[PET-CT in head and neck cancer]. / PET-CT bei Karzinomen im Kopf­Hals­Bereich.

The importance of 18F-fluorodesoxyglucose positron-emission tomography (FDG-PET) for the diagnosis of malignant disease is increasing. On one hand, this is due to the high sensitivity of this method, on the other, because the entire body can be examined. FDG-PET can be particularly advantageous for the diagnosis of head and neck tumors, where tumor staging is an important prognostic parameter and essentially determines the therapeutic regimen. This article presents the different possibilities for combined evaluation with PET and computed tomography (CT) for the diagnosis of patients with head and neck cancer. Special focus is placed on primary staging and tumor follow-up, as well as on the role of PET-CT in the diagnosis of patients with cancer of unknown primary origin (CUP). The use of PET-CT for radiotherapy planning and new aspects of PET technology are also discussed.

Positron-emission tomography CT to identify local recurrence in stage I lung cancer patients 1 year after stereotactic body radiation therapy.

PURPOSE: To evaluate the diagnostic value of positron-emission tomography/computed tomography (PET/CT) in stage I lung cancer patients treated with stereotactic body radiation therapy (SBRT), who have suspicious or unclear local recurrence findings in CT 1 year after treatment. PATIENTS AND METHODS: A group of 29 patients with unclear or suspicious CT findings 1 year after SBRT were examined with PET/CT. The ability of standard uptake values (SUVmax, SUVmean and posttherapeutic reduction in SUV) to detect local failure and identify patients at a high risk of disease-specific death was evaluated using logrank statistics. Histology and clinical follow-up were the gold standards for local recurrence. RESULTS: SUVmean greater than 3.44 (p = 0.001); SUVmax greater than 5.48 (p = 0.009) or a relative reduction in SUVmean or SUVmax of less than 43 (p = 0.030) or 52 % (p = 0.025), respectively, was indicative of local recurrence. These parameters also correlated with an increased risk of disease-specific death: SUVmean greater than 2.81 (p = 0.023); SUVmax greater than 3.45 (p = 0.007) or a relative reduction in SUVmean or SUVmax of less than 32 (p = 0.015) or 52 % (p = 0.013), respectively, was indicative of an increased risk of disease-specific death. CONCLUSION: PET/CT performed 1 year after SBRT can reliably identify local recurrence and therefore help to clarify unclear CT findings. As posttherapeutic glucose metabolism also correlates with disease-specific survival, PET/CT may help to stratify lung cancer patients for additional treatment 1 year after SBRT.

Decision making for osteoporotic treatment using FRAX or DVO risk algorithms in a clinical setting.

OBJECTIVES: To evaluate the therapy decisive clinical risk factors (CRFs) in tools provided by WHO (WHO-FRAX) and the Head Osteology Organization of Germany (DVO) in a clinical setting, and, the degree of agreement between them. METHODS: Three hundred subjects, 40 to 88 years of age, were consecutively referred for an evaluation of osteoporosis-related fracture risk, and therapy was possibly recommended. The evaluation used the 12 CRFs in the FRAX tool and the 21 CRFs in the DVO tool. We analyzed the degree of agreement and the strength of the CRFs in determining the therapy decision. RESULTS: Before evaluation, 52 (17.3%) of the patients took anti-osteoporotic medication. The FRAX tool indicated 36 (12.0%) patients suggested for treatment when hip density was included as a CRF, whereas the DVO tool indicated 80 (26.7%) and 91(30.3%), depending on bone density site. The pre- and post-test results agreed poorly to fair, whereas agreement was poor to good within both models and using the plain T-score to define the therapy intervention threshold. CONCLUSIONS: CRFs with debatable evidence reached significant influence on therapy decision. A considerably divergent number of patients were identified as treatment candidates, deserving further investigation to confirm the usefulness of some CRFs.

DEPROMP Trial: the additive value of PSMA-PET/CT-guided biopsy for prostate cancer management in biopsy naïve men-study protocol for a randomized trial.

