionate use protocol. Eligibility criteria for 177Lu-PSMA-I&T therapy included previous treatment with abiraterone or enzalutamide, previous taxane-based chemotherapy or unsuitability for taxanes as well as positive 68Ga-PSMA tracer uptake of metastases in a prior PET-scan. Intravenous treatment with 177Lu-PSMA-I&T was given 6- to 8-weekly with an activity of 7.4GBq up to 6 cycles in patients without clinical or radiographic progression. We report prostate-specific antigen (PSA) decline, PSA progression-free survival (PSA-PFS), clinical progression-free survival (cPFS) and overall survival (OS) as well as toxicity. Results: Median age was 72 years (range 46-85) and median PSA level was 164 ng/ml (range 0-6178). Bone, lymph node and visceral metastases were present in 94%, 85% and 33% of patients, respectively. The median number of previous treatment regimens for mCRPC was 3 (range 1-6) and 84% of patients were pretreated with chemotherapy. At the time of evaluation, 286 cycles with 177Lu-PSMA-I&T were applied (median 2 cycles per patient, range 1-6), while treatment was still ongoing in 27% of patients. Overall, 4 and 6 cycles were applied in 33 and 15 patients, respectively. PSA decline ≥30%, ≥50% and ≥90% was achieved in 40%, 32% and 9% of patients, respectively. Median PSA-PFS was 3.4 months (95%CI 2.7-4.0), median cPFS was 4.1 months (95%CI 2.5-5.7) and median OS was 12.2 months (95%CI 8.8-15.7). Treatment-emergent hematologic grade 3/4 toxicities were anemia in 7%, thrombocytopenia in 5% and neutropenia in 4% of patients. Grade 3/4-non-hematologic toxicities were not observed. The main non-hematologic grade 1/2 toxicities were dry mouth in 18%, fatigue in 16% and loss of appetite in 9/% of patients. Conclusions: Radioligand therapy with 177Lu-PSMA I&T appears to be safe and active in late-stage mCRPC.

The Effect of Total Tumor Volume on the Biologically Effective Dose to Tumor and Kidneys for 177Lu-Labeled PSMA Peptides

The aim of this work was to simulate the effect of prostate-specific membrane antigen (PSMA)-positive total tumor volume (TTV) on the biologically effective doses (BEDs) to tumors and organs at risk in patients with metastatic castration-resistant prostate cancer who are undergoing ¹⁷⁷Lu-PSMA radioligand therapy. Methods: A physiologically based pharmacokinetic model was fitted to the data of 13 patients treated with ¹⁷⁷Lu-PSMA I&T (a PSMA inhibitor for imaging and therapy). The tumor, kidney, and salivary gland BEDs were simulated for TTVs of 0.1-10 L. The activity and peptide amounts leading to an optimal tumor-to-kidneys BED ratio were also investigated. Results: When the TTV was increased from 0.3 to 3 L, the simulated BEDs to tumors, kidneys, parotid glands, and submandibular glands decreased from 22 ± 15 to 11.0 ± 6.0 Gy_1.49, 6.5 ± 2.3 to 3.7 ± 1.4 Gy_2.5, 11.0 ± 2.7 to 6.4 ± 1.9 Gy_4.5, and 10.9 ± 2.7 to 6.3 ± 1.9 Gy_4.5, respectively (where the subscripts denote that an α/β of 1.49, 2.5, or 4.5 Gy was used to calculate the BED). The BED to the red marrow increased from 0.17 ± 0.05 to 0.32 ± 0.11 Gy₁₅ For patients with a TTV of more than 0.3 L, the optimal amount of peptide was 273 ± 136 nmol and the optimal activity was 10.4 ± 4.4 GBq. Conclusion: This simulation study suggests that in patients with large PSMA-positive tumor volumes, higher activities and peptide amounts can be safely administered to maximize tumor BEDs without exceeding the tolerable BED to the organs at risk.

