Recurrent differentiated thyroid cancer: towards personalized treatment based on evaluation of tumor characteristics with PET (THYROPET Study): study protocol of a multicenter observational cohort study

Tumor Microenvironment Features as Predictive Biomarkers in Metastatic Differentiated Thyroid Cancer and Their Relationship With 18F-Fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (18F-FDG PET/CT) Metabolic Parameters

OBJECTIVE

The role of the tumor microenvironment in tumor progression and treatment response is being investigated for different types of cancer. This study aimed to determine the relationships between tumor microenvironment, histopathology, 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT)-based metabolic parameters, treatment response, and overall survival (OS) in metastatic differentiated thyroid cancer (DTC).  Methods: Metastatic DTC patients who underwent 18F-FDG PET/CT between 2015-2019 were evaluated. Clinicopathological, histopathological features and PET/CT parameters of patients were recorded. Microenvironmental characteristics of the primary tumor, such as mitosis, intratumoral and peritumoral lymphocytosis, intratumoral and peritumoral fibrosis, were evaluated from the tissue samples. The relationships between these factors were statistically analyzed.

RESULTS

 Sixty-five patients (38 females, 27 males, age: 49±15 years) were included. Mitosis, intra/peritumoral lymphocytosis, and intra/peritumoral fibrosis were frequent; however, none of them had a statistically significant association with PET-positive metastases, treatment response, or OS. Univariate analysis showed that gender, size, thyroglobulin values, residual thyroid tissue, PET-positive metastases, and maximum standardized uptake value (SUVmax) were significant predictors of OS. At multivariate analysis, PET-positive metastases (HR=-2.65, 95%CI 0.007-0.707, p=0.024) and SUVmax (HR=-2.74, 95%CI 0.006-0.687, p=0.023) were the only independent predictors for OS.  Conclusion: Our study revealed that microenvironmental characteristics of the primary tumor did not show prognostic significance in metastatic DTC. PET-positive metastases and SUVmax levels were the only significant factors that predicted overall survival in DTC. Supporting the results of our study with further studies with a larger sample size may be necessary to determine the relationship between the tumor microenvironment and prognosis in DTC.

Impact of thyroiditis on 131I uptake during ablative therapy for differentiated thyroid cancer

CONTEXT

Differentiated thyroid cancer (DTC) is usually treated by thyroidectomy followed by radioiodine ablation and generally has a good prognosis. It may now be possible to limit the amount of treatment without impacting on efficacy. It is not known whether coexistent thyroiditis impacts on radioiodine uptake or on its potential efficacy, but this could provide a rationale for modification to current therapeutic protocols.

DESIGN

This was a retrospective cohort study of radioiodine uptake on imaging after radioiodine ablation for DTC in patients with and without concurrent thyroiditis. All patients with histologically confirmed DTC treated with radioiodine ablation after thyroidectomy in a single centre from 2012 to 2015 were included. The primary outcome assessed was the presence of low or no iodine uptake on post-ablation scan, as reported by a nuclear medicine physician blinded to the presence or absence of thyroiditis.

RESULTS

One hundred thirty patients with available histopathology results were included. Thyroiditis was identified in 42 post-operative specimens and 15 of these patients had low or no iodine uptake on post-ablation scan, compared to only 2 of 88 patients without thyroiditis (P < 0.0001) with further data analysis dividing the groups by ablation activity received (1100 MBq or 3000 MBq).

CONCLUSIONS

Concurrent thyroiditis may impair the uptake of radioactive iodine in management of DTC. Given that patients with DTC and thyroiditis already have a good prognosis, adopting a more selective approach to this step in therapy may be indicated. Large, longitudinal studies would be required to determine if omitting radioactive iodine therapy from those patients with concurrent thyroiditis has a measurable impact on mortality from thyroid cancer.

Central compartment revision surgery for persistent or recurrent thyroid carcinoma: analysis of survival and complication rate

PURPOSE

Locoregional recurrence of thyroid carcinoma is relatively common and reported rate are between 5 and 20%. Cervical nodes are usually involved, especially at the central compartment. The management of recurrent thyroid carcinoma at central compartment still remains challenging because of higher incidence of complication rate. The aim of the study is to evaluate the survival and complications rate after revision surgery.

