Innovations in radiotherapy planning of head and neck cancers: role of PET

Interobserver Variability in a Spanish Society of Radiation Oncology (SEOR) Head and Neck Course. Is Current Contouring Training Sufficient?

Purpose

External beam radiation therapy has grown significantly, incorporating advanced techniques like intensity modulation or stereotactic treatments, which enhance precision and accuracy. Nevertheless, variability in target volume delineation by radiation oncologists remains a challenge, influencing dose distribution. This study analyzes an online training course by the Spanish Society of Radiation Oncology, focusing on head and neck tumor contouring, to evaluate interobserver variability.

Material and Methods

Eight instructors provided clinical directives for 8 head and neck pathologies. Participants contoured structures using their own treatment planning systems, emphasizing gross tumor volume and high-, medium-, and low-risk clinical target volumes (CTV) contouring. Delineation variability was evaluated using the Dice similarity coefficient and volume relative change.

Results

The results reveal significant variability in contouring, with mean Dice similarity coefficient values ranging from 0.57 to 0.69. High-risk CTV demonstrated higher variability compared with medium-risk CTV. The presence of a gross tumor volume and supporting positron emission tomography/computed tomography or magnetic resonance imaging studies did not significantly improve the concordance. Parotid cases exhibited the greatest differences.

Conclusions

Despite the introduction of new automatic tools, this study points to the need for uniform contouring criteria. Training and standardization efforts are essential to enhance radiation therapy treatment consistency and quality.

Current and Emerging Molecular Therapies for Head and Neck Squamous Cell Carcinoma

Head and neck cancer affects nearly 750,000 patients, with more than 300,000 deaths annually. Advances in first line surgical treatment have improved survival rates marginally particularly in developed countries, however survival rates for aggressive locally advanced head and neck cancer are still poor. Recurrent and metastatic disease remains a significant problem for patients and the health system. As our knowledge of the genomic landscape of the head and neck cancers continues to expand, there are promising developments occurring in molecular therapies available for advanced or recalcitrant disease. The concept of precision medicine is underpinned by our ability to accurately sequence tumour samples to best understand individual patient genomic variations and to tailor targeted therapy for them based on such molecular profiling. Not only is their purported response to therapy a factor of their genomic variation, but so is their inclusion in biomarker-driven personalised medicine therapeutic trials. With the ever-expanding number of molecular druggable targets explored through advances in next generation sequencing, the number of clinical trials assessing these targets has significantly increased over recent years. Although some trials are focussed on first-line therapeutic approaches, a greater majority are focussed on locally advanced, recurrent or metastatic disease. Similarly, although single agent monotherapy has been found effective in some cases, it is the combination of drugs targeting different signalling pathways that seem to be more beneficial to patients. This paper outlines current and emerging molecular therapies for head and neck cancer, and updates readers on outcomes of the most pertinent clinical trials in this area while also summarising ongoing efforts to bring more molecular therapies into clinical practice.

Volumetric parameters derived from FLT-PET performed at completion of treatment predict efficacy of Carbon-ion Radiotherapy in patients with locally recurrent Nasopharyngeal Carcinoma

The purpose of this study was to investigate the role of 3'-deoxy-3'-[¹⁸F]fluorothymidine (FLT)-PET for predicting the outcome of patients with locally recurrent nasopharyngeal carcinoma (LR-NPC) treated by carbon-ion radiotherapy (CIRT). Patients received FLT-PET/CT scan one-week prior to or after completion of CIRT were enrolled in the study. All patients were from prospective trials or treated using a standardized protocol. Time-dependent receiver operator characteristics (ROC) were used to determine the optimal cutoff values for FLT-PET parameters. Univariable and multivariable analyses of local progression-free survival (LPFS) were performed using Cox regression, to examine the prognostic value of FLT-PET parameters, including SUV_max, metabolic tumor volume (MTV) and total lesion thymidine (TLT). A total of 41 patients were enrolled. Elevated MTV and TLT were significantly associated with worse LPFS, in both univariable and multivariable analyses. ROC analysis revealed that both an MTV value higher than 8.6 and a TLT value higher than 14.9 were predictive of increased risk of developing local recurrence, the adjusted HRs were 5.59 (p=0.009) and 7.76 (p=0.002), respectively. In conclusion, FLT-PET was found to be a promising prognostic tool for LR-NPC patients and might play a role in the treatment guidance.

Predictive value of quantitative 18F-FDG-PET radiomics analysis in patients with head and neck squamous cell carcinoma

BACKGROUND

Radiomics is aimed at image-based tumor phenotyping, enabling application within clinical-decision-support-systems to improve diagnostic accuracy and allow for personalized treatment. The purpose was to identify predictive 18-fluor-fluoro-2-deoxyglucose (¹⁸F-FDG) positron-emission tomography (PET) radiomic features to predict recurrence, distant metastasis, and overall survival in patients with head and neck squamous cell carcinoma treated with chemoradiotherapy.

METHODS

Between 2012 and 2018, 103 retrospectively (training cohort) and 71 consecutively included patients (validation cohort) underwent ¹⁸F-FDG-PET/CT imaging. The 434 extracted radiomic features were subjected, after redundancy filtering, to a projection resulting in outcome-independent meta-features (factors). Correlations between clinical, first-order ¹⁸F-FDG-PET parameters (e.g., SUVmean), and factors were assessed. Factors were combined with ¹⁸F-FDG-PET and clinical parameters in a multivariable survival regression and validated. A clinically applicable risk-stratification was constructed for patients' outcome.

