Tumor volume assessment by 18F-FDG PET/CT in patients with oral cavity cancer with dental artifacts on CT or MR images

Evaluation of bone marrow invasion on the machine learning of 18 F-FDG PET texture analysis in lower gingival squamous cell carcinoma

OBJECTIVES

Lower gingival squamous cell carcinoma (LGSCC) has the potential to invade the alveolar bone. Traditionally, the diagnosis of LGSCC relied on morphological imaging, but inconsistencies between these assessments and surgical findings have been observed. This study aimed to assess the correlation between LGSCC bone marrow invasion and PET texture features and to enhance diagnostic accuracy by using machine learning.

METHODS

A retrospective analysis of 159 LGSCC patients with pretreatment 18 F-fluorodeoxyglucose (FDG) PET/computed tomography (CT) examination from 2009 to 2017 was performed. We extracted radiomic features from the PET images, focusing on pathologic bone marrow invasion detection. Extracted features underwent the least absolute shrinkage and selection operator algorithm-based selection and were then used for machine learning via the XGBoost package to distinguish bone marrow invasion presence. Receiver operating characteristic curve analysis was performed.

RESULTS

From the 159 patients, 88 qualified for further analysis (59 men; average age, 69.2 years), and pathologic bone marrow invasion was identified in 69 (78%) of these patients. Three significant radiological features were identified: Gray level co-occurrence matrix_Correlation, INTENSITY-BASED_IntensityInterquartileRange, and MORPHOLOGICAL_SurfaceToVolumeRatio. An XGBoost machine-learning model, using PET radiomic features to detect bone marrow invasion, yielded an area under the curve value of 0.83.

CONCLUSION

Our findings highlighted the potential of 18 F-FDG PET radiomic features, combined with machine learning, as a promising avenue for improving LGSCC diagnosis and treatment. Using 18 F-FDG PET texture features may provide a robust and accurate method for determining the presence or absence of bone marrow invasion in LGSCC patients.

Accurate preoperative staging with [68Ga]Ga-FAPI PET/CT for patients with oral squamous cell carcinoma: a comparison to 2-[18F]FDG PET/CT

OBJECTIVE

To evaluate the potential value of [⁶⁸Ga]Ga-labelled fibroblast activation protein inhibitor ([⁶⁸Ga]Ga-FAPI) positron emission tomography/computed tomography (PET/CT) in preoperative staging for patients with oral squamous cell carcinoma (OSCC) as compared to 2-[¹⁸F]fluoro-2-deoxy-D-glucose (2-[¹⁸F]FDG) PET/CT.

METHODS

Thirty-six treatment-naïve patients with OSCC who underwent 2-[¹⁸F]FDG and [⁶⁸Ga]Ga-FAPI PET/CT for preoperative staging were enrolled. The maximum standardised uptake value (SUV_max) of the primary tumour and suspected cervical metastatic lymph nodes, and the tumour-to-background ratio (TBR) of the primary tumour, were measured. The accuracy of two imaging modalities for preoperative diagnosis of metastatic lymph nodes was analysed. Histopathology served as the standard of reference.

RESULTS

Thirty-seven primary lesions of 36 patients were accurately detected by both [⁶⁸Ga]Ga-FAPI and 2-[¹⁸F]FDG PET/CT. Regarding primary tumours, the SUV_max and TBR of the two imaging modalities in stage T3-T4 were significantly higher than those of stage T1-T2 (all p < 0.05). On the patient analysis, the accuracy for the evaluation of N1-N3 neck status was 52.6% (10/19) for [⁶⁸Ga]Ga-FAPI PET/CT and 57.9% (11/19) for 2-[¹⁸F]FDG PET/CT. Notably, the accuracy for the evaluation of the N0 neck status between [⁶⁸Ga]Ga-FAPI and 2-[¹⁸F]FDG PET/CT was 100% (17/17) and 29% (5/17), respectively. Based on the patient, neck side and neck level, [⁶⁸Ga]Ga-FAPI PET/CT resulted in higher specificity and accuracy in diagnosing metastatic neck lymph nodes than 2-[¹⁸F]FDG PET/CT (all p < 0.05).

CONCLUSION

[⁶⁸Ga]Ga-FAPI PET/CT is a promising tool for preoperative staging of OSCC, and appears to reduce the false positivity seen with 2-[¹⁸F]FDG PET/CT for the detection of neck lymph node metastases.

KEY POINTS

• [⁶⁸Ga]Ga-FAPI PET/CT is a promising tool targeting cancer-associated fibroblasts with comparable diagnostic performance to 2-[¹⁸F]FDG PET/CT for identifying the primary lesions of OSCC. • [⁶⁸Ga]Ga-FAPI PET/CT showed higher specificity and accuracy for the evaluation of neck lymph node metastases of OSCC than 2-[¹⁸F]FDG PET/CT, especially for N0 neck status.

KSNM60 in Clinical Nuclear Oncology

Since the foundation of the Korean Society of Nuclear Medicine in 1961, clinical nuclear oncology has been a major part of clinical nuclear medicine in Korea. There are several important events for the development of clinical nuclear oncology in Korea. First, a scintillating type gamma camera was adopted in 1969, which enabled to perform modern oncological gamma imaging. Second, Tc-99 m generator was imported to Korea since 1979, which promoted the wide clinical use of gamma camera imaging by using various kinds of Tc-99 m labeled radiopharmaceuticals. Third, a gamma camera with single photon emission tomography (SPECT) capability was first installed in 1980, which has been used for various kinds of tumor SPECT imaging. Fourth, in 1994, clinical positron emission tomography (PET) scanner and cyclotron with a production of F-18 fluorodeoxyglucose were first installed in Korea. Fifth, Korean Board of Nuclear Medicine was established in 1995, which contributed in the education and manpower training of dedicated nuclear medicine physicians in Korea. Finally, an integrated PET/CT scanner was first installed in 2002. Since that, PET/CT imaging has been a major imaging tool in clinical nuclear oncology in Korea. In this review, a brief history of clinical nuclear oncology in Korea is described.

Measurement variations of MRI and CT in the assessment of tumor depth of invasion in oral cancer: A retrospective study

PURPOSE

In oral squamous cell carcinoma (OSCC), depth of invasion (DOI) is an important predictive, prognostic, and staging parameter. While it is known that DOI can be estimated from preoperative imaging, an analysis of measurements variations according to imaging modality and to depth of tumor itself is lacking. The aim of the study was to assess the accuracy of imaging-based estimation of DOI in relation with the tumor histological DOI.