METHODS

Retrospective cohort study on a group of patients that underwent revision surgery for persistent or recurrent thyroid carcinoma from January 1, 2003 to December 31, 2017. Survival outcomes were calculated using Kaplan-Meier method. Significant variables on univariate analysis were subjected to a Cox proportional hazards regression multivariate model.

RESULTS

Fifty-two patients involved, 22 male (40%) and 30 female (60%). Mean age was 54 years old (range 24-85). Mean follow-up was 79 months, median follow-up was 85 months, with a range between 8 and 153 months. The 5-year overall survival was 90.8% while at 10 years it was 69.8%. The 5-year disease-specific survival was 93.5%, while at 10 years it dropped to 77.9%. The rate of recurrent laryngeal nerve paralysis and persistent hypocalcemia in our series were 1.3% and 5.9%, respectively. No evidence of thoracic duct, esophageal or laryngeal and tracheal injury was found in this case series. Regarding prognostic factors, univariate and multivariate analysis highlighted as statistically significant: the aggressive histological variants, the presence extranodal extension or soft-tissue metastasis.

CONCLUSION

The surgical option remains the gold standard in locoregional recurrences of thyroid carcinoma and should be performed by experienced surgeons to reduce postoperative complications.

Therapeutic response and side effects of repeated radioligand therapy with 177Lu-PSMA-DKFZ-617 of castrate-resistant metastatic prostate cancer

Prostate-specific membrane antigen (PSMA) is highly expressed on prostate epithelial cells and strongly up-regulated in prostate cancer (PC), making it an optimal target for the treatment of metastasized PC. Radioligand therapy (RLT) with ¹⁷⁷Lu-PSMA-DKFZ-617 (Lu-PSMA) is a targeted therapy for metastatic PC. In this study, we retrospectively analyzed the side effects and the response rate of 24 hormone and/or chemorefractory PC patients with a mean age of 75.2 years (range: 64–82) with distant metastases and progressive disease according to the PSA level, who were treated with Lu-PSMA. Median PSA was 522 ng/ml (range: 17–2360). Forty-six cycles of Lu-PSMA were performed. Of the 24 patients, 22 received two cycles. Eight weeks after the first cycle of Lu-PSMA therapy 79.1% experienced a decline in PSA level. Eight weeks after the second cycle of Lu-PSMA therapy 68.2% experienced a decline in PSA relative to the baseline value. Apart from two cases of grade 3 anemia, there was no relevant hemato- or nephrotoxicity (grade 3 or 4). These results confirmed that Lu-PSMA is a safe treatment option for metastatic PC patients and has a low toxicity profile. A positive response to therapy in terms of decline in PSA occurs in about 70% of patients.

A phantom study: Should 124 I-mIBG PET/CT replace 123 I-mIBG SPECT/CT?

PURPOSE

The isotope ¹²³ I is commonly labeled with meta-iodobenzylguanidine (mIBG) for imaging of neuroendocrine tumors, such as pheochromocytomas and neuroblastomas. ¹²³ I-mIBG SPECT/CT imaging is performed for staging, follow-up and selection of patients for treatment with ¹³¹ I mIBG. As an alternative to ¹²³ I, ¹²⁴ I-mIBG PET/CT may be used, potentially taking advantage of the superior PET image quality. The purpose of this study was to investigate whether ¹²⁴ I PET/CT improves image quality as compared with ¹²³ I SPECT/CT for equal patient effective radiation dose (in mSv).

METHODS

Phantom measurements were performed using the NEMA-2007 image quality phantom. SPECT and PET reconstruction settings were used with and without time-of-flight (TOF) and point-spread-function (PSF) modeling. As a measure of image quality, the contrast-to-noise ratio (CNR) was calculated. The ratio of the ¹²³ I to ¹²⁴ I activity concentration was determined at which the contrast-to-noise ratio was equal for both modalities. This metric was defined as the contrast equivalent activity ratio (CEAR).

