Theranostics in oncology: What radiologists want to know

Combination of radioligand imaging and therapy, so called radiotheranostics, is a novel tool of precision oncology with proven clinical value. In-depth knowledge of functional imaging nuances is critically needed for precise prognostication and guidance of management. Here, we review theranostic applications with up to Phase III type evidence for outcome improvement: Imaging and therapy of neuroendocrine neoplasms (NEN) exploiting high levels of somatostatin receptor (SSTR) expression and radiotheranostics of prostate cancer targeting the prostate specific membrane antigen (PSMA). This narrative review focusses on these two applications and elucidates patient selection and response assessment by radioligand scintigraphy and/or positron emission tomography. Furthermore, we provide a brief outlook on future applications for novel targets outside of NEN and prostate cancer.

Cardiac fibroblast activation detected by Ga-68 FAPI PET imaging as a potential novel biomarker of cardiac injury/remodeling

BACKGROUND

Fibroblast activation protein (FAP) as a specific marker of activated fibroblasts can be visualized by positron emission tomography (PET) using Ga-68-FAP inhibitors (FAPI). Gallium-68-labeled FAPI is increasingly used in the staging of various cancers. In addition, the first cases of theranostic approaches have been reported. In this work, we describe the phenomenon of myocardial FAPI uptake in patients who received a Ga-68 FAPI PET for tumor staging.

METHOD AND RESULTS

Ga-68 FAPI PET examinations for cancer staging were retrospectively analyzed with respect to cardiac tracer uptake. Standardized uptake values (SUV) were correlated to clinical covariates in a univariate regression model. From 09/2018 to 11/2019 N = 32 patients underwent FAPI PET at our institution. Six out of 32 patients (18.8%) demonstrated increased localized myocardial tracer accumulation, with remote FAPI uptake being significantly higher in patients with vs without localized focal myocardial uptake (SUVmax 2.2 ± .6 vs 1.5 ± .4, P < .05 and SUVmean 1.6 ± .4 vs 1.2 ± .3, P < .05, respectively). Univariate regression demonstrated a significant correlation of coronary artery disease (CAD), age and left ventricular ejection fraction (LVEF) with remote SUVmean uptake, the latter with a very strong correlation with remote uptake (R2 = .74, P < .01).

CONCLUSION

Our study indicates an association of CAD, age, and LVEF with FAPI uptake. Further studies are warranted to assess if fibroblast activation can be reliably measured and may be used for risk stratification regarding early detection or progression of CAD and left ventricular remodeling.

Complete metabolic response in advanced non-small cell lung cancer patients with prolonged response to immune checkpoint inhibitor therapy

9050

Background: Recently reported, extended follow-up data from KEYNOTE-024 or -010 indicates that non-small-cell lung cancer (NSCLC) patients can experience long-term benefit from immunotherapy irrespective of discontinuation (per protocol: 35 cycles ∼24 months) or type of response in computed tomography (CT). Similar results were observed in the pooled analysis of 5-year follow-up data from CheckMate-017 and -057. This raises the question, whether patients may safely discontinue immunotherapy after achieving durable response. However, recently published results from CheckMate-153 demonstrated inferior survival rates in patients ceasing immunotherapy after one year, therefore optimal treatment duration of immunotherapy in advanced NSCLC remains unknown. Protocols from published Phase-III trials implemented treatment for a period of approximately 24 months or until evidence of disease progression or unbearable toxicity. Therefore, the ideal duration of immunotherapy remains unclear, and finding markers of beneficial outcome is of great importance. Here, we determine the proportion of complete metabolic responses (CMR) in patients that have not progressed after 24 months of immunotherapy. Methods: This is a retrospective analysis of forty-five patients with positron emission tomography using 2-[18F]fluoro-2-deoxy-D-glucose (FDG-PET) imaging for assessment of residual metabolic activity after at least 24 months of immunotherapy. Lesion-uptake in FDG PET on or below background level (using mediastinum as reference) was considered as CMR. Time until best objective morphological response including disease stabilization was measured from start of immunotherapy until first stable CT-scan (i.e. no progression or further response compared to previous scan) using RECIST 1.1. Results: Out of 45 patients, 29 patients had a CMR (64%). CMR was observed more frequently in non-first line patients. Patients with CMR were younger (median 65.7 vs. 75.5, P = 0.03). Fourteen patients with CMR have discontinued therapy and have not progressed until time of analysis; however median follow-up was only 5.6 (range 0.8-17.0) months. Conclusions: After a minimum of 24 months of palliative immunotherapy for NSCLC, CMR occurred in almost two thirds of patients. Potentially, achievement of CMR might identify patients, for whom palliative immunotherapy may be safely discontinued.

Interim PSMA PET/CT for response evaluation during LuPSMA treatment in mCRPC (INTERIM PET): An explorative, multicenter study