METHODS

We retrospectively reviewed 121 patients with OSCC treated at University Hospital Zurich. The radiologic DOI of CT, T1-weighted, and T2-weighted MRI were compared with histological DOI. Frequency of relevant imaging artifacts was assessed as well.

RESULTS

A total of 110 CT (90.9 %) and 90 MRI (74 %) were analyzed. Both modalities were available for 79 patients (65.3 %). The median histological depth of invasion was 9 mm (IQR 4.5-14). The median depth of invasion was 14 mm (IQR 10-20) on CT, 13 mm (IQR 8.25-18) on T1-weighted MRI, and 13 mm (IQR 9-18.75) on T2-weighted MRI. All diagnostic modalities tended towards an overestimation of the histopathologic DOI from about 5-15 %. This trend was most pronounced for thin tumors, for which both CT and MRI lead to upstaging in over 50 % of the cases. For 25 (22.7 %) patients, dental scattering on CT rendered DOI not estimable. For MRI, 18 patients (20 %) had artifacts (blooming, motion artifacts) rendering DOI not estimable.

CONCLUSION

CT and MRI measurements of DOI in OSCC lead to an overestimation of histological DOI, especially in tumors with DOI<5 mm, with upstaging by imaging in over 50 % of the cases. Artifacts were present in more than 20 % of performed images.

Advances in Functional Imaging in the Assessment of Head and Neck Cancer

This article discusses the application of fludeoxyglucose PET/computed tomography (CT) technology in head and neck cancer diagnosis and management, as well as advantages and disadvantages relative to traditional imaging modalities. A successful scan relies on precise patient preparation, and compliance to specific protocols before and during the scan. Finally, this article briefly introduces a PET/CT scan recently approved by the Food and Drug Administration for neuroendocrine tumors.

Prognostic value of FDG PET/CT during radiotherapy in head and neck cancer patients

PURPOSE

To evaluate the prognostic value of 18F-fluorodeoxyglucose positron-emission tomography (FDG PET) with computed tomography (CT) before and during radiotherapy (RT) in patients with head and neck cancer.

METHODS

Twenty patients with primary head and neck squamous cell carcinoma were enrolled in this study, of whom 6 had oropharyngeal cancer, 10 had hypopharyngeal cancer, and 4 had laryngeal cancer. Fifteen patients received concurrent cisplatin and 2 received concurrent cetuximab chemotherapy. FDG PET/CT was performed before RT and in the 4th week of RT. The parameters of maximum standardized uptake value, metabolic tumor volume, and total lesion glycolysis (TLG) of the primary tumor were measured, and the prognostic significance of each was analyzed with the Cox proportional hazards model.

RESULTS

Higher TLG (&gt;19.0) on FDG PET/CT during RT was a poor prognostic factor for overall survival (OS) (p = 0.001) and progression-free survival (PFS) (p = 0.007). In the multivariate analysis, TLG during RT as a continuous variable was significantly associated with OS and PFS rate (p = 0.023 and p = 0.016, respectively). Tumor response worse than partial remission at 1 month after RT was another independent prognostic factor for PFS (p = 0.024). Conclusions: Higher TLG of the primary tumor on FDG PET/CT during RT was a poor prognostic factor for OS and PFS in patients with head and neck cancer.

Voxel-wise correlation of functional imaging parameters in HNSCC patients receiving PET/MRI in an irradiation setup

PURPOSE

The purpose of this study was to demonstrate the feasibility of voxel-wise multiparametric characterization of head and neck squamous cell carcinomas (HNSCC) using hybrid multiparametric magnetic resonance imaging and positron emission tomography with [¹⁸F]-fluorodesoxyglucose (FDG-PET/MRI) in a radiation treatment planning setup.

METHODS

Ten patients with locally advanced HNSCC were examined with a combined FDG-PET/MRI in an irradiation planning setup. The multiparametric imaging protocol consisted of FDG-PET, T2-weighted transverse short tau inversion recovery sequence (STIR) and diffusion-weighted MRI (DWI). Primary tumours were manually segmented and quantitative imaging parameters were extracted. PET standardized uptake values (SUV) and DWI apparent diffusion coefficients (ADC) were correlated on a voxel-wise level.

RESULTS

Images acquired in this specialised radiotherapy planning setup achieved good diagnostic quality. Median tumour volume was 4.9 [1.1-42.1] ml. Mean PET SUV and ADC of the primary tumours were 5 ± 2.5 and 1.2 ± 0.3 10^-3 mm²/s, respectively. In voxel-wise correlation between ADC values and corresponding FDG SUV of the tumours, a significant negative correlation was observed (r = -0.31 ± 0.27, p < 0.05).

CONCLUSION

Multiparametric voxel-wise characterization of HNSCC is feasible using combined PET/MRI in a radiation planning setup. This technique may provide novel insights into tumour biology with regard to radiation therapy in the future.

PET/CT and PET/MRI in head and neck malignancy

Combined 2-[18F]-fluoro-2-deoxy-d-glucose (FDG) positron-emission tomography (PET)/computed tomography (CT) has an established role in the staging of difficult cases of head and neck (HN) squamous cell carcinoma (SCC), looking for an unknown primary, assessing response post-chemotherapy at 3-6 months, and differentiating relapse from treatment effects in patients suspected to have tumour recurrence. The PET NECK trial, comparing PET/CT surveillance versus neck dissection in advanced head and neck cancer showed survival was similar among patients who underwent PET/CT-guided surveillance and those who underwent planned neck dissection, but surveillance was more cost-effective. There is growing interest in the use of hypoxia PET tracers, especially in targeting radiotherapy, where the radiotherapy dose can be boosted in regions of hypoxia; the use of 68Ga peptide tracers in neuroendocrine malignancy and also in the growing field of combined PET/magnetic resonance imaging (MRI). PET/MRI has the advantage of increased anatomical detail and radiation dose reduction combined with the molecular and metabolic data from PET, although PET/CT has the advantage in better sensitivity for imaging lung metastases. Thus far, there is good agreement between PET/CT and PET/MRI with high correlation between semi-quantitative measurements in primary, nodal, osseous, and soft-tissue lesions imaging. PET/MRI may indeed provide greater accuracy than the currently available imaging procedures in the staging and later treatment response evaluation in HNSCC.