RESULTS

Based on 124 retained radiomic features from 103 patients, 8 factors were constructed. Recurrence prediction was significantly most accurate by combining HPV-status, SUVmean, SUVpeak, factor 3 (histogram gradient and long-run-low-grey-level-emphasis), factor 4 (volume-difference, coarseness, and grey-level-non-uniformity), and factor 6 (histogram variation coefficient) (CI = 0.645). Distant metastasis prediction was most accurate assessing metabolic-active tumor volume (MATV)(CI = 0.627). Overall survival prediction was most accurate using HPV-status, SUVmean, SUVmax, factor 1 (least-axis-length, non-uniformity, high-dependence-of-high grey-levels), and factor 5 (aspherity, major-axis-length, inversed-compactness and, inversed-flatness) (CI = 0.764).

CONCLUSIONS

Combining HPV-status, first-order ¹⁸F-FDG-PET parameters, and complementary radiomic factors was most accurate for time-to-event prediction. Predictive phenotype-specific tumor characteristics and interactions might be captured and retained using radiomic factors, which allows for personalized risk stratification and optimizing personalized cancer care.

TRIAL REGISTRATION

Trial NL3946 (NTR4111), local ethics commission reference: Prediction 2013.191 and 2016.498. Registered 7 August 2013, https://www.trialregister.nl/trial/3946.

Patient-Centric Head and Neck Cancer Radiation Therapy: Role of Advanced Imaging

The traditional 'one-size-fits-all' approach to H&N cancer therapy is archaic. Advanced imaging can identify radioresistant areas by using biomarkers that detect tumor hypoxia, hypercellularity etc. Highly conformal radiotherapy can target resistant areas with precision. The critical information that can be gleaned about tumor biology from these advanced imaging modalities facilitates individualized radiotherapy. The tumor imaging world is pushing its boundaries. Molecular imaging can now detect protein expression and genotypic variations across tumors that can be exploited for tailoring treatment. The exploding field of radiomics and radiogenomics extracts quantitative, biologic and genetic information and further expands the scope of personalized therapy.

Imaging in oral cancers: A comprehensive review

This review aims at simplifying the relevant imaging anatomy, guiding the optimal imaging method and highlighting the key imaging findings that influence prognosis and management of oral cavity squamous cell carcinoma (OSCC). Early OSCC can be treated with either surgery alone while advanced cancers are treated with a combination of surgery, radiotherapy and/or chemotherapy. Considering the complex anatomy of the oral cavity and its surrounding structures, imaging plays an indispensable role not only in locoregional staging but also in the distant metastatic work-up and post treatment follow-up. Knowledge of the anatomy with understanding of common routes of spread of cancer, allows the radiologist to accurately determine disease extent and augment clinical findings to plan appropriate therapy. This review aims at simplifying the relevant imaging anatomy, guiding the optimal imaging method and highlighting the key imaging findings that influence prognosis and management.

Use of baseline 18F-FDG PET scan to identify initial sub-volumes with local failure after concomitant radio-chemotherapy in head and neck cancer

Introduction

Head and neck squamous cell carcinoma (HNSCC) treated by radio-chemotherapy have a significant local recurrence rate. It has been previously suggested that 18F-FDG PET could identify the high uptake areas that can be potential targets for dose boosting. The purpose of this study was to compare the location of initial hypermetabolic regions on baseline scans with the metabolic relapse sites after radio-chemotherapy in HNSCC.

Results

The initial functional tumor volume was significantly higher for patients with proven local recurrence or residual disease (23.5 cc vs. 8.9 cc; p = 0.0005). The overlap between baseline and follow-up sub-volumes were moderate with an overlap fraction ranging from 0.52 to 0.39 between R40 and I30 to I60.

Conclusion

In our study the overlap between baseline and post-therapeutic metabolic tumor sub-volumes was only moderate. These results need to be investigated in a larger cohort acquired with a more standardized patient repositioning protocol for sequential PET imaging.

Methods

Pre and post treatment PET/CT scans of ninety four HNSCC patients treated with radio-chemotherapy were retrospectively reviewed. Follow-up 18F-FDG PET/CT images were registered to baseline scans using a rigid body transformation. Seven metabolic tumor sub-volumes were obtained on the baseline scans using a fixed percentage of SUV_max (I30, I40, I50, I60, I70, I80, and I90) and were subsequently compared with two post-treatment sub-volumes (R40, R90) in 38 cases of local recurrence or residual metabolic disease. Overlap fraction, Dice and Jaccard indices, common volume/baseline volume and common volume/recurrent volume were used to determine the overlap of the different estimated sub-volumes.

Role of Fluorodeoxyglucose-Positron Emission Tomography/Computed Tomography in the Evaluation of Head and Neck Carcinoma

Fluorodeoxyglucose (FDG)-positron emission tomography-computed tomography (PET-CT) has been playing a pivotal role in tumor imaging for the past 20 years. Head and neck (HN) cancers are a good example that can illustrate such unique role of FDG imaging contributing to the patient's management. In this review article, we will describe the normal physiological distribution of FDG within HN structures focusing on its limitations and pitfalls. In addition, we will be also describing its role in the initial staging and restaging of the disease, particularly with regard to therapy response assessment. Furthermore, its role in the evaluation of patients with malignant cervical adenopathy from an unknown primary will be described. In 2016, the Royal College of Radiologists in its third edition published evidence-based guidelines for PET-CT use in HN cancer emphasizing its rule in all these clinical scenarios that are being described in this review. Finally, we will be highlighting future directions in the field of molecular imaging of HN tumors with a special emphasis on the new PET tracers.