5066

Background: The aim of this analysis was to evaluate the prognostic value of interim PSMA PET/CT in men with metastatic castration-resistant prostate cancer (mCRPC) treated with 177Lu-PSMA and to develop a novel framework for Response Evaluation Criteria In PSMA-imaging (RECIP). Methods: This was an explorative, multicenter, retrospective study; 124 men with mCRPC who underwent 177Lu-PSMA treatment and received PSMA-PET/CT at baseline (bPET) and at interim after two cycles of treatment (iPET) met the eligibility criteria and were included in this analysis. The primary endpoint was overall survival (OS). Pairs of bPET and iPET were interpreted by three independent readers for appearance of new lesions. Whole-body tumor lesions were segmented using qPSMA software and total PSMA-positive tumor volume (PSMA-VOL) was obtained. Changes in PSMA-VOL on iPET relative to bPET were calculated. After being tested separately for associations with OS, appearance of new lesions and changes in PSMA-VOL were combined to develop RECIP. Results: The median OS was 13.5 months (95%CI, 11.6-15.4). Appearance of at least one new lesion on iPET was observed in 73 (59%) patients and was associated with poor OS (hazard ratio [HR] 2.23; 95%CI, 1.51-3.28; P <.001). Based on the current data, RECIP were defined as: partial response (PSMA-PR) as a decline ≥20% in PSMA-VOL and no appearance of new lesions; progressive disease (PSMA-PD) as an increase ≥20% in PSMA-VOL and appearance of new lesions; stable disease (PSMA-SD) was defined as any condition but not PSMA-PR or PSMA-PD. The OS of men with PSMA-PD (n = 41) was significantly worse compared to men with PSMA-SD (n = 47; HR 2.52; 95%CI, 1.61–3.93; P <.001) and PSMA-PR (n = 36; HR 4.16; 95%CI, 2.54–6.78; P <.001). PSMA-SD was associated with significantly worse OS compared to PSMA-PR (HR 1.65; 95%CI, 1.02–2.65; P =.039). The time dependent C-index of associations with OS for response according to RECIP was 0.68 (95%CI, 0.63-0.72). Conclusions: Interim staging using PSMA-PET/CT and response classification by RECIP is prognostic for survival of men with mCRPC treated with 177Lu-PSMA. Validation of these findings in clinical trials is warranted.

FDG-PET avidity as a prognostic biomarker for overall survival in renal cell carcinoma

e16564

Background: Positron emission tomography with (18F)-fluorodeoxyglucose (FDG-PET) is not considered a standard of care (SOC) in renal cell carcinoma (RCC) because of its variability in metabolic activity. We investigated the rate of PET-positivity in our institutional cohort and tested whether PET-positivity had prognostic value in metastatic (m)RCC. Methods: Patients with FDG-PET imaging at any time during the course of disease were identified from medical records. PET-positivity was defined according to PERCIST criteria and a five-point rating scale analogue to Deauville Scoring was used to stratify PET-avidity. Tracer uptake of the hottest lesion was measured as SUVmax. Clinical parameters and PET-positivitywere correlated with overall survival (OS). Kaplan-Meier plots, log-rank analyses, kendall rank correlation, univariate and multivariable cox regression models were employed, where appropriate. Results: A totalof 90 patients was analyzed. The median age was 64.0 (34.0-83.0) and 56 (62.2%) patients had clear cell RCC. Metastatic disease was present in 64 (71.1%) and 22 (24.4%) patients received ongoing medical treatment. 72 (80.0%) patients had prior nephrectomy. PET-positivity occurred in 57 (63.3%) patients, with similar rates among metastatic (41/64; 64%) and non-metastatic patients (16/26; 62%). PET-positive patients had shorter median OS compared to PET-negative patients (38.5 months (CI95:24.5-NR) vs. not reached (CI95: 69.6-NR), P= 0.0013). A weak correlation was found between PET-Uptake and histologic grade (Kendall’s tau 0.22; P= 0.03). Prior nephrectomy, presence of primary lesions, presence of distant metastases, histologic grade and PET-positivity were significant predictors of OS in univariate regression. In multivariable analysis, only PET-positivity remained significant (HR 4.1 (CI95: 1.1-15.4), P= 0.04). Conclusions: RCC is a metabolically active cancer, which in the majority of patients is suitable for FDG-PET diagnostic procedures. PET-positivity was an independent prognostic factor for OS in RCC, indicating its putative clinical use. Further studies to define the role of FDG-PET imaging in RCC are ongoing.

Determining the axillary nodal status with four current imaging modalities including 18F-FDG PET/MRI in newly diagnosed breast cancer: A comparative study using histopathology as reference standard

Purpose: To compare breast magnetic resonance imaging (MRI), thoracal MRI, thoracal 18F-fluorodeoxyglucose positron emission tomography (18F-FDG PET)/MRI and axillary sonography for the detection of axillary lymph node metastases in women with newly diagnosed breast cancer. Materials and Methods: This prospective double-center study included patients with newly diagnosed breast cancer between March 2018 and December 2019. Patients underwent thoracal (18F-FDG PET/)MRI, axillary sonography, and dedicated prone breast MRI. Datasets were evaluated separately regarding nodal status (nodal+ vs. nodal-). Histopathology served as reference standard in all patients. The diagnostic performance of breast MRI, thoracal MRI, thoracal PET/MRI and axillary sonography in detecting nodal positive patients was tested by creating receiver-operating-characteristic curves (ROC) with a calculated area under the curve (AUC). Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy were calculated for all four modalities. A McNemar test was used to assess differences. Results: 112 female patients (mean age 53.04 ± 12.6 years) were evaluated. Thoracal PET/MRI showed the highest ROC-AUC with a value of 0.892. The AUC for breast MRI, thoracal MRI and sonography were 0.782, 0.814 and 0.834, respectively. Differences between thoracal PET/MRI and axillary sonography, thoracal MRI and breast MRI were statistically significant (PET/MRI vs. axillary sonography, P = 0.01; PET/MRI vs. thoracal MRI, P = 0.02; PET/MRI vs. breast MRI, P = 0.03). PET/MRI showed the highest sensitivity (81.8%, 36/44) (95%-CI: 67.29-91.81%) while axillary sonography had the highest specificity (98.5%, 65/66), 95%-CI: 91.84-99.96%). Conclusion: 18F-FDG PET/MRI outperforms axillary sonography, breast MRI and thoracal MRI in determining the axillary lymph node status. In a clinical setting, the combination of 18F-FDG PET/MRI and axillary sonography might be considered to provide even more accuracy in diagnosis.