RESULTS

CEARs of 47.7, 25.6, 23.1, 14.6, 10.0, and 9.1 were obtained for a TOF and PSF modeled ¹²⁴ I reconstruction method and an attenuation and scatter-corrected ¹²³ I reconstruction method for sphere sizes of 10 to 37 mm, respectively. As the effective radiation dose of ¹²⁴ I-mIBG is higher than of ¹²³ I-mIBG (in mSv/MBq), an equal effective dose corresponds to a CEAR of 5 to 10. Therefore, CEARs higher than 5 to 10 indicate that ¹²⁴ I PET/CT outperforms ¹²³ I SPECT/CT in the sense of image quality for equal patient effective radiation dose.

CONCLUSION

The CEAR is much larger than a factor of 5 to 10 (needed for equal patient effective radiation dose) for most of the reconstruction methods and sphere sizes. Therefore, ¹²⁴ I-mIBG PET/CT is expected to improve image quality and/or may be used to reduce effective patient dose as compared with ¹²³ I-mIBG SPECT/CT.

Cell penetrating peptide of sodium-iodide symporter effect on the I-131 radiotherapy on thyroid cancer

The aim of the present study was to clarify whether the cell penetrating peptide of sodium-iodide symporter (NIS) has an effect on the I-131 radiotherapy of thyroid cancer. Firstly, we combined the HIV-1 TAT peptide (a cell penetrating peptide, dTAT) and established a nanoparticle vector (dTAT NP) to study the delivery efficiency of this cell-penetrating strategy for tumor-targeted gene delivery. dTAT NP was transfected into cultured TPC-1 cells as a model to study the effects of I-131 radiotherapy on thyroid cancer. Reverse transcription-quantitative polymerase chain reaction and western blotting results showed that the mRNA and protein expression levels of NIS in the transfected TPC-1 cells were substantially higher than in the negative control cells. MTT and flow cytometric analyses demonstrated that the cell growth and apoptosis rates of the TPC-1 cells were significantly inhibited and activated, respectively, by treatment with dTAT NP. The results of DAPI staining showed that treatment with dTAT NP visibly increased the nuclear apoptosis rate of the TPC-1 cells. The effect of dTAT NP on TPC-1 cells was associated with the promotion of caspase-3 and downregulation of the PI3K/Akt signaling pathway. In summary, the present data provide a pre-clinical proof-of-concept for a novel gene delivery system that efficiently delivers NIS to the targeted cancer cells and presents a satisfactory efficacy. This approach may offer an effective strategy for improving thyroid cancer gene therapy.

Calibration of PET/CT scanners for multicenter studies on differentiated thyroid cancer with (124)I

BACKGROUND

Studies on imaging of differentiated thyroid cancer (DTC) using (124)I often require a multicenter approach, as the prevalence of DTC is low. Calibration of participating scanners is required to obtain comparable quantification. As determination of a well-defined range of recovery coefficients is complicated for various reasons, a simpler approach based on the assumption that the iodine uptake is highly focal with a background that significantly lacks radioactivity might be more efficient. For each scanner, a linear conversion between known and observed activity can be derived, allowing quantification that can be traced to a common source for all scanners within one study-protocol. The aim of this paper is to outline a procedure using this approach in order to set up a multicenter calibration of PET/CT scanners for (124)I.

METHODS

A cylindrical polyethylene phantom contained six 2-ml vials with reference activities of ~2, 10, 20, 100, 400, and 2000 kBq, produced by dilution from a known activity. The phantom was scanned twice on PET/CT scanners of participating centers within 1 week. For each scanner, the best proportional and linear fit between measured and known activities were derived and based on statistical analyses of the results of all scanners; it was determined which fit should be applied. In addition, a Bland-Altman analysis was done on calibrated activities with respect to reference activities to asses the relative precision of the scanners.

RESULTS

Nine Philips (vendor A) and nine Siemens (vendor B) PET/CT scanners were calibrated in a time period of 3 days before and after the reference time. No significant differences were detected between the two subsequent scans on any scanner. Six fitted intercepts of vendor A were significantly different from zero, so the linear model was used. Intercepts ranged from -8 to 26 kBq and slopes ranged from 0.80 to 0.98. Bland-Altman analysis of calibrated and reference activities showed that the relative error of calibrated activities was smaller than that of uncalibrated activities.

CONCLUSIONS

A simplified multicenter calibration procedure for PET/CT scans that show highly focal uptake and negligible background is feasible and results in more precise quantification. Our procedure can be used in multicenter (124)I PET scans focusing on (recurrent) DTC.