The role of PET/CT in the management of patients affected by head and neck tumors: a review of the literature

The management of head and neck tumor (HNSCC) has been changing over the years, especially due to the aid of imaging techniques that help physicians to attain a correct diagnosis. These techniques represent a valuable tool to help tailor treatment and during follow-up of patients affected by malignancies. The aim of this review is to summarize the results of the most recent and relevant studies about the use of PET imaging in HNSCCs. This review is divided into six chapters: (1) The role of PET/CT in the pre-treatment phase; (2) PET/CT and radiotherapy planning; (3) PET/CT in the post-treatment setting; (4) PET/CT and SUVmax for prediction of prognosis; (5) miscellanea on the utility of PET in specific HNSCCs; (6) non-FDG PET tracers used in HNSCC. Promising results have been obtained so far. Despite the encouraging outcomes, more investigations are needed to warrant the value of this technique, especially in the pre-treatment setting.

Multimodality imaging with CT, MR and FDG-PET for radiotherapy target volume delineation in oropharyngeal squamous cell carcinoma

Background

This study aimed to quantify the variation in oropharyngeal squamous cell carcinoma gross tumour volume (GTV) delineation between CT, MR and FDG PET-CT imaging.

Methods

A prospective, single centre, pilot study was undertaken where 11 patients with locally advanced oropharyngeal cancers (2 tonsil, 9 base of tongue primaries) underwent pre-treatment, contrast enhanced, FDG PET-CT and MR imaging, all performed in a radiotherapy treatment mask. CT, MR and CT-MR GTVs were contoured by 5 clinicians (2 radiologists and 3 radiation oncologists). A semi-automated segmentation algorithm was used to contour PET GTVs. Volume and positional analyses were undertaken, accounting for inter-observer variation, using linear mixed effects models and contour comparison metrics respectively.

Results

Significant differences in mean GTV volume were found between CT (11.9 cm³) and CT-MR (14.1 cm³), p < 0.006, CT-MR and PET (9.5 cm³), p < 0.0009, and MR (12.7 cm³) and PET, p < 0.016. Substantial differences in GTV position were found between all modalities with the exception of CT-MR and MR GTVs. A mean of 64 %, 74 % and 77 % of the PET GTVs were included within the CT, MR and CT-MR GTVs respectively. A mean of 57 % of the MR GTVs were included within the CT GTV; conversely a mean of 63 % of the CT GTVs were included within the MR GTV. CT inter-observer variability was found to be significantly higher in terms of position and/or volume than both MR and CT-MR (p < 0.05). Significant differences in GTV volume were found between GTV volumes delineated by radiologists (9.7 cm³) and oncologists (14.6 cm³) for all modalities (p = 0.001).

Conclusions

The use of different imaging modalities produced significantly different GTVs, with no single imaging technique encompassing all potential GTV regions. The use of MR reduced inter-observer variability. These data suggest delineation based on multimodality imaging has the potential to improve accuracy of GTV definition.

Trial registration

ISRCTN Registry: ISRCTN34165059. Registered 2nd February 2015.

The effect of SUV discretization in quantitative FDG-PET Radiomics: the need for standardized methodology in tumor texture analysis

FDG-PET-derived textural features describing intra-tumor heterogeneity are increasingly investigated as imaging biomarkers. As part of the process of quantifying heterogeneity, image intensities (SUVs) are typically resampled into a reduced number of discrete bins. We focused on the implications of the manner in which this discretization is implemented. Two methods were evaluated: (1) R_D, dividing the SUV range into D equally spaced bins, where the intensity resolution (i.e. bin size) varies per image; and (2) R_B, maintaining a constant intensity resolution B. Clinical feasibility was assessed on 35 lung cancer patients, imaged before and in the second week of radiotherapy. Forty-four textural features were determined for different D and B for both imaging time points. Feature values depended on the intensity resolution and out of both assessed methods, R_B was shown to allow for a meaningful inter- and intra-patient comparison of feature values. Overall, patients ranked differently according to feature values–which was used as a surrogate for textural feature interpretation–between both discretization methods. Our study shows that the manner of SUV discretization has a crucial effect on the resulting textural features and the interpretation thereof, emphasizing the importance of standardized methodology in tumor texture analysis.

Imaging of tumour hypoxia and metabolism in patients with head and neck squamous cell carcinoma

BACKGROUND

Tumour hypoxia and a high tumour metabolism increase radioresistance in patients with head and neck squamous cell carcinoma (HNSCC). The aim of this study was to evaluate the correlation between hypoxia ([(18)F]HX4 PET) and glucose metabolism ([(18)F]FDG PET) molecular imaging.

MATERIAL AND METHODS

[(18)F]HX4 and [(18)F]FDG PET/CT images of 20 HNSCC patients were acquired prior to (chemo)radiotherapy, in an immobilisation mask, with a median time interval of seven days (NCT01347281). Gross tumour volumes of the primary lesions (GTVprim) and pathological lymph nodes (GTVln) were included in the analysis. [(18)F]FDG PET/CT images were rigidly registered to the [(18)F]HX4 PET/CT images. The maximum and mean standardised uptake values (SUVmax, SUVmean) within both GTVs were determined. In addition, the overlap was compared between the [(18)F]HX4 high volume ([(18)F]HX4 HV) with a tumour-to-muscle ratio > 1.4 and the [(18)F]FDG high volume ([(18)F]FDG HV) with an SUV > 50% of the SUVmax. We report the mean ± standard deviation.

