Qualitative 18F-FDG PET/CT Response Evaluation After Chemotherapy or Radiotherapy for Head and Neck Squamous Cell Carcinoma: Is There an Equivocal Group?

Post-treatment FDG PET-CT in head and neck carcinoma: comparative analysis of 4 qualitative interpretative criteria in a large patient cohort

There is no consensus regarding optimal interpretative criteria (IC) for Fluorine-18 fluorodeoxyglucose (FDG) Positron Emission Tomography – Computed Tomography (PET-CT) response assessment following (chemo)radiotherapy (CRT) for head and neck squamous cell carcinoma (HNSCC). The aim was to compare accuracy of IC (NI-RADS, Porceddu, Hopkins, Deauville) for predicting loco-regional control and progression free survival (PFS). All patients with histologically confirmed HNSCC treated at a specialist cancer centre with curative-intent non-surgical treatment who underwent baseline and response assessment FDG PET-CT between August 2008 and May 2017 were included. Metabolic response was assessed using 4 different IC harmonised into 4-point scales (complete response, indeterminate, partial response, progressive disease). IC performance metrics (sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV), accuracy) were compared. Kaplan-Meier and Cox proportional hazards regression analyses were performed for survival analysis. 562 patients were included (397 oropharynx, 53 hypopharynx, 48 larynx, 64 other/unknown primary). 420 patients (75%) received CRT and 142 (25%) had radiotherapy alone. Median follow-up was 26 months (range 3–148). 156 patients (28%) progressed during follow-up. All IC were accurate for prediction of primary tumour (mean NPV 85.0% (84.6–85.3), PPV 85.0% (82.5–92.3), accuracy 84.9% (84.2–86.0)) and nodal outcome (mean NPV 85.6% (84.1–86.6), PPV 94.7% (93.8–95.1), accuracy 86.8% (85.6–88.0)). Number of indeterminate scores for NI-RADS, Porceddu, Deauville and Hopkins were 91, 25, 20, 13 and 55, 70, 18 and 3 for primary tumour and nodes respectively. PPV was significantly reduced for indeterminate uptake across all IC (mean PPV primary tumour 36%, nodes 48%). Survival analyses showed significant differences in PFS between response categories classified by each of the four IC (p <0.001). All four IC have similar diagnostic performance characteristics although Porceddu and Deauville scores offered the best trade off of minimising indeterminate outcomes whilst maintaining a high NPV.

Accuracy of [18Fluorine]-Fluoro-2-Deoxy-d-Glucose Positron Emission Tomography-Computed Tomography Response Assessment Following (Chemo)radiotherapy for Locally Advanced Laryngeal/Hypopharyngeal Carcinoma

INTRODUCTION

The accuracy of response assessment positron emission tomography (PET)-computed tomography (CT) following radiotherapy with or without chemotherapy for laryngeal/hypopharyngeal squamous cell carcinoma is uncertain.

METHODS

In all, 35 patients with laryngeal or hypopharyngeal squamous cell carcinoma who were treated between 2009 and 2014 with (chemo)radiotherapy were identified. The accuracy of response assessment PET-CT was made by correlation with clinical follow-up and pathological findings.

RESULTS

Of the 35 patients, 20 (57%) had an overall complete metabolic response. Sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for response assessment [18Fluorine]-fluoro-2-deoxy-d-glucose (FDG) PET-CT for primary and nodal sites, respectively, were 100%, 73%, 46%, and 100% and 83%, 95%, 83%, and 95%.

CONCLUSIONS

Response assessment FDG PET-CT following (chemo)radiotherapy for laryngeal and hypopharyngeal carcinomas has a high NPV for both primary site and lymph nodes and can be used to guide treatment decisions. The PPV of residual FDG uptake at the primary tumour site is limited and requires examination and biopsy confirmation.

Radiotherapy response evaluation using FDG PET-CT-established and emerging applications

Radiation therapy is a common component of curative cancer treatment. However, there is a significant incidence of treatment failure. In these cases, salvage surgical options are sometimes appropriate. Accurate assessment of response and early recognition of treatment success or failure is therefore critical to guide treatment decisions and impacts on survival and the morbidity of treatment. Traditionally, treatment response has depended upon the anatomical measurement of disease. However, this may not correlate well with the presence of disease, especially after radiotherapy. Combined positron emission tomography (PET) and CT imaging employs radioactive tracers to identify molecular characteristics of tissues. PET imaging exploits the fact that malignancies have characteristic molecular profiles which differ compared with surrounding tissues. The complementary anatomical and functional information facilitates accurate non-invasive assessment of surrogate biomarkers of disease activity.

Assessment of outcomes with delayed (18)F-FDG PET-CT response assessment in head and neck squamous cell carcinoma

OBJECTIVE

To assess the accuracy of a 4-month post-(chemo)radiotherapy 18-fludeoxyglucose ((18)F-FDG) positron emission tomography (PET)-CT for head and neck squamous cell carcinoma (HNSCC).

METHODS

105 patients who underwent a baseline and response assessment (18)F-FDG PET-CT scan between 2008 and April 2013 were identified. (18)F-FDG PET-CT outcomes were analysed with reference to clinicopathological outcomes.

RESULTS

79 of 105 (75%) (18)F-FDG PET-CT scans demonstrated a complete metabolic response; 19 of 101 (19%) for assessable primary tumours were positive; and 19 of 93 (20%) for patients with nodal disease were equivocal (n = 10) or positive (n = 9). The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for primary and nodal disease were 90%, 89%, 47%, 99% and 91%, 89%, 53% and 99%, respectively. Eight of nine patients with a positive nodal response scan had clinicopathological evidence of residual nodal disease (PPV, 89%). 2 of 10 patients with equivocal nodal responses had clinicopathological evidence of residual nodal disease (PPV, 20%).

CONCLUSION

(18)F-FDG PET-CT 4 months post treatment has a very high NPV. A positive (18)F-FDG PET-CT has a high PPV for residual nodal disease. By contrast, patients who have an equivocal nodal response have a low PPV.

ADVANCES IN KNOWLEDGE

Response assessment (18)F-FDG PET-CT is a valuable tool in guiding the selective use of neck dissection following (chemo)radiotherapy for HNSCC. An equivocal lymph node response has a limited predictive value for persistent disease, and optimal management remains a clinical challenge.