Automated lung cancer assessment on 18F-PET/CT using Retina U-Net and anatomical region segmentation

OBJECTIVES

To develop and test a Retina U-Net algorithm for the detection of primary lung tumors and associated metastases of all stages on FDG-PET/CT.

METHODS

A data set consisting of 364 FDG-PET/CTs of patients with histologically confirmed lung cancer was used for algorithm development and internal testing. The data set comprised tumors of all stages. All lung tumors (T), lymphatic metastases (N), and distant metastases (M) were manually segmented as 3D volumes using whole-body PET/CT series. The data set was split into a training (n = 216), validation (n = 74), and internal test data set (n = 74). Detection performance for all lesion types at multiple classifier thresholds was evaluated and false-positive-findings-per-case (FP/c) calculated. Next, detected lesions were assigned to categories T, N, or M using an automated anatomical region segmentation. Furthermore, reasons for FPs were visually assessed and analyzed. Finally, performance was tested on 20 PET/CTs from another institution.

RESULTS

Sensitivity for T lesions was 86.2% (95% CI: 77.2-92.7) at a FP/c of 2.0 on the internal test set. The anatomical correlate to most FPs was the physiological activity of bone marrow (16.8%). TNM categorization based on the anatomical region approach was correct in 94.3% of lesions. Performance on the external test set confirmed the good performance of the algorithm (overall detection rate = 88.8% (95% CI: 82.5-93.5%) and FP/c = 2.7).

CONCLUSIONS

Retina U-Nets are a valuable tool for tumor detection tasks on PET/CT and can form the backbone of reading assistance tools in this field. FPs have anatomical correlates that can lead the way to further algorithm improvements. The code is publicly available.

KEY POINTS

• Detection of malignant lesions in PET/CT with Retina U-Net is feasible. • All false-positive findings had anatomical correlates, physiological bone marrow activity being the most prevalent. • Retina U-Nets can build the backbone for tools assisting imaging professionals in lung tumor staging.

Repeatability of metabolic tumor burden and lesion glycolysis between clinical readers

The Metabolic Tumor Volume (MTV) and Tumor Lesion Glycolysis (TLG) has been shown to be independent prognostic predictors for clinical outcome in Diffuse Large B-cell Lymphoma (DLBCL). However, definitions of these measurements have not been standardized, leading to many sources of variation, operator evaluation continues to be one major source. In this study, we propose a reader reproducibility study to evaluate computation of TMV (& TLG) metrics based on differences in lesion delineation. In the first approach, reader manually corrected regional boundaries after automated detection performed across the lesions in a body scan (Reader M using a manual process, or manual). The other reader used a semi-automated method of lesion identification, without any boundary modification (Reader A using a semi- automated process, or auto). Parameters for active lesion were kept the same, derived from standard uptake values (SUVs) over a 41% threshold. We systematically contrasted MTV & TLG differences between expert readers (Reader M & A). We find that MTVs computed by Readers M and A were both concordant between them (concordant correlation coefficient of 0.96) and independently prognostic with a P-value of 0.0001 and 0.0002 respectively for overall survival after treatment. Additionally, we find TLG for these reader approaches showed concordance (CCC of 0.96) and was prognostic for over -all survival (p ≤ 0.0001 for both). In conclusion, the semi-automated approach (Reader A) provides acceptable quantification & prognosis of tumor burden (MTV) and TLG in comparison to expert reader assisted measurement (Reader M) on PET/CT scans.

The value of the Standardized Uptake Value (SUV) and Metabolic Tumor Volume (MTV) in lung cancer

The diagnosis, staging and therapeutic monitoring of lung cancer were amongst the first applications for which the utility of FDG PET was documented and FDG PET/CT is now a routine diagnostic tool for clinical decision-making. As well as having high sensitivity for detection of disease sites, which provides critical information about stage, the intensity of uptake provides deeper biological characterization, while the burden of disease also has potential clinical significance. These disease characteristics can easily be quantified on delayed whole-body imaging as the maximum standardized uptake value (SUV_max) and metabolic tumor volume (MTV), respectively. There have been significant efforts to harmonize the measurement of these features, particularly within the context of clinical trials. Nevertheless, however calculated, in general, a high SUV_max and large MTV have been shown to have an adverse prognostic significance. Nevertheless, the use of these parameters in the interpretation and reporting of clinical scans remains inconsistent and somewhat controversial. This review details the current status of semi-quantitative FDG PET/CT in the evaluation of lung cancer.