RESULTS

PET/CT scans including 20 GTVprim and 12 GTVln were analysed. There was a significant correlation between several [(18)F]FDG and [(18)F]HX4 parameters, the most pronounced being the correlation between [(18)F]FDG HV and [(18)F]HX4 HV (R = 0.93, p < 0.001). The fraction of the GTVprim with a high HX4 uptake (9 ± 10%) was on average smaller than the FDG high fraction (51 ± 26%; p < 0.001). In 65% (13/20) of the patients, the GTVprim was hypoxic. In four of these patients the [(18)F]HX4 HV was located within the [(18)F]FDG HV, whereas for the remaining nine GTVprim a partial mismatch was observed. In these nine tumours 25 ± 21% (range 5-64%) of the HX4 HV was located outside the FDG HV.

CONCLUSIONS

There is a correlation between [(18)F]HX4 and [(18)F]FDG uptake parameters on a global tumour level. In the majority of lesions a partial mismatch between the [(18)F]HX4 and [(18)F]FDG high uptake volumes was observed, therefore [(18)F]FDG PET imaging cannot be used as a surrogate for hypoxia. [(18)F]HX4 PET provides complementary information to [(18)F]FDG PET imaging.

(18)F-FDG uptake on PET correlates with biological potential in early oral squamous cell carcinoma

CONCLUSION

The maximum standardized uptake value (SUVmax) of early oral squamous cell carcinoma (OSCC) may have a role as an imaging biomarker for assessment of malignant potential, including cell metabolism and angiogenesis.

OBJECTIVE

The usefulness of (18)F-fluorodeoxyglucose positron emission tomography (FDG-PET) has been proven in various cancers, including OSCC. Moreover, in several carcinomas, the SUVmax of the tumor has been shown to correlate with the histological type, tumor stage, differentiation, and prognosis. Here, we investigated whether the SUVmax of early OSCC was associated with the biological features.

METHODS

Twenty-seven patients with newly diagnosed early OSCC who underwent preoperative FDG-PET and curative surgical resection were included in this study. Tumor sections were stained by immunohistochemistry for glucose transporter 1 (GLUT1), L-type amino acid transporter 1 (LAT1), CD98, microvessels (CD34), cell proliferation marker (Ki-67), and cell cycle regulator (p53). The correlation between SUVmax and clinicopathological findings or the expression level of these molecules was analyzed.

RESULTS

SUVmax of primary OSCC was significantly higher in patients with T2 stage. Moreover, patients whose tumors showed vascular invasion had a tendency to show higher SUVmax. A significant correlation was observed between SUVmax and the expression of LAT1 or microvessel density.

Reproducibility of (18)F-FDG PET uptake measurements in head and neck squamous cell carcinoma on both PET/CT and PET/MR

OBJECTIVE

To investigate reproducibility of fluorine-18 fludeoxyglucose ((18)F-FDG) uptake on (18)F-FDG positron emission tomography (PET)/CT and (18)F-FDG PET/MR scans in patients with head and neck squamous cell carcinoma (HNSCC).

METHODS

30 patients with HNSCC were included in this prospective study. The patients were scanned twice before radiotherapy treatment with both PET/CT and PET/MR. Patients were scanned on the same scanners, 3 days apart and according to the same protocol. Metabolic tumour activity was measured by the maximum and peak standardized uptake value (SUVmax and SUVpeak, respectively), and total lesion glycolysis from the metabolic tumour volume defined from ≥50% SUVmax. Bland-Altman analysis with limits of agreement, coefficient of variation (CV) from the two modalities were performed in order to test the reproducibility. Furthermore, CVs from SUVmax and SUVpeak were compared. The area under the curve from cumulative SUV-volume histograms were measured and tested for reproducibility of the distribution of (18)F-FDG uptake.

RESULTS

24 patients had two pre-treatment PET/CT scans and 21 patients had two pre-treatment PET/MR scans available for further analyses. Mean difference for SUVmax, peak and mean was approximately 4% for PET/CT and 3% for PET/MR, with 95% limits of agreement less than ±20%. CV was small (5-7%) for both modalities. There was no significant difference in CVs between PET/CT and PET/MR (p = 0.31). SUVmax was not more reproducible than SUVpeak (p = 0.09).

CONCLUSION

(18)F-FDG uptake in PET/CT and PET/MR is highly reproducible and we found no difference in reproducibility between PET/CT and PET/MR.

ADVANCES IN KNOWLEDGE

This is the first report to test reproducibility of PET/CT and PET/MR.

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.

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.

18F-FLT PET during radiotherapy or chemoradiotherapy in head and neck squamous cell carcinoma is an early predictor of outcome

This prospective study used sequential PET with the proliferation tracer 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) to monitor the early response to treatment of head and neck cancer and evaluated the association between PET parameters and clinical outcome.

METHODS

Forty-eight patients with head and neck cancer underwent (18)F-FLT PET/CT before and during the second and fourth weeks of radiotherapy or chemoradiotherapy. Mean maximum standardized uptake values for the hottest voxel in the tumor and its 8 surrounding voxels in 1 transversal slice (SUVmax(9)) of the PET scans were calculated, as well as PET-segmented gross tumor volumes using visual delineation (GTVVIS) and operator-independent methods based on signal-to-background ratio (GTVSBR) and 50% isocontour of the maximum signal intensity (GTV50%). PET parameters were evaluated for correlations with outcome.