BACKGROUND: The primary objective is to determine the proportion of men with suspected prostate cancer (PCA) in whom the management plans are changed by additive gallium-68 prostate-specific membrane antigen positron emission tomography/computed tomography (PSMA-PET/CT) guided prostate biopsy (PET-TB) in combination with standard of care (SOC) using systematic (SB) and multiparametric magnetic resonance imaging-guided biopsy (MR-TB) compared with SOC alone. The major secondary objectives are to determine the additive value of the combined approach of SB + MR-TB + PET-TB (PET/MR-TB) for detecting clinically significant PCA (csPCA) compared to SOC; to determine sensitivity, specificity, positive and negative predictive value and diagnostic accuracy of imaging techniques, respective imaging classification systems, and each biopsy method; and to compare preoperatively defined tumor burden and biomarker expression and pathological tumor extent in prostate specimens. METHODS: The DEPROMP study is a prospective, open-label, interventional investigator-initiated trial. Risk stratification and management plans after PET/MR-TB are conducted randomized and blinded by different evaluation teams of experienced urologists based on histopathological analysis and imaging information: one including all results of the PET/MR-TB and one excluding the additional information gained by PSMA-PET/CT guided biopsy. The power calculation was centered on pilot data, and we will recruit up to 230 biopsy-naïve men who will undergo PET/MR-TB for suspected PCA. Conduct and reporting of MRI and PSMA-PET/CT will be performed in a blinded fashion. DISCUSSION: The DEPROMP Trial will be the first to evaluate the clinically relevant effects of the use of PSMA-PET/CT in patients with suspected PCA compared to current SOC. The study will provide prospective data to determine the diagnostic yields of additional PET-TB in men with suspected PCA and the impact on treatment plans in terms of intra- and intermodal changes. The results will allow a comparative analysis of risk stratification by each biopsy method, including a performance analysis of the corresponding rating systems. This will reveal potential intermethod and pre- and postoperative discordances of tumor stage and grading, providing the opportunity to critically assess the need for multiple biopsies. TRIAL REGISTRATION: German Clinical Study Register DRKS 00024134. Registered on 26 January 2021.

Respiratory gated [18F]FDG PET/CT for target volume delineation in stereotactic radiation treatment of liver metastases.

PURPOSE: The use of 4D-[(18)F]fluorodeoxyglucose (FDG) PET/CT in combination with respiratory gated magnet resonance imaging (MRI) in target volume definition for stereotactic radiation of liver metastases was investigated. METHODS AND MATERIALS: A total of 18 patients received respiration gated FDG-PET/CT and MRI. Data were fused using a rigid co-registration algorithm. The quality of the co-registration was rated on a scale from 1 (excellent) to 5 (poor) for co-registration of MRI with gated PET and ungated PET. Gross tumor volume (GTV) was delineated in CT (GTV (CT)), MRI (GTV(MRI)), and PET (GTV(PET)). MRI- and PET-based GTVs were defined by three observers each. Interobserver variability was calculated for all patients as well as for subgroups with and without previous treatment of liver metastases. All GTVs were compared for all patients and separately for patients with previous local therapy. In addition, a semiautomatic segmentation algorithm was applied on the PET images. RESULTS: Co-registration between MR and PET images was rated with 3.3 in average when non-gated PET was used and improved significantly (p < 0.01) to 2.1 using gated PET. The average GTV(CT) was 51.5 ml, GTV(MRI) 51.8 ml, and the average GTV(PET) 48.1 ml. Volumes delineated in MRI were 9.9% larger compared to those delineated in CT. Volumes delineated in PET were 13.8% larger than in MRI. The differences between the GTVs were more pronounced in patients with previous treatment. The GTVs defined in MRI showed an interobserver variability of 47.9% (84.1% with previous treatment and 26.2% without previous treatment). The PET-defined GTVs showed an interobserver variability of 21% regardless of previous treatment. Semiautomatic segmentation did not provide satisfying results. CONCLUSION: FDG-PET can distinguish vital tumor tissue and scar tissue, and therefore alters the GTV especially in patients with previous local treatment. In addition, it reduces the interobserver variability significantly compared to MRI. However, respiratory gated PET is necessary for good co-registration of PET and MRI.

Antihormone treatment differentially regulates PSA secretion, PSMA expression and 68Ga-PSMA uptake in LNCaP cells.

