PET-CT in radiation oncology: the impact on diagnosis, treatment planning, and assessment of treatment response

A scoping review of interpretability and explainability concerning artificial intelligence methods in medical imaging

PURPOSE

To review eXplainable Artificial Intelligence/(XAI) methods available for medical imaging/(MI).

METHOD

A scoping review was conducted following the Joanna Briggs Institute's methodology. The search was performed on Pubmed, Embase, Cinhal, Web of Science, BioRxiv, MedRxiv, and Google Scholar. Studies published in French and English after 2017 were included. Keyword combinations and descriptors related to explainability, and MI modalities were employed. Two independent reviewers screened abstracts, titles and full text, resolving differences through discussion.

RESULTS

228 studies met the criteria. XAI publications are increasing, targeting MRI (n = 73), radiography (n = 47), CT (n = 46). Lung (n = 82) and brain (n = 74) pathologies, Covid-19 (n = 48), Alzheimer's disease (n = 25), brain tumors (n = 15) are the main pathologies explained. Explanations are presented visually (n = 186), numerically (n = 67), rule-based (n = 11), textually (n = 11), and example-based (n = 6). Commonly explained tasks include classification (n = 89), prediction (n = 47), diagnosis (n = 39), detection (n = 29), segmentation (n = 13), and image quality improvement (n = 6). The most frequently provided explanations were local (78.1 %), 5.7 % were global, and 16.2 % combined both local and global approaches. Post-hoc approaches were predominantly employed. The used terminology varied, sometimes indistinctively using explainable (n = 207), interpretable (n = 187), understandable (n = 112), transparent (n = 61), reliable (n = 31), and intelligible (n = 3).

CONCLUSION

The number of XAI publications in medical imaging is increasing, primarily focusing on applying XAI techniques to MRI, CT, and radiography for classifying and predicting lung and brain pathologies. Visual and numerical output formats are predominantly used. Terminology standardisation remains a challenge, as terms like "explainable" and "interpretable" are sometimes being used indistinctively. Future XAI development should consider user needs and perspectives.

Nasopharyngeal Carcinoma Radiomic Evaluation with Serial PET/CT: Exploring Features Predictive of Survival in Patients with Long-Term Follow-Up

Simple Summary

Nasopharyngeal carcinoma (NPC) is a frequent head and neck cancer, especially in Asian countries. Our studies investigated the value of minable data derived from standard of care PET/CT imaging in patients with NPC. The here presented evaluation found that certain specific imaging features in this patient population can be potentially used to predict overall survival and progression free survival at different time points in those patients.

Abstract

Purpose: We aim determine the value of PET and CT radiomic parameters on survival with serial follow-up PET/CT in patients with nasopharyngeal carcinoma (NPC) for which curative intent therapy is undertaken. Methods: Patients with NPC and available pre-treatment as well as follow up PET/CT were included from 2005 to 2006 and were followed to 2021. Baseline demographic, radiological and outcome data were collected. Univariable Cox proportional hazard models were used to evaluate features from baseline and follow-up time points, and landmark analyses were performed for each time point. Results: Sixty patients were enrolled, and two-hundred and seventy-eight (278) PET/CT were at baseline and during follow-up. Thirty-eight percent (38%) were female, and sixty-two patients were male. All patients underwent curative radiation or chemoradiation therapy. The median follow-up was 11.72 years (1.26–14.86). Five-year and ten-year overall survivals (OSs) were 80.0% and 66.2%, and progression-free survival (PFS) was 90.0% and 74.4%. Time-dependent modelling suggested that, among others, PET gray-level zone length matrix (GLZLM) gray-level non-uniformity (GLNU) (HR 2.74 95% CI 1.06, 7.05) was significantly associated with OS. Landmark analyses suggested that CT parameters were most predictive at 15 month, whereas PET parameters were most predictive at time points 3, 6, 9 and 15 month. Conclusions: This study with long-term follow up data on NPC suggests that mainly PET-derived radiomic features are predictive for OS but not PFS in a time-dependent evaluation. Furthermore, CT radiomic measures may predict OS and PFS best at initial and long-term follow-up time points and PET measures may be more predictive in the interval. These modalities are commonly used in NPC surveillance, and prospective validation should be considered.

Prediction of pathological response to preoperative chemotherapy for pancreatic ductal adenocarcinoma using 2-[18F]-fluoro-2-deoxy-d-glucose positron-emission tomography

AIM

To determine whether the pathological response to preoperative chemotherapy for pancreatic ductal adenocarcinoma (PDAC) can be predicted using 2-[18F]-fluoro-2-deoxy-d-glucose positron-emission tomography (F-18 FDG-PET).

MATERIALS AND METHODS

Twenty-eight patients with PDAC who underwent only neoadjuvant chemotherapy (NAC) before surgery were enrolled in the study. All patients had F-18 FDG-PET examinations before NAC. The resected specimen was pathologically evaluated according to the Classification of Pancreatic Carcinoma (7th edn). Patients were categorised into a non-response group and a response group based on the pathological findings. The non-response group (Grades 1a and 1b) showed ≤50% necrosis in the specimen, while the specimens of the response group (Grades 2-3) showed >50% necrosis. The maximum standardised uptake values (SUVmax) of the tumours on F-18 FDG-PET were measured. The mean values of SUVmax were compared between the two groups. The diagnostic performance of SUVmax in distinguishing the two groups was also evaluated using receiver operating characteristic analysis.

RESULTS

The mean SUVmax of the response group was higher than that of the non-response group (9.00 ± 1.78 versus 4.26 ± 2.35; p<0.001). The optimal cut-off value of SUVmax was 9.28 for distinguishing the two groups. The sensitivity, specificity, and accuracy for the prediction in the response group were 80%, 95.7%, and 92.9%, respectively.

CONCLUSIONS

SUVmax on F-18 FDG-PET may be useful as a biomarker to predict the pathological response to NAC in patients with PDAC.

Quantitative PET Imaging and Clinical Parameters as Predictive Factors for Patients With Cervical Carcinoma: Implications of a Prediction Model Generated Using Multi-Objective Support Vector Machine Learning

Purpose:

Quantitative features from pre-treatment positron emission tomography (PET) have been used to predict treatment outcomes for patients with cervical carcinoma. The purpose of this study is to use quantitative PET imaging features and clinical parameters to construct a multi-objective machine learning predictive model.

