Long term survival in patients with human papillomavirus-positive oropharyngeal cancer and equivocal response on 12-week PET-CT is not compromised by the omission of neck dissection.

BACKGROUND AND AIM: The aim of this study was to evaluate the long-term safety of the omission of immediate neck dissections (IND) in patients with human papillomavirus (HPV)-positive head and neck squamous cell carcinoma (HNSCC) achieving a less than complete nodal response on 12-week FDG PET-CT. MATERIAL AND METHODS: Patients with HPV-positive, node-positive HNSCC that were treated with radical (chemo) radiotherapy (RT) between January 2013 and September 2019 were identified. PET-CT responses were classified as complete (CR), incomplete (ICR) or equivocal (EQR) nodal responses. Clinical outcomes were obtained. RESULTS: 347 patients were identified. Median follow-up was 43.9 (IQR, 30.8-61.2) months. 62.8% (218/347) achieved a CR, 23.4% (81/347) EQR and 13.8% (48/347) ICR nodal response. 70 of 81 (86.4%) patients with an EQR and 25 of 48 (52.1%) with an ICR had no residual disease during follow up (a pathologically negative ND if surgery undertaken or no subsequent neck or distant relapse clinically/radiologically). Median survival of the EQR and CR groups were not reached, and despite the omission of IND in 95% of the EQR group there was no statistically significant differences in overall survival (OS) between the groups, p = 1.0. Median survival of ICR was not reached. However, OS for ICR group was significantly worse than that of CR, and EQR, both p < 0.001. CONCLUSION: The omission of IND in those achieving an EQR nodal response does not compromise long-term survival. This supports the safety of extended surveillance in patients with HPV-positive disease and an EQR on 12-week FDG PET-CT.

12 week PET-CT has low positive predictive value for nodal residual disease in human papillomavirus-positive oropharyngeal cancers.

OBJECTIVES: Surveillance PET-CT scans at 12 weeks post-radiotherapy for head and neck cancer can be used to omit neck dissections with no detriment in overall survival. Human Papillomavirus (HPV) driven tumours behave differently on conventional imaging after radiotherapy but it is unknown if this effect is seen on PET-CT and if HPV status affects the accuracy of PET-CT. We aimed to determine the negative and positive predictive values (NPV and PPV) of 12 week surveillance PET-CT in HPV positive and negative tumours, and investigate predictors of relapse in equivocal responders. MATERIALS AND METHODS: A retrospective cohort study in a UK tertiary level oncology hospital, between 2013 and 2016 included adults with oropharyngeal squamous cell carcinoma, or HPV positive head and neck squamous cell cancers of unknown primary, treated with radiotherapy. RESULTS: The PPVs of 12 week PET-CT in HPV positive and negative disease are 30% and 81.8% respectively (p < 0.01). The NPVs of 12 week PET-CT in HPV positive and negative disease are 92.9% and 55.6% respectively (p < 0.01). 67% of HPV positive patients with equivocal responses on 12 week PET-CT achieved complete response by 24 weeks. Equivocal responses in HPV positive disease had statistically similar survival to patients with complete responses. Comparing disease and imaging characteristics, there were no predictors of residual tumour. CONCLUSIONS: HPV positive tumours have a poor PPV of 30% on 12 week surveillance PET-CTs and take longer to achieve complete response. A period of further surveillance can be considered instead of an immediate neck dissection in this group of patients.

Influence of slice overlap on positron emission tomography image quality.

PET scans use overlapping acquisition beds to correct for reduced sensitivity at bed edges. The optimum overlap size for the General Electric (GE) Discovery 690 has not been established. This study assesses how image quality is affected by slice overlap. Efficacy of 23% overlaps (recommended by GE) and 49% overlaps (maximum possible overlap) were specifically assessed. European Association of Nuclear Medicine (EANM) guidelines for calculating minimum injected activities based on overlap size were also reviewed. A uniform flood phantom was used to assess noise (coefficient of variation, (COV)) and voxel accuracy (activity concentrations, Bq ml(-1)). A NEMA (National Electrical Manufacturers Association) body phantom with hot/cold spheres in a background activity was used to assess contrast recovery coefficients (CRCs) and signal to noise ratios (SNR). Different overlap sizes and sphere-to-background ratios were assessed. COVs for 49% and 23% overlaps were 9% and 13% respectively. This increased noise was difficult to visualise on the 23% overlap images. Mean voxel activity concentrations were not affected by overlap size. No clinically significant differences in CRCs were observed. However, visibility and SNR of small, low contrast spheres (⩽13 mm diameter, 2:1 sphere to background ratio) may be affected by overlap size in low count studies if they are located in the overlap area. There was minimal detectable influence on image quality in terms of noise, mean activity concentrations or mean CRCs when comparing 23% overlap with 49% overlap. Detectability of small, low contrast lesions may be affected in low count studies-however, this is a worst-case scenario. The marginal benefits of increasing overlap from 23% to 49% are likely to be offset by increased patient scan times. A 23% overlap is therefore appropriate for clinical use. An amendment to EANM guidelines for calculating injected activities is also proposed which better reflects the effect overlap size has on image noise.

PET-CT evaluation of solitary pulmonary nodules: correlation with maximum standardized uptake value and pathology.