Quantification of Metastatic Prostate Cancer Whole-Body Tumor Burden with 18F-FDG PET Parameters and Associations with Overall Survival After First-Line Abiraterone or Enzalutamide: A Single-Center Retrospective Cohort Study

New biomarkers for metastatic prostate cancer are needed. The aim of this study was to evaluate the prognostic value of 18F-FDG PET whole-body tumor burden parameters in patients with metastatic prostate cancer who received first-line abiraterone or enzalutamide therapy. Methods: This was a retrospective study of patients with metastatic castration-sensitive prostate cancer (mCSPC, n = 25) and metastatic castration-resistant prostate cancer (mCRPC, n = 71) who underwent 18F-FDG PET/CT within 90 d before first-line treatment with abiraterone or enzalutamide at a tertiary-care academic cancer center. Whole-body tumor burden on PET/CT was quantified as metabolic tumor volume (MTV) and total lesion glycolysis (TLG) and correlated with overall survival (OS) probabilities using Kaplan-Meier curves and Cox models. Results: The median follow-up in survivors was 56.3 mo (interquartile range, 37.7-66.8 mo); the median OSs for patients with mCRPC and mCSPC were 27.8 and 76.1 mo, respectively (P < 0.001). On univariate analysis, the OS probability of mCRPC patients was significantly associated with plasma levels of alkaline phosphatase (hazard ratio [HR], 1.90; P < 0.001), plasma levels of lactate dehydrogenase (HR, 1.01; P < 0.001), hemoglobin levels (HR, 0.80; P = 0.013), whole-body SUVmax (HR, 1.14; P < 0.001), the number of 18F-FDG-avid metastases (HR, 1.08; P < 0.001), whole-body metabolic tumor volume (HR, 1.86; P < 0.001), and TLG (HR, 1.84; P < 0.001). On multivariable analysis with stepwise variable selection, hemoglobin levels (HR, 0.81; P = 0.013) and whole-body TLG (HR, 1.88; P < 0.001) were independently associated with OS. In mCSPC patients, no significant association was observed between these variables and OS. Conclusion: In patients with mCRPC receiving first-line treatment with abiraterone or enzalutamide, 18F-FDG PET WB TLG is independently associated with OS and might be used as a quantitative prognostic imaging biomarker.

Prognostic utility of pre- and post-treatment FDG-PET parameters in anal squamous cell carcinoma

BACKGROUND AND PURPOSE

We prospectively assessed the contributions of PET to initial staging, early detection of treatment failures, and prognostication in patients with anal squamous cell carcinoma (ASCC).

MATERIALS AND METHODS

Consecutive patients with ASCC referred for radical chemoradiotherapy (CRT) consented to undergo FDG-PET imaging pre-treatment and at 3 and 6 months post-treatment. Clinicopathologic data were collected and CT and PET imaging reviewed for contribution to staging and recurrence detection. Maximum standardized uptake value (SUVmax), peak standardized uptake value (SUVpeak), metabolic tumour volume (MTV), and total lesion glycolysis (TLG) were assessed for association with progression-free survival (PFS), cause-specific survival (CSS), and overall survival (OS) using the Kaplan-Meier and Cox regression models.

RESULTS

Between 2009 and 2016, 73 patients with clinical stages I-IIIB ASCC completed curative-intent CRT. Median follow-up was 48 months. 14 patients died and 18 patients experienced disease progression. 4-year PFS, CSS, and OS were 73%, 87%, and 84%, respectively. A pre-treatment MTV >35 cm³ predicted for worse PFS (p = 0.011) and CSS (p = 0.024) on univariate and multivariate analyses, employing an MTV definition of voxels ≥25% of SUVmax. Higher 6-month post-treatment SUVmax and SUVpeak predicted for worse PFS and OS (p ≤ 0.011). Pre-treatment SUVmax, SUVpeak, and TLG, and 3-month post-treatment SUVmax and SUVpeak did not significantly correlate with survival outcomes.

