Quantitation of Cancer Treatment Response by 18F-FDG PET/CT: Multicenter Assessment of Measurement Variability

Radiological, Pathological, and Surgical Outcomes with Neoadjuvant Cemiplimab for Stage II-IV Cutaneous Squamous Cell Carcinoma in the Deep Sequencing in Cutaneous Squamous Cell Carcinomas (DISCERN) Trial

Background: A previous published Phase 2 trial using 2-4 doses of neoadjuvant cemiplimab in stage II-IV resectable cutaneous squamous cell carcinoma (CSCC) demonstrated that a complete pathological (pCR) rate of 51% and major pathological response (mPR) rate of 13% could be achieved with durable disease control. Methods: In this open-label, single-institution phase II trial (NCT05878288), patients with stage II-IV resectable CSCC received up to four doses of neoadjuvant cemiplimab prior to surgery. The primary endpoint of the study was to perform comprehensive molecular profiling. The focus of this report are the secondary clinical endpoints of pCR rate, mPR (defined as <10% viable tumour) rate, overall response rate (ORR) using Response Evaluation Criteria in Solid Tumours (RECIST) 1.1, immune-modified RECIST (imRECIST) and Immune PET Response Criteria in Solid Tumours (iPERCIST), disease-free survival (DFS), overall survival (OS), safety, and to describe changes in planned surgery. Results: Eleven patients were enrolled, with all proceeding with surgery. An ORR and pCR rate of 73% (8/11; 95% CI 0.39-0.93) was achieved, whilst 3/11 patients progressed on treatment. On pre-operative imaging, all 8/11 pCR patients demonstrated a partial response (RECIST 1.1), whilst 6/8 achieved a complete metabolic response and 2/8 a partial metabolic response (iPERCIST). Median follow-up was 10.2 (IQR 6.7-16.4) months. DFS was 91% (95% CI 0.57-1) and OS was 100% (95% CI 0.68-1), with one non-responder patient who developed recurrent locoregional and distant metastatic disease. There were no unexpected safety signals. Pathological features of response to neoadjuvant immunotherapy most commonly were granulomatous inflammation with keratin, fibrosis and inflammation. No cases with a dense inflammatory infiltrate were observed. Neoadjuvant immunotherapy did not impact the intra-operative planning and execution of surgery, but in the eight pCR cases, it reduced the extent of required surgery, whilst in the three non-responder cases, surgery was more extensive than originally planned. Conclusions: The DISCERN trial confirms that an excellent complete response rate can be achieved with four doses of neoadjuvant immunotherapy in stage II-IV CSCC. Proposed refinements to the pathological assessment of response and metabolic response criteria in CSCC for the neoadjuvant context are provided.

Trimodality therapy for locally advanced esophageal squamous cell carcinoma: the role of volume-based PET/CT in patient management and prognostication

PURPOSE

To evaluate the role of positron emission tomography/computed tomography (PET/CT) in predicting pathologic complete response (pCR) and identify relevant prognostic factors from clinico-imaging-pathologic features of locally advanced esophageal squamous cell carcinoma (eSCC) patients undergoing trimodality therapy.

METHODS

We evaluated 275 patients with eSCCs of T3-T4aN0M0 and T1-T4aN1-N3M0 who received trimodality therapy. We correlated volume-based PET/CT parameters before and after concurrent chemoradiation therapy with pCR after surgery, clinico-imaging-pathologic features, and patient survival.

RESULTS

pCR occurred in 75 (27.3%) of 275 patients, of whom 61 (80.9%) showed 5-year survival. Pre-total lesion glycolysis (pre-TLG, OR = 0.318, 95% CI 0.169 to 0.600), post-metabolic tumor volume (post-MTV, OR = 0.572, 95% CI 0.327 to 0.999), and % decrease of average standardized uptake value (% SUVavg decrease, OR = 2.976, 95% CI = 1.608 to 5.507) were significant predictors for pCR. Among them, best predictor for pCR was pre-TLG with best cutoff value of 205.67 and with AUC value of 0.591. Performance status (HR = 5.171, 95% CI 1.737 to 15.397), pathologic tumor size (HR = 1.645, 95% CI 1.351 to 2.002), pathologic N status (N1, HR = 1.572, 95% CI 1.010 to 2.446; N2, HR = 3.088, 95% CI 1.845 to 5.166), and post-metabolic tumor volume (HR = 1.506, 95% CI 1.033 to 2.195) were significant predictors of overall survival.