Chapter 3 The Role of PET/CT in Squamous Cell Carcinoma of the Head and Neck

Head and neck squamous cell carcinoma is an important cause of cancer morbidity worldwide and has been stratified into human papillomavirus-related and human papillomavirus-unrelated subgroups that affect prognosis and now staging. Conventional anatomical imaging methods are suboptimal for the detection of regional and distant metastases that are important prognosticators associated with poor outcomes. Functional imaging with (F18)-fluorodeoxyglucose-positron emission tomography/computed tomography (PET/CT) is a useful tool in the management of head and neck squamous cell carcinoma, providing complementary physiological and anatomical information. In this article, optimal PET/CT technique will be reviewed and the pretreatment and posttreatment applications of PET/CT will be described. A simplified approach to imaging interpretation, including review of pearls and pitfalls will be discussed. An initial framework for follow-up evaluation will be provided.

Role of fluorine-18 fluorodeoxyglucose PET/CT in head and neck oncology: the point of view of the radiation oncologist

Squamous cell carcinoma is the most common malignant tumour of the head and neck. The initial TNM staging, the evaluation of the tumour response during treatment, and the long-term surveillance are crucial moments in the approach to head and neck squamous cell carcinoma (HNSCC). Thus, at each of these moments, the choice of the best diagnostic tool providing the more precise and larger information is crucial. Positron emission tomography with fluorine-18 fludeoxyglucose integrated with CT (¹⁸F-FDG-PET/CT) rapidly gained clinical acceptance, and it has become an important imaging tool in routine clinical oncology. However, controversial data are currently available, for example, on the role of ¹⁸F-FDG-PET/CT imaging during radiotherapy planning, the prognostic value or its real clinical impact on treatment decisions. In this article, the role of ¹⁸F-FDG-PET/CT imaging in HNSCC during pre-treatment staging, radiotherapy planning, treatment response assessment, prognosis and follow-up is reviewed focusing on current evidence and controversial issues. A proposal on how to integrate ¹⁸F-FDG-PET/CT in daily clinical practice is also described.

Application of positron emission tomography/computed tomography in radiation treatment planning for head and neck cancers

18-fluorodeoxygluocose positron emission tomography/computed tomography (¹⁸FDG-PET/CT) provides significant information in multiple settings in the management of head and neck cancers (HNC). This article seeks to define the additional benefit of PET/CT as related to radiation treatment planning for squamous cell carcinomas (SCCs) of the head and neck through a review of relevant literature. By helping further define both primary and nodal volumes, radiation treatment planning can be improved using PET/CT. Special attention is paid to the independent benefit of PET/CT in targeting mucosal primaries as well as in detecting nodal metastases. The utility of PET/CT is also explored for treatment planning in the setting of SCC of unknown primary as PET/CT may help define a mucosal target volume by guiding biopsies for examination under anesthesia thus changing the treatment paradigm and limiting the extent of therapy. Implications of the use of PET/CT for proper target delineation in patients with artifact from dental procedures are discussed and the impact of dental artifact on CT-based PET attenuation correction is assessed. Finally, comment is made upon the role of PET/CT in the high-risk post-operative setting, particularly in the context of radiation dose escalation. Real case examples are used in these settings to elucidate the practical benefits of PET/CT as related to radiation treatment planning in HNCs.

Added value of a single-energy projection-based metal-artifact reduction algorithm for the computed tomography evaluation of oral cavity cancers

PURPOSE

The purpose of our study was to investigate the added value of the single-energy projection-based metallic artifact reduction (SEMAR) technique on the visualization and diagnostic confidence of oral cavity cancers.

MATERIALS AND METHODS

Contrast-enhanced CT was performed on 40 patients with dental metalwork. Of these, 18 patients had pathologically confirmed oral cavity cancer, and the other 22 patients had no lesions. CT attenuation and noise in the oral cavity were compared between the conventional and SEMAR images. Two radiologists visually graded the diagnostic confidence on a 5-point scale from 1 (definitely absent) to 5 (definitely present). The value of the SEMAR was assessed in a receiver-operating characteristic curve analysis.

RESULTS

The artifact of the SEMAR images was significantly lower than that of the conventional images (38.4 ± 18.0 HU vs. 187.7 ± 162.7 HU; P < 0.01). Reviewers 1 and 2 detected 10 and 7 more lesions with the SEMAR, respectively. Areas under the curve for the conventional and SEMAR reconstruction were 0.761 and 0.942, respectively, for reviewer 1 and 0.701 and 0.864, respectively, for reviewer 2.

CONCLUSION

The SEMAR significantly improved the oral cavity cancer visualization and diagnostic confidence.

Simultaneous PET/MR head-neck cancer imaging: Preliminary clinical experience and multiparametric evaluation

PURPOSE

To evaluate the role of simultaneous hybrid PET/MR imaging and to correlate metabolic PET data with morpho-functional parameters derived by MRI in patients with head-neck cancer.

METHODS

Forty-four patients, with histologically confirmed head and neck malignancy (22 primary tumors and 22 follow-up) were studied. Patients initially received a clinical exam and endoscopy with direct biopsy. Next patients underwent whole body PET/CT followed by PET/MR of the head/neck region. PET and MRI studies were separately evaluated by two blinded groups (both included one radiologist and one nuclear physician) in order to define the presence or absence of lesions/recurrences. Regions of interest (ROIs) analysis was conducted on the primary lesion at the level of maximum size on metabolic (SUV and MTV), diffusion (ADC) and perfusion (K(trans), Ve, kep and iAUC) parameters.

RESULTS

PET/MR examinations were successfully performed on all 44 patients. Agreement between the two blinded groups was found in anatomic allocation of lesions by PET/MR (Primary tumors: Cohen's kappa 0.93;

FOLLOW-UP

Cohen's kappa 0.89). There was a significant correlation between CT-SUV measures and MR (e.g., CT-SUV VOI vs.

MR-SUV VOI

ρ=0.97, p<0.001 for the entire sample). There was also significant positive correlations between the ROI area, SUV measures, and the metabolic parameters (SUV and MTV) obtained during both PET/CT and PET/MR. A significant negative correlation was observed between ADC and K(trans) values in the primary tumors. In addition, a significant negative correlation existed between MR SUV and ADC in recurrent tumors.