Materials/Methods:

Seventy-five patients with stage IB2-IVA disease treated at our institution from 2009–2012 were analyzed. Models predicting locoregional and distant failure were generated using clinical parameters (age, race, stage, histology, tumor size, nodal status) and imaging features (12 textural, 9 intensity, 8 geometric features, 2 additional imaging features) from pre-treatment PET. Model features were selected based on a multi-objective evolutionary algorithm to maximize specificity given a fixed moderately high sensitivity using support vector machine learning methods. Model 1 used clinical parameters only (C), Model 2 used imaging features only (I), and Model 3 used clinical and imaging features (C+I). Sensitivity, specificity, area under a receiver-operating characteristic curve (AUC), and p-values were compared to assess ability to predict locoregional and distant failure.

Results:

C+I had the highest performance for both locoregional failure (AUC 0.84, p < 0.01; specificity: 0.86; sensitivity: 0.79) and distant failure (AUC 0.75, p < 0.01; specificity: 0.75; sensitivity: 0.75).

Conclusions:

Based on a moderately high fixed sensitivity and optimized for specificity, the model using both clinical parameters and imaging features (C+I) had the best performance in predicting both locoregional failure and distant failure.

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.

PET Scan Contribution in Chest Tumor Management: A Systematic Review for Thoracic Surgeons

Aims and background

In the 90s, the introduction of positron emission tomography (PET) represented a milestone in the staging of thoracic tumors. In the last 10 years, PET scan has been widely adopted in thoracic oncology, showing high accuracy in diagnosis and staging and with promising issues in defining prognosis. The aim of this systematic review was to focus on the results and pitfalls of PET scan use in the modern management of chest tumors.

Methods and study design.

The literature search was performed on May 2010 in PubMed, Embase, and Cochrane according to PRISMA protocol. The search was restricted to publications in English, using in the same string the word “PET” with 9 different chest tumors; results were then filtered by eliminating technical articles, focusing only on papers in which surgery was considered as a potential diagnostic or therapeutic tool. From 6600 papers initially selected, 99 manuscripts were fully analyzed.

Results

Glucose uptake is a metabolic marker useful in the diagnosis and staging of chest tumors. In lung cancer screening, standard uptake value is helpful in defining the risk of malignancy of isolated pulmonary nodules. The addition of PET scan to conventional staging increases detection of nodal and distant metastases in lung cancer, esophageal cancer and malignant mesothelioma. In thymoma, a close relationship between standard uptake value, histology, and Masaoka stage has been advocated. This link between glucose uptake and prognosis suggests that PET translates biological tumor behavior into clinically detectable findings.

Conclusions

PET scan has a crucial role in thoracic oncology due to its impact on diagnosis, staging and prognosis. PET scan expresses the biological behavior of tumors, opening interesting perspectives in chest tumor management and improving detection and stage grouping in lung cancer. It anticipates the diagnosis in long-incubating diseases such as mesothelioma and increases biological knowledge of rare diseases, such as thymoma and other mediastinal tumors.

Regulation of glucose uptake in lymphoma cell lines by c-MYC- and PI3K-dependent signaling pathways and impact of glycolytic pathways on cell viability

BACKGROUND

Changes in glucose and energy metabolism contribute to the altered phenotype of cancer cells and are the basis for positron emission tomography with ¹⁸F-fluoro-2-deoxy-D-glucose (FDG) to visualize tumors in vivo. The molecular background of the enhanced glucose uptake and its regulation in lymphoma cells is not fully clarified and may provide new possibilities to reverse the altered metabolism. Thus in this study we investigated regulation of glucose uptake by different signaling pathways. Furthermore, the effect of the glucose analog 2-deoxy-D-glucose (2-DG) alone and in combination with other inhibitors on cell survival was studied.

METHODS

An FDG uptake assay was established and uptake of FDG by lymphoma cells was determined after incubation with inhibitors of the c-MYC and the PI3K signalling pathways that are known to be activated in lymphoma cells and able to regulate glucose metabolism. Inhibitors of MAPK signalling pathways whose role in altered metabolism is still unclear were also investigated. Expression of mRNAs of the glucose transporter 1 (GLUT1), hexokinase 2 (HK2), glucose-6-phosphatase (G6Pase) and lactate dehydrogenase A (LDHA) and of the glucose metabolism-regulating micro RNAs (miRNA) miR21, -23a, -133a, -133b, -138-1 and -143 was determined by RT-PCR. Cell viability was analysed by MTT assay.

RESULTS

Treatment with the c-MYC inhibitor 10058-F4 and inhibitors of the PI3K/mTOR pathway diminished uptake of FDG in all three cell lines, while inhibition of MAPK pathways had no effect on glucose uptake. Expression of glycolysis-related genes and miRNAs were diminished, although to a variable degree in the three cell lines. The c-MYC inhibitor, the PI3K inhibitor LY294002, the mTOR inhibitor Rapamycin and 2-DG all diminished the number of viable cells. Interestingly, in combination with 2-DG, the c-MYC inhibitor, LY294002 and the p38 MAPK inhibitor SB203580 had synergistic effects on cell viability in all three cell lines.

CONCLUSIONS

c-MYC- and PI3K/mTOR-inhibitors decreased viability of the lymphoma cells and led to decreased glucose uptake, expression of glycolysis-associated genes, and glucose metabolism-regulating miRNAs. Inhibition of HK by 2-DG reduced cell numbers as a single agent and synergistically with inhibitors of other intracellular pathways. Thus, targeted inhibition of the pathways investigated here could be a strategy to suppress the glycolytic phenotype of lymphoma cells and reduce proliferation.

Predictive modeling of outcomes following definitive chemoradiotherapy for oropharyngeal cancer based on FDG-PET image characteristics

In this study, we investigate the use of imaging feature-based outcomes research ('radiomics') combined with machine learning techniques to develop robust predictive models for the risk of all-cause mortality (ACM), local failure (LF), and distant metastasis (DM) following definitive chemoradiation therapy (CRT). One hundred seventy four patients with stage III-IV oropharyngeal cancer (OC) treated at our institution with CRT with retrievable pre- and post-treatment 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) scans were identified. From pre-treatment PET scans, 24 representative imaging features of FDG-avid disease regions were extracted. Using machine learning-based feature selection methods, multiparameter logistic regression models were built incorporating clinical factors and imaging features. All model building methods were tested by cross validation to avoid overfitting, and final outcome models were validated on an independent dataset from a collaborating institution. Multiparameter models were statistically significant on 5 fold cross validation with the area under the receiver operating characteristic curve (AUC)  =  0.65 (p  =  0.004), 0.73 (p  =  0.026), and 0.66 (p  =  0.015) for ACM, LF, and DM, respectively. The model for LF retained significance on the independent validation cohort with AUC  =  0.68 (p  =  0.029) whereas the models for ACM and DM did not reach statistical significance, but resulted in comparable predictive power to the 5 fold cross validation with AUC  =  0.60 (p  =  0.092) and 0.65 (p  =  0.062), respectively. In the largest study of its kind to date, predictive features including increasing metabolic tumor volume, increasing image heterogeneity, and increasing tumor surface irregularity significantly correlated to mortality, LF, and DM on 5 fold cross validation in a relatively uniform single-institution cohort. The LF model also retained significance in an independent population.

