PET/Computed Tomography: Post-therapy Follow-up in Head and Neck Cancer.

PET/computed tomography (CT) is a valuable tool in post-therapy follow-up of head and neck cancers. PET/CT is sensitive and specific, can detect recurrences that otherwise may be missed on routine clinical examination or conventional imaging, and also can have an impact on patient management. National Comprehensive Cancer Network guidelines recommend PET/CT be performed within 3 months to 6 months after therapy. After this baseline scan, however, further routine PET/CT surveillance in asymptomatic patients has unclear benefit. Additional post-therapy PET/CT imaging should be individualized to patients based on considerations such as tumor type, stage, prognostic factors, symptoms, and clinical assessment.

Ga-68 DOTATATE PET/CT and F-18 FDG PET/CT in the evaluation of low and intermediate versus high-grade neuroendocrine tumors.

OBJECTIVE: We investigated the role of Ga-68 DOTATATE PET/CT in comparison to F-18 FDG PET/CT in patients with low and intermediate versus high-grade neuroendocrine tumors (NETs). METHODS: We identified 81 patients who underwent Ga-68 DOTATATE PET/CT at our institution between May 2017 and December 2018 and met inclusion criteria of biopsy-proven NET with known Ki-67 index, histologic grade, or differentiation. Patients were divided into two groups. Control group included Ki-67 ≤20%, grade 1 or 2, or well-differentiated tumors. Experimental group included Ki-67 >20%, grade 3, or poorly-differentiated tumors. RESULTS: Mean age was 57 years, with 36 males and 45 females. Most common primary sites were small bowel, pancreas, and lung. Most common distant metastatic sites were liver and bone. In the control group (n = 67), median Ki-67 was 4% (range 1-30%). 55/67 (82.1%) DOTATATE and 6/11 (54.5%) FDG scans were positive (P = 0.04). Positive scans showed >10 lesions in 25/55 (45.5%) DOTATATE and 1/6 (16.7%) FDG scans (P = 0.18). 40/55 (72.7%) positive DOTATATE and 3/6 (50%) FDG scans showed distant disease (P = 0.25). In the experimental group (n = 14), median Ki-67 was 68% (range 25-95%). All 14 DOTATATE and all nine FDG scans were positive. Positive scans showed >10 lesions in 4/14 (28.6%) DOTATATE and 5/9 (55.6%) FDG scans (P = 0.20). 10/14 (71.4%) positive DOTATATE and 7/9 (77.8%) FDG scans showed distant disease (P = 0.74). CONCLUSION: All patients with high grade, poorly-differentiated NETs had positive DOTATATE PET/CTs. In these patients, DOTATATE PET/CT did not significantly differ from FDG PET/CT in identifying >10 lesions or distant disease.

Impact of Point-Spread Function Reconstruction on 68Ga-DOTATATE PET/CT Quantitative Imaging Parameters.

OBJECTIVE. The objective of our study was to investigate the impact of point-spread function (PSF) reconstruction and lesion size on 68Ga-tetraazacyclododecanetetraacetic acid-DPhe1-Tyr3-octreotate (DOTATATE) PET/CT quantitative parameters. MATERIALS AND METHODS. A total of 38 patients with 42 68Ga-DOTATATE PET/CT studies and 125 lesions were included. Scans were reconstructed with and without PSF modulation. For each lesion, the maximum standardized uptake value (SUVmax) and peak standardized uptake value (SUVpeak), metabolic tumor volume (MTV), total lesion somatostatin avidity, and tumor somatostatin receptor expression heterogeneity using the AUC method were measured. Intraclass correlation coefficient (ICC) and Bland-Altman analyses were used to compare PSF and non-PSF values. A subgroup analysis was performed to determine the impact of lesion size. RESULTS. Of the 125 lesions, 51 were in the liver, 31 in lymph nodes, 17 in bone, eight in pancreas, four in lung, and 14 in other sites. The ICCs between PSF and non-PSF values were excellent for SUVmax, SUVpeak, MTV, and total lesion somatostatin avidity (ICC = 0.97-0.99), and the ICC was good for tumor somatostatin receptor expression heterogeneity (ICC = 0.81). Comparison of PSF with non-PSF values showed a bias (mean percentage change ± SD) of 27.5% ± 14.7% for SUVmax, 15.5% ± 9.5% for SUVpeak, -18.6% ± 37.6% for MTV, 0.8% ± 28.1% for total lesion somatostatin avidity, and -7.1% ± 11.0% for tumor somatostatin receptor expression heterogeneity. Comparison of PSF with non-PSF values for lesions less than 2 cm (n = 75) showed corresponding biases greater than those for lesions 2 cm or larger (n = 50). CONCLUSION. PSF reconstruction effected higher values for SUVmax and SUVpeak, produced decreased values for tumor somatostatin receptor expression heterogeneity, and had a variable effect on MTV and total lesion somatostatin avidity depending on lesion size.