CONCLUSIONS

Our findings support that pre-treatment MTV provides meaningful prognostic information, with suggestion that an MTV delineation threshold of voxels ≥25% of SUVmax is appropriate in the anal region. Post treatment, the combination of clinical examination and PET effectively detected all treatment failures. Higher 6-month post-treatment SUVmax and SUVpeak predicted worse PFS and OS; however, the optimal timing of post-treatment PET imaging remains unclear.

Quantitative PET/CT in clinical practice: assessing the agreement of PET tumor indices using different clinical reading platforms

OBJECTIVE

The aim of this study was to determine whether various fluorine-18-fluorodeoxyglucose PET/CT-derived parameters used in oncology vary significantly depending on the interpretation software systems used in clinical practice for multiple human solid tumors.

PATIENTS AND METHODS

A total of 120 fluorine-18-fluorodeoxyglucose PET/CT studies carried out in patients with pancreatic, lung, colorectal, and head and neck cancers were evaluated retrospectively on two different vendor software platforms including Mirada and MIMVista. Regions of interest were placed on the liver to determine the liver mean standardized uptake value at lean body mass (SUL) and on each tumor to determine the SULmax, SULpeak. Total lesion glycolysis (TLG) and metabolic tumor volume (MTV) were determined using fixed thresholds of 50% of SULmax and SULpeak. Inter-reader, intersystem intraclass correlations, systematic bias, and variability reflected by the 95% limits of agreement, and precision were determined.

RESULTS

There was excellent inter-reader reliability between the readers and the two software systems, with intraclass correlations more than 0.9 for all PET metrics, with P values less than 0.0001. The bias and SD on Bland-Altman analysis between the two software platforms for tumor SULmax, SULpeak, Max50MTV, and Peak50MTV, respectively, for Reader 1 were -1.52±2.24, 0.80±3.67, -0.80±13.01, and -4.49±20.6. For Reader 2, the biases were -1.62±1.95, 0.18±3.60, -0.27±4.64, and -3.13±8.30. The precision between the two systems was better for SULmax and SULpeak, with less variance observed, than for volume-based metrics such as Max50MTV and Peak50MTV or TLG.

CONCLUSION

Excellent correlation has been found between two tested software reading platforms for all PET-derived metrics in a dual-reader analysis. Overall, the SULmax and SULpeak values had less bias and better precision compared with the MTV and TLG.

The assessment of correlation and prognosis among 18F-FDG uptake parameters, Glut1, pStat1 and pStat3 in surgically resected non-small cell lung cancer patients

Introduction

To assess the correlation among ¹⁸F-FDG uptake, Glut1, pStat1 and pStat3, and to investigate the relationship between the prognosis and ¹⁸F-FDG uptake and these molecular markers in surgically resected non-small cell lung cancer (NSCLC) patients.

Results

Knockdown of Glut1 led to a significant increase in pStat1 expression. Glut1 expression positively correlated with the SUVmax, SUVmean, and TLG significantly (P<0.001). pStat3 expression negatively correlated with all PET parameters significantly (P<0.001). pStat1 had positive weak correlations with the SUVmax and SUVmean. All PET parameters and Glut1 were significantly associated with DFS (P<0.05). TLG, MTV, Glut1 and pStat1 were significantly associated with OS (P<0.05).

Conclusion

pStat3 and Glut1 may be associated with ¹⁸F-FDG uptake mechanism. TLG, MTV, and Glut1 may be independent prognostic factors.

Methods

The SUVmax, SUVmean, MTV and TLG of primary lesions were calculated in 140 patients. The expressions of Glut1 and Stat pathway proteins in NSCLC cell lines were examined by immune blots. Excised tumor tissue was analyzed by immunohistochemistry. OS and DFS were evaluated by the Kaplan-Meier method. The difference in survival between subgroups was analyzed by log-rank test. The prognostic significance of clinicopathological, molecular and PET parameters was assessed by Cox proportional hazard regression analysis.