CONCLUSION

Pre-TLG, post-MTV, and % SUVavg decrease are predictive of pCR. Additionally, several clinico-imaging-pathologic factors are significant survival predictors in locally advanced eSCC patients undergoing trimodality therapy.

Quantitation of cancer treatment response by 2-[18F]FDG PET/CT: multi-center assessment of measurement variability using AUTO-PERCIST™

Background

The aim of this study was to assess the reader variability in quantitatively assessing pre- and post-treatment 2-deoxy-2-[¹⁸F]fluoro-d-glucose positron emission tomography/computed tomography ([¹⁸F]FDG PET/CT) scans in a defined set of images of cancer patients using the same semi-automated analytical software (Auto-PERCIST™), which identifies tumor peak standard uptake value corrected for lean body mass (SUL_peak) to determine [¹⁸F]FDG PET quantitative parameters.

Methods

Paired pre- and post-treatment [¹⁸F]FDG PET/CT images from 30 oncologic patients and Auto-PERCIST™ semi-automated software were distributed to 13 readers across US and international sites. One reader was aware of the relevant medical history of the patients (read_reference), whereas the 12 other readers were blinded to history but had access to the correlative images. Auto-PERCIST™ was set up to first automatically identify the liver and compute the threshold for tumor measurability (1.5 × liver mean) + (2 × liver standard deviation [SD]) and then detect all sites with SUL_peak greater than the threshold. Next, the readers selected sites they believed to represent tumor lesions. The main performance metric assessed was the percent change in the SUL_peak (%ΔSUL_peak) of the hottest tumor identified on the baseline and follow-up images.

Results

The intra-class correlation coefficient (ICC) for the %ΔSUL_peak of the hottest tumor was 0.87 (95%CI: [0.78, 0.92]) when all reads were included (n = 297). Including only the measurements that selected the same target tumor as the read_reference (n = 224), the ICC for %ΔSUL_peak was 1.00 (95%CI: [1.00, 1.00]). The Krippendorff alpha coefficient for response (complete or partial metabolic response, versus stable or progressive metabolic disease on PET Response Criteria in Solid Tumors 1.0) was 0.91 for all reads (n = 380) and 1.00 including for reads with the same target tumor selection (n = 270).

Conclusion

Quantitative tumor [¹⁸F]FDG SUL_peak changes measured across multiple global sites and readers utilizing Auto-PERCIST™ show very high correlation. Harmonization of methods to single software, Auto-PERCIST™, resulted in virtually identical extraction of quantitative tumor response data from [¹⁸F]FDG PET images when the readers select the same target tumor.

Interrater Agreement and Reliability of PERCIST and Visual Assessment When Using 18F-FDG-PET/CT for Response Monitoring of Metastatic Breast Cancer

Response evaluation at regular intervals is indicated for treatment of metastatic breast cancer (MBC). FDG-PET/CT has the potential to monitor treatment response accurately. Our purpose was to: (a) compare the interrater agreement and reliability of the semi-quantitative PERCIST criteria to qualitative visual assessment in response evaluation of MBC and (b) investigate the intrarater agreement when comparing visual assessment of each rater to their respective PERCIST assessment. We performed a retrospective study on FDG-PET/CT in women who received treatment for MBC. Three specialists in nuclear medicine categorized response evaluation by qualitative assessment and standardized one-lesion PERCIST assessment. The scans were categorized into complete metabolic response, partial metabolic response, stable metabolic disease, and progressive metabolic disease. 37 patients with 179 scans were included. Visual assessment categorization yielded moderate agreement with an overall proportion of agreement (PoA) between raters of 0.52 (95% CI 0.44-0.66) and a Fleiss kappa estimate of 0.54 (95% CI 0.46-0.62). PERCIST response categorization yielded substantial agreement with an overall PoA of 0.65 (95% CI 0.57-0.73) and a Fleiss kappa estimate of 0.68 (95% CI 0.60-0.75). The difference in PoA between overall estimates for PERCIST and visual assessment was 0.13 (95% CI 0.06-0.21; p = 0.001), that of kappa was 0.14 (95% CI 0.06-0.21; p < 0.001). The overall intrarater PoA was 0.80 (95% CI 0.75-0.84) with substantial agreement by a Fleiss kappa of 0.74 (95% CI 0.69-0.79). Semi-quantitative PERCIST assessment achieved significantly higher level of overall agreement and reliability compared with qualitative assessment among three raters. The achieved high levels of intrarater agreement indicated no obvious conflicting elements between the two methods. PERCIST assessment may, therefore, give more consistent interpretations between raters when using FDG-PET/CT for response evaluation in MBC.