Classification and evaluation strategies of auto-segmentation approaches for PET: Report of AAPM task group No. 211

PURPOSE

The purpose of this educational report is to provide an overview of the present state-of-the-art PET auto-segmentation (PET-AS) algorithms and their respective validation, with an emphasis on providing the user with help in understanding the challenges and pitfalls associated with selecting and implementing a PET-AS algorithm for a particular application.

APPROACH

A brief description of the different types of PET-AS algorithms is provided using a classification based on method complexity and type. The advantages and the limitations of the current PET-AS algorithms are highlighted based on current publications and existing comparison studies. A review of the available image datasets and contour evaluation metrics in terms of their applicability for establishing a standardized evaluation of PET-AS algorithms is provided. The performance requirements for the algorithms and their dependence on the application, the radiotracer used and the evaluation criteria are described and discussed. Finally, a procedure for algorithm acceptance and implementation, as well as the complementary role of manual and auto-segmentation are addressed.

FINDINGS

A large number of PET-AS algorithms have been developed within the last 20 years. Many of the proposed algorithms are based on either fixed or adaptively selected thresholds. More recently, numerous papers have proposed the use of more advanced image analysis paradigms to perform semi-automated delineation of the PET images. However, the level of algorithm validation is variable and for most published algorithms is either insufficient or inconsistent which prevents recommending a single algorithm. This is compounded by the fact that realistic image configurations with low signal-to-noise ratios (SNR) and heterogeneous tracer distributions have rarely been used. Large variations in the evaluation methods used in the literature point to the need for a standardized evaluation protocol.

CONCLUSIONS

Available comparison studies suggest that PET-AS algorithms relying on advanced image analysis paradigms provide generally more accurate segmentation than approaches based on PET activity thresholds, particularly for realistic configurations. However, this may not be the case for simple shape lesions in situations with a narrower range of parameters, where simpler methods may also perform well. Recent algorithms which employ some type of consensus or automatic selection between several PET-AS methods have potential to overcome the limitations of the individual methods when appropriately trained. In either case, accuracy evaluation is required for each different PET scanner and scanning and image reconstruction protocol. For the simpler, less robust approaches, adaptation to scanning conditions, tumor type, and tumor location by optimization of parameters is necessary. The results from the method evaluation stage can be used to estimate the contouring uncertainty. All PET-AS contours should be critically verified by a physician. A standard test, i.e., a benchmark dedicated to evaluating both existing and future PET-AS algorithms needs to be designed, to aid clinicians in evaluating and selecting PET-AS algorithms and to establish performance limits for their acceptance for clinical use. The initial steps toward designing and building such a standard are undertaken by the task group members.

False Positive Positron Emission Tomography / Computed Tomography Scans in Treated Head and Neck Cancers

OBJECTIVE

Positron emission tomography/computed tomography (PET/CT) imaging for head and neck cancers (HNC) is commonly utilized for post-treatment assessment. Though PET/CT in this setting has been reported to have high negative predictive values (> 90%), positive predictive values have been reported at approximately 50%, leading to high rates of false positivity (FP) and troubling management decisions for both patient and practitioner. The objective of this study was to identify patient, disease, treatment and imaging factors that might be associated with a higher likelihood of FP on initial post-treatment PET/CT imaging for patients treated for HNC.

MATERIALS AND METHODS

A retrospective chart review was performed on 84 patients treated for HNC who received radiation therapy (RT) as part of their overall management from October 2005 to August 2013. Of the patients screened, 19 were found to have mucosally based squamous cell carcinoma (SCC) with positive initial post-treatment PET/CT studies (23%). Fisher's exact test was used to analyze the association between categorical variables and FP, including patient's gender, disease laterality, primary tumor site and stage, nodal and overall stage, high dose RT fraction size, number of RT fractions completed, total RT dose, biologically effective dose and timing of PET/CT acquisition. Wilcoxon rank-sum test was used to analyze the association between continuous variables and FP, including patient age, total elapsed days of RT, an amount of infused fluorodeoxyglucose 18F-FDG, pre-PET/CT serum glucose levels, and maximum standardized uptake value SUVmax. Statistically significant findings were those that were deemed p <0.05.

RESULTS

Among patients with positive initial post-treatment PET/CT scans for treated HNC, there was a lower proportion of higher primary disease stage associated with FP versus true positivity (T-stage 3-4: 20 vs 78%, respectively, p=0.023). We also discovered that 50% of patients that underwent confirmation for FP findings suffered serious complications as a direct consequence of invasive exploratory procedures.

CONCLUSIONS

Although PET/CT is known for its exceptional negative predictive value (> 90%) in the post-treatment setting for HNC, high rates of FP remains a clinical challenge. Our study suggests that tumor stage (T-stage) may impact FP rates in positive initial post-treatment PET/CT scans. We recommend careful multidisciplinary discussion regarding positive PET/CT studies in the post-treatment setting for HNC, particularly if invasive intervention is considered.

The use of hyperpolarized carbon-13 magnetic resonance for molecular imaging

Until recently, molecular imaging using magnetic resonance (MR) has been limited by the modality's low sensitivity, especially with non-proton nuclei. The advent of hyperpolarized (HP) MR overcomes this limitation by substantially enhancing the signal of certain biologically important probes through a process known as external nuclear polarization, enabling real-time assessment of tissue function and metabolism. The metabolic information obtained by HP MR imaging holds significant promise in the clinic, where it could play a critical role in disease diagnosis and therapeutic monitoring. This review will provide a comprehensive overview of the developments made in the field of hyperpolarized MR, including advancements in polarization techniques and delivery, probe development, pulse sequence optimization, characterization of healthy and diseased tissues, and the steps made towards clinical translation.

Correlation between histological grade and positron emission tomography parameters in cervical carcinoma

The aim of the present study was to evaluate the changes in cervical cancer glucose metabolism for different levels of cellular differentiation. The metabolic activity was measured by standardized uptake value (SUV), SUV normalized to lean body mass, metabolic tumor volume and total lesion glycolysis using fluorine-18 fluorodeoxyglucose positron emission tomography (PET). A correlation study of these values could be used to facilitate therapeutic choice and to improve clinical practice and outcome. This study considered 32 patients with diagnosed cervical cancers, at different International Federation of Gynecology and Obstetrics stages. Glucose metabolism was assessed by PET examination, and histological specimens were examined to determine their initial grade of differentiation. A correlation study of these values was evaluated. Histological examination showed that all cases were of squamous cell carcinoma. Regarding the differentiation of the tumor, 19 well- to moderately-differentiated tumors and 13 poorly-differentiated tumors were determined. Negative findings for correlations between metabolic parameters and initial grade of histological differentiation were found, and considering that histological grade has been shown to have no consistent prognostic value in cervical cancer treatment, PET imaging could play a significant role in cervical cancer prognosis.