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

The aim of this study was to assess the interobserver variability of quantitative ¹⁸F-FDG PET/CT parameters used in assessments of treatment response across multiple sites and readers. Methods: Paired pre- and posttreatment ¹⁸F-FDG PET/CT images of 30 oncologic patients were distributed to 22 readers across 15 U.S. and international sites. One reader was aware of the full medical history (read_reference) of the patients, whereas the 21 other readers were unaware. The readers selected the single hottest tumor from each study, and made SUV measurements from this target lesion and the liver. Descriptive statistics, percentage changes in the measurements, and their agreements were obtained. Results: The intraclass correlation coefficient for the percentage change in SUV_max (%ΔSUV_max) of the hottest tumor was 0.894 (95% confidence interval [CI], 0.813-0.941), and the individual equivalence coefficient was 1.931 (95% CI, 0.568-6.449) when all reads were included (n = 638). When only the measurements that selected the same target tumor as the read_reference (n = 486) were included, the intraclass correlation coefficient for the %ΔSUV_max was 0.944 (95% CI, 0.841-0.989), and the individual equivalence coefficient was -0.688 (95% CI, -1.810 to -0.092). The absolute change in SUV_mean of liver corrected for lean body mass showed upper and lower limits of agreement (average bias ± 2 SDs) of 0.13 and -0.13 g/mL. Conclusion: The quantitative tumor SUV changes measured across multiple sites and readers show a high correlation. Selection of the same tumor target among readers further increased the degree of correlation.

Correlation between fluorodeoxyglucose hotspots on pretreatment positron emission tomography/CT and preferential sites of local relapse after chemoradiotherapy for head and neck squamous cell carcinoma

BACKGROUND

The potential benefits of ¹⁸ F-fluoro-2-deoxy-D-glucose-positron emission tomography/CT (FDG-PET/CT) imaging for radiotherapy (RT) treatment planning of head and neck squamous cell carcinoma (HNSCC) are increasingly being recognized. It has been suggested that intratumoral subvolumes with high FDG avidity ("hotspots") are potential targets for selected dose escalation. The purposes of this study were to demonstrate that pre-RT FDG-PET/CT can identify intratumoral sites at increased risk of local relapse after RT and to determine an optimal threshold to delineate smaller RT target volumes that would facilitate RT dose escalation without impaired tolerance.

METHODS

Seventy-two consecutive patients with locally advanced HNSCC treated by RT ± chemotherapy were included in this study. All patients underwent FDG-PET/CT at initial staging (PET_A ) and during systematic follow-up (PET_R ). FDG-PET/CT was coregistered on the initial CT scan with a rigid method. Various subvolumes (A_X ; × = 30%, 40%, 50%, 60%, 70%, 80%, and 90% standardized uptake value maximum [SUVmax] thresholds) within the primary tumor and in the subsequent local relapse (R_X ; × = 40% and 70% SUVmax thresholds) were compared together (Dice, Jaccard, overlap fraction, common volume/baseline volume, and common volume/recurrent volume).

RESULTS

Nineteen patients (26%) had local relapses. Using a 40% SUVmax threshold, the initial metabolic tumor volume was significantly higher in patients with local relapses than in controlled patients (10.4 ± 8.6 vs 5.1 ± 4.9 cc; p = .002) as well as total lesion glycolysis (117.9 ± 88.6 vs 60.6 ± 80.4; p = .013). For both methods, the overlap index among A₃₀ , A₄₀ , and A₅₀ subvolumes on PET_A and the whole metabolic volume of recurrence R₄₀ and R₇₀ on PET_R showed a moderate agreement (0.52 to 0.43).

CONCLUSION

Our study does not find high overlap index values between the initial tumor and recurrence subvolumes, probably because of a suboptimal coregistration. Our results also confirm that metabolic tumor volume and total lesion glycolysis are independently correlated with recurrence-free survival in patients with HNSCC. Further larger prospective studies with FDG-PET/CT performed in the same RT position and with a validated elastic registration method are needed. © 2017 Wiley Periodicals, Inc. Head Neck 39: 1155-1165, 2017.