CONCLUSION

Our study demonstrates the feasibility of PET/MR imaging for primary tumors and recurrent tumors evaluations of head/neck malignant lesions. When assessing HNC, PET/MR allows simultaneous collection of multiparametric metabolic and functional data. This technique therefore allows for a more complete characterization of malignant lesions.

Clinical values of (18) F-FDG PET/CT in oral cavity cancer with dental artifacts on CT or MRI

LEVEL OF EVIDENCE

2a

BACKGROUND AND OBJECTIVES

To investigate the role of (18) F-FDG PET/CT in tumor staging, extent, and volume measurements in oral cavity squamous cell carcinoma (OSCC) patients with/without dental artifacts on CT or MRI.

METHODS

This study was conducted in 63 consecutive patients with OSCC who received initial workups including (18) F-FDG PET/CT and MRI. The results of the imaging modalities were compared to those of pathology, using McNemar's test and the paired t-test.

RESULTS

Thirty-seven patients (59%) had dental or metallic artifacts obscuring primary tumors. (18) F-FDG PET/CT scanning was superior to MRI in tumor staging (weighted κ = 0.870 vs. 0.518, P = 0.004) in patients with dental artifacts. In addition, (18) F-FDG PET/CT scans were more specific than MRI in detecting sublingual gland (P = 0.014) and mouth floor (P = 0.011) involvement. In patients with dental artifacts, there was a significant discrepancy between primary tumor volume (PTV) measured by pathology and MRI (P = 0.018), but not between PTV measured from pathology and (18) F-FDG PET/CT at SUV2.5 (P = 0.245), which showed the highest intraclass correlation coefficient value (0.860).

CONCLUSION

(18) F-FDG PET/CT scans provide accurate tumor staging and volume measurements in OSCC patients with CR/MRI dental artifacts, leading to improved preoperative planning.

LEVEL OF EVIDENCE

2b CONDENSED ABSTRACT This study evaluated the clinical value of (18) F-FDG PET/CT in 63 patients with oral cavity cancers. In 37 (59%) patients with dental artifacts on CT/MRI, (18) F-FDG PET/CT showed superior results compared to MRI in tumor staging and represented the highest intraclass correlation coefficient value to tumor volume determined by pathology.

Feasibility and incremental benefit of puffed-cheek 18F-FDG PET/CT on oral cancer patients

PURPOSE

The complexity of small oral cavity and intimate apposition of the oral cavity mucosal surfaces make CT identification of obvious masses difficult. Puffed-cheek CT improves the evaluation of oral cavity lesions. We used the puffed-cheek maneuver with 18F-FDG PET/CT scans to determine the feasibility and accuracy in clinical practice and to identify any benefits.

PATIENTS AND METHODS

Twenty-two patients with oral cancer were included. They were instructed to perform the puffed-cheek maneuver after a conventional 18F-FDG PET/CT scan. Two physicians reviewed the puffed-cheek and conventional 18F-FDG PET/CT images and achieved consensus about the cancer extent, location, and dental artifacts before classifying and grading the oral cancers. Dichotomous results of localized or extended cancer and artifact grading scores from the puffed-cheek and conventional 18F-FDG PET/CT methods were compared using McNemar test and the Wilcoxon signed-rank test. P < 0.05 was considered significant.

RESULTS

The puffed-cheek maneuver with 18F-FDG PET/CT was practical and had incremental benefits. The conventional 18F-FDG PET/CT classified 12 patients correctly as having localized or extended cancer, and the puffed-cheek 18F-FDG PET/CT classified 21 patients correctly. Puffed-cheek 18F-FDG PET/CT found a synchronous skip cancer and provided detailed cancer delineation. This method might reduce the effects of dental artifacts without undesirable muscular FDG uptake.

CONCLUSIONS

Puffed-cheek PET/CT is feasible in the current clinical setting and can improve the delineation of oral cancer extent and location, with a potential benefit of reducing dental artifacts.

Imaging in head and neck squamous cell carcinoma: the potential role of PET/MRI

In head and neck oncology, the information provided by positron emission tomography (PET)/CT and MRI is often complementary because both the methods are based on different biophysical foundations. Therefore, combining diagnostic information from both modalities can provide additional diagnostic gain. Debates about integrated PET/MRI systems have become fashionable during the past few years, since the introduction and wide adoption of software-based multimodality image registration and fusion and the hardware implementation of integrated hybrid PET/MRI systems in pre-clinical and clinical settings. However, combining PET with MRI has proven to be technically and clinically more challenging than initially expected and, as such, research into the potential clinical role of PET/MRI in comparison with PET/CT, diffusion-weighted MRI (DW MRI) or the combination thereof is still ongoing. This review focuses on the clinical applications of PET/MRI in head and neck squamous cell carcinoma (HNSCC). We first discuss current evidence about the use of combined PET/CT and DW MRI, and, then, we explain the rationale and principles of PET/MR image fusion before summarizing the state-of-the-art knowledge regarding the diagnostic performance of PET/MRI in HNSCC. Feasibility and quantification issues, diagnostic pitfalls and challenges in clinical settings as well as ongoing research and potential future applications are also discussed.

Usefulness of Integrated PET/MRI in Head and Neck Cancer: A Preliminary Study

PURPOSE

The new modality of an integrated positron emission tomography/magnetic resonance imaging (PET/MRI) has recently been introduced but not validated. Our objective was to evaluate clinical performance of (18)F-fluoro-2-deoxyglucose ((18)F-FDG) PET/MRI in patients with head and neck cancer.

METHODS

This retrospective study was conducted between January 2013 and February 2013. Ten patients (eight men, two women; mean age, 61.4 ± 13.4 years) with histologically proven head and neck tumors were enrolled. Whole-body PET/MRI and regional positron emission tomography (PET) with dedicated MRI were sequentially obtained. Maximum standardized uptake value (SUVmax), SUVmean, metabolic tumor volume, total lesion glycolysis and contrast enhancement were analyzed. A total of ten whole-body positron emission tomography (PET), ten regional positron emission tomography (PET), ten dedicated MRI and ten regional PET/gadolinium-enhanced T1-weighted (Gd)-MRI images were analyzed for initial staging. Two nuclear medicine physicians analyzed positron emission tomography (PET) and PET/MRI with a consensus. One radiologist analyzed dedicated MRI. The primary lesions and number of metastatic lymph nodes analyzed from each image were compared.