Pre-treatment non-target lung FDG-PET uptake predicts symptomatic radiation pneumonitis following Stereotactic Ablative Radiotherapy (SABR)

PURPOSE

To determine if pre-treatment non-target lung FDG-PET uptake predicts for symptomatic radiation pneumonitis (RP) following lung stereotactic ablative radiotherapy (SABR).

METHODS

We reviewed a 258 patient database from our institution to identify 28 patients who experienced symptomatic (grade ⩾ 2) RP after SABR, and compared them to 57 controls who did not develop symptomatic RP. We compared clinical, dosimetric and functional imaging characteristics between the 2 cohorts including pre-treatment non-target lung FDG-PET uptake.

RESULTS

Median follow-up time was 26.9 months. Patients who experienced symptomatic RP had significantly higher non-target lung FDG-PET uptake as measured by mean SUV (p < 0.0001) than controls. ROC analysis for symptomatic RP revealed area under the curve (AUC) of 0.74, with sensitivity 82.1% and specificity 57.9% with cutoff mean non-target lung SUV > 0.56. Predictive value increased (AUC of 0.82) when mean non-target lung SUV was combined with mean lung dose (MLD). We developed a 0-2 point model using these 2 variables, 1 point each for SUV > 0.56 or MLD > 5.88 Gy equivalent dose in 2 Gy per fraction (EQD2), predictive for symptomatic RP in our cohort with hazard ratio 10.01 for score 2 versus 0 (p < 0.001).

CONCLUSIONS

Patients with elevated pre-SABR non-target lung FDG-PET uptake are at increased risk of symptomatic RP after lung SABR. Our predictive model suggests patients with mean non-target lung SUV > 0.56 and MLD > 5.88 Gy EQD2 are at highest risk. Our predictive model should be validated in an external cohort before clinical implementation.

Overall and disease-free survival outcomes of patients receiving intensity-modulated radiation therapy (IMRT) with PET-CT-based planning for cancers of the head and neck

Introduction

Combined modality treatment regimens have provided modest gains in locoregional control rates of cancers of the head and neck (HNC), and intensity-modulated radiation therapy (IMRT) has gained widespread use. The methodology for determining contours of the gross tumour volume (GTV) in the radiation treatment plan is often based on combined anatomic and metabolic data from positron emission tomography–computed tomography (PET-CT). This study aimed to retrospectively evaluate the overall survival and disease-free survival outcomes of patients with HNC who received definitive IMRT with or without chemotherapy, planned with PET-CT.

Materials and Methods

A total of 1,200 patients underwent treatment for HNC during the study period, from 1 January 2002 to 31 December 2010. Of those, 261 cases had evaluable data that met the inclusion criteria for the study. The incidence and timing of locoregional recurrence, distant metastatic disease, new primary malignancies and death were evaluated retrospectively. Overall and disease-free survival (survival to time of first recurrence) were determined by the life table method. Incidence of distance metastatic disease and additional cancers were also studied.

Results

Median follow-up from treatment initiation was 26·4 months (range 1·2–84·7 months). Overall survival and disease-free survival rates were 0·883 and 0·791, respectively, at 1 year; 0·793 and 0·688, respectively, at 2 years; and 0·732 and 0·619, respectively, at 3 years. The cumulative risk of recurrence was 22·6% at 3 years following definitive IMRT and the median time to recurrence was 345 days. There was an overall low incidence of distant metastatic disease (3·07%) and additional cancers (8·05%).

Conclusion

Overall and disease-free survival outcomes of a large cohort of HNC patients treated with definitive IMRT radiotherapy following treatment planning with PET-CT shows a similar high level of disease control and mortality rate as previously published outcome studies of shorter terms and/or smaller numbers of patients.

Computerized PET/CT image analysis in the evaluation of tumour response to therapy

Current cancer therapy strategy is mostly population based, however, there are large differences in tumour response among patients. It is therefore important for treating physicians to know individual tumour response. In recent years, many studies proposed the use of computerized positron emission tomography/CT image analysis in the evaluation of tumour response. Results showed that computerized analysis overcame some major limitations of current qualitative and semiquantitative analysis and led to improved accuracy. In this review, we summarize these studies in four steps of the analysis: image registration, tumour segmentation, image feature extraction and response evaluation. Future works are proposed and challenges described.

18[F]FDG-PET/CT is a useful molecular marker in evaluating tumour aggressiveness: a revised understanding of an in-vivo FDG-PET imaging that alludes the alteration of cancer biology

Molecular imaging employing (18)[F]FDG-PET/CT enables in-vivo visualization, characterisation and measurement of biological process in tumour at the molecular and cellular level. In oncology, this approach can be directly applied as translational biomarkers of disease progression. In this article, the improved roles of FDG as an in-vivo glycolytic marker which reflect biological changes across in-vitro cellular environment are discussed. New understanding in how altered metabolism via glycolytic downstream drivers of malignant transformation as reviewed below offers unique promise as to monitor tumour aggressiveness and hence optimize the therapeutic management.

New PET/CT Features for the Evaluation of Tumor Response

With the emerging multi-modality imaging performed at multiple time points for each patient, it becomes more important to analyze the serial images quantitatively, select and combine both complementary and contradictory information from various sources, for accurate and personalized evaluation of tumor response to therapy.

Genotyping analysis and ¹⁸FDG uptake in breast cancer patients: a preliminary research

Background

Diagnostic imaging plays a relevant role in the care of patients with breast cancer (BC). Positron Emission Tomography (PET) with 18F-fluoro-2-deoxy-D-glucose (FDG) has been widely proven to be a clinical tool suitable for BC detection and staging in which the glucose analog supplies metabolic information about the tumor. A limited number of studies, sometimes controversial, describe possible associations between FDG uptake and single nucleotide polymorphisms (SNPs). For this reason this field has to be explored and clarified. We investigated the association of SNPs in GLUT1, HIF-1a, EPAS1, APEX1, VEGFA and MTHFR genes with the FDG uptake in BC.

Methods

In 26 caucasian individuals with primary BC, whole-body PET-CT scans were obtained and quantitative analysis was performed by calculating the maximum Standardized Uptake Value normalized to body-weight (SUVmax) and the mean SUV normalized to body-weight corrected for partial volume effect (SUVpvc). Human Gene Mutation Database and dbSNP Short Genetic Variations database were used to analyze gene regions containing the selected SNPs. Patient genotypes were obtained using Sanger DNA sequencing analysis performed by Capillary Electrophoresis.