Practical no-gold-standard evaluation framework for quantitative imaging methods: application to lesion segmentation in positron emission tomography

Recently, a class of no-gold-standard (NGS) techniques have been proposed to evaluate quantitative imaging methods using patient data. These techniques provide figures of merit (FoMs) quantifying the precision of the estimated quantitative value without requiring repeated measurements and without requiring a gold standard. However, applying these techniques to patient data presents several practical difficulties including assessing the underlying assumptions, accounting for patient-sampling-related uncertainty, and assessing the reliability of the estimated FoMs. To address these issues, we propose statistical tests that provide confidence in the underlying assumptions and in the reliability of the estimated FoMs. Furthermore, the NGS technique is integrated within a bootstrap-based methodology to account for patient-sampling-related uncertainty. The developed NGS framework was applied to evaluate four methods for segmenting lesions from F-Fluoro-2-deoxyglucose positron emission tomography images of patients with head-and-neck cancer on the task of precisely measuring the metabolic tumor volume. The NGS technique consistently predicted the same segmentation method as the most precise method. The proposed framework provided confidence in these results, even when gold-standard data were not available. The bootstrap-based methodology indicated improved performance of the NGS technique with larger numbers of patient studies, as was expected, and yielded consistent results as long as data from more than 80 lesions were available for the analysis.

Combined fuzzy logic and random walker algorithm for PET image tumor delineation

PURPOSE

The random walk (RW) technique serves as a powerful tool for PET tumor delineation, which typically involves significant noise and/or blurring. One challenging step is hard decision-making in pixel labeling. Fuzzy logic techniques have achieved increasing application in edge detection. We aimed to combine the advantages of fuzzy edge detection with the RW technique to improve PET tumor delineation.

METHODS

A fuzzy inference system was designed for tumor edge detection from RW probabilities. Three clinical PET/computed tomography datasets containing 12 liver, 13 lung, and 18 abdomen tumors were analyzed, with manual expert tumor contouring as ground truth. The standard RW and proposed combined method were compared quantitatively using the dice similarity coefficient, the Hausdorff distance, and the mean standard uptake value.

RESULTS

The dice similarity coefficient of the proposed method versus standard RW showed significant mean improvements of 21.0±7.2, 12.3±5.8, and 18.4%±6.1% for liver, lung, and abdominal tumors, respectively, whereas the mean improvements in the Hausdorff distance were 3.6±1.4, 1.3±0.4, 1.8±0.8 mm, and the mean improvements in SUVmean error were 15.5±6.3, 11.7±8.6, and 14.1±6.8% (all P's<0.001). For all tumor sizes, the proposed method outperformed the RW algorithm. Furthermore, tumor edge analysis demonstrated further enhancement of the performance of the algorithm, relative to the RW method, with decreasing edge gradients.

CONCLUSION

The proposed technique improves PET lesion delineation at different tumor sites. It depicts greater effectiveness in tumors with smaller size and/or low edge gradients, wherein most PET segmentation algorithms encounter serious challenges. Favorable execution time and accurate performance of the algorithm make it a great tool for clinical applications.

Prognostic value of (18)F-FDG PET/CT volumetric parameters in recurrent epithelial ovarian cancer

OBJECTIVE

Metabolic tumour volume (MTV) and total lesion glycolysis (TLG) from (18)F-FDG PET/CT are emerging prognostic biomarkers in various solid neoplasms. These volumetric parameters and the SUVmax have shown to be useful criteria for disease prognostication in preoperative and post-treatment epithelial ovarian cancer (EOC) patients. The purpose of this study was to evaluate the utility of (18)F-FDG PET/CT measurements to predict survival in patients with recurrent EOC.

MATERIAL AND METHODS

Twenty-six patients with EOC who underwent a total of 31 (18)F-FDG PET/CT studies for suspected recurrence were retrospectively included. SUVmax and volumetric parameters whole-body MTV (wbMTV) and whole-body TLG (wbTLG) with a threshold of 40% and 50% of the SUVmax were obtained. Correlation between PET parameters and progression-free survival (PFS) and the survival analysis of prognostic factors were calculated.

RESULTS

Serous cancer was the most common histological subtype (76.9%). The median PFS was 12.5 months (range 10.7-20.6 months). Volumetric parameters showed moderate inverse correlation with PFS but there was no significant correlation in the case of SUVmax. The correlation was stronger for first recurrences. By Kaplan-Meier analysis and log-rank test, wbMTV 40%, wbMTV 50% and wbTLG 50% correlated with PFS. However, SUVmax and wbTLG 40% were not statistically significant predictors for PFS.