RESULTS

Eight patients were diagnosed with head and neck cancer (one tongue cancer, four tonsillar cancers, one nasopharyngeal cancer and two hypopharyngeal cancers) by histological diagnosis. Two benign tumors (pleomorphic adenoma and Warthin tumor) were diagnosed with surgical operation. Whole-body positron emission tomography (PET) and regional positron emission tomography (PET) attenuated by MRI showed good image quality for the lesion detection. Whole-body positron emission tomography (PET) and regional positron emission tomography (PET) detected ten primary sites and compensated for a missed lesion on dedicated MRI. A discordant number of suspicious lymph node metastases was noted according to the different images; 22, 16, 39 and 40 in the whole-body positron emission tomography (PET) only, dedicated MR, regional positron emission tomography (PET) only and regional PET/Gd-MRI, respectively. There was no distant metastasis based on analysis of whole-body positron emission tomography (PET) and whole-body PET/Dixon-volume interpolated breathhold examination (VIBE) MRI. Regional PET/Gd-MRI combined with whole-body PET/MRI modified staging in three patients. Lesions of primary tumor and suspicious metastasis were well detected on both value of SUVmax and visual analysis. The regional PET/Gd-MRI combined with whole-body PET/MRI showed convenient clinical staging performance compared with positron emission tomography (PET) and MRI alone.

CONCLUSION

In this preliminary study, PET attenuated by MRI showed good image quality to detect lesions. And whole-body PET/MRI as a single modality was feasible for staging in a clinical setting. Whole-body positron emission tomography (PET), regional positron emission tomography (PET), dedicated MRI and regional PET/Gd-MRI showed discordant results in lesion detection. These discordant results might be synergistic effect for accurate staging.

Functional imaging in radiation therapy planning for head and neck cancer

Functional imaging and its application to radiotherapy (RT) is a rapidly expanding field with new modalities and techniques constantly developing and evolving. As technologies improve, it will be important to pay attention to their implementation. This review describes the main achievements in the field of head and neck cancer (HNC) with particular remarks on the unsolved problems.

Interactions between magnetic resonance imaging and dental material

Magnetic resonance imaging (MRI) has become a common and important life-saving diagnostic tool in recent times, for diseases of the head and neck region. Dentists should be aware of the interactions of various restorative dental materials and different technical factors put to use by an MRI scanning machine. Specific knowledge about these impacts, at the dentist level and at the level of the personnel at the MRI centers can save valuable time for the patient and prevent errors in MRI images. Artifacts from metal restorations are a major hindrance at such times, as they result in disappearance or distortion of the image and loss of important information.

Pathology-based validation of FDG PET segmentation tools for volume assessment of lymph node metastases from head and neck cancer

PURPOSE

FDG PET is increasingly incorporated into radiation treatment planning of head and neck cancer. However, there are only limited data on the accuracy of radiotherapy target volume delineation by FDG PET. The purpose of this study was to validate FDG PET segmentation tools for volume assessment of lymph node metastases from head and neck cancer against the pathological method as the standard.

METHODS

Twelve patients with head and neck cancer and 28 metastatic lymph nodes eligible for therapeutic neck dissection underwent preoperative FDG PET/CT. The metastatic lymph nodes were delineated on CT (NodeCT) and ten PET segmentation tools were used to assess FDG PET-based nodal volumes: interpreting FDG PET visually (PETVIS), applying an isocontour at a standardized uptake value (SUV) of 2.5 (PETSUV), two segmentation tools with a fixed threshold of 40% and 50%, and two adaptive threshold based methods. The latter four tools were applied with the primary tumour as reference and also with the lymph node itself as reference. Nodal volumes were compared with the true volume as determined by pathological examination.

RESULTS

Both NodeCT and PETVIS showed good correlations with the pathological volume. PET segmentation tools using the metastatic node as reference all performed well but not better than PETVIS. The tools using the primary tumour as reference correlated poorly with pathology. PETSUV was unsatisfactory in 35% of the patients due to merging of the contours of adjacent nodes.

CONCLUSION

FDG PET accurately estimates metastatic lymph node volume, but beyond the detection of lymph node metastases (staging), it has no added value over CT alone for the delineation of routine radiotherapy target volumes. If FDG PET is used in radiotherapy planning, treatment adaptation or response assessment, we recommend an automated segmentation method for purposes of reproducibility and interinstitutional comparison.

Positron emission tomography (PET) attenuation correction artefacts in PET/CT and PET/MRI

OBJECTIVE

To compare the effect of implanted medical materials on (18)F-fludeoxyglucose ((18)F-FDG) positron emission tomography (PET)/MRI using a Dixon-based segmentation method for MRI-based attenuation correction (MRAC), PET/CT and CT-based attenuation-corrected PET (PETCTAC).

METHODS

12 patients (8 males and 4 females; age 58±11 years) with implanted medical materials prospectively underwent whole-body (18)F-FDG PET/CT and PET/MRI. CT, MRI and MRAC maps as well as PETCTAC and PETMRAC images were reviewed for the presence of artefacts. Their morphology and effect on the estimation of the (18)F-FDG uptake (no effect, underestimation, overestimation compared with non-corrected images) were compared. In PETMRAC images, a volume of interest was drawn in the area of the artefact and in a reference site (contralateral body part); the mean and maximum standardised uptake values (SUVmean; SUVmax) were measured.

RESULTS

Of 27 implanted materials (20 dental fillings, 3 injection ports, 3 hip prostheses and 1 sternal cerclage), 27 (100%) caused artefacts in CT, 19 (70%) in T1 weighted MRI and 17 (63%) in MRAC maps. 20 (74%) caused a visual overestimation of the (18)F-FDG uptake in PETCTAC, 2 (7%) caused an underestimation and 5 (19%) had no effect. In PETMRAC, 19 (70%) caused spherical extinctions and 8 (30%) had no effect. Mean values for SUVmean and SUVmax were significantly decreased in artefact-harbouring sites (p<0.001).

CONCLUSION

Contrary to PET attenuation correction artefacts in PET/CT, which often show an overestimation of the (18)F-FDG uptake, MRAC artefacts owing to implanted medical materials in most cases cause an underestimation.

ADVANCES IN KNOWLEDGE

Being aware of the morphology of artefacts owing to implanted medical materials avoids interpretation errors when reading PET/MRI.