Predictions of Pathological Features and Recurrence Based on FDG-PET Findings of Esophageal Squamous Cell Carcinoma after Trimodal Therapy

BACKGROUND

The degree of metabolic activity in tumor cells can be determined by 18F-fluorodeoxyglucose-positron emission tomography (FDG-PET). Associations between FDG uptake by primary tumors of locally advanced esophageal squamous cell carcinoma (ESCC) under trimodal therapy and the pathological features of such tumors have not been fully investigated.

PATIENTS AND METHODS

We evaluated relationships between the maximal standardized uptake (SUVmax) in primary tumors on preoperative PET images and pathological features as well as cancer recurrence in 143 patients with ESCC who underwent neoadjuvant chemoradiotherapy (NCRT) followed by surgery.

RESULTS

The post-SUVmax significantly differed after NCRT for ypT and ypN status, lymphatic invasion (LI), venous invasion (VI), and recurrence. Furthermore, the %ΔSUVmax (rate of decrease between before and after NCRT) for LI, VI, and recurrence significantly differed. Univariate and multivariate analyses selected post-SUVmax and %ΔSUVmax as independent preoperative predictors of recurrence-free survival [hazard ratio (HR) 1.46; 95% confidence interval (CI) 1.24-1.72 and HR 0.97; 95% CI 0.96-0.99, respectively; p < 0.001 for both]. Recurrence-free and overall survival were significantly stratified according to optimal SUVmax cutoffs for predicting recurrence (post- and %ΔSUVmax: 2.8 and 70, respectively).

CONCLUSIONS

The post- and %ΔSUVmax of primary tumors were significantly associated with the pathological features and recurrence of ESCC under trimodal therapy. Therefore, FDG-PET can preoperatively predict the degree of aggressive tumor behavior in ESCC under trimodal therapy.

The impact of iterative reconstruction protocol, signal-to-background ratio and background activity on measurement of PET spatial resolution

OBJECTIVES

The present study aims to assess the impact of acquisition time, different iterative reconstruction protocols as well as image context (including contrast levels and background activities) on the measured spatial resolution in PET images.

METHODS

Discovery 690 PET/CT scanner was used to quantify spatial resolutions in terms of full width half maximum (FWHM) as derived (i) directly from capillary tubes embedded in air and (ii) indirectly from 10 mm-diameter sphere of the NEMA phantom. Different signal-to-background ratios (SBRs), background activity levels and acquisition times were applied. The emission data were reconstructed using iterative reconstruction protocols. Various combinations of iterations and subsets (it × sub) were evaluated.

RESULTS

For capillary tubes, improved FWHM values were obtained for higher it × sub, with improved performance for PSF algorithms relative to non-PSF algorithms. For the NEMA phantom, by increasing acquisition times from 1 to 5 min, intrinsic FWHM for reconstructions with it × sub 32 (54) was improved by 15.3% (13.2%), 15.1% (13.8%), 14.5% (12.8%) and 13.7% (12.7%) for OSEM, OSEM + PSF, OSEM + TOF and OSEM + PSF + TOF, respectively. Furthermore, for all reconstruction protocols, the FWHM improved with more impact for higher it × sub.

CONCLUSION

Our results indicate that PET spatial resolution is greatly affected by SBR, background activity and the choice of the reconstruction protocols.

Joint compensation of motion and partial volume effects by iterative deconvolution incorporating wavelet-based denoising in oncologic PET/CT imaging

OBJECTIVES

We aim to develop and rigorously evaluate an image-based deconvolution method to jointly compensate respiratory motion and partial volume effects (PVEs) for quantitative oncologic PET imaging, including studying the impact of various reconstruction algorithms on quantification performance.

PROCEDURES

An image-based deconvolution method that incorporated wavelet-based denoising within the Lucy-Richardson algorithm was implemented and assessed. The method was evaluated using phantom studies with signal-to-background ratios (SBR) of 4 and 8, and clinical data of 10 patients with 42 lung lesions ≤30 mm in diameter. In each study, PET images were reconstructed using four different algorithms: OSEM-basic, PSF, TOF, and TOFPSF. The performance was quantified using contrast recovery (CR), coefficient of variation (COV) and contrast-to-noise-ratio (CNR) metrics. Further, in each study, variabilities arising due to the four different reconstruction algorithms were assessed.