Results

BC patients were genotyped for the following nine SNPs: GLUT1: rs841853 and rs710218; HIF-1a: rs11549465 and rs11549467; EPAS1: rs137853037 and rs137853036; APEX1: rs1130409; VEGFA: rs3025039 and MTHFR: rs1801133. In this work correlations between the nine potentially useful polymorphisms selected and previously suggested with tracer uptake (using both SUVmax and SUVpvc) were not found.

Conclusions

The possible functional influence of specific SNPs on FDG uptake needs further studies in human cancer. In summary, this is the first pilot study, to our knowledge, which investigates the association between a large panel of SNPs and FDG uptake specifically in BC patients. This work represents a multidisciplinary and translational medicine approach to study BC where, the possible correlation between SNPs and tracer uptake, may be considered to improve personalized cancer treatment and care.

[Evaluation of the effectiveness of ¹⁸F-FDG-PET/CT examination of head and neck cancer--own experience]

PURPOSE

The aim of the study was to evaluate the usefulness of ¹⁸F-FDG-PET/CT in diagnosis of head and neck cancer.

MATERIAL AND METHODS

60 ¹⁸F-FDG-PET/CT examinations were performed in 50 patients diagnosed and treated for head and neck cancer in Department of Head and Neck Surgery and Nuclear Medicine Department of The Greater Poland Cancer Centre in Poznan, Poland from 2007 to 2011. Patients were divided into 2 subgroups: CUP Syndrome patients (25 PET/CT exams) and patients being under control after treatment (35 PET/CT exams).

RESULTS

In the group of CUP Syndrome patients 6 PET/CT examinations were negative, in 7--possible primary tumor was indicated, in 10--only cervical lymph node metastases were diagnosed, in 2 cases--distant metastases occured. Within the second subgroup 14 PET/CT examinations were negative, 11 exams--indicated the recurrent disease, 2--cervical lymph node metastases and 8--distant metastases. The sensitivity and specificity of ¹⁸F-FDG-PET/CT in this study within the CUP Syndrome patients group were 100% and 55% respectively. The positive predictive value was 74%. The negative predictive value was 100%. The sensitivity and specificity of ¹⁸F-FDG-PET/CT in this study within the second group of patients were 88% and 66% respectively. The positive predictive value was 71%. The negative predictive value was 86%.

CONCLUSIONS

¹⁸F-FDG-PET/CT is useful for staging of head and neck cancer, identification of an unknown primary tumor, delineation of the extent of regional lymph node involvement, detection of distant metastases and occasional synchronous primary tumor.

Stereotactic Body Radiotherapy (SBRT) for primary and recurrent head and neck tumors

Stereotactic Body Radiotherapy (SBRT) is increasingly used to treat a variety of head and neck tumors as a result of its highly conformal dose distributions and stereotactic spatial accuracy in delivery. Our experience and other previous reports have shown that SBRT is technically feasible, well-tolerated and compares favorably to other alternatives of salvage therapy in the management of patients with recurrent and/or previously irradiated head and neck cancers. Furthermore, it has the advantage of a shorter treatment schedule, greater compliance, and safe delivery in the outpatient setting. This affords an opportunity to introduce SBRT as a definitive treatment in select patients. This review presents an overview of the use of SBRT for managing head and neck tumors by highlighting the existing indications and the expanding role of SBRT in managing these patients.

The utility of FDG-PET for assessing outcomes in oligometastatic cancer patients treated with stereotactic body radiotherapy: a cohort study

Background

Studies suggest that patients with metastases limited in number and destination organ benefit from metastasis-directed therapy. Stereotactic body radiotherapy (SBRT) is commonly used for metastasis directed therapy in this group. However, the characterization of PET response following SBRT is unknown in this population. We analyzed our cohort of patients to describe the PET response following SBRT.

Methods

Patients enrolled on a prospective dose escalation trial of SBRT to all known sites of metastatic disease were reviewed to select patients with pre- and post-therapy PET scans. Response to SBRT was characterized on PET imaging based on standard PET response criteria and compared to CT based RECIST criteria for each treated lesion.

Results

31 patients had PET and CT data available before and after treatment for analysis in this study. In total, 58 lesions were treated (19 lung, 11 osseous, 11 nodal, 9 liver, 6 adrenal and 2 soft tissue metastases). Median follow-up was 14 months (range: 3–41). Median time to first post-therapy PET was 1.2 months (range; 0.5-4.1). On initial post-therapy PET evaluation, 96% (56/58) of treated metastases responded to therapy. 60% (35/58) had a complete response (CR) on PET and 36% (21/58) had a partial response (PR). Of 22 patients with stable disease (SD) on initial CT scan, 13 had CR on PET, 8 had PR, and one had SD. Of 21 metastases with PET PR, 38% became CR, 52% remained PR, and 10% had progressive disease on follow-up PET. 10/35 lesions (29%) with an initial PET CR progressed on follow-up PET scan with median time to progression of 4.11 months (range: 2.75-9.56). Higher radiation dose correlated with long-term PET response.

Conclusions

PET response to SBRT enables characterization of metastatic response in tumors non-measurable by CT. Increasing radiation dose is associated with prolonged complete response on PET.

A retrospective, deformable registration analysis of the impact of PET-CT planning on patterns of failure in stereotactic body radiation therapy for recurrent head and neck cancer

BACKGROUND

Stereotactic body radiation therapy (SBRT) has seen increasing use as a salvage strategy for selected patients with recurrent, previously-irradiated squamous cell carcinoma of the head and neck (rSCCHN). PET-CT may be advantageous for tumor delineation and evaluation of treatment failures in SBRT. We analyzed the patterns of failure following SBRT for rSCCHN and assessed the impact of PET-CT treatment planning on these patterns of failure.

METHODS

We retrospectively reviewed 96 patients with rSCCHN treated with SBRT. Seven patients (7%) were treated after surgical resection of rSCCHN and 89 patients (93%) were treated definitively. PET-CT treatment planning was used for 45 patients whereas non-PET-CT planning was used for 51 patients. Categories of failure were assigned by comparing recurrences on post-treatment scans to the planning target volume (PTV) from planning scans using the deformable registration function of VelocityAI™. Failures were defined: In-field (>75% inside PTV), Overlap (20-75% inside PTV), Marginal (<20% inside PTV but closest edge within 1cm of PTV), or Regional/Distant (more than 1cm from PTV).