[¹⁸F]fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography imaging in oncology: initial staging and evaluation of cancer therapy

Positron emission tomography (PET) with [¹⁸F]fluoro-2-deoxy-D-glucose (FDG) has proven to be a valuable diagnostic modality in various diseases. Its accuracy has been improved with the hybrid PET/computed tomography (CT) technique because of precise anatomic location of areas of abnormal FDG accumulation. This integrated PET/CT modality has been widely adopted, particularly in oncology. This paper reviews the role of FDG-PET/CT imaging in breast cancer, non-small-cell lung cancer, colorectal cancer, head and neck cancer as well as lymphoma on the basis of recent key articles. Special attention is paid to preoperative diagnostic workup, evaluation of treatment response and survival prognosis. Experience from specialized centers indicates that there is strong evidence for the clinical effectiveness of FDG-PET/CT in staging, restaging and the prediction of response to therapy in the above-mentioned malignancies. It is concluded that this imaging modality contributes considerably to improved patient management and paves the way to personalize cancer treatment in a cost-effective way.

18F-FDG PET/CT metabolic tumor volume and total lesion glycolysis predict outcome in oropharyngeal squamous cell carcinoma

Treatment of oropharyngeal squamous cell carcinoma with chemoradiotherapy can now accomplish excellent locoregional disease control, but patient overall survival (OS) remains limited by development of distant metastases (DM). We investigated the prognostic value of staging (18)F-FDG PET/CT, beyond clinical risk factors, for predicting DM and OS in 176 patients after definitive chemoradiotherapy.

METHODS

The PET parameters maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) were recorded. Univariate Cox regression was used to examine the prognostic value of these variables and clinical prognosticators for local treatment failure (LTF), OS, and DM. Multivariate analysis examined the effect of SUVmax, TLG, and MTV in the presence of other covariates. Kaplan-Meier curves were used to evaluate prognostic values of PET/CT parameters.

RESULTS

Primary tumors were distributed across all stages. Most patients underwent chemoradiotherapy only, and 11 also underwent tonsillectomy. On univariate analysis, primary tumor MTV was predictive of LTF (P = 0.005, hazard ratio [HR] = 2.4 for a doubling of MTV), DM and OS (P < 0.001 for both, HR = 1.9 and 1.8, respectively). The primary tumor TLG was associated with DM and OS (P < 0.001, HR = 1.6 and 1.7, respectively, for a doubling of TLG). The primary tumor SUVmax was associated with death (P = 0.029, HR = 1.1 for a 1-unit increase in standardized uptake value) but had no relationship with LTF or DM. In multivariate analysis, TLG and MTV remained associated with death after correcting for T stage (P = 0.0125 and 0.0324, respectively) whereas no relationship was seen between standardized uptake value and death after adjusting for T stage (P = 0.158).

CONCLUSION

Parameters capturing the volume of (18)F-FDG-positive disease (MTV or TLG) provide important prognostic information in oropharyngeal squamous cell carcinoma treated with chemoradiotherapy and should be considered for risk stratification in this disease.

Improving target definition for head and neck radiotherapy: a place for magnetic resonance imaging and 18-fluoride fluorodeoxyglucose positron emission tomography?

Defining the target for head and neck radiotherapy is a critical issue with the introduction of steep dose gradients associated with intensity-modulated radiotherapy. Tumour delineation inaccuracies are a major source of error in radiotherapy planning. The integration of 18-fluoride fluorodeoxyglucose positron emission tomography ((18)FDG-PET) and magnetic resonance imaging directly into the radiotherapy planning process has the potential to greatly improve target identification/selection and delineation. This raises a range of new issues surrounding image co-registration, delineation methodology and the use of functional data and treatment adaptation. This overview will discuss the practical aspects of integrating (18)FDG-PET and magnetic resonance imaging into head and neck radiotherapy planning.

Artifacts in magnetic resonance imaging and computed tomography caused by dental materials

BACKGROUND

Artifacts caused by dental restorations, such as dental crowns, dental fillings and orthodontic appliances, are a common problem in MRI and CT scans of the head and neck. The aim of this in-vitro study was to identify and evaluate the artifacts produced by different dental restoration materials in CT and MRI images.

METHODS

Test samples of 44 materials (Metal and Non-Metal) commonly used in dental restorations were fabricated and embedded with reference specimens in gelatin moulds. MRI imaging of 1.5T and CT scan were performed on the samples and evaluated in two dimensions. Artifact size and distortions were measured using a digital image analysis software.

RESULTS

In MRI, 13 out of 44 materials produced artifacts, while in CT 41 out of 44 materials showed artifacts. Artifacts produced in both MRI and CT images were categorized according to the size of the artifact.

SIGNIFICANCE

Metal based restoration materials had strong influence on CT and less artifacts in MRI images. Rare earth elements such as Ytterbium trifluoride found in composites caused artifacts in both MRI and CT. Recognizing these findings would help dental materials manufacturers and developers to produce materials which can cause less artifacts in MRI and CT images.

[Revisiting the dose-effect correlations in irradiated head and neck cancer using automatic segmentation tools of the dental structures, mandible and maxilla]

PURPOSE

Manual delineation of dental structures is too time-consuming to be feasible in routine practice. Information on dose risk levels is crucial for dentists following irradiation of the head and neck to avoid postextraction osteoradionecrosis based on empirical dose-effects data established on bidimensional radiation therapy plans.

MATERIAL AND METHODS

We present an automatic atlas-based segmentation framework of the dental structures, called Dentalmaps, constructed from a patient image-segmentation database.

RESULTS

This framework is accurate (within 2 Gy accuracy) and relevant for the routine use. It has the potential to guide dental care in the context of new irradiation techniques.

CONCLUSION

This tool provides a user-friendly interface for dentists and radiation oncologists in the context of irradiated head and neck cancer patients. It will likely improve the knowledge of dose-effect correlations for dental complications and osteoradionecrosis.

A comparative study of fused FDG PET/MRI, PET/CT, MRI, and CT imaging for assessing surrounding tissue invasion of advanced buccal squamous cell carcinoma

PURPOSE

This study aimed to evaluate the diagnostic value of fused fluorodeoxyglucose positron emission tomography and magnetic resonance imaging (PET/MRI) compared with PET/computed tomography (CT), MRI, and CT in assessing surrounding tissue invasion of advanced buccal squamous cell carcinoma (BSCC).