BACKGROUND: In recent years, a variety of innovative therapeutics for castration-resistant prostate cancer have been developed, including novel anti-androgenic drugs, such as abiraterone or VPC-13566. Therapeutic monitoring of these pharmaceuticals is performed either by measuring PSA levels in serum or by imaging. PET using PSMA ligands labeled with Fluor-18 or Gallium-68 is the most sensitive and specific imaging modality for detection of metastases in advanced prostate cancer. To date, it remains unclear how PSMA expression is modulated by anti-hormonal treatment and how it correlates with PSA secretion. METHODS: We analyzed modulation of PSMA-mRNA and protein expression, 68Ga-PSMA uptake and regulation of PSA secretion by abiraterone or VPC-13566 in LNCaP cells in vitro. RESULTS: We found that abiraterone and VPC-13566 upregulate PSMA protein and mRNA expression but block PSA secretion in LNCaP cells. Both anti-androgens also enhanced 68Ga-PSMA uptake normalized by the number of cells, whereas abiraterone and VPC-13566 reduced 68Ga-PSMA uptake in total LNCaP monolayers treated due to cell death. CONCLUSION: Our data indicate that PSA secretion and PSMA expression are differentially regulated upon anti-androgen treatment. This finding might be important for the interpretation of 68Ga-PSMA PET images in monitoring therapies with abiraterone and VPC-13566 in prostate cancer patients, but needs to be validated in vivo.

Clinical evaluation of [68Ga]Ga-DATA-TOC in comparison to [68Ga]Ga-DOTA-TOC in patients with neuroendocrine tumours.

INTRODUCTION: [68Ga]Ga-DATA-TOC is a new radiolabelled somatostatin-analogue for positron emission tomography (PET) imaging of neuroendocrine tumours. Its advantage over DOTA-conjugated compounds is the possibility for high-efficiency labelling with gallium-68 quickly at room temperature with high reliability and without the need for product purification, which enables the development of an instant kit-type labelling method. We evaluated its imaging characteristics in patients with neuroendocrine tumours in comparison to [68Ga]Ga-DOTA-TOC. METHODS: 19 patients imaged with [68Ga]Ga-DATA-TOC were retrospectively analysed and uptake in normal tissues was compared with a group of 19 patients imaged with [68Ga]Ga-DOTA-TOC. 10 patients imaged with [68Ga]Ga-DATA-TOC had a history of [68Ga]Ga-DOTA-TOC imaging before and were additionally analysed to obtain biodistribution data of both tracers in the same patients. In 5 patients showing stable disease between both examinations, tumour uptake, lesion detectability and lesion conspicuity of both tracers were evaluated. RESULTS: Uptake of [68Ga]Ga-DATA-TOC in normal organs with expression of the somatostatin receptor was 25-47% lower compared to [68Ga]Ga-DOTA-TOC. Background of [68Ga]Ga-DATA-TOC was 40-41% lower in the liver. A higher retention of [68Ga]Ga-DATA-TOC was observed in the blood (up to 67%) and in the lungs (up to 44%). Tumour uptake (SUV) was 22-31% lower for [68Ga]Ga-DATA-TOC. However, no significant differences were observed for tumour-to-background ratios and lesion detectability. Regarding liver metastases, [68Ga]Ga-DATA-TOC uptake (SUV) reached 69-73% of [68Ga]Ga-DOTA-TOC uptake, but tumour-to-background ratios of [68Ga]Ga-DATA-TOC were 105-110% of [68Ga]Ga-DOTA-TOC ratios. CONCLUSIONS, ADVANCES IN KNOWLEDGE AND IMPLICATIONS FOR PATIENT CARE: We demonstrated the feasibility of the new PET tracer [68Ga]Ga-DATA-TOC for imaging of patients with neuroendocrine tumours, showing a comparable performance to [68Ga]Ga-DOTA-TOC. [68Ga]Ga-DATA-TOC has the potential for development of an instant kit-type labelling method at room temperature similar to 99mTc-labelled radiopharmaceuticals, which might help to increase the availability of 68Ga-labelled somatostatin analogues for clinical routine use.

Stability of radiomic features in CT perfusion maps.