Ga-68-FAPI as diagnostic tool in sarcoma: Data from the FAPI-PET prospective observational trial

Introduction: Bone and soft tissue sarcomas express fibroblast activation protein (FAP) on tumor cells and associated fibroblast. Therefore, FAP is a promising therapeutic and diagnostic target. Novel radio-labelled FAP-Inhibitors (e.g. ⁶⁸Ga-FAPI46) have shown high tumor uptake in positron emission tomography (PET) in sarcoma patients. Here we report endpoints of the FAPI-PET prospective observational trial. Methods: Forty-seven patients with bone or soft tissue sarcomas undergoing clinical ⁶⁸Ga-FAPI-PET were eligible for enrollment into the FAPI-PET observational trial. Of these patients, 43 patients also underwent ¹⁸F-Fluordesoxyglucose PET (FDG). The primary study endpoint was the association of ⁶⁸Ga-FAPI-PET uptake intensity and histopathological FAP-expression analyzed with Spearman's r correlation. Secondary endpoints were detection rate, positive predictive value (PPV), interreader reproducibility, and change in management. Datasets were interpreted by two blinded readers. Results: Primary endpoint was met and the association between FAPI-PET uptake intensity and histopathological FAP-expression was significant (Spearman's r = 0.43; P = 0.03). By histopathological validation PPV was 1.00 (95% CI, 0.87-1.00) on a per-patient and 0.97 (95% CI, 0.84-1.00) on a per-region basis. In cases with histopathologic validation, 27 of 28 (96%) confirmed patients and 32 of 34 (94%) confirmed regions were PET positive resulting in an SE of 0.96 (95%CI, 0.82-1.00) on a per-patient and 0.94 (95%CI, 0.80-0.99) on a per-region basis. The detection rate on a per-patient basis in FAPI- and FDG-PET was 76.6% and 81.4%, respectively. In 8 (18.6%) patients FAPI-PET resulted in an upstaging compared to FDG-PET. FAPI-PET readers showed substantial to almost perfect agreement for the defined regions (Fleiss kappa: primary κ = 0.78; local nodal κ = 0.54; distant nodal κ = 0.91; lung κ = 0.86; bone κ = 0.69 and other κ = 0.65). Clinical management changed in 13 (30%) patients after FAPI-PET. Conclusion: We confirm an association of tumoral FAPI-PET uptake intensity and histopathological FAP expression in sarcoma patients. Further, using blinded reads and independent histopathological validation we report high PPV and sensitivity of FAPI-PET for sarcoma staging.

Complete metabolic response in patients with advanced nonsmall cell lung cancer with prolonged response to immune checkpoint inhibitor therapy

Introduction

Immunotherapy is the new standard of care in advanced non-small cell lung cancer (NSCLC). Recently published data show that treatment discontinuation after 12 months of nivolumab treatment is associated with shorter survival. Therefore, the ideal duration of immunotherapy remains unclear, and finding markers of beneficial outcomes is of great importance. Here, we determine the proportion of complete metabolic responses (CMR) in patients who have not progressed after 24 months of immunotherapy.

Methods

This is a retrospective analysis of 45 patients with positron emission tomography using 2-[18F]fluoro-2-deoxy-D-glucose imaging for assessment of residual metabolic activity after at least 24 months. CMR was defined as uptake in tumor lesions below background levels, using mediastinum as a reference.

Results

Out of 45 patients, 29 patients had a CMR (64%). CMR was observed more frequently in non-first-line patients. Patients with CMR were younger (median 65.7 vs 75.5, p=0.03). Fourteen patients with CMR have discontinued therapy and have not progressed until time of analysis; however, median follow-up was only 5.6 (range 0.8–17.0) months.

Conclusion

After a minimum of 24 months of palliative immunotherapy for NSCLC, CMR occurred in almost two thirds of patients. Potentially, achievement of CMR might identify patients, for whom palliative immunotherapy may be safely discontinued.

Evaluation of [68Ga]Ga-PSMA PET/CT images acquired with a reduced scan time duration in prostate cancer patients using the digital biograph vision

Aim

[⁶⁸Ga]Ga-PSMA-11 PET/CT allows for a superior detection of prostate cancer tissue, especially in the context of a low tumor burden. Digital PET/CT bears the potential of reducing scan time duration/administered tracer activity due to, for instance, its higher sensitivity and improved time coincidence resolution. It might thereby expand [⁶⁸Ga]Ga-PSMA-11 PET/CT that is currently limited by ⁶⁸Ge/⁶⁸Ga-generator yield. Our aim was to clinically evaluate the influence of a reduced scan time duration in combination with different image reconstruction algorithms on the diagnostic performance.

Methods

Twenty prostate cancer patients (11 for biochemical recurrence, 5 for initial staging, 4 for metastatic disease) sequentially underwent [⁶⁸Ga]Ga-PSMA-11 PET/CT on a digital Siemens Biograph Vision. PET data were collected in continuous-bed-motion mode with a mean scan time duration of 16.7 min (reference acquisition protocol) and 4.6 min (reduced acquisition protocol). Four iterative reconstruction algorithms were applied using a time-of-flight (TOF) approach alone or combined with point-spread-function (PSF) correction, each with 2 or 4 iterations. To evaluate the diagnostic performance, the following metrics were chosen: (a) per-region detectability, (b) the tumor maximum and peak standardized uptake values (SUVmax and SUVpeak), and (c) image noise using the liver’s activity distribution.