RESULTS

(18)F-FLT uptake decreased significantly between consecutive scans. An SUVmax(9) decline ≥ 45% and a GTVVIS decrease ≥ median during the first 2 treatment weeks were associated with better 3-y disease-free survival (88% vs. 63%, P = 0.035, and 91% vs. 65%, P = 0.037, respectively). A GTVVIS decrease ≥ median in the fourth treatment week was also associated with better 3-y locoregional control (100% vs. 68%, P = 0.021). These correlations were most prominent in the subset of patients treated with chemoradiotherapy. Because of low (18)F-FLT uptake levels during treatment, GTVSBR and GTV50% were unsuccessful in segmenting primary tumor volume.

CONCLUSION

In head and neck cancer, a change in (18)F-FLT uptake early during radiotherapy or chemoradiotherapy is a strong indicator for long-term outcome. (18)F-FLT PET may thus aid in personalized patient management by steering treatment modifications during an early phase of therapy.

Current oncologic concepts and emerging techniques for imaging of head and neck squamous cell cancer

The incidence of head and neck squamous cell carcinoma (HNSCC) is increasing and currently they account for 5% of all malignancies worldwide. Inspite of ongoing developments in diagnostic imaging and new therapeutic options, HNSCC still represents a multidisciplinary challenge.One of the most important prognostic factors in HNSCC is the presence of lymph node metastases. Patients with confirmed nodal involvement have a considerable reduction of their 5-year overall survival rate. In the era of individually optimised surgery, chemotherapy and intensity modulated radiotherapy, the main role of pre- and posttherapeutic imaging remains cancer detection at an early stage and accurate follow-up. The combined effort of early diagnosis and close patient monitoring after surgery and/or radio-chemotherapy influences disease progression and outcome predicition in patients with HNSCC.This review article focuses on currrent oncologic concepts and emerging tools in imaging of head and neck squamous cell cancer. Besides the diagnostic spectrum of the individual imaging modalities, their limitations are also discussed. One main part of this article is dedicated to PET-CT which combines functional and morphological imaging. Furthermore latest developments in MRI are presented with regard to lymph node staging and response prediction. Last but not least, a clinical contribution in this review explains, which information the head and neck surgeon requires from the multimodality imaging and its impact on operation planning.

Clinical imaging of tumor angiogenesis

Angiogenesis is an integral part of tumor growth and invasion. This has led to the emergence of several antiangiogenic therapies and stimulated efforts to accurately evaluate the extent of angiogenesis before and in response to anticancer treatment. The most commonly used approach has been the assessment of new vessel formation in histological samples. However, it is becoming apparent that this is insufficient for a full understanding of tumor physiology and for in vivo guidance of cancer management. Imaging has the potential to provide noninvasive and repeatable assessment of the angiogenic process. Imaging approaches use a variety of modalities and are aimed at either assessment of the functional integrity of tumor vasculature or assessment of its molecular status. This review summarizes the aims and methods of clinical tumor angiogenesis imaging, including present technologies and ones that will be developed within the next 5-10 years.

Tumor volume delineation in head and neck cancer with 18-fluor-fluorodeoxiglucose positron emission tomography: adaptive thresholding method applied to primary tumors and metastatic lymph nodes

PURPOSE

There are several potential advantages of using 18-fluor-fluorodeoxiglucose (18F-FDG) PET for target volume contouring, but before PET-based gross tumor volumes (GTVs) can reliably and reproducibly be incorporated into high-precision radiotherapy planning, operator-independent segmentation tools have to be developed and validated. The purpose of the present work was to apply the adaptive to the signal/background ratio (R(S/B)) thresholding method for head and neck tumor delineation, and compare these GTV(PET) to reference GTV(CT) volumes in order to assess discrepancies.

MATERIALS AND METHODS

A cohort of 19 patients (39 lesions) with a histological diagnosis of head and neck cancer who would undergo definitive concurrent radiochemotherapy or radical radiotherapy with intensity-modulated radiotherapy technique (IMRT), were enrolled in this prospective study. Contouring on PET images was accomplished through standardized uptake value (SUV)-threshold definition. The threshold value was adapted to R(S/B). To determine the relationship between the threshold and the R(S/B), we performed a phantom study. A discrepancy index (DI) between both imaging modalities, overlap fraction (OF) and mismatch fraction (MF) were calculated for each lesion and imaging modality.

RESULTS

The median DI value for lymph nodes was 2.67 and 1.76 for primary lesions. The OF values were larger for CT volumes than for PET volumes (p < 0.001), for both types of lesions. The MF values were smaller for CT volumes than for PET volumes (p < 0.001), for both types of lesions. The GTV(PET) coverage (OF(PET)) was strongly correlated with the lesion volume (GTV(CT)) for metastatic lymph nodes (Pearson correlation = 0.665; p < 0.01). For smaller lesions, despite the GTV volumes were relatively larger on PET than in CT contours, the coverage was poorer. Accordingly, the MF(PET/CT) was negatively correlated with the lesion volume for metastatic lymph nodes.

CONCLUSIONS

The present study highlights the considerable challenges involved in using FDG PET imaging for the delineation of GTV in head and neck neoplasms. The methods that rely mainly on SUV(max) for thresholding, as the RS/B method, are very sensitive to partial volume effects and may provide unreliable results when applied on small lesions.

Non-FDG PET in oncology

Although FDG PET and PET/CT have a well established role in the management of most cancer patients, they also have some limitations. For the last 15-20 years a growing number of non-FDG PET tracers have been used in research. Many of these new PET tracers are being investigated for the non-invasive assessment of different biologic functions in cancer cells. This unique information should contribute to making personalized cancer therapy a reality. This paper reviews the non-FDG PET tracers that are most likely to find clinical application, some of them in the near future.

