Is unenhanced 18F-FDG-PET/CT better than enhanced CT in the detection of retropharyngeal lymph node metastasis in nasopharyngeal carcinoma?

Positron-emission tomography/computed tomography (PET/CT) has been proposed as a means to enhance the pretreatment evaluation of cervical lymph node status in patients with nasopharyngeal carcinoma (NPC). We conducted a prospective study to compare PET/CT and enhanced CT for the detection of retropharyngeal lymph node (RLN) metastasis in NPC, and to ascertain the factors that affect its diagnostic performance. Our study population was made up of 33 patients-24 men and 9 women, aged 30 to 81 years (mean: 52)-with newly diagnosed NPC who had been treated over a 2-year period. All patients underwent enhanced CT first, followed by unenhanced 18F-fluorodeoxyglucose (FDG) PET/CT. The detection rate of RLN metastasis on PET/CT was significantly lower than that on enhanced CT (36.4 vs. 75.8%; p < 0.001). A total of 25 of 26 nodes with a discordant finding were negative on PET/CT; they included 13 metastatic lymph nodes with low FDG uptake, 9 that were located close to the primary tumor, 2 that were confluent RLNs, and 1 that was adjacent to the physiologic FDG-avid prevertebral muscle. The maximum standardized uptake value (SUVmax) of RLNs was positively correlated with the minimum axial diameter (r = 0.803, p < 0.001). The PET/CT detection rate was 0% for lymph nodes smaller than 5 mm, 9% for those 5 to 10 mm, and 73% for those 1 cm or larger. The detection rate of PET/CT at level C1 was significantly lower than that at C2 (22 vs. 67%; p = 0.035). We conclude that unenhanced PET/CT is markedly inferior to enhanced CT for detecting RLN metastasis in NPC, especially in lymph nodes with a minimum axial diameter of less than 1 cm and those in proximity to the primary tumor. Using enhanced CT in PET/CT is justified to improve the recognition of RLN metastasis in patients with NPC.

Primary tumor volume measured by FDG PET and CT in nasopharyngeal carcinoma.

BACKGROUND: The prognostic value of CT-derived primary tumor volume in patients with nasopharyngeal carcinoma (NPC) has been demonstrated in our previous serial studies. The purpose of the present study is to compare the primary tumor volume measured by FDG PET and traditional CT in NPC, and to ascertain their prognostic value. MATERIALS AND METHODS: From 2007 to 2008, 32 patients with newly diagnosed NPC were prospectively studied. All patients underwent a CT scan, followed by a FDG PET/CT scan. CT-derived primary tumor volume (VolumeCT) was measured using the summation-of-area technique. PET-volume was measured using 3 methods: delineating the contour of tumor with the threshold of standardized uptake value (SUV) ≧2.5 (Volume2.5), ≧40% of maximal SUV (Volume40%), and ≧50% of maximal SUV (Volume50%). The primary tumor volumes derived from the 4 methods, VolumeCT, Volume2.5, Volume40%, and Volume50%, were compared. Univariate Cox regression was used to identify the above parameters as prognosticators. RESULTS: The volumes derived from the VolumeCT, Volume2.5, Volume40%, and Volume50% methods were 16.48 ± 12.46 cm(3), 25.87 ± 16.96 cm(3), 13.66 ± 6.90 cm(3), and 8.25 ± 4.52 cm(3), respectively. There was decent correlation between VolumeCT and Volume2.5 (r = 0.64, P = 0.0001), and Volume2.5 was systemically larger than VolumeCT. No significant difference was noted between VolumeCT and Volume40% (P = 0.24), but the correlation was poor (r = 0.15, P = 0.39). For VolumeCT and Volume50%, the difference was significant (P = 0.0006) and the correlation was poor (r = 0.23, P = 0.20). Larger tumor volumes presented as VolumeCT, Volume2.5, and Volume50% were associated with shorter overall survival. CONCLUSION: PET-derived primary tumor volumes are substantially different from CT-derived tumor volumes, only decent correlation is noted between VolumeCT and Volume2.5. Volume2.5 and Volume50% seem to be reasonable alternatives for VolumeCT in predicting the patient outcomes.

Value of lateral neck radiography for ingested foreign bodies using the likelihood ratio.

OBJECTIVE: To determine the diagnostic accuracy of lateral neck radiography and its value in related radiographic findings in the detection of foreign bodies using the likelihood ratio. PATIENTS AND METHODS: This retrospective study comprised 114 patients who had neck radiography followed by rigid esophagoscopy. Interpretations of the radiographs were correlated with esophagoscopic findings and clinical follow-up for at least 1 month. Data were mainly assessed by likelihood ratio and detection rate. RESULTS: Plain radiography had a positive likelihood ratio of 2.4 (95% confidence interval [CI] 1.8-3.1) and a negative likelihood ratio of 0.6 (95% CI 0.40-0.7). It had a sensitivity of 57.4% (95% CI 45.6-69.1) and a specificity of 76.1% (95% CI 63.8-88.4). Positive likelihood ratios for each radiographic finding (foreign body shadow, air, and soft tissue swelling) were 3.4 (95% CI 2.6-4.4), 1.5 (95% CI 0.9-2.6), and 4.1 (95% CI 1.9-8.7), respectively. Plain radiography had a high detection rate (72.5%) when foreign bodies were lodged in the hypopharynx and cervical esophagus. On the contrary, the detection rate was poor (0%) in the oropharynx. CONCLUSIONS: A lateral neck radiograph is better taken after a negative finding in a thorough oral examination and fibre-optic laryngoscopy. Judging from the possible site of impacted foreign body and radiographic findings, we can better predict the presence of foreign bodies.

Comparison of the effectiveness between a single low dose and fractionated doses of radioiodine in ablation of post-operative thyroid remnants.

Due to the lack of radiation isolation wards in most hospitals in Taiwan, high-dose (exceeding 30 mCi) radioiodine therapy is usually performed in a fractionated manner (successively administering multiple low doses). This study compared the ablating efficacies of post-operative thyroid remnants using a single low dose (30 mCi) and fractionated doses (four doses of 30 mCi given at weekly intervals) in 59 patients with differentiated thyroid cancer who received total or near-total thyroidectomy. Successful ablation was obtained in 20 of 38 patients (52.6%) treated with a single low dose compared with 14 of 21 patients (66.7%) treated in a fractionated manner. There was no statistically significant difference between these two treatment protocols (P = 0.296). As the fractionated-dose protocol has the drawbacks of a much longer hypothyroid state and a higher total expense, we suggest that a single low dose is more feasible than fractionated doses for outpatient ablation therapy.