CONCLUSION

Volumetric parameters wbMTV and wbTLG 50% measured by (18)F-FDG PET/CT appear to be useful prognostic predictors of outcome and may provide valuable information to individualize treatment strategies in patients with recurrent EOC.

PET/CT imaging correlates with treatment outcome in patients with multidrug-resistant tuberculosis

Definitive clinical trials of new chemotherapies for treating tuberculosis (TB) require following subjects until at least 6 months after treatment discontinuation to assess for durable cure, making these trials expensive and lengthy. Surrogate endpoints relating to treatment failure and relapse are currently limited to sputum microbiology, which has limited sensitivity and specificity. We prospectively assessed radiographic changes using 2-deoxy-2-[(18)F]-fluoro-D-glucose (FDG) positron emission tomography/computed tomography (PET/CT) at 2 and 6 months (CT only) in a cohort of subjects with multidrug-resistant TB, who were treated with second-line TB therapy for 2 years and then followed for an additional 6 months. CT scans were read semiquantitatively by radiologists and were computationally evaluated using custom software to provide volumetric assessment of TB-associated abnormalities. CT scans at 6 months (but not 2 months) assessed by radiologist readers were predictive of outcomes, and changes in computed abnormal volumes were predictive of drug response at both time points. Quantitative changes in FDG uptake 2 months after starting treatment were associated with long-term outcomes. In this cohort, some radiologic markers were more sensitive than conventional sputum microbiology in distinguishing successful from unsuccessful treatment. These results support the potential of imaging scans as possible surrogate endpoints in clinical trials of new TB drug regimens. Larger cohorts confirming these results are needed.

Colonoscopic Findings in Patients With Incidental Colonic Focal FDG Uptake

OBJECTIVE

The purpose of this study was to investigate the nature of FDG-avid and non-FDG-avid lesions detected at colonoscopy in patients presenting with incidental focal colonic FDG uptake at PET/CT.

MATERIALS AND METHODS

Among 9073 patients who underwent PET/CT over a 4-year period, 82 patients without a history of colonic disease had focal colonic FDG uptake and underwent colonoscopy. In consensus, a radiologist and a nuclear physician read images from these PET/CT examinations. They recorded the location of focal FDG uptake in the colon and associated CT abnormalities and measured maximum standardized uptake value (SUVmax) and metabolic volume (MV). Readings were performed twice--first without and second with knowledge of lesion location at colonoscopy. The final diagnosis was based on colonoscopic findings and histopathologic results categorized into benign, premalignant, or malignant.

RESULTS

One hundred seven foci of colonic FDG uptake at PET/CT and 150 lesions at colonoscopy were detected. Among 107 foci of FDG uptake, 65 (61%) corresponded to a lesion at colonoscopy (true-positive findings), and 42 (39%) did not (false-positive findings). Among 150 lesions found at colonoscopy, 85 (57%) were not FDG avid (false-negative findings). The MV of true-positive findings was lower than that of false-positive findings (4.0 ± 0.4 cm(3) vs 6.2 ± 0.7 cm(3); p = 0.006), but SUVmax did not differ (7.4 ± 0.5 vs 7.7 ± 0.5; p = 0.649). Considering the histopathologic categories of the lesions and the false-positive findings, there was no difference in SUVmax (p = 0.103), but MV was lower in premalignant lesions than in false-positive findings (p = 0.005).

CONCLUSION

Focal colonic FDG uptake may indicate the presence of a benign, pre-malignant, or malignant lesion. Subsequent colonoscopy should not be restricted to the colonic site of FDG uptake.

High FDG uptake areas on pre-radiotherapy PET/CT identify preferential sites of local relapse after chemoradiotherapy for locally advanced oesophageal cancer

PURPOSE

The high failure rates in the radiotherapy (RT) target volume suggest that patients with locally advanced oesophageal cancer (LAOC) would benefit from increased total RT doses. High 2-deoxy-2-[(18)F]fluoro-D-glucose (FDG) uptake (hotspot) on pre-RT FDG positron emission tomography (PET)/CT has been reported to identify intra-tumour sites at increased risk of relapse after RT in non-small cell lung cancer and in rectal cancer. Our aim was to confirm these observations in patients with LAOC and to determine the optimal maximum standardized uptake value (SUVmax) threshold to delineate smaller RT target volumes that would facilitate RT dose escalation without impaired tolerance.