Results

Overall, 98% of regions (91% of affected regions) were correctly classified in the reduced acquisition protocol independent of the image reconstruction algorithm. Two nodal lesions (each ≤ 4 mm) were not identified (leading to downstaging in 1/20 cases). Mean absolute percentage deviation of SUVmax (SUVpeak) was approximately 9% (6%) for each reconstruction algorithm. The mean image noise increased from 13 to 21% (4 iterations) and from 10 to 15% (2 iterations) for PSF + TOF and TOF images.

Conclusions

High agreement at 3.5-fold reduction of scan time in terms of per-region detection (98% of regions) and image quantification (mean deviation ≤ 10%) was demonstrated; however, small lesions can be missed in about 10% of patients leading to downstaging (T1N0M0 instead of T1N1M0) in 5% of patients. Our results suggest that a reduction of scan time duration or administered [⁶⁸Ga]Ga-PSMA-11 activities can be considered in metastatic patients, where missing small lesions would not impact patient management. Limitations include the small and heterogeneous sample size and the lack of follow-up.

Impact of PSMA PET/CT on SRT planning: Preliminary results from the randomized phase III trial NCT03582774

30

Background: The purpose of this trial is to evaluate the success rate of salvage radiation therapy (SRT) for recurrence of prostate cancer (PCa) after radical prostatectomy with and without planning based on prostate specific membrane antigen (PSMA) positron emission tomography (PET). Methods: This is a multicenter, prospective, randomized, controlled, open-label, Phase 3 clinical imaging trial powered for clinical outcome at 5 years. UCLA is the leading central site in which PSMA PET, clinical follow-up and data management are being done. UCSF was a participating site in which PSMA PET imaging can be done. SRT can be performed anywhere, patients are followed remotely by the UCLA investigators. Patients scheduled for SRT for recurrence after primary prostatectomy and with PSA ≥ 0.1ng/ml at time of enrollment were eligible. Patients were randomized to proceed with standard SRT allowing for any conventional imaging aside from PSMA PET/CT (control arm) or undergo a 68Ga-PSMA-11 PET/CT scan prior to SRT planning (investigational arm). The primary endpoint is the success rate of SRT at 5 years in patients who undergo SRT. We report here the preliminary results of a secondary endpoint: the impact of PSMA PET on SRT planning by comparing the pre-randomization RT plans prospectively obtained on surveys before randomization to the actually delivered RT plans obtained after follow-up. Results: Enrollment of the trial was complete. 193 patients were enrolled from 09.06.2018 to 08.17.2020. 7/90 patients (9%) in the control arm dropped-out the study because they underwent a PSMA PET at another institution, while 1/103 (1%) patients of the intervention arm dropped-out due to COVID-19 related complications. After a median follow-up of 13.3 months (last follow-up date 09/01/2020), delivered RT plans were obtained in 60/83 (72%) and 70/102 (69%) of patients of the control and the PSMA arms, respectively. Median PSA at enrollment was 0.32 ng/ml (IQR 0.17-1.35) and 0.22 ng/ml (IQR 0.14-0.50) in the control and PSMA arms, respectively. There was a change between the intended pre-randomization RT plan and the actually delivered RT plan in 17/60 (28%) and 40/70 (57%) of the patients in the control and PSMA arms, respectively (p = 0.002). SRT was aborted in favor of systemic therapy and/or metastasis directed RT for extra-pelvic M1 disease in 2/60 (3%) and 12/70 (17%) of the control and PSMA arms, respectively (p = 0.17). Dose prescription and/or target volume delineation was changed in 2/60 (3%) and 1/70 (26%) in the control and PSMA arms, respectively (p = 0.001). Conclusions: In this prospective randomized phase 3 study, PSMA PET had an impact on the SRT plan in more than half of the patients. Long-term follow-up will show if the impact of PSMA PET on SRT planning translates into improved outcome or not. Clinical trial information: NCT03582774.

Phase III randomized trial of PSMA PET prior to definitive radiation therapy for unfavorable intermediate-risk or high-risk prostate cancer [PSMA dRT]: Study protocol NCT04457245

TPS172

Background: Definitive radiation therapy (dRT) is an effective initial treatment of intermediate-risk (IR) and high-risk (HR) prostate cancer (PCa). Positron emission tomography (PET) using small molecule probes targeting prostate-specific membrane antigen (PSMA PET) is superior to standard of care imaging (CT, MRI, bone scan) for detecting regional and distant metastatic PCa. PSMA PET thus has the potential to guide primary radiotherapy planning in patients and improve outcomes. The purpose of the present randomized trial is to evaluate the success rate of dRT for IR or HR PCa with and without planning based on PSMA PET. Methods: We will randomize 312 patients to proceed with standard dRT (control Arm 1, n=150), or undergo a PSMA PET scan prior to dRT planning (intervention arm 2, n = 162). In the control arm, dRT will be performed as routinely planned in accordance with initial stratification. In the intervention arm, the treating radiation oncologist can incorporate PSMA PET findings into the RT planning. We assume that approximately 8% of subjects randomized to arm 2 will be found to have M1 disease and thus will be more appropriate candidates for long-term systemic or multimodal therapy, rather than curative intent dRT. PET M1 patients will thus not be included in the analysis of the primary endpoint. The primary endpoint is the success rate of dRT measured as PFS after initiation of dRT. Progression is defined as (whichever occurs first): biochemical recurrence defined as a rise by 2 ng/mL or more above the nadir PSA (defined as the lowest PSA achieved) after radiotherapy with or without short-term hormonal therapy; appearance of metastasis or loco-regional recurrence (diagnosed by any imaging or biopsy); initiation of any new salvage therapy, or death from any cause. Discussion: This is the first randomized phase 3 prospective trial designed to determine whether PSMA PET molecular imaging can improve outcomes in patients with PCa who receive dRT. In this trial the incorporation of PSMA PET may improve the success rate of curative intent radiotherapy in two ways: to optimize patient selection and to personalizes the radiotherapy plan. Clinical trial registration: IND#147591, UCLA IRB #20-000378, ClinicalTrials.gov Identifier NCT04457245. Clinical trial information: NCT04457245.