MATERIALS AND METHODS

PET/CT and MRI were performed in 17 consecutive patients with suspected masticator space invasion of BSCC from CT images. Attenuation-corrected PET and head and neck MRI datasets were registered. For pathologic correlation, 4 regions of interest were examined, including the maxilla, mandible, pterygoid, and masseter muscle. The tumor maximal diameter, measured by different imaging modalities, was correlated with pathology results.

RESULTS

All PET/MRI fusions were verified as well matched using specific anatomic criteria. For pathology results, 1 patient had inflammation only, 1 had spindle cell cancer, and 15 had squamous cell cancer. Of 64 regions of interest, 20 (31.3%) harbored tumor invasion. The likelihood ratio was highest in fused PET/MRI (42.56) compared with PET/CT (25.02), MRI (22.94), and CT (8.6; all P < 0.05). The sensitivity and specificity of fused PET/MRI were also highest among the 4 modalities (90.0%/90.9%, 80.0%/84.1%, 80.0%/79.5%, and 55.0%/81.8%, respectively). The level of confidence was higher in fused PET/MRI or MRI than in PET/CT or CT (85.9%, 85.9%, 70.3%, 73.4%, respectively). The maximal lesion size was 3.0 to 6.0 cm in the pathology specimen. Regression analysis showed better agreement between fused PET/MRI and pathology results.

CONCLUSIONS

Fused PET/MRI is more reliable for focal invasion assessment and tumor size delineation in advanced BSCC compared with PET/CT, MRI, and CT. PET/CT has the lowest confidence level, which may limit its use in the clinical setting.

Evaluation of a metal artifact reduction technique in tonsillar cancer delineation

PURPOSE

Metal artifacts can degrade computed tomographic (CT) simulation imaging and impair accurate delineation of tumors for radiation treatment planning purposes. We investigated a Digital Imaging and Communications in Medicine-based metal artifact reduction technique in tonsillar cancer delineation.

METHODS AND MATERIALS

Eight patients with significant artifact and tonsil cancer were evaluated. Each patient had a positron emission tomography (PET)-CT and a contrast-enhanced CT obtained at the same setting during radiotherapy simulation. The CTs were corrected for artifact using the metal deletion technique (MDT). Two radiation oncologists independently delineated primary gross tumor volumes (GTVs) for each patient on native (CTnonMDT), metal corrected (CTMDT), and reference standard (CTPET/nonMDT) imaging, 1 week apart. Mixed effects models were used to determine if differences among GTVs were statistically significant. Two diagnostic radiologists and 2 radiation oncologists independently qualitatively evaluated CTs for each patient. Ratings were on an ordinal scale from -3 to +3, denoting that CTMDT was markedly, moderately, or slightly worse or better than CTnonMDT. Scores were compared with a Wilcoxon signed-rank test.

RESULTS

The GTVPET/nonMDT were significantly smaller than GTVnonMDT (P = .004) and trended to be smaller than GTVMDT (P = .084). The GTVnonMDT and GTVMDT were not significantly different (P = .93). There was no significant difference in the extent to which GTVnonMDT or GTVMDT encompassed GTVPET/nonMDT (P = .33). In the subjective assessment of image quality, CTMDT did not significantly outperform CTnonMDT. In the majority of cases, the observer rated the CTMDT equivalent to (53%) or slightly superior (41%) to the corresponding CTnonMDT.

CONCLUSIONS

The MTD modified images did not produce GTVMDT that more closely reproduced GTVPET/nonMDT than did GTVnonMDT. Moreover, the MTD modified images were not judged to be significantly superior when compared to the uncorrected images in terms of subjective ability to visualize the tonsilar tumors. This study failed to demonstrate value of the adjunctive use of a CT corrected for artifacts in the tumor delineation process. Artifacts do make tumor delineation challenging, and further investigation of other body sites is warranted.

Dentalmaps: automatic dental delineation for radiotherapy planning in head-and-neck cancer

PURPOSE

To propose an automatic atlas-based segmentation framework of the dental structures, called Dentalmaps, and to assess its accuracy and relevance to guide dental care in the context of intensity-modulated radiotherapy.

METHODS AND MATERIALS

A multi-atlas-based segmentation, less sensitive to artifacts than previously published head-and-neck segmentation methods, was used. The manual segmentations of a 21-patient database were first deformed onto the query using nonlinear registrations with the training images and then fused to estimate the consensus segmentation of the query.

RESULTS

The framework was evaluated with a leave-one-out protocol. The maximum doses estimated using manual contours were considered as ground truth and compared with the maximum doses estimated using automatic contours. The dose estimation error was within 2-Gy accuracy in 75% of cases (with a median of 0.9 Gy), whereas it was within 2-Gy accuracy in 30% of cases only with the visual estimation method without any contour, which is the routine practice procedure.

CONCLUSIONS

Dose estimates using this framework were more accurate than visual estimates without dental contour. Dentalmaps represents a useful documentation and communication tool between radiation oncologists and dentists in routine practice. Prospective multicenter assessment is underway on patients extrinsic to the database.

Fluorine-18-labeled boronophenylalanine positron emission tomography for oral cancers: Qualitative and quantitative analyses of malignant tumors and normal structures in oral and maxillofacial regions

The present study aimed to demonstrate the features of fluorine-18-labeled boronophenylalanine positron emission tomography ((18)F-BPA-PET) to reveal oral cancer, as well as normal structures in the oral and maxillofacial regions. We analyzed (18)F-BPA-PET findings from 8 patients with histologically confirmed recurrent and/or advanced oral cancer scheduled for boron neutron capture therapy. The capacity of (18)F-BPA-PET to delineate tumor and normal structures was assessed qualitatively and quantitatively. Tumors were easily identified as high uptake areas in all cases. Although the eyes, which were depicted as a low uptake area, and tongue musculature were readily identified, major vessels were not noted in any of the cases. Areas corresponding to the surface of the dorsum tongue to middle pharynx were expressed as high uptake areas in all of the cases. Quantitatively, tumors were expressed as the highest uptake area in 6 of the 8 cases, while the dorsum tongue had the highest uptake area in the remaining 2 cases. (18)F-BPA-PET is useful in demonstrating the presence of a tumor. Thus, it is crucial to note the presence of a high uptake area corresponding to the dorsum area of the tongue when diagnosing a tumor using this technique.

18F-FDG PET/CT-based gross tumor volume definition for radiotherapy in head and neck cancer: a correlation study between suitable uptake value threshold and tumor parameters

Background

To define a suitable threshold setting for gross tumor volume (GTV) when using ¹⁸Fluoro-deoxyglucose positron emission tomography and computed tomogram (PET/CT) for radiotherapy planning in head and neck cancer (HNC).