METHODS

The study included 98 consecutive patients with LAOC treated by chemoradiotherapy (CRT). All patients underwent FDG PET/CT at initial staging and during systematic follow-up in a single institution. FDG PET/CT acquisitions were coregistered on the initial CT scan. Various subvolumes within the initial tumour (30, 40, 50, 60, 70, 80 and 90% SUVmax thresholds) and in the subsequent local recurrence (LR, 40 and 90% SUVmax thresholds) were pasted on the initial CT scan and compared[Dice, Jaccard, overlap fraction (OF), common volume/baseline volume, common volume/recurrent volume].

RESULTS

Thirty-five patients had LR. The initial metabolic tumour volume was significantly higher in LR tumours than in the locally controlled tumours (mean 25.4 vs 14.2 cc; p = 0.002). The subvolumes delineated on initial PET/CT with a 30-60% SUVmax threshold were in good agreement with the recurrent volume at 40% SUVmax (OF = 0.60-0.80). The subvolumes delineated on initial PET/CT with a 30-60% SUVmax threshold were in good to excellent agreement with the core volume (90% SUVmax) of the relapse (common volume/recurrent volume and OF indices 0.61-0.89).

CONCLUSION

High FDG uptake on pretreatment PET/CT identifies tumour subvolumes that are at greater risk of recurrence after CRT in patients with LAOC. We propose a 60% SUVmax threshold to delineate high FDG uptake areas on initial PET/CT as reduced target volumes for RT dose escalation.

Areas of high 18F-FDG uptake on preradiotherapy PET/CT identify preferential sites of local relapse after chemoradiotherapy for non-small cell lung cancer

The high rates of failure in the radiotherapy target volume suggest that patients with stage II or III non-small cell lung cancer (NSCLC) should receive an increased total dose of radiotherapy. Areas of high (18)F-FDG uptake on preradiotherapy (18)F-FDG PET/CT have been reported to identify intratumor subvolumes at high risk of relapse after radiotherapy. We wanted to confirm these observations on a cohort of patients included in 3 sequential prospective studies. Our aim was to assess an appropriate threshold (percentage of maximum standardized uptake value [SUVmax]) to delineate subvolumes on staging (18)F-FDG PET/CT scans assuming that a smaller target volume would facilitate isotoxic radiotherapy dose escalation.

METHODS

Thirty-nine patients with inoperable stage II or III NSCLC, treated with chemoradiation or with radiotherapy alone, were extracted from 3 prospective studies (ClinicalTrials.gov identifiers NCT01261585, NCT01261598, and RECF0645). All patients underwent (18)F-FDG PET/CT at initial staging, before radiotherapy, during radiotherapy, and during systematic follow-up in a single institution. All (18)F-FDG PET/CT acquisitions were coregistered on the initial scan. Various subvolumes in the initial acquisition (30%, 40%, 50%, 60%, 70%, 80%, and 90% SUVmax thresholds) and in the 3 subsequent acquisitions (40% and 90% SUVmax thresholds) were pasted on the initial scan and compared.

RESULTS

Seventeen patients had a local relapse. The SUVmax measured during radiotherapy was significantly higher in locally relapsed tumors than in locally controlled tumors (mean, 6.8 vs. 4.6; P = 0.02). The subvolumes delineated on initial PET/CT scans with 70%-90% SUVmax thresholds were in good agreement with the recurrent volume at a 40% SUVmax threshold (common volume/baseline volume, 0.60-0.80). The subvolumes delineated on initial PET/CT scans with 30%-60% SUVmax thresholds were in good to excellent agreement with the core volume of the relapse (90% SUVmax threshold) (common volume/recurrent volume and overlap fraction indices, 0.60-0.93). The agreement was moderate (>0.51) when a 70% SUVmax threshold was used to delineate on initial PET/CT scans.

CONCLUSION

High (18)F-FDG uptake areas on pretreatment PET/CT scans identify tumor subvolumes at greater risk of relapse in patients with NSCLC treated by concomitant chemoradiation. We propose a 70% SUVmax threshold to delineate areas of high (18)F-FDG uptake on initial PET/CT scans as the target volumes for potential radiotherapy dose escalation.