The role of early 18F-FDG PET/CT in therapeutic management and ongoing risk stratification of high/intermediate-risk thyroid carcinoma

Little is known about the role in ongoing risk stratification of fluorine-18-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) performed early after radioactive iodine (RAI) ablation in differentiated thyroid carcinoma (DTC). The aim of the study is to investigate whether 18F-FDG PET/CT performed early after RAI ablation is useful to detect disease and to influence therapy and ongoing risk stratification. Patients with high/intermediate risk of recurrent DTC were included. 18F-FDG PET/CT scan was performed within 6 months after RAI ablation. We confirmed results with other imaging techniques, pathology reports, or follow-up. We classified the patient response as excellent, acceptable, or incomplete. Modified Hicks criteria were used to evaluate clinical impact. We included 81 patients with high/intermediate risk of recurrent DTC. Forty-one (50.6%) had positive uptake in 18F-FDG PET/CT, with negative (131)I whole-body scan ((131)I WBS). Sensitivity, specificity, and diagnostic accuracy of 18F-FDG PET/CT were 92.5, 90.2, and 91.4%, respectively. 18F-FDG PET/CT results had an impact on therapy in 38.3% of patients. One year after initial therapy, 45.7% showed excellent response, 8.6% acceptable response, and 45.7% incomplete response. A statistically significant relationship was found between negative 18F-FDG PET/CT and excellent response (80 vs. 12.2%, p < 0.001; OR 52.8). 18F-FDG PET/CT scan performed early in surveillance of patients with high/intermediate-risk thyroid carcinoma provides important additional information not available with conventional follow-up methods and had a high impact on therapy. A negative 18F-FDG PET/CT predicts an excellent response to therapy in the new ongoing risk stratification.

Quantitative Comparison of 124I PET/CT and 131I SPECT/CT Detectability

Radioiodine therapy with (131)I is used for treatment of suspected recurrence of differentiated thyroid carcinoma. Pretherapeutic (124)I PET/CT with a low activity (~1% of (131)I activity) can be performed to determine whether uptake of (131)I, and thereby the desired therapeutic effect, may be expected. However, false-negative (124)I PET/CT results as compared with posttherapeutic (131)I SPECT/CT have been reported by several groups. The purpose of this study was to investigate whether the reported discrepancies may be ascribed to a difference in lesion detectability between (124)I PET/CT and (131)I SPECT/CT and, hence, whether the administered (124)I activity is sufficient to achieve equal detectability.

METHODS

Phantom measurements were performed using the National Electrical Manufacturers Association 2007 image-quality phantom. As a measure of detectability, the contrast-to-noise ratio was calculated. The (124)I activity was expressed as the percentage of (131)I activity required to achieve the same contrast-to-noise ratio. This metric was defined as the detectability equivalence percentage (DEP).

RESULTS

Because lower DEPs were obtained for smaller spheres, a relatively low (124)I activity was sufficient to achieve similar lesion detectability between (124)I PET/CT and (131)I SPECT/CT. DEP was 1.5%, 1.9%, 1.9%, 4.4%, 9.0%, and 16.2% for spheres with diameters of 10, 13, 17, 18, 25, and 37 mm, respectively, for attenuation- and scatter-corrected SPECT versus point-spread function (PSF) model-based and time-of-flight (TOF) PET. For no-PSF no-TOF PET, DEP was 3.6%, 2.1%, 3.5%, 7.8%, 15.1%, and 23.3%, respectively.

CONCLUSION

A relatively low (124)I activity of 74 MBq (~1% of (131)I activity) is sufficient to achieve similar lesion detectability between (124)I PSF TOF PET/CT and (131)I SPECT/CT for small spheres (≤10 mm), since the reported DEPs are close to 1%. False-negative (124)I PET/CT results as compared with posttherapeutic (131)I SPECT/CT may be ascribed to differences in detectability for large lesions (>10 mm) and for no-PSF no-TOF PET, since DEPs are greater than 1%. On the basis of DEPs of 3.5% for lesion diameters of up to 17 mm on no-PSF no-TOF PET, (124)I activities as high as 170 MBq may be warranted to obtain equal detectability.