Nanoprobes for hybrid SPECT/MR molecular imaging

Hybrid imaging techniques provide enhanced visualization of biological targets by synergistically combining multiple imaging modalities, thereby providing information on specific aspects of structure and function, which is difficult to obtain by a single imaging modality. Advances in the field of hybrid imaging have resulted in the recent approval of PET/magnetic resonance (MR) imaging by the US FDA for clinical use in the USA and Europe. Single-photon emission computed tomography (SPECT)/MR imaging is another evolving hybrid imaging modality with distinct advantages. Recently reported progress in the development of a SPECT/MR imaging hybrid scanner provides a cue towards the need for multimodal SPECT/MR imaging nanoprobes to take full advantage of a scanner’s simultaneous imaging capability. In this review, we present some of the latest developments in the domain of SPECT/MR hybrid imaging, particularly focusing on multimodal nanoprobes.

The role of FDG PET-CT in the therapeutic evaluation for HNSCC patients

F-18 FDG PET/CT has been widely used to diagnose primary tumors and lymph node metastases and to evaluate the response of head and neck squamous cell carcinoma (HNSCC) to therapy. The advantage of using PET/CT is that this combination allows metabolic information to be precisely overlapped with anatomical information, thereby improving the identification of sites with an abnormal accumulation of F-18 FDG. The role of FDG PET/CT in the therapeutic evaluation (such as in treatment planning, the therapeutic response, and the surveillance and examination of HNSCC patients) is discussed in this manuscript. When evaluating the post-treatment outcome via FDG PET/CT, it is important to exclude the post-treatment inflammation-related increase in glucose metabolism in lymph nodes, salivary gland, muscles, and soft tissues. The influence of inflammation can be eliminated if PET/CT is performed after 12 weeks, by which time post-treatment inflammation subsides. Further, FDG PET/CT affords a high negative predictive value. Based on the results of an FDG PET/CT test, some invasive tests that are performed to detect recurrence can be omitted.

Tumour microenvironment heterogeneity affects the perceived spatial concordance between the intratumoural patterns of cell proliferation and 18F-fluorothymidine uptake

BACKGROUND AND PURPOSE

PET imaging with (18)F-fluorothymidine ((18)F-FLT) can potentially be used to identify tumour subvolumes for selective dose escalation in radiation therapy. The purpose of this study is to analyse the co-localization of intratumoural patterns of cell proliferation with (18)F-FLT tracer uptake.

MATERIALS AND METHODS

Mice bearing FaDu or SQ20B xenograft tumours were injected with (18)F-FLT, and bromodeoxyuridine (proliferation marker). Ex vivo images of the spatial pattern of intratumoural (18)F-FLT uptake and that of bromodeoxyuridine DNA incorporation were obtained from thin tumour tissue sections. These images were segmented by thresholding and Relative Operating Characteristic (ROC) curves and Dice similarity indices were evaluated.

RESULTS

The thresholds at which maximum overlap occurred between FLT-segmented areas and areas of active cell proliferation were significantly different for the two xenograft tumour models, whereas the median Dice values were not. However, ROC analysis indicated that segmented FLT images were more specific at detecting the proliferation pattern in FaDu tumours than in SQ20B tumours.

CONCLUSION

Highly dispersed patterns of cell proliferation observed in certain tumours can affect the perceived spatial concordance between the spatial pattern of (18)F-FLT uptake and that of cell proliferation even when high-resolution ex vivo autoradiography imaging is used for (18)F-FLT imaging.

Application of metabolic PET imaging in radiation oncology

Positron emission tomography (PET) is a noninvasive imaging technique that provides functional or metabolic assessment of normal tissue or disease conditions and is playing an increasing role in cancer radiotherapy planning. (18)F-Fluorodeoxyglucose PET imaging (FDG-PET) is widely used in the clinic for tumor imaging due to increased glucose metabolism in most types of tumors; its role in radiotherapy management of various cancers is reviewed. In addition, other metabolic PET imaging agents at various stages of preclinical and clinical development are reviewed. These agents include radiolabeled amino acids such as methionine for detecting increased protein synthesis, radiolabeled choline for detecting increased membrane lipid synthesis, and radiolabeled acetate for detecting increased cytoplasmic lipid synthesis. The amino acid analogs choline and acetate are often more specific to tumor cells than FDG, so they may play an important role in differentiating cancers from benign conditions and in the diagnosis of cancers with either low FDG uptake or high background FDG uptake. PET imaging with FDG and other metabolic PET imaging agents is playing an increasing role in complementary radiotherapy planning.

Biologic imaging of head and neck cancer: the present and the future

While anatomic imaging (CT and MR imaging) of HNC is focused on diagnosing and/or characterizing the disease, defining its local extent, and evaluating distant spread, accurate assessment of the biologic status of the cancer (cellularity, growth rate, response to nonsurgical chemoradiation therapy, and so forth) can be invaluable for prognostication, planning therapy, and follow-up of lesions after therapy. The combination of anatomic and biologic imaging techniques can thus provide a more comprehensive evaluation of the patient. The purpose of this work was to review the present and future clinical applications of advanced biologic imaging techniques in HNC evaluation and management. As part of the biologic imaging array, we discuss MR spectroscopy, diffusion and perfusion MR imaging, CTP, and FDG-PET scanning and conclude with exciting developments that hold promise in assessment of tumor hypoxia and neoangiogenesis.

Extranodal spread in the neck: MRI detection on the basis of pixel-based time-signal intensity curve analysis

PURPOSE

We evaluated dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) for the preoperative detection of extranodal spread (ENS) in metastatic nodes in the neck.