Timing and Impact of Posttreatment PET/CT After First 6 Months on Patient Management and Outcomes in Oropharyngeal Squamous Cell Carcinoma.

OBJECTIVE. The objective of this study was to investigate the impact of PET/CT on patient management and outcomes of oropharyngeal squamous cell carcinoma (OPSCC) after the first 6 months following treatment. MATERIALS AND METHODS. We retrospectively identified patients with OPSCC who underwent chemoradiation therapy and had at least 2 years of posttreatment follow-up. Patients were grouped on the basis of whether they underwent PET/CT, as a result of clinical suspicion of recurrence or routine follow-up, in the last 18 months of the 2-year posttreatment period (experimental group) or not (control group). Association between PET/CT use and change in management was tested using chi-square analysis. Survival analyses were performed with Cox and Kaplan-Meier analyses. RESULTS. In total, 149 patients underwent 294 PET/CT studies in the 2-year follow-up period. Eighty-three patients (55.7%) underwent PET/CT in the last 18 months of the 2 years. This group underwent 223 PET/CT studies, 22 (9.9%) of which were positive. Sixteen of the 22 (72.7%) changed management. Sixty-six patients (44.3%) did not undergo PET/CT in the last 18 months. This group underwent 71 PET/CT studies, six (8.5%) of which were positive. Two of the six studies (33.3%) changed management. Of first-time positive PET/CT studies in the last 18 months, five of nine (55.6%) were performed 6-12 months after treatment. PET/CT in the last 18 months was positively associated with change in management (odds ratio, 4.88; p = 0.02). Patients with positive PET/CT findings had worse overall survival (hazard ratio [HR], 31.6; p < 0.0001) and progression-free survival (HR, 40.8; p < 0.0001). CONCLUSION. PET/CT in the last 18 months of the 2-year posttreatment period impacted patient management. Most first-time positive PET/CT studies in the last 18 months of the 2 years were performed 6-12 months after treatment.

Olfactory receptor accessory proteins play crucial roles in receptor function and gene choice.

Each of the olfactory sensory neurons (OSNs) chooses to express a single G protein-coupled olfactory receptor (OR) from a pool of hundreds. Here, we show the receptor transporting protein (RTP) family members play a dual role in both normal OR trafficking and determining OR gene choice probabilities. Rtp1 and Rtp2 double knockout mice (RTP1,2DKO) show OR trafficking defects and decreased OSN activation. Surprisingly, we discovered a small subset of the ORs are expressed in larger numbers of OSNs despite the presence of fewer total OSNs in RTP1,2DKO. Unlike typical ORs, some overrepresented ORs show robust cell surface expression in heterologous cells without the co-expression of RTPs. We present a model in which developing OSNs exhibit unstable OR expression until they choose to express an OR that exits the ER or undergo cell death. Our study sheds light on the new link between OR protein trafficking and OR transcriptional regulation.