[PSMA-targeted radioligand therapy in prostate cancer]

Radioligand therapy (RLT) directed against prostate-specific membrane antigen (PSMA) enables tumor-specific treatment directed against PSMA-overexpressing prostate cancer cells. Several PSMA ligands such as PSMA-617 or PSMA-I&T have been developed that can be labeled with β‑radiating lutetium-177. These are currently applied in compassionate use programs to treat metastatic castration-resistant prostate cancer (mCRPC). PSMA-directed RLT is currently being offered in several nuclear medicine departments throughout Germany. Several retrospective case series demonstrate its activity with a prostate-specific antigen (PSA) decrease >50% in 30-60% of mCRPC patients. The toxicity seems to be low. Hematologic grade 4 toxicity has not been observed and grade 3 toxicities rarely occur. The main nonhematologic adverse events are intermittent dry mouth because of unspecific PSMA expression in the salivary glands as well as fatigue and nausea. Currently there are no prospective studies available for evaluation of PSMA-targeted RLT and a survival benefit over approved standard therapies such as abiraterone, enzalutamide, radium-223-dichloride, docetaxel or cabazitaxel has not been shown. PSMA-targeted RLT should therefore currently only be offered after critical evaluation in patients who exhausted the approved standard therapies.

AR-V7 in Peripheral Whole Blood of Patients with Castration-resistant Prostate Cancer: Association with Treatment-specific Outcome Under Abiraterone and Enzalutamide

BACKGROUND

It has been demonstrated that androgen receptor splice variant 7 (AR-V7) expression in circulating tumor cells (CTCs) predicts poor treatment response in metastatic castration-resistant prostate cancer (mCRPC) patients treated with abiraterone or enzalutamide.

OBJECTIVE

To develop a practical and robust liquid profiling approach for direct quantification of AR-V7 in peripheral whole blood without the need for CTC capture and to determine its potential for predicting treatment response in mCRPC patients.

DESIGN, SETTING, AND PARTICIPANTS

Whole blood samples from a prospective biorepository of 85 mCRPC patients before treatment initiation with abiraterone (n=56) or enzalutamide (n=29) were analyzed via droplet digital polymerase chain reaction.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

The association of AR-V7 status with prostate-specific antigen (PSA) response defined by PSA decline ≥50% and with PSA-progression-free survival (PSA-PFS), clinical PFS, and overall survival (OS) was assessed.

RESULTS AND LIMITATIONS

High AR-V7 expression levels in whole blood were detectable in 18% (15/85) of patients. No patient with high AR-V7 expression achieved a PSA response, and AR-V7 status was an independent predictor of PSA response in multivariable logistic regression analysis (p=0.03). High AR-V7 expression was associated with shorter PSA-PFS (median 2.4 vs 3.7 mo; p<0.001), shorter clinical PFS (median 2.7 vs 5.5 mo; p<0.001), and shorter OS (median 4.0 vs. 13.9 mo; p<0.001). On multivariable Cox regression analysis, high AR-V7 expression remained an independent predictor of shorter PSA-PFS (hazard ratio [HR] 7.0, 95% confidence interval [CI] 2.3-20.7; p<0.001), shorter clinical PFS (HR 2.3, 95% CI 1.1-4.9; p=0.02), and shorter OS (HR 3.0, 95% CI 1.4-6.3; p=0.005).

CONCLUSIONS

Testing of AR-V7 mRNA levels in whole blood is a simple and promising approach to predict poor treatment outcome in mCRPC patients receiving abiraterone or enzalutamide.

PATIENT SUMMARY

We established a method for determining AR-V7 status in whole blood. This test predicted treatment resistance in patients with metastatic castration-resistant prostate cancer undergoing treatment with abiraterone or enzalutamide. Prospective validation is needed before application to clinical practice.