MATERIALS AND METHODS

The time-signal intensity curve (TIC) profiles of 54 histologically proven metastatic nodes (26 ENS-positive and 28 ENS-negative) from 43 patients with head and neck squamous cell carcinoma (SCC) were retrospectively analyzed to determine the effective TIC criteria for ENS-positive nodes. The TICs were semiautomatically classified into four distinctive patterns (flat, slow uptake, rapid uptake with low washout ratio, and rapid uptake with high washout ratio) on a pixel-by-pixel basis.

RESULTS

A number of the MRI findings were significantly correlated with ENS. However, multivariate logistic regression analysis revealed that only a short-axis diameter and an area with slow uptake TIC patterns were significantly and independently indicative of the presence of ENS. The combined MRI criteria of nodal size (>25 mm) or TIC profile (>44% nodal areas with slow-uptake TIC patterns) yielded the best results for differentiation between ENS-positive and ENS-negative nodes, providing 96% sensitivity, 100% specificity, 98% accuracy, and 100% positive, and 97% negative predictive values.

CONCLUSION

When combined with size criteria, pixel-based MR factor analysis may be a promising tool for detecting ENS.

Analysis of cancer metabolism by imaging hyperpolarized nuclei: prospects for translation to clinical research

A major challenge in cancer biology is to monitor and understand cancer metabolism in vivo with the goal of improved diagnosis and perhaps therapy. Because of the complexity of biochemical pathways, tracer methods are required for detecting specific enzyme-catalyzed reactions. Stable isotopes such as (13)C or (15)N with detection by nuclear magnetic resonance provide the necessary information about tissue biochemistry, but the crucial metabolites are present in low concentration and therefore are beyond the detection threshold of traditional magnetic resonance methods. A solution is to improve sensitivity by a factor of 10,000 or more by temporarily redistributing the populations of nuclear spins in a magnetic field, a process termed hyperpolarization. Although this effect is short-lived, hyperpolarized molecules can be generated in an aqueous solution and infused in vivo where metabolism generates products that can be imaged. This discovery lifts the primary constraint on magnetic resonance imaging for monitoring metabolism-poor sensitivity-while preserving the advantage of biochemical information. The purpose of this report was to briefly summarize the known abnormalities in cancer metabolism, the value and limitations of current imaging methods for metabolism, and the principles of hyperpolarization. Recent preclinical applications are described. Hyperpolarization technology is still in its infancy, and current polarizer equipment and methods are suboptimal. Nevertheless, there are no fundamental barriers to rapid translation of this exciting technology to clinical research and perhaps clinical care.

Principles and Application of PET in Brain Tumors

For tumors of the central nervous system (CNS), the ability to accurately delineate the extent of tumor has implications for diagnosis, prognosis, and treatment. PET, mainly with (18)F-fluorodeoxyglucose (FDG), has become commonplace in the work-up of many extracranial tumors. However, the relative high background of FDG-PET activity of normal brain tissue has limited the applicability of this modality in CNS tumors to date. More recently, novel PET tracers for imaging of CNS tumors have been developed. This article outlines recent advances in PET as a complementary imaging modality with implications for diagnosis, prognosis, surgical and radiation treatment planning, and post-therapy surveillance in malignancies of the CNS. Pharmacokinetic properties of the radiotracers and the influence of blood-brain-barrier integrity are also incorporated into the discussion.

Investigation of tumor hypoxia using a two-enzyme system for in vitro generation of oxygen deficiency

Background

Oxygen deficiency in tumor tissue is associated with a malign phenotype, characterized by high invasiveness, increased metastatic potential and poor prognosis. Hypoxia chambers are the established standard model for in vitro studies on tumor hypoxia. An enzymatic hypoxia system (GOX/CAT) based on the use of glucose oxidase (GOX) and catalase (CAT) that allows induction of stable hypoxia for in vitro approaches more rapidly and with less operating expense has been introduced recently. Aim of this work is to compare the enzymatic system with the established technique of hypoxia chamber in respect of gene expression, glucose metabolism and radioresistance, prior to its application for in vitro investigation of oxygen deficiency.

Methods

Human head and neck squamous cell carcinoma HNO97 cells were incubated under normoxic and hypoxic conditions using both hypoxia chamber and the enzymatic model. Gene expression was investigated using Agilent microarray chips and real time PCR analysis. ¹⁴C-fluoro-deoxy-glucose uptake experiments were performed in order to evaluate cellular metabolism. Cell proliferation after photon irradiation was investigated for evaluation of radioresistance under normoxia and hypoxia using both a hypoxia chamber and the enzymatic system.

Results

The microarray analysis revealed a similar trend in the expression of known HIF-1 target genes between the two hypoxia systems for HNO97 cells. Quantitative RT-PCR demonstrated different kinetic patterns in the expression of carbonic anhydrase IX and lysyl oxidase, which might be due to the faster induction of hypoxia by the enzymatic system. ¹⁴C-fluoro-deoxy-glucose uptake assays showed a higher glucose metabolism under hypoxic conditions, especially for the enzymatic system. Proliferation experiments after photon irradiation revealed increased survival rates for the enzymatic model compared to hypoxia chamber and normoxia, indicating enhanced resistance to irradiation. While the GOX/CAT system allows independent investigation of hypoxia and oxidative stress, care must be taken to prevent acidification during longer incubation.

Conclusion

The results of our study indicate that the enzymatic model can find application for in vitro investigation of tumor hypoxia, despite limitations that need to be considered in the experimental design.