RESULTS

Median follow-up was 7.4 months (range, 2.6-52 months). Of 96 patients, 47 (49%) developed post-SBRT failure. Failure distribution was: In-field-12.3%, Overlap-24.6%, Marginal-36.8%, Regional/Distant-26.3%. There was a significant improvement in overall failure-free survival (log rank p = 0.037) and combined Overlap/Marginal failure-free survival (log rank p = 0.037) for those receiving PET-CT planning vs. non-PET-CT planning in the overall cohort (n = 96). Analysis of the definitive SBRT subgroup (n = 89) increased the significance of these findings (overall failure: p = 0.008, Overlap/Marginal failure: p = 0.009). There were no significant differences in age, gender, time from prior radiation, dose, use of cetuximab with SBRT, tumor differentiation, and tumor volume between the PET-CT and non-PET-CT groups.

CONCLUSIONS

Most failures after SBRT treatment for rSCCHN were near misses, i.e. Overlap/Marginal failures (61.4%), suggesting an opportunity to improve outcomes with more sensitive imaging. PET-CT treatment planning showed the lowest rate of overall and near miss failures and is beneficial for SBRT treatment planning.

Muscle metastases from gallbladder cancer

Gallbladder cancer is a highly fatal disease with poor prognosis; indeed, a high proportion of tumours are diagnosed at an advanced stage. Metastases are commonly detected in regional lymph nodes, liver and peritoneum, but unusual sites of spread such as thyroid and breast have also been described in the literature.We report a case of unsuspected muscle metastases, associated to pulmonary metastases, detected by FDG-PET/CT in a patient with previously removed gallbladder cancer and persistent episodes of haemoptysis.

Functional and molecular image guidance in radiotherapy treatment planning optimization

Functional and molecular imaging techniques are increasingly being developed and used to quantitatively map the spatial distribution of parameters, such as metabolism, proliferation, hypoxia, perfusion, and ventilation, onto anatomically imaged normal organs and tumor. In radiotherapy optimization, these imaging modalities offer the promise of increased dose sparing to high-functioning subregions of normal organs or dose escalation to selected subregions of the tumor as well as the potential to adapt radiotherapy to functional changes that occur during the course of treatment. The practical use of functional/molecular imaging in radiotherapy optimization must take into cautious consideration several factors whose influences are still not clearly quantified or well understood including patient positioning differences between the planning computed tomography and functional/molecular imaging sessions, image reconstruction parameters and techniques, image registration, target/normal organ functional segmentation, the relationship governing the dose escalation/sparing warranted by the functional/molecular image intensity map, and radiotherapy-induced changes in the image intensity map over the course of treatment. The clinical benefit of functional/molecular image guidance in the form of improved local control or decreased normal organ toxicity has yet to be shown and awaits prospective clinical trials addressing this issue.

Convergence technology in cancer medicine

The field of convergence technology may be defined as an area of technologic innovation in which multiple devices or functionalities are combined within a single platform in a way that adds functional, operational or economic synergies. Within the field of medical devices, this concept embodies many different types of novel combinations representing syntheses of therapeutic, diagnostic and digital information technologies. In the current era of healthcare reform, such combinatorial technologies will be pressed to demonstrate improvements in comparative effectiveness compared with the use of separate independent components. Moreover, the new more stringent regulatory environment will require much greater levels of pre- and post-market safety reviews conducted under the auspices and authority of the US FDA Office of Combination Products. This branch of the FDA scrutinizes submissions and divides them into drugs, devices and biological products and includes many submissions previously regulated by disparate centers, such as the Center for Devices and Radiologic Health and the Center for Drug Evaluation and Research. The field of convergence technologies already amounts to a worldwide market extending to tens of billions of dollars and this article will attempt to summarize some of the key elements of this continued push for added value and more personalized medicine.

Correction of motion-induced misalignment in co-registered PET/CT and MRI (T1/T2/FLAIR) head images for stereotactic radiosurgery

The purpose was to evaluate and correct the co‐registration of diagnostic PET/CT and MRI/MRI images for stereotactic radiosurgery (SRS) using 3D volumetric image registration (3DVIR). The 3DVIR utilizes the homogeneity of color distribution over a volumetric anatomical landmark as the registration criterion with submillimeter accuracy. Fifty‐three PET/CT and MRI (T1, T2 and FLAIR) image sets of patients with brain lesions were acquired sequentially from a hybrid PET/CT or an MRI scanner with common diagnostic head holding devices. Twenty‐five sets of head  18F−FDG−PET/CT images were scanned over a 10‐minute interval and 14 whole‐body sets were scanned over a 30‐minute interval. Fourteen sets of MRI images were acquired, and each 3‐modal image set (T1, T2 and FLAIR) was scanned in sequence at time 0, ~5 and ~20 minutes. The misalignments in these “co‐registered” images were evaluated and corrected using the 3DVIR. Using the head immobilization devices commonly found in diagnostic PET/CT and MRI/MRI imaging, 80%–100% of these “co‐registered” images were identified as misaligned. For PET/CT, the magnitude of misalignment was 0.4°±0.5° and 0.7±0.4mm for 10‐minute scans, and 0.8°±1.2° and 2.7±1.7mm for 30‐minute scans. For MRI/MRI, the magnitude was 0.2°±0.4° and 0.3±0.2mm for 5‐minute scan intervals, and 1.1°±0.7° and 1.2±1.4mm for 20‐minute intervals. Small, but significant, misalignment is present in the co‐registered diagnostic PET/CT and MRI/MRI images and can be corrected in SRS treatment planning using the volumetric image registration for improved target localization within the clinical error tolerance.

PACS numbers: 87.53.Ly, 87.57.nj, 87.57.uk, 87.57.Q‐, 87.61.jc, 87.19.xc

Conflict of Interest Statement: The authors do not have any conflict of interest on this research report.

Variability of textural features in FDG PET images due to different acquisition modes and reconstruction parameters

BACKGROUND

Characterization of textural features (spatial distributions of image intensity levels) has been considered as a tool for automatic tumor segmentation. The purpose of this work is to study the variability of the textural features in PET images due to different acquisition modes and reconstruction parameters.

MATERIAL AND METHODS

Twenty patients with solid tumors underwent PET/CT scans on a GE Discovery VCT scanner, 45-60 minutes post-injection of 10 mCi of [(18)F]FDG. Scans were acquired in both 2D and 3D modes. For each acquisition the raw PET data was reconstructed using five different reconstruction parameters. Lesions were segmented on a default image using the threshold of 40% of maximum SUV. Fifty different texture features were calculated inside the tumors. The range of variations of the features were calculated with respect to the average value.

RESULTS

Fifty textural features were classified based on the range of variation in three categories: small, intermediate and large variability. Features with small variability (range ≤ 5%) were entropy-first order, energy, maximal correlation coefficient (second order feature) and low-gray level run emphasis (high-order feature). The features with intermediate variability (10% ≤ range ≤ 25%) were entropy-GLCM, sum entropy, high gray level run emphsis, gray level non-uniformity, small number emphasis, and entropy-NGL. Forty remaining features presented large variations (range > 30%).