A phantom-based method to standardize dose-calibrators for new β+-emitters

Quantitative imaging with PET requires accurate measurements of the amount of radioactivity injected into the patient and the concentration of radioactivity in a given region. Recently, new positron emitters, such as (124)I, (89)Zr, (82)Rb, (68)Ga, and (64)Cu, have emerged to promote PET development, but standards are still largely lacking. Therefore, we propose to validate a simple, robust, and replicable methodology, not requiring the use of any standards, to accurately calibrate a dose-calibrator for any β(+)-emitter. On the basis of (18)F cross-calibration, routinely performed with fluorine-18-fluorodeoxyglucose (F-FDG) in nuclear medicine departments, a methodology was developed using β(+)-emitting' phantoms to cross-calibrate the dose-calibrator for measuring the activity of positron emitters and quantifying the standardized uptake value (SUV). Ga phantoms filled with activities measured with various dose-calibrator settings were imaged to establish calibration curves (SUV values as a function of the dose-calibrator settings) and to identify the setting value, yielding an SUV value of 1.00 g/ml, reflecting an accurate measurement of (68)Ga activity. Activities measured with the identified setting were finally checked with a γ-counter. The setting of 772±1 was identified as ensuring that the studied dose-calibrator is correctly calibrated for (68)Ga to ensure an SUV value of 1.00±0.01 g/ml. γ-Ray spectrometry confirmed the accurate measurement of Ga activities by the dose-calibrator (relative error of 2.9±1.5%). We have developed a phantom-based method to accurately standardize dose-calibrators for any β(+)-emitter, without any standards.

Prognostic value of positron emission tomography-assessed tumor heterogeneity in patients with thyroid cancer undergoing treatment with radiopeptide therapy

INTRODUCTION

Peptide receptor radionuclide therapy (PRRT) is a treatment option for both iodine-refractory differentiated and advanced medullary thyroid cancer (TC). It requires over-expression of somatostatin receptor subtype II (SSTR) that can be non-invasively assessed by positron emission tomography (PET). Assessment of tumor heterogeneity is increasingly used as a tool for prognostication prediction. We investigated the potential of SSTR-PET to assess intraindividual tumor heterogeneity and thereby treatment response prior to PRRT.

METHODS

12 patients with progressive radioiodine-refractory differentiated (1 papillary, 1 oxyphilic, 2 oncocytic, 4 follicular) or medullary (n=4) TC were enrolled. SSTR-PET was performed at baseline. Conventional PET parameters and heterogeneity parameters were analyzed regarding their potential to predict progression-free (PFS, mean, 221 days) and overall survival (OS, mean, 450 days). Parameters of a subgroup of lesions (n=23) were also correlated with morphological response according to modified RECIST criteria.

RESULTS

In patient-based analysis, all conventional parameters failed to predict PFS. Several textural parameters showed a significant capability to assess PFS. Thereby, "Grey level non uniformity" had the highest area under the curve (AUC, 0.93) in Receiver operating characteristics analysis followed by "Contrast" (AUC, 0.89). In lesion-based analysis, only "Entropy" revealed potential to evaluate disease progression. OS could not be assessed by any parameter investigated.

CONCLUSIONS

Tumor heterogeneity seems to be a predictor of response to PRRT in patients with iodine-refractory differentiated/advanced medullary thyroid cancer and outperforms conventional PET parameters like standardized uptake value. In a "theranostic" approach, assessment of textural parameters may help in selecting patients who might benefit from PRRT.

Radioiodine therapy for thyroid cancer in the era of risk stratification and alternative targeted therapies

Differentiated thyroid cancers are typically iodine-avid and can be effectively treated with radioiodine. In most patients, radioiodine treatment is done for ablation of residual tissue, and in these cases the focus should be on using the minimum effective dose. Adjuvant therapy can be done to reduce the risk of recurrence, but optimal patient selection and dose are unclear. Patients with advanced disease benefit most from treatment with the maximum-tolerated dose. Recent research has focused on better patient selection and reduced radioiodine doses for remnant ablation. There are emerging targeted therapeutic approaches in patients who are appropriately shown to have iodine-refractory disease, with 1 drug approved by the Food and Drug Administration. Numerous trials are ongoing to assess targeted therapeutics alone or in combination with radioiodine.