Methods

Fifteen HNC patients prospectively received PET/CT simulation for their radiation treatment planning. Biological target volume (BTV) was derived from PET/CT-based GTV of the primary tumor. The BTVs were defined as the isodensity volumes when adjusting different percentage of the maximal standardized uptake value (SUVmax), excluding any artifact from surrounding normal tissues. CT-based primary GTV (C-pGTV) that had been previously defined by radiation oncologists was compared with the BTV. Suitable threshold level (sTL) could be determined when BTV value and its morphology using a certain threshold level was observed to be the best fitness of the C-pGTV. Suitable standardized uptake value (sSUV) was calculated as the sTL multiplied by the SUVmax.

Results

Our result demonstrated no single sTL or sSUV method could achieve an optimized volumetric match with the C-pGTV. The sTL was 13% to 27% (mean, 19%), whereas the sSUV was 1.64 to 3.98 (mean, 2.46). The sTL was inversely correlated with the SUVmax [sTL = -0.1004 Ln (SUVmax) + 0.4464; R² = 0.81]. The sSUV showed a linear correlation with the SUVmax (sSUV = 0.0842 SUVmax + 1.248; R² = 0.89). The sTL was not associated with the value of C-pGTVs.

Conclusion

In PET/CT-based BTV for HNC, a suitable threshold or SUV level can be established by correlating with SUVmax rather than using a fixed threshold.

An exploratory pilot study into the association between microcirculatory parameters derived by MRI-based pharmacokinetic analysis and glucose utilization estimated by PET-CT imaging in head and neck cancer

OBJECTIVES

To examine the feasibility of deriving quantitative microcirculatory parameters and to investigate the relationship between vascular and metabolic characteristics of head and neck tumours in vivo, using dynamic contrast-enhanced (DCE) MRI and fluorodeoxyglucose (FDG) PET imaging.

METHODS

Twenty-seven patients with primary squamous cell carcinoma (SCCA) underwent DCE-MRI and combined PET/CT imaging. DCE-MRI data were post-processed by using commercially available software. Transfer constant (K (trans)), extravascular extracellular blood volume (v (e)), transfer constant from the extracellular extravascular space to plasma (k (ep)) and iAUC (initial area under the signal intensity-time curve) were calculated. 3D static PET data were acquired and standardised uptake values (SUV) calculated.

RESULTS

All microcirculatory parameters in tumours were higher than in normal muscle tissue (P ≤ 0.0019). Significant correlations were shown between k (ep) and K (trans) (ρ = 0.77), v (e) and k (ep) (ρ = -0.7), and iAUC and v (e) (ρ = 0.53). Significant correlations were observed for SUV(mean) and v (e) as well as iAUC (ρ = 0.42 and ρ = 0.66, respectively). SUV(max) was significantly correlated with iAUC (ρ = 0.69).

CONCLUSIONS

The demonstrated relationships between vascular and metabolic characteristics of primary SCCA imply a complex interaction between vascular delivery characteristics and tumour metabolism. The lack of correlation between SUV and K (trans)/k (ep) suggests that both diagnostic techniques may provide complementary information.

18F-Fluorodeoxyglucose-PET/CT to evaluate tumor, nodal disease, and gross tumor volume of oropharyngeal and oral cavity cancer: comparison with MR imaging and validation with surgical specimen

INTRODUCTION

The purpose of this paper is to evaluate the impact of adding combined 18F-PET/CT to MRI for T and N staging of the oral and oropharyngeal cancer and calculation of the gross tumor volume (GTV) having histopathology as reference standard.

METHODS

PET/CT and MRI were performed in 66 patients with suspected oral and oropharyngeal cancer (41 primary tumors/25 recurrent tumors) and nodal disease (114 nodes). Statistical analysis included the McNemar test, sensitivity, specificity for the diagnostic modalities as well as regression analysis, and Bland-Altman graphs for calculated tumor volumes.

RESULTS

There was no statistically significant difference between the two modalities compared to pathological findings regarding detection of disease (P > or =0.72). The sensitivity/specificity for tumor detection were 100/80% and 96.72/60% for MRI and PET/CT, respectively. The sensitivity/specificity for nodal metastases were 88.46/75% and 83.81/73.91% for MRI and PET/CT, respectively. In 18% of cases, the MRI-based T staging resulted in an overestimation of the pathologic tumor stage. The corresponding rate for PET/CT was 22%. Regarding the treated necks, both modalities showed 100% sensitivity for detection of the recurrent lesions. In necks with histologically N0 staging, MRI and PET/CT gave 22% and 26% false positive findings, respectively. The mean tumor volume in the pathologic specimen was 16.6 +/- 18.6 ml, the mean volume derived by the MR imaging was 17.6 +/- 19.1 ml while the estimated by PET/CT volume was 18.8 +/- 18.1 ml (P < or =0.007 between the three methods). The Bland-Altman analysis showed a better agreement between PET/CT and MRI.

CONCLUSION

The diagnostic performance of FDG-PET/CT in the local staging of oral cancer is not superior to MRI.

Clinical Applications of FDG PET and PET/CT in Head and Neck Cancer

18F-FDG PET plays an increasing role in diagnosis and management planning of head and neck cancer. Hybrid PET/CT has promoted the field of molecular imaging in head and neck cancer. This modality is particular relevant in the head and neck region, given the complex anatomy and variable physiologic FDG uptake patterns. The vast majority of 18F-FDG PET and PET/CT applications in head and neck cancer related to head and neck squamous cell carcinoma. Clinical applications of 18F-FDG PET and PET/CT in head and neck cancer include diagnosis of distant metastases, identification of synchronous 2nd primaries, detection of carcinoma of unknown primary and detection of residual or recurrent disease. Emerging applications are precise delineation of the tumor volume for radiation treatment planning, monitoring treatment, and providing prognostic information. The clinical role of 18F-FDG PET/CT in N0 disease is limited which is in line with findings of other imaging modalities. MRI is usually used for T staging with an intense discussion concerning the preferable imaging modality for regional lymph node staging as PET/CT, MRI, and multi-slice spiral CT are all improving rapidly. Is this review, we summarize recent literature on 18F-FDG PET and PET/CT imaging of head and neck cancer.