This study aimed to identify a set of stable radiomic parameters in CT perfusion (CTP) maps with respect to CTP calculation factors and image discretization, as an input for future prognostic models for local tumor response to chemo-radiotherapy. Pre-treatment CTP images of eleven patients with oropharyngeal carcinoma and eleven patients with non-small cell lung cancer (NSCLC) were analyzed. 315 radiomic parameters were studied per perfusion map (blood volume, blood flow and mean transit time). Radiomics robustness was investigated regarding the potentially standardizable (image discretization method, Hounsfield unit (HU) threshold, voxel size and temporal resolution) and non-standardizable (artery contouring and noise threshold) perfusion calculation factors using the intraclass correlation (ICC). To gain added value for our model radiomic parameters correlated with tumor volume, a well-known predictive factor for local tumor response to chemo-radiotherapy, were excluded from the analysis. The remaining stable radiomic parameters were grouped according to inter-parameter Spearman correlations and for each group the parameter with the highest ICC was included in the final set. The acceptance level was 0.9 and 0.7 for the ICC and correlation, respectively. The image discretization method using fixed number of bins or fixed intervals gave a similar number of stable radiomic parameters (around 40%). The potentially standardizable factors introduced more variability into radiomic parameters than the non-standardizable ones with 56-98% and 43-58% instability rates, respectively. The highest variability was observed for voxel size (instability rate >97% for both patient cohorts). Without standardization of CTP calculation factors none of the studied radiomic parameters were stable. After standardization with respect to non-standardizable factors ten radiomic parameters were stable for both patient cohorts after correction for inter-parameter correlations. Voxel size, image discretization, HU threshold and temporal resolution have to be standardized to build a reliable predictive model based on CTP radiomics analysis.

Preliminary study of the detectability of coronary plaque with PET.

The evaluation of coronary plaque vulnerability could be of great diagnostic value in cardiology. Positron emission tomography (PET) is a good candidate due to its ability to quantify micromolar concentrations of targeted drugs. However, the detectability of sub-voxel targets such as coronary plaque is limited by partial volume effects and by cardiorespiratory motion. The goal of this paper is to investigate the impact of these factors in the detectability of plaque uptake. Radioactive markers were implanted on the epicardium of a pig and in vivo scans were performed. This was complemented with phantom measurements to determine the minimum detectable uptake as a function of background activity. Simulations were used to evaluate the effect of cardiorespiratory motion on the reconstructed lesions. Despite cardiorespiratory motion of up to 7 mm, the markers were detectable in the in vivo scans even after the injection of background. A lower limit of 250 Bq was found for a target to be detectable. Motion reduced the contrast of the reconstructed lesions to 23% of their static counterpart. Respiratory gating improved this to 49% of the static value. The results suggest that coronary plaque evaluation with PET is possible, provided that sufficient plaque-to-myocardium uptake contrast (50 to 100) can be achieved. This requirement increases exponentially for lesions with uptake below 250 Bq. The described experiments provide a means of estimating the minimum uptake and contrast required to ensure the detectability of plaque lesions.

Evaluation of the attenuation properties of MR equipment for its use in a whole-body PET/MR scanner.

The combination of magnetic resonance imaging (MR) and positron emission tomography (PET) scanners can provide a powerful tool for clinical diagnosis and investigation. Among the challenges of developing a combined scanner, obtaining attenuation maps for PET reconstruction is of critical importance. This requires accounting for the presence of MR hardware in the field of view. The attenuation introduced by this hardware cannot be obtained from MR data. We propose the creation of attenuation models of MR hardware, to be registered into the MR-based attenuation map prior to PET reconstruction. Two steps were followed to assess the viability of this method. First, transmission and emission measurements were performed on MR components (RF coils and medical probes). The severity of the artifacts in the reconstructed PET images was evaluated. Secondly, a high-exposure computed tomography (CT) scan was used to obtain a model of a head coil. This model was registered into the attenuation map of PET/CT scans of a uniform phantom fitted with the coil. The resulting PET images were compared to the PET/CT reconstruction in the absence of coils. The artifacts introduced by misregistration of the model were studied. The transmission scans revealed 17% count loss due to the presence of head and neck coils in the field of view. Important sources of attenuation were found in the lock, signal cables and connectors. However, the worst source of attenuation was the casing between both coils. None of the measured medical probes introduced a significant amount of attenuation. Concerning the attenuation model of the head coil, reconstructed PET images with model-based correction were comparable to the reference PET/CT reconstruction. However, inaccuracies greater than 1-2 mm in the axial positioning of the model led to important artifacts. In conclusion, the results show that model-based attenuation correction is possible. Using a high-exposure scan to create an attenuation model of the coils has been proved feasible. However, adequate registration of the model is mandatory.