PURPOSE: 18-fluorine fluorodeoxyglucose ((18)F-FDG) positron emission tomography-computed tomography (PET-CT) has an established role for the characterization of solitary pulmonary nodules (SPN). Visual assessment of nodule morphology, together with maximum standardized uptake value (SUVmax), is used to estimate likelihood of malignancy. We correlated SUVmax value with pathology of SPN and assessed diagnostic accuracy in differentiating malignant from benign nodule, using 2.5 as threshold SUVmax. METHODS: Retrospective review of PET-CT scans for SPN characterization between April 2008 and June 2011 was performed. Only cases with pathological verification were included. RESULTS: A total of 641 PET-CTs were performed for SPN characterization and staging; 186 patients (77 males, 109 females) with pathological confirmation were included, and 158 (85 %) nodules were malignant: adenocarcinomas (n = 66), squamous cell carcinomas (n = 40), and metastases (n = 20) were the commonest. 28 lesions (15 %) were benign, including granuloma/chronic inflammation (n = 8), infection (n = 7), and hamartomas (n = 5). Using cutoff SUVmax of 2.5, the accuracy of PET-CT in diagnosing malignant SPN is 81.2 %, with sensitivity 86.7 %, specificity 50 %, PPV 90.7 %, and NPV 40 %. The likelihood of malignancy increases with SUVmax. Nevertheless, even with SUVmax <2.5, there is a 62 % chance that a nodule is malignant. CONCLUSIONS: Although PET-CT is useful in diagnostic workup of SPN, it cannot replace "gold standard" tissue diagnosis.

Quantitative analysis shows that contrast medium in positron emission tomography/computed tomography may cause significant artefacts.

OBJECTIVES: Attenuation correction algorithms are required for accurate quantification of PET data and for mapping of radioactive tracers. Modern PET systems incorporate computed tomography (CT) systems to perform attenuation correction. However, high-density media, such as contrast agents, may introduce potentially clinically significant artefacts in PET images when CT-based attenuation correction algorithms are used. Although various groups have investigated this issue, no study has quantitatively assessed the clinical significance of these artefacts by comparing artefact and lesion standardized uptake values (SUVs) in controlled phantom experiments. Furthermore, previous studies have focussed on the effects of increasing the concentration of contrast medium, without investigating the effects of increasing its transaxial area. This study quantifies the clinical significance of increasing the concentration and transaxial area of contrast agents and evaluates a commercially available contrast agent correction algorithm. METHODS: Images of a phantom containing background activity, a volume of contrast agent and varying sizes of hot lesions were acquired using clinical acquisition protocols. Quantitative analysis was performed on transaxial image slices of PET data. RESULTS: The densest medium caused a 125% SUV(mean) increase in the area containing, and immediately adjacent to, contrast medium when compared with a reference water phantom. As the transaxial area of the contrast medium increased, artefacts appeared as a ring of activity around the periphery of the contrast medium. The contrast correction algorithm reduced these artefacts to within ± 39% of the reference results. CONCLUSION: Oral and IV contrast agents can cause clinically significant artefacts in CT-based attenuation-corrected PET images and should be used with caution.

Investigation of 18F-FDG 3D mode PET image quality versus acquisition time.

OBJECTIVE: Three-dimensional (3D) mode positron emission tomography (PET) is being used increasingly for clinical PET imaging. However, as yet, optimal acquisition parameters have not been established. The aim of this study was to investigate the effect of varying acquisition time on 3D image quality using standard clinical activities of F-fluorodeoxyglucose (FDG). METHODS: F-FDG phantom and patient PET images were acquired with varying acquisition times on a GE Discovery-STE PET/CT system. The NEMA Image-Quality phantom was imaged with four hot lesions in a uniform background. Images were acquired for 1, 2, 3, 4, and 5-min frames with three different lesion-to-background contrast ratios. Patient data were investigated using list mode acquisition to obtain comparable 2, 3, and 4-min frames. Qualitative analysis involved grading image quality and lesion detectability. Quantitative analysis of phantom images involved assessing the coefficient of variation (COV) of background areas as a measure of noise, and lesion over background variability as a measure of image quality. Patient data were also assessed using COV analysis of liver uptake. RESULTS: Qualitative and quantitative analysis showed no significant difference in image quality between 4 and 5-min acquisition frames for 3D mode F-FDG PET imaging with standard clinical activities. The observers noted no difference in perceived image quality. This finding was supported by COV analysis. CONCLUSION: This study shows that GE Discovery-STE acquisition frame time can be reduced to 3 min for standard 3D mode imaging at standard clinical activities of F-FDG.

Serotonin transporter residual availability during long-term antidepressant therapy does not differentiate responder and nonresponder unipolar patients.

BACKGROUND: Serotonin transporters (SERT) are a major target for antidepressant medication, although there have been limited in vivo studies of SERT availability in patients being treated with antidepressants. It is not known whether SERT availability differs in treatment-responsive and -nonresponsive patients receiving long-term treatment. In this study, we used single photon emission computed tomography (SPECT) to compare SERT residual availability in unipolar responders and nonresponders during long-term antidepressant treatment. Dopamine transporter (DAT) availability was also assessed in the same patients to examine the relationship between the two transporter systems. METHODS: Twenty-four medicated unipolar patients were recruited, of whom 11 were responders and 13 were nonresponders. All patients underwent SPECT with [123I] beta-carbomethoxy-3-beta-(4 iodophenyl)tropane. Brain SERT was measured in the brain stem and diencephalon, and DAT was measured in the striatum. Residual availability was calculated as a ratio of specific to nonspecific uptake, with the occipital region used as the nonspecific reference region. RESULTS: There was no difference between responders and nonresponders in SERT availability. Dopamine transporter availability was similar in responders and nonresponders, and there was no association between SERT and DAT availability. CONCLUSIONS: Serotonin transporter availability does not discriminate responders and nonresponders during long-term treatment with antidepressants.