[The role of immunooncology in the treatment of urothelial cancer]

Data published in November 2016 showed a significant survival benefit for the PD-1 antibody Pembrolizumab in the second-line treatment of metastatic urothelial cancer in comparison to standard chemotherapy. Other PD-1/PD-L1 antibodies are being tested in advanced clinical trials. This class of substances will become standard of care from the time of their approval which is expected for 2017 and will replace vinflunine, which is currently recommended in the German guideline. PD-1/PD-L1 directed substances are also being tested as a first line treatment of metastatic urothelial carcinoma. Monotherapy is evaluated as well as combination treatments with CTLA-4 inhibitors of conventional chemotherapy. First data are expected at the end of 2017.A new strategy is the application of PD-1/PD-L1 directed substances in the perioperative treatment of patients with a muscle-invasive urothelial carcinoma after complete surgical resection (cystectomy or nephroureterectomy). Two international phase III trials evaluate an adjuvant immunotherapy with nivolumab and atezolizumab. Recruitment will be completed in 2018.

Exploring New Multimodal Quantitative Imaging Indices for the Assessment of Osseous Tumor Burden in Prostate Cancer Using 68Ga-PSMA PET/CT

PET combined with CT and prostate-specific membrane antigen (PSMA) ligands has gained significant interest for staging prostate cancer (PC). In this study, we propose 2 multimodal quantitative indices as imaging biomarkers for the assessment of osseous tumor burden using ⁶⁸Ga-PSMA PET/CT and present preliminary clinical data. Methods: We defined 2 bone PET indices (BPIs) that incorporate anatomic information from CT and functional information from ⁶⁸Ga-PSMA PET: BPI_VOL is the percentage of bone volume affected by tumor and BPI_SUV additionally considers the level of PSMA expression. We describe a semiautomatic computation method based on segmentation of bones in CT and of lesions in PET. Data from 45 patients with castration-resistant PC and bone metastases during ²²³Ra-dichloride were retrospectively analyzed. We evaluated the computational stability and reproducibility of the proposed indices and explored their relation to the prostate-specific antigen blood value, the bone scan index (BSI), and disease classification using PERCIST. Results: On the technical side, BPI_VOL and BPI_SUV showed an interobserver maximum difference of 3.5%, and their computation took only a few minutes. On the clinical side, BPI_VOL and BPI_SUV showed significant correlations with BSI (r = 0.76 and 0.74, respectively, P < 0.001) and prostate-specific antigen values (r = 0.57 and 0.54, respectively, P < 0.01). When the proposed indices were compared against expert rating using PERCIST, BPI_VOL and BPI_SUV showed better agreement than BSI, indicating their potential for objective response evaluation. Conclusion: We propose the evaluation of BPI_VOL and BPI_SUV as imaging biomarkers for ⁶⁸Ga-PSMA PET/CT in a prospective study exploring their potential for outcome prediction in patients with bone metastases from PC.

[Bone-specific therapy with radium-223 dichloride : Castration-resistant prostate cancer with symptomatic bone metastases]

Radium-223 dichloride (Xofigo®, Alpharadin) is approved for the treatment of metastatic castration-resistant prostate cancer with symptomatic bone metastases and no known visceral metastases. As a calcium mimetic, it is integrated into osteoplastic bone lesions and emits alpha particles with high energy which leads to local destruction of tumor cells. In the 2013 published ALSYMPCA trial, a significant advantage for overall survival and quality of life in comparison to placebo was found. Recent data suggest an increased potential in combination with next generation hormonal treatment.

Radiation Dosimetry for 177Lu-PSMA I&T in Metastatic Castration-Resistant Prostate Cancer: Absorbed Dose in Normal Organs and Tumor Lesions