CONCLUSION

Textural features such as entropy-first order, energy, maximal correlation coefficient, and low-gray level run emphasis exhibited small variations due to different acquisition modes and reconstruction parameters. Features with low level of variations are better candidates for reproducible tumor segmentation. Even though features such as contrast-NGTD, coarseness, homogeneity, and busyness have been previously used, our data indicated that these features presented large variations, therefore they could not be considered as a good candidates for tumor segmentation.

The association of 18F-deoxyglucose (FDG) uptake of PET with polymorphisms in the glucose transporter gene (SLC2A1) and hypoxia-related genes (HIF1A, VEGFA, APEX1) in non-small cell lung cancer. SLC2A1 polymorphisms and FDG-PET in NSCLC patients

BACKGROUND

Positron emission tomography imaging of lung cancers with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose is a non-invasive diagnostic, and prognostic tool that measures tumor metabolism. We have analyzed the effect of solute carrier family 2 (facilitated glucose transporter), member 1 polymorphisms on 2-[fluorine-18]-fluoro-2-deoxy-D-glucose-uptake with a combination of polymorphisms of hypoxia-inducible factor 1 alpha, apurinic/apyimidinic endonuclease, and vascular endothelial growth factor A in a hypoxia-related pathway.

METHODS

We investigated the association between solute carrier family 2 (facilitated glucose transporter), member 1 -2841A>T, hypoxia-inducible factor 1 alpha Pro582Ser, Ala588Thr, apurinic/apyimidinic endonuclease Asp148Glu, or vascular endothelial growth factor A +936C>T and 2-[fluorine-18]-fluoro-2-deoxy-D-glucose-uptake among 154 patients with non-small-cell lung cancer.

RESULTS

The solute carrier family 2 (facilitated glucose transporter), member 1 -2841A>T polymorphism was significantly associated with 2-[fluorine-18]-fluoro-2-deoxy-D-glucose-uptake in combination with the apurinic/apyimidinic endonuclease Asp148Glu (T>G) polymorphism in the squamous cell type of non-small-cell lung cancer. The solute carrier family 2 (facilitated glucose transporter), member 1 TT genotype had a higher maximum standardized uptake values than the AA + AT genotype when the apurinic/apyimidinic endonuclease genotype was TT (mean maximum standardized uptake values, 12.47 +/- 1.33 versus 8.46 +/- 2.90, respectively; P = 0.028). The mean maximum standardized uptake values were not statistically different with respect to vascular endothelial growth factor A and hypoxia-inducible factor 1 alpha polymorphisms.

CONCLUSION

A glucose transporter gene polymorphism was shown to be statistically associated with glucose-uptake when the apurinic/apyimidinic endonuclease genotype is TT in patients with the squamous cell type of non-small-cell lung cancer. Our findings suggest that a newly developed tracer for positron emission tomography could be affected by genetic polymorphisms.

[Utility of PET-CT on radiotherapy planning of head and neck cancer. Our initial experience]

OBJECTIVE

To describe the methods used for the incorporation of FDG-PET-CT on radiotherapy planning of patients with head and neck cancer and also to evaluate the impact of FDG-PET-CT on staging and tumor volume definition.

MATERIAL AND METHODS

A prospective study in which 20 patients with head and neck tumor submitted for radiotherapy treatment were included. All underwent a whole body PET- CT (GE DSTE 16) for staging and restaging, also acquiring an additional 3h delayed PET image with diagnostic CT parameters for planning. A CT scan with diagnostic protocol, tabletop available for radiotherapy treatment and the same personalized head-shoulder mask were used in the latter. Lymph node involvement and/or distant involvement were evaluated, considering the changes in staging. We also evaluated the differences in volumes obtained between the different techniques. The threshold value used for delineating PET gross tumor volume (GTV) was empirically established and ranged from 20-40% of the maximum SUV.

RESULTS

Radiotherapy planning was performed with PET-CT in 20 patients between October 2007 to September 2008. A total of 29 lesions (18 primary lesions because 2 patients were excluded as no tumor was observed on the PET CT images, and 11 nodes). The most frequent location was oropharynx (5 patients). Mean maxSUV of the 29 lesions was 14.4 (range 5.0 and 26.4). No statistically significant differences were found between the GTV PET and GTV CT (mean 21.9cm³ and 19.3cm³, respectively). PET-CT modified the staging in 20% of the patients, with a diagnostic and therapeutic impact of 50 and 25%, respectively.

CONCLUSION

The incorporation of PET-CT in routine radiotherapy planning is a promising technique that requires close collaboration between the nuclear medicine and radiotherapy oncology departments. PET-CT achieves better staging in patients and has a significant diagnostic and therapeutic impact. The use of the hybrid technique avoids problems arising from co-registry as well as a second examination for planning with the consequent advantage for the patient. Nonetheless, more prospective and randomized studies with pathology specimens are needed to evaluate the real impact in the tumor volume definition.

Hyperpolarized 13C magnetic resonance metabolic imaging: application to brain tumors

In order to compare in vivo metabolism between malignant gliomas and normal brain, (13)C magnetic resonance (MR) spectroscopic imaging data were acquired from rats with human glioblastoma xenografts (U-251 MG and U-87 MG) and normal rats, following injection of hyperpolarized [1-(13)C]-pyruvate. The median signal-to-noise ratio (SNR) of lactate, pyruvate, and total observed carbon-13 resonances, as well as their relative ratios, were calculated from voxels containing Gadolinium-enhanced tissue in T(1) postcontrast images for rats with tumors and from normal brain tissue for control rats. [1-(13)C]-labeled pyruvate and its metabolic product, [1-(13)C]-lactate, demonstrated significantly higher SNR in the tumor compared with normal brain tissue. Statistical tests showed significant differences in all parameters (P < .0004) between the malignant glioma tissue and normal brain. The SNR of lactate, pyruvate, and total carbon was observed to be different between the U-251 MG and U-87 MG models, which is consistent with inherent differences in the molecular characteristics of these tumors. These results suggest that hyperpolarized MR metabolic imaging may be valuable for assessing prognosis and monitoring response to therapy for patients with brain tumors.

[Utility of PET/CT in evaluation of haed and neck carcinoma--preliminary report on the basis of presented cases]

18F-fluorodeoxyglucose (FDG)-positron emission tomography (PET)/computed tomography (CT) offers advantages over PET alone, which is limited by poor anatomic localization and CT alone, which provides morphologic data only. Fusion of PET and CT images allows for precise target delineation for head and neck cancer compared with CT alone. The aim of this article is to evaluate the effect of the use of PET/CT in patients with head and neck cancer. We present four patients whose management was influenced by the implementation of combined PET/CT imaging. We conclude that PET/CT allows detection of recurrent neoplasm, carcinoma of unknown origin, second primary sites, distant metastases, tumor surveillance, staging, and planning radiation therapy.