Comparing lesion detection efficacy and image quality across different PET system generations to optimize the iodine-124 PET protocol for recurrent thyroid cancer

Background

In recurrent differentiated thyroid cancer patients, detectability in ¹²⁴I PET is limited for lesions with low radioiodine uptake. We assess the improvements in lesion detectability and image quality between three generations of PET scanners with different detector technologies. The results are used to suggest an optimized protocol.

Methods

Datasets of 10 patients with low increasing thyroglobulin or thyroglobulin antibody levels after total thyroidectomy and radioiodine therapies were included. PET data were acquired and reconstructed on a Biograph mCT PET/CT (whole-body, 4-min acquisition time per bed position; OSEM, OSEM-TOF, OSEM-TOF+PSF), a non-TOF Biograph mMR PET/MR (neck region, 4 min and 20 min; OSEM), and a new generation Biograph Vision PET/CT (whole-body, 4 min; OSEM, OSEM-TOF, OSEM-TOF+PSF). The 20-min image on the mMR was used as reference to calculate the detection efficacy in the neck region. Image quality was rated on a 5-point scale.

Results

All detected lesions were in the neck region. Detection efficacy was 8/9 (Vision OSEM-TOF and OSEM-TOF+PSF), 4/9 (Vision OSEM), 3/9 (mMR OSEM and mCT OSEM-TOF+PSF), and 2/9 (mCT OSEM and OSEM-TOF). Median image quality was 4 (Vision OSEM-TOF and OSEM-TOF+PSF), 3 (Vision OSEM, mCT OSEM-TOF+PSF, and mMR OSEM 20-min), 2 (mCT OSEM-TOF), 1.5 (mCT OSEM), and 1 (mMR OSEM 4 min).

Conclusion

At a clinical standard acquisition time of 4 min per bed position, the new generation Biograph Vision using a TOF-based image reconstruction demonstrated the highest detectability and image quality and should, if available, be preferably used for imaging of low-uptake lesions. A prolonged acquisition time for the mostly affected neck region can be useful.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-021-00361-y.

Evaluation of 18F-FDG PET/CT images acquired with a reduced scan time duration in lymphoma patients using the digital biograph vision

BACKGROUND

The superior accuracy and sensitivity of 18F-FDG-PET/CT in comparison to morphological imaging alone leads to an upstaging in up to 30% of lymphoma patients. Novel digital PET/CT scanners might enable to reduce administered tracer activity or scan time duration while maintaining diagnostic performance; this might allow for a higher patient throughput or a reduced radiation exposure, respectively. In particular, the radiation exposure reduction is of interest due to the often young age and high remission rate of lymphoma patients.

METHODS

Twenty patients with (suspected) lymphoma (6 for initial staging, 12 after systemic treatment, 2 in suspicion of recurrence) sequentially underwent 18F-FDG-PET/CT examinations on a digital PET/CT (Siemens Biograph Vision) with a total scan time duration of 15 min (reference acquisition protocol) and 5 min (reduced acquisition protocol) using continuous-bed-motion. Both data sets were reconstructed using either standalone time of flight (TOF) or in combination with point spread function (PSF), each with 2 and 4 iterations. Lesion detectability by blinded assessment (separately for supra- and infradiaphragmal nodal lesions and for extranodal lesions), lesion image quantification, and image noise were used as metrics to assess diagnostic performance. Additionally, Deauville Score was compared for all patients after systemic treatment.

RESULTS

All defined regions were correctly classified in the images acquired with reduced emission time, and therefore, no changes in staging were observed. Lesion quantification was acceptable, that is, mean absolute percentage deviation of maximum and peak standardized uptake values were 6.8 and 6.4% (derived from 30 lesions). A threefold reduction of scan time duration led to an increase in image noise from 7.1 to 11.0% (images reconstructed with 4 iterations) and from 4.7 to 7.2% (images reconstructed with 2 iterations). No deviations in Deauville Score were observed.

CONCLUSION

These results suggest that scan time duration or administered tracer activity can be reduced threefold without compromising diagnostic performance. Especially a reduction of administered activity might allow for a lower radiation exposure and better health economics. Larger trials are warranted to confirm our results.

Outcome After 68Ga-PSMA-11 versus Choline PET-Based Salvage Radiotherapy in Patients with Biochemical Recurrence of Prostate Cancer: A Matched-Pair Analysis

The purpose of this analysis was primarily to analyze biochemical-recurrence free survival (BRFS) after positron emission tomography (PET)-guided salvage radiotherapy (sRT) in a large cohort, and to further compare BRFS after PSMA vs. choline PET/ computer tomography (CT)-based sRT. This retrospective analysis is based on 421 patients referred for PSMA or choline PET/CT after radical prostatectomy due to biochemically recurrent or persistent disease. BRFS (PSA: 0.2 ng/mL) was defined as the study endpoint. Cox regression analyses were performed to assess the impact of different clinical parameters on BRFS. Additionally, propensity score matching was performed to adjust patient cohorts (PSMA vs. choline PET/CT-based sRT). The median follow-up time was 30 months. BRFS at three years after sRT was 58%. In the multivariate analysis, only PSA before PET imaging and PSA before sRT were significantly associated with BRFS (p < 0.05). After propensity score matching, 272 patients were further analyzed; there was no significant difference in three-year BRFS between patients with PSMA PET-based vs. choline PET-based sRT (55% vs. 63%, p = 0.197). The present analysis confirmed the overall high BRFS rates after PET-based sRT and the strong prognostic effect of PSA level prior to sRT. PSMA PET-based sRT did not have superior BRFS rates when compared with choline PET-based sRT.