RESULTS

In phantom studies, incorporation of wavelet-based denoising improved COV in all cases. Processing images using proposed method yielded significantly higher CR and CNR particularly in small spheres, for all reconstruction algorithms and all SBRs (P < 0.05). In patient studies, processing images using the proposed method yielded significantly higher CR and CNR (P < 0.05). The choice of the reconstruction algorithm impacted quantification performance for changes in motion amplitude, tumor size and SBRs.

CONCLUSIONS

Our results provide strong evidence that the proposed joint-compensation method can yield improved PET quantification. The choice of the reconstruction algorithm led to changes in quantitative accuracy, emphasizing the need to carefully select the right combination of reconstruction-image-based compensation methods.

18F-FDG PET/CT Can Predict Development of Thyroiditis Due to Immunotherapy for Lung Cancer

Our primary purpose was to determine whether increased ¹⁸F-FDG uptake in the thyroid gland predicts development of thyroiditis with subsequent hypothyroidism in patients undergoing immunotherapy with nivolumab for lung cancer. Secondarily, we determined whether ¹⁸F-FDG uptake in the thyroid gland correlates with number of administered cycles of nivolumab. Methods: Retrospective chart review over 2 y found 18 lung cancer patients treated with nivolumab who underwent ¹⁸F-FDG PET/CT before and during therapy. SUV_mean, SUV_max, and total lesion glycolysis of the thyroid gland were measured. SUVs were also measured for the pituitary gland, liver, and spleen. Patients underwent monthly thyroid testing. PET/CT parameters were analyzed by unpaired t testing for differences between 2 groups (patients who developed hypothyroidism and those who did not). Correlation between development of thyroiditis and number of cycles of nivolumab was also tested. Results: Six of 18 patients developed hypothyroidism. The t test comparing the 2 groups demonstrated significant differences in SUV_mean (P = 0.04), SUV_max (P = 0.04), and total lesion glycolysis (P = 0.02) of the thyroid gland. Two of 4 patients who developed thyroiditis and had increased ¹⁸F-FDG uptake in the thyroid gland had a normal TSH level at the time of follow-up ¹⁸F-FDG PET/CT. Patients who developed thyroiditis with subsequent hypothyroidism stayed longer on therapy (10.6 cycles) than patients without thyroiditis (7.6 cycles), but the trend was not statistically significant. No significant difference in PET/CT parameters was observed for pituitary gland, liver, or spleen. Conclusion:¹⁸F-FDG PET/CT can predict the development of thyroiditis with subsequent hypothyroidism before laboratory testing. Further study is required to confirm the positive trend between thyroiditis and duration of therapy.

EBONI: A Tool for Automated Quantification of Bone Metastasis Load in PSMA PET/CT

Prostate-specific membrane antigen (PSMA) PET/CT has a high diagnostic accuracy for lesion detection in metastatic prostate cancer, including bone metastases. Novel therapeutic approaches require valid biomarkers for standardized disease staging and for evaluation of progression and therapy response. Here, we introduce EBONI (Evaluation of Bone Involvement), a software tool to automatically quantify the bone metastasis load in PSMA PET/CT. Lesion quantity, mean and maximum lesional SUV, z score, and percentage of affected bone volume are determined. EBONI is open source and freely available. Methods: To validate EBONI, the results of automated quantification of 38 PSMA PET/CT scans with different levels of bone involvement were compared with visual expert reading. The influence of SUV threshold and Hounsfield unit thresholds was analyzed. Results: A high correlation between bone lesion quantity as determined visually and automatically was found (SUV_max, r² = 0.97; SUV_mean, r² = 0.88; lesion count, r² = 0.97). The Hounsfield unit threshold had no significant influence, whereas an SUV threshold of 2.5 proved optimal for automated lesion quantification. The systematic error of false-positive tissue misclassification was low, occurred mainly around the salivary and lacrimal glands, and could easily be corrected. There were no false-negative ratings. Conclusion: EBONI analysis is robust, quick (<3 min per scan), and 100% reproducible. It allows rater-independent quantification of bone metastasis in metastatic prostate cancer. It provides lesion quantification equivalent to that of visual assessment, as well as providing complementary information. It can be easily implemented as an add-on to visual analysis of PSMA PET/CT scans and has the potential to reduce turnaround time.