Can FDG PET predict radiation treatment outcome in head and neck cancer? Results of a prospective study

Purpose

In head and neck cancer (HNC) various treatment strategies have been developed to improve outcome, but selecting patients for these intensified treatments remains difficult. Therefore, identification of novel pretreatment assays to predict outcome is of interest. In HNC there are indications that pretreatment tumour ¹⁸F-fluorodeoxyglucose (FDG) uptake may be an independent prognostic factor. The aim of this study was to assess the prognostic value of FDG uptake and CT-based and FDG PET-based primary tumour volume measurements in patients with HNC treated with (chemo)radiotherapy.

Methods

A total of 77 patients with stage II–IV HNC who were eligible for definitive (chemo)radiotherapy underwent coregistered pretreatment CT and FDG PET. The gross tumour volume of the primary tumour was determined on the CT (GTV_CT) and FDG PET scans. Five PET segmentation methods were applied: interpreting FDG PET visually (PET_VIS), applying an isocontour at a standardized uptake value (SUV) of 2.5 (PET_2.5), using fixed thresholds of 40% and 50% (PET_40%, PET_50%) of the maximum intratumoral FDG activity (SUV_MAX) and applying an adaptive threshold based on the signal-to-background (PET_SBR). Mean FDG uptake for each PET-based volume was recorded (SUV_mean). Subsequently, to determine the metabolic volume, the integrated SUV was calculated as the product of PET-based volume and SUV_mean. All these variables were analysed as potential predictors of local control (LC), regional recurrence-free survival (RRFS), distant metastasis-free survival (DMFS), disease-free survival (DFS) and overall survival (OS).

Results

In oral cavity/oropharynx tumours PET_VIS was the only volume-based method able to predict LC. Both PET_VIS and GTV_CT were able to predict DMFS, DFS and OS in these subsites. Integrated SUVs were associated with LC, DMFS, DFS and OS, while SUV_mean and SUV_MAX were not. In hypopharyngeal/laryngeal tumours none of the variables was associated with outcome.

Conclusion

There is no role yet for pretreatment FDG PET as a predictor of (chemo)radiotherapy outcome in HNC in daily routine. However, this potential application needs further exploration, focusing both on FDG PET-based primary tumour volume, integrated SUV and SUV_MAX of the primary tumour.

Positron emission tomography imaging approaches for external beam radiation therapies: current status and future developments

In an era in which it is possible to deliver radiation with high precision, there is a heightened need for enhanced imaging capabilities to improve tumour localisation for diagnostic, planning and delivery purposes. This is necessary to increase the accuracy and overall efficacy of all types of external beam radiotherapy (RT), including particle therapies. Positron emission tomography (PET) has the potential to fulfil this need by imaging fundamental aspects of tumour biology. The key areas in which PET may support the RT process include improving disease diagnosis and staging; assisting tumour volume delineation; defining tumour phenotype or biological tumour volume; assessment of treatment response; and in-beam monitoring of radiation dosimetry. The role of PET and its current developmental status in these key areas are overviewed in this review, highlighting the advantages and drawbacks.

Detection of point landmarks in 3D medical images via phase congruency model

This paper presents a novel technique for detection of point landmarks in volumetric medical images based on a three-dimensional (3D) Phase Congruency (PC) model. A bank of 3D log-Gabor filters is specially designed in the frequency domain and used to compute 3D energy maps, which are further combined to form the phase congruency measure. The PC measure is invariant to intensity variations and contrast resolution and provides a good indication of feature significance in an image. To detect significant 3D point landmarks, eigen-analysis of a 3×3 matrix of second-order PC moments, computed for each point in the image, is performed followed by local maxima detection. Two different application scenarios in radiation therapy planning of the head and neck anatomy are used to illustrate the feasibility and usefulness of the proposed method.

Best practices: consensus on performing positron emission tomography-computed tomography for radiation therapy planning and for therapy response assessment

The incorporation of positron emission tomography-computed tomography (PET-CT) into oncological imaging has expanded rapidly since the hybrid scanners were introduced approximately 10 years ago. PET-CT is becoming the standard of practice for the imaging diagnosis and staging of most cancers. Since its introduction, hardware-registered PET and CT images produced by a PET-CT scan were recognized as valuable not only for detection, staging and restaging applications but also for optimizing radiation treatment planning. Even before the introduction of PET-CT, the value of metabolic imaging with the use of FDG PET was recognized as a potentially powerful means of assessing response to various therapies, particularly chemotherapy regimens. To better understand the optimal use of PET-CT in radiation therapy planning and the role of PET-CT in assessing response to therapy, we invited experts from various disciplines to participate in focus group meetings that took place in 2009 and 2010. The Symposia focused on the use of PET-CT imaging in radiation therapy planning (2009) and the use of PET-CT in therapy response assessment (2010). This article will summarize areas of consensus reached by the group regarding many of the discussion topics. The consensus summaries covered in this article are meant to provide direction for future discussions on how to improve the application of this hybrid modality to optimize patient care.

Molecular imaging in radiotherapy planning for head and neck tumors

Molecular imaging uses noninvasive techniques to visualize various biologic pathways and physiologic characteristics of tumors and normal tissues. In relation to radiation therapy, PET with the tracer (18)F-FDG offers a unique opportunity to refine the target volume delineation in patients with squamous cell carcinoma of the head and neck, in turn affecting dose distribution and, it is hoped, patient outcome. Even more so, in the framework of adaptive treatment and theragnostics, whereby dose distribution is adapted in space and time over the typical course of radiotherapy, molecular imaging with PET offers an elegant research avenue to further improve the therapeutic ratio. Such implementation could be of particular interest with tracers other than (18)F-FDG, such as tracers of hypoxia and proliferation.