Overall survival after 177Lu-PSMA-617 molecular radiotherapy in patients with metastatic castrate-resistant prostate cancer: Post-hoc analysis of a prospective phase II trial

5549

Background: This was an open-label randomized prospective bi-centric single-arm phase II clinical trial of 177Lu-PSMA-617 molecular radiotherapy in patients with progressive metastatic castrate-resistant prostate cancer (mCRPC) conducted at University of California Los Angeles (USA) and Excel Diagnostics & Nuclear Oncology Center (Houston, TX, USA) (NCT03042312). The study was investigator-initiated under an investigational new drug approval protocol (IND#133661) with authorization of charging for investigational drug (cost-recovery, Title 21 CFR 312.8). We report here the post-hoc analysis of overall survival (OS) in a single-study site cohort (UCLA). Methods: Patients with progressive mCRPC (biochemical, radiographic, or clinical) after ≥1 novel androgen axis drug (NAAD), either chemotherapy (CTX) naïve or post-CTX, with sufficient bone marrow reserve, normal kidney function, and sufficient PSMA-target expression by PET were eligible. Patients received up to 4 cycles of 177Lu-PSMA-617 every 8±1 weeks and were randomized into 2 treatment activities groups (6.0 or 7.4 GBq). Efficacy was defined as serum PSA decline of ≥50% from baseline and served as primary endpoint (hypothesis: ≥40% of responders after 2 cycles). Results: 43 patients were randomized to the 6.0 GBq (n= 14) and 7.4 GBq (n=29) treatment arms. 11/43 (26%) were CTX naïve while 10/43 (23%), 12/43 (28%), 5/43 (12%) and 5/43 (12%) had received 1, 2, 3 or 4 CTX regimens. Median baseline PSA was 29.2 ng/ml (mean 228.8, range 0.5-2082.6). 21/43 (49%) completed 4 cycles of 177Lu-PSMA-617 whereas 4/43 (9%), 13/43 (30%) and 5/43 (12%) underwent 1, 2 and 3 cycles. PSA decline of ≥50% was observed in 11/43 of patients (26%) after 2 cycles and in 16/43 (37%) at any time (best PSA response). 9/43 (21%) had a PSA decline of ≥90% and 23/43 (53%) had any PSA decline (>0%). After a median follow-up of 19.5 months the median OS was 14.8, 15.7 and 13.5 months in the whole cohort, the 6.0 GBq and 7.4 GBq treatment arms, respectively (p=0.68). Patients showing a PSA decline of ≥50% after 2 cycles and at any time had a longer OS: median 20.1 months vs. 13.6 (p=0.091) and 20.1 vs. 11.6 (p=0.002), respectively. Conclusions: In this post-hoc analysis of a single-site cohort of 43 patients included in a prospective phase II trial the median OS after 177Lu-PSMA-617 molecular radiotherapy in patients with progressive mCRPC was 14.8 months. There was no difference of efficacy between the 6.0 GBq and 7.4 GBq treatment arms. Clinical trial information: NCT03042312 .

Prognostic markers for overall survival and outcome to LuPSMA radionuclide treatment in patients with metastatic castration-resistant prostate cancer

5548

Background: The aim of this international multicenter retrospective analysis was to identify prognostic markers for the clinical outcome in late-stage mCRPC patients treated with 177Lutetium-prostate-specific membrane antigen (LuPSMA) radionuclide treatment. Methods: Patients with progressive mCRPC treated with LuPSMA at six centers in Germany, USA, and Australia were considered for inclusion. Eligible patients had 24 predefined, pretherapeutic covariates (demographics, prior mCRPC treatments, and PSMA PET/CT derived parameters) and survival data available. Endpoints included overall survival (OS) and PSA progression-free survival (PSA-PFS). Covariates were tested using univariate and mulitvariate proportional hazards regression Cox models. Results: 267/414 (64%) patients met inclusion criteria and were analyzed. 113 patients participated in clinical trials (ACTRN12615000912583, NCT03042312), while 154 were enrolled in compassionate-access programs. After a median follow-up of 22.5 months, median OS was 13.0 months (95%CI 11.6-14.4); 83% of the patients died. Median PSA-PFS was 4.0 months (95%CI 3.2-4.7). In the multivariate analysis, factors associated with shorter OS were: shorter time since diagnosis of prostate cancer (HR=2.04; p=0.002), lower number of prior systemic therapies (≤3; HR=1.56; p=0.006), prior exposure to chemotherapy (HR=1.42; p=0.05), lower hemoglobin levels (HR=1.13; p=0.002), higher number of lesions (≥20: HR=1.53; p=0.009), multiple sites of metastases (bone/LN only vs. bone + LN; HR=1.39; p=0.03) and visceral involvement (M1c) (HR=1.45; p=0.01). Factors associated with longer PSA-PFS were: longer time since diagnosis of prostate cancer (HR=0.44; p<0.001), higher hemoglobin levels (HR=0.32; p=0.03), presence of pelvic lymph nodes (LN) metastasis (N1) (HR=0.68; p=0.01), no distant lymph node metastases (M1a) (HR=0.66; p=0.01), no skeleton involvement (HR=0.44; p=0.01), no visceral metastases (M1c) (HR=0.51; p<0.001), higher PSMA-positive tumor volume (HR=0.87; p=0.04), and higher SUVmean (HR=0.94; p=0.002). Conclusions: This retrospective analysis identified prognostic factors for survival and treatment response to LuPSMA. Along with the conventional risk factors in mCRPC, PSMA PET/CT can be a useful tool for stratifying patients and guide patient’s selection for LuPSMA radionuclide treatment.