Prostate-specific membrane antigen (PSMA)-targeted radioligand therapy is increasingly used in metastatic castration-resistant prostate cancer. We aimed to estimate the absorbed doses for normal organs and tumor lesions using ¹⁷⁷Lu-PSMA I&T (I&T is imaging and therapy) in patients undergoing up to 4 cycles of radioligand therapy. Results were compared with pretherapeutic Glu-NH-CO-NH-Lys-(Ahx)-[⁶⁸Ga(HBEDCC)] (⁶⁸Ga-PSMA-HBED-CC) PET. Methods: A total of 34 cycles in 18 patients were analyzed retrospectively. In 15 patients the first, in 9 the second, in 5 the third, and in 5 the fourth cycle was analyzed, respectively. Whole-body scintigraphy was performed at least between 30-120 min, 24 h, and 6-8 d after administration. Regions of interest covering the whole body, organs, and up to 4 tumor lesions were drawn. Organ and tumor masses were derived from pretherapeutic ⁶⁸Ga-PSMA-HBED-CC PET/CT. Absorbed doses for individual cycles were calculated using OLINDA/EXM. SUVs from pretherapeutic PET were compared with absorbed doses and with change of SUV. Results: The mean whole-body effective dose for all cycles was 0.06 ± 0.03 Sv/GBq. The mean absorbed organ doses were 0.72 ± 0.21 Gy/GBq for the kidneys; 0.12 ± 0.06 Gy/GBq for the liver; and 0.55 ± 0.14 Gy/GBq for the parotid, 0.64 ± 0.40 Gy/GBq for the submandibular, and 3.8 ± 1.4 Gy/GBq for the lacrimal glands. Absorbed organ doses were relatively constant among the 4 different cycles. Tumor lesions received a mean absorbed dose per cycle of 3.2 ± 2.6 Gy/GBq (range, 0.22-12 Gy/GBq). Doses to tumor lesions gradually decreased, with 3.5 ± 2.9 Gy/GBq for the first, 3.3 ± 2.5 Gy/GBq for the second, 2.7 ± 2.3 Gy/GBq for the third, and 2.4 ± 2.2 Gy/GBq for the fourth cycle. SUVs of pretherapeutic PET moderately correlated with absorbed dose (r = 0.44, P < 0.001 for SUV_max; r = 0.43, P < 0.001 for SUV_mean) and moderately correlated with the change of SUV (r = 0.478, P < 0.001 for SUV_max, and r = 0.50, P < 0.001 for SUV_mean). Conclusion: Organ- and tumor-absorbed doses for ¹⁷⁷Lu-PSMA I&T are comparable to recent reports and complement these with information on an excellent correlation between the 4 therapy cycles. With the kidneys representing the critical organ, a cumulative activity of 40 GBq of ¹⁷⁷Lu-PSMA I&T appears to be safe and justifiable. The correlation between pretherapeutic SUV and absorbed tumor dose emphasizes the need for PSMA-ligand PET imaging for patient selection.

Comparison of bone scintigraphy and 68Ga-PSMA PET for skeletal staging in prostate cancer

PURPOSE

The aim of our study was to compare the diagnostic performance of ⁶⁸Ga-PSMA PET and ^99mTc bone scintigraphy (BS) for the detection of bone metastases in prostate cancer (PC) patients.

METHODS

One hundred twenty-six patients who received planar BS and PSMA PET within three months and without change of therapy were extracted from our database. Bone lesions were categorized into benign, metastatic, or equivocal by two experienced observers. A best valuable comparator (BVC) was defined based on BS, PET, additional imaging, and follow-up data. The cohort was further divided into clinical subgroups (primary staging, biochemical recurrence, and metastatic castration-resistant prostate cancer [mCRPC]). Additionally, subgroups of patients with less than 30 days delay between the two imaging procedures and with additional single-photon emission computed tomography (SPECT) were analyzed.

RESULTS

A total of 75 of 126 patients were diagnosed with bone metastases. Sensitivities and specificities regarding overall bone involvement were 98.7-100 % and 88.2-100 % for PET, and 86.7-89.3 % and 60.8-96.1 % (p < 0.001) for BS, with ranges representing results for 'optimistic' or 'pessimistic' classification of equivocal lesions. Out of 1115 examined bone regions, 410 showed metastases. Region-based analysis revealed a sensitivity and specificity of 98.8-99.0 % and 98.9-100 % for PET, and 82.4-86.6 % and 91.6-97.9 % (p < 0.001) for BS, respectively. PSMA PET also performed better in all subgroups, except patient-based analysis in mCRPC.

CONCLUSION

Ga-PSMA PET outperforms planar BS for the detection of affected bone regions as well as determination of overall bone involvement in PC patients. Our results indicate that BS in patients who have received PSMA PET for staging only rarely offers additional information; however, prospective studies, including a standardized integrated x-ray computed tomography (SPECT/CT) protocol, should be performed in order to confirm the presented results.