Imaging the immune response to monitor tumor immunotherapy

The goal of cancer immunotherapy is to promote antitumor immunity, and novel approaches include vaccination, adoptive transfer of tumor-reactive T cells, and administration of monoclonal antibodies and small molecules that target immune regulatory pathways. The molecular and cellular events responsible for tumor rejection are not completely defined and correlative studies have been used to help understand the mechanisms and extent of immune activation and tumor regression with these approaches. The real-time monitoring of immune responses to immunotherapy has been challenging as specific cell subsets may be difficult to define, and molecular pathways have evolved functionally diverse outcomes in different cells and in different tissues. Recently, improvements in optics and digital imaging have led to novel imaging techniques that make it possible to track the migration of individual immune cells ex vivo and in vivo, and to detect the dynamic interactions between T cells and antigen-presenting cells or tumor cells within complex microenvironments, including lymphoid tissue and established tumors. This review will explain some of the more established imaging techniques and discuss their role in monitoring the immune response in patients treated with various tumor immunotherapy approaches.

PET/CT in Radiation Therapy Planning for Breast Cancer

PET/computed tomography-based imaging is a valuable and useful test in the staging and restaging of breast cancer, especially in patients who have recurrent or locally advanced breast cancer. Its greatest clinical applications are in the detection and definition of the extent of recurrent or metastatic disease. However, the potential to improve radiation treatment planning by allowing for the tailoring of comprehensive radiation portals, particularly for locally advanced or recurrent breast cancer, makes it one of the most promising tools in the era of image-guided radiation therapy.

A Markov decision process approach to temporal modulation of dose fractions in radiation therapy planning

The current state of the art in cancer treatment by radiation optimizes beam intensity spatially such that tumors receive high dose radiation whereas damage to nearby healthy tissues is minimized. It is common practice to deliver the radiation over several weeks, where the daily dose is a small constant fraction of the total planned. Such a 'fractionation schedule' is based on traditional models of radiobiological response where normal tissue cells possess the ability to repair sublethal damage done by radiation. This capability is significantly less prominent in tumors. Recent advances in quantitative functional imaging and biological markers are providing new opportunities to measure patient response to radiation over the treatment course. This opens the door for designing fractionation schedules that take into account the patient's cumulative response to radiation up to a particular treatment day in determining the fraction on that day. We propose a novel approach that, for the first time, mathematically explores the benefits of such fractionation schemes. This is achieved by building a stylistic Markov decision process (MDP) model, which incorporates some key features of the problem through intuitive choices of state and action spaces, as well as transition probability and reward functions. The structure of optimal policies for this MDP model is explored through several simple numerical examples.

PET/CT for the staging and follow-up of patients with malignancies

Positron emission tomography (PET) and computed tomography (CT) complement each other's strengths in integrated PET/CT. PET is a highly sensitive modality to depict the whole-body distribution of positron-emitting biomarkers indicating tumour metabolic activity. However, conventional PET imaging is lacking detailed anatomical information to precisely localise pathologic findings. CT imaging can readily provide the required morphological data. Thus, integrated PET/CT represents an efficient tool for whole-body staging and functional assessment within one examination. Due to developments in system technology PET/CT devices are continually gaining spatial resolution and imaging speed. Whole-body imaging from the head to the upper thighs is accomplished in less than 20 min. Spatial resolution approaches 2-4mm. Most PET/CT studies in oncology are performed with (18)F-labelled fluoro-deoxy-D-glucose (FDG). FDG is a glucose analogue that is taken up and trapped within viable cells. An increased glycolytic activity is a characteristic in many types of cancers resulting in avid accumulation of FDG. These tumours excel as "hot spots" in FDG-PET/CT imaging. FDG-PET/CT proved to be of high diagnostic value in staging and restaging of different malignant diseases, such as colorectal cancer, lung cancer, breast cancer, head and neck cancer, malignant lymphomas, and many more. The standard whole-body coverage simplifies staging and speeds up decision processes to determine appropriate therapeutic strategies. Further development and implementation of new PET-tracers in clinical routine will continually increase the number of PET/CT indications. This promotes PET/CT as the imaging modality of choice for working-up of the most common tumour entities as well as some of the rare malignancies.

PET monitoring of therapy response in head and neck squamous cell carcinoma

In the Western world, more than 90% of head and neck cancers are head and neck squamous cell carcinomas (HNSCCs). The most appropriate treatment approach for HNSCC varies with the disease stage and disease site in the head and neck. Concurrent chemoradiotherapy has become a widely used means for the definitive treatment of locoregionally advanced HNSCC. Although this multimodality treatment provides higher response rates than radiotherapy alone, the detection of residual viable tumor after the end of therapy remains an important issue and is one of the major applications of (18)F-FDG PET. Studies have shown that negative (18)F-FDG PET or PET/CT results after concurrent chemoradiotherapy have a high negative predictive value (>95%), whereas the positive predictive value is only about 50%. However, when applied properly, FDG PET/CT can exclude residual disease in most patients, particularly patients with residual enlarged lymph nodes who would otherwise undergo neck dissection. In contrast to other malignancies, data are limited on the utility of (18)F-FDG PET for monitoring the response to induction chemotherapy in HNSCC or for assessing treatment response early during the course of definitive chemoradiotherapy. The proliferation marker (18)F-3'-deoxy-3'fluorothymidine is currently under study for this purpose. Beyond standard chemotherapy, newer treatment regimens in HNSCC take advantage of our improved understanding of tumor biology. Two molecules important in the progression of HNSCC are the epidermal growth factor receptor and the vascular endothelial growth factor (VEGF) and its receptor VEGF-R. Drugs attacking these molecules are now under study for HNSCC. PET probes have been developed for imaging the presence of these molecules in HNSCC and their inhibition by specific drug interaction; the relevance of these probes for response assessment in HNSCC will be discussed. Hypoxia is a common phenomenon in HNSCC and renders cancers resistant to chemo- and radiotherapy. Imaging and quantification of hypoxia with PET probes is under study and may become a prerequisite for overcoming chemo- and radioresistance using radiosensitizing drugs or hypoxia-directed irradiation techniques and for monitoring the response to these techniques in selected groups of patients. Although (18)F-FDG PET/CT will remain the major clinical tool for monitoring treatment in HNSCC, other PET probes may have a role in identifying patients who are likely to benefit from treatment strategies that include biologic agents such as epidermal growth factor receptor inhibitors or VEGF inhibitors.