Accuracy of 68Ga-PSMA-11 for pelvic nodal metastasis detection prior to radical prostatectomy and pelvic lymph node dissection: A multicenter prospective phase III imaging study

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Background: To determine the accuracy of 68Ga-PSMA-11 PET for the detection of pelvic nodal metastases (N1) compared to histopathology at time of radical prostatectomy (RP). Methods: This is a prospective multicenter single-arm open-label phase 3 imaging trial. Patients with intermediate to high risk prostate cancer (PCa) considered for RP with lymph node dissection (PLND) were enrolled at the University of California, Los Angeles (UCLA) and at the San Francisco (UCSF) (NCT03368547, NCT02611882, NCT02919111), and underwent one 68Ga-PSMA-11 PET. The primary endpoint was the sensitivity (Se) and specificity (Sp) of 68Ga-PSMA-11 PET for the N1 detection compared to PLND histopathology (reference-standard) on a per patient basis using nodal region-based correlation. Each scan was read by three blinded independent central readers (BICR). Consensus was based on majority rule. Results: From December 2015 to August 2019, 633 patients underwent one 68Ga-PSMA-11 PET for primary staging, and 277/633 (44%) subsequently underwent RP and PLND. The median initial PSA was 11.1 [0.04-147]. 75/277 patients (27%) had N1 disease per histopathology. Using a regional based analysis, Se, Sp, positive predictive value (PPV) and negative predictive value (NPV) for N1 detection was 0.40 [0.34, 0.46], 0.95 [0.92, 0.97], 0.75 [0.70, 0.80], 0.81 [0.76, 0.85], respectively. Se was higher for patients with higher PSA: 0.29 [0.24, 0.35] for PSA < 11 ng/ml versus 0.48 [0.42, 0.54] for PSA > 11. Se was higher when the nodes were larger: 0.30 [0.25, 0.36] for nodes < 10 mm versus 0.68 [0.63, 0.74] for nodes > 10. The average node size in true positive patients was 10 mm versus 4 mm in false negative patients. Conclusions: In intermediate to high risk PCa patients who underwent RP and PLND, 68Ga-PSMA-11 PET detected pelvic nodal metastases with a sensitivity of 0.40 and a specificity of 0.95. Higher PSAs and larger node size correlated with increased sensitivity. Clinical trial information: NCT03368547, NCT02611882, NCT02919111 .

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

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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.

Treatment-related changes in neuroendocrine tumors as assessed by textural features derived from 68Ga-DOTATOC PET/MRI with simultaneous acquisition of apparent diffusion coefficient

Background

Neuroendocrine tumors (NETs) frequently overexpress somatostatin receptors (SSTRs), which is the molecular basis for ⁶⁸Ga-DOTATOC positron-emission tomography (PET) and radiopeptide therapy (PRRT). However, SSTR expression fluctuates and can be subject to treatment-related changes. The aim of this retrospective study was to assess, which changes in PET and apparent diffusion coefficient (ADC) occur for different treatments and if pre-therapeutic ⁶⁸Ga-DOTATOC-PET/MRI was able to predict treatment response to PRRT.

Methods

Patients with histopathologically confirmed NET, at least one liver metastasis > 1 cm and at least two ⁶⁸Ga-DOTATOC-PET/MRI including ADC maps were eligible. ⁶⁸Ga-DOTATOC-PET/MRI of up to 5 liver lesions per patients was subsequently analyzed. Extracted features comprise conventional PET parameters, such as maximum and mean standardized uptake value (SUVmax and SUVmean) and ADC values. Furthermore, textural features (TFs) from both modalities were extracted. In patients with multiple ⁶⁸Ga-DOTATOC-PET/MRI a pair of 2 scans each was analyzed separately and the parameter changes between both scans calculated. The same image analysis was performed in patients with ⁶⁸Ga-DOTATOC-PET/MRI before PRRT. Differences in PET and ADC maps parameters between PRRT-responders and non-responders were compared using Mann-Whitney test to test differences among groups for statistical significance.

Results

29 pairs of ⁶⁸Ga-DOTATOC-PET/MRI scans of 18 patients were eligible for the assessment of treatment-related changes. In 12 cases patients were treated with somatostatin analogues between scans, in 9 cases with PRRT and in 2 cases each patients received local treatment, chemotherapy and sunitinib. Treatment responders showed a statistically significant decrease in lesion volume and a borderline significant decrease in entropy on ADC maps when compared to non-responders. Patients treated with standalone SSA showed a borderline significant decrease in mean and maximum ADC, compared to patients treated with PRRT. No parameters were able to predict treatment response to PRRT on pre-therapeutic ⁶⁸Ga-DOTATOC-PET/MRI.

Conclusions

Patients responding to current treatment showed a statistically significant decrease in lesion volume on ADC maps and a borderline significant decrease in entropy. No statistically significant changes in PET parameters were observed. No PET or ADC maps parameters predicted treatment response to PRRT. However, the sample size of this preliminary study is small and further research needed.

Mapping Prostate Cancer Lesions Before and After Unsuccessful Salvage Lymph Node Dissection Using Repeat PSMA PET

The aim of this study was to analyze patterns of persistent versus recurrent or new PET lesions in a selected patient cohort with prostate-specific antigen (PSA) persistence after salvage lymph node dissection (SLND) and pre-procedure and post-procedure prostate-specific membrane antigen (PSMA) ligand PET. Methods: Sixteen patients were included in this multicenter study. The inclusion criteria were PSMA PET performed for biochemical recurrence before SLND (pre-SLND PET) and repeat PSMA PET performed for a persistently elevated PSA level (≥0.1 ng/mL) at least 6 wk after SLND (post-SLND PET). Image analysis was performed by 3 independent nuclear medicine physicians applying the molecular imaging TNM system PROMISE. Lesions were confirmed by histopathology, presence on correlative CT/MRI/bone scanning, or PSA response after focal therapy. Results: Post-SLND PET identified prostate cancer lesions in 88% (14/16) of patients with PSA persistence after SLND. Median PSA was 1.2 ng/mL (interquartile range, 0.6-2.8 ng/mL). Disease was confined to the pelvis in 56% of patients (9/16), and most of these men had common iliac (6/16, 38%) and internal iliac lymph node metastases (6/16, 38%). Extrapelvic disease was detected in 31% of patients (5/16). In pre- and post-SLND PET comparison, 10 of 16 had at least one lesion already detected at baseline (63% PET persistence), 4 of 16 had new lesions only (25% PET recurrence), and 2 had no disease on post-SLND PET. All validated regions (11 regions in 9 patients) were true-positive. Nine of 14 (64%) patients underwent repeat local therapies after SLND (7/14 radiotherapy, 2/14 surgery). Conclusion: SLND of pelvic nodal metastases was often not complete according to PSMA PET. About two thirds of patients had PET-positive nodal disease after SLND already seen on pre-SLND PSMA PET. Notably, about one quarter of patients had new lesions, not detected by presurgical PSMA PET.

EANM procedure guidelines for radionuclide therapy with 177Lu-labelled PSMA-ligands (177Lu-PSMA-RLT)

Prostate-specific membrane antigen (PSMA) is expressed in most prostate cancers and can be identified by PSMA-ligand imaging, which has already become clinically accepted in several countries in- and outside Europe. PSMA-directed radioligand therapy (PSMA-RLT) with Lutetium-177 (¹⁷⁷Lu-PSMA) is currently undergoing clinical validation. Retrospective observational data have documented favourable safety and striking clinical responses. Recent results from a prospective clinical trial (phase II) have been published confirming high response rates, low toxicity and reduction of pain in metastatic castration-resistant prostate cancer (mCRPC) patients who had progressed after conventional treatments. Such patients typically survive for periods less than 1.5 years. This has led some facilities to adopt compassionate or unproven use of this therapy, even in the absence of validation within a randomised-controlled trial. As a result, a consistent body of evidence exists to support efficacy and safety data of this treatment. The purpose of this guideline is to assist nuclear medicine specialists to deliver PSMA-RLT as an "unproven intervention in clinical practice", in accordance with the best currently available knowledge.

Salvage PRRT with 177Lu-DOTA-octreotate in extensively pretreated patients with metastatic neuroendocrine tumor (NET): dosimetry, toxicity, efficacy, and survival

Background

NETTER-1 trial demonstrated high efficacy and low toxicity of four cycles of Peptide Receptor Radionuclide Therapy (PRRT) in patients with metastasized NET. The present study evaluates the outcome of further PRRT cycles in the so called salvage setting in patients after initial response to four therapy cycles and later progression.

Methods

Thirty five patients (pat.) (25 male, 10 female, 63 ± 9 years) with progressive, metastasized NET (23 small intestinal, 5 lung, 4 CUP, 1 rectal, 1 gastric and 1 paraganglioma) were included. All patients previously received 4 PRRT cycles with ¹⁷⁷Lu-DOTATATE and showed initial response. SPECT based dosimetry was applied to determine kidney and tumor doses. Therapy response was evaluated using ⁶⁸Ga-DOTATATE PET/CT (with high dose CT), CT alone or MRI (RECIST 1.1), toxicity was defined using CTCAE 5.0 criteria. ^99mTc99-MAG3 scintigraphy was used to assess potential renal tubular damage. Progression free survival (PFS) and Overall survival (OS) analysis was performed with the Kaplan-Meier-method.

Results

The median PFS after initial PRRT was 33 months (95% CI: 30–36). The mean cumulative dose for including salvage PRRT was 44 GBq (range 33.5–47). One pat. (2.9%) showed grade 3 hematotoxicity. Kidney dosimetry revealed a mean cumulative kidney dose after a median of 6 PRRT cycles of 23.8 Gy. No grade 3 / 4 nephrotoxicity or relevant decrease in renal function was observed. Follow-up imaging was available in 32 patients after salvage therapy. Best response according to RECIST 1.1. was PR in one patient (3.1%), SD in 26 patients (81.3%) and PD in 5 patients (15.6%). PFS after salvage therapy was 6 months (95% CI: 0–16; 8 patients censored). Mean OS after initial PRRT was 105 months (95% CI: 92–119) and 51 months (95% CI: 41–61) after start of salvage therapy. Median OS was not reached within a follow-up of 71 months after initial PRRT and 25 months after start of salvage PRRT, respectively.

Conclusions

Salvage therapy with ¹⁷⁷Lu-DOTATATE is safe and effective even in patients with extensive previous multimodal therapies during disease progression and represents a feasible and valuable therapy option for progressive NET.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-6000-y) contains supplementary material, which is available to authorized users.