The clinical application of PET/CT: a contemporary review

The combination of positron emission tomography (PET) scanners and x-ray computed tomography (CT) scanners into a single PET/CT scanner has resulted in vast improvements in the diagnosis of disease, particularly in the field of oncology. A decade on from the publication of the details of the first PET/CT scanner, we review the technology and applications of the modality. We examine the design aspects of combining two different imaging types into a single scanner, and the artefacts produced such as attenuation correction, motion and CT truncation artefacts. The article also provides a discussion and literature review of the applications of PET/CT to date, covering detection of tumours, radiotherapy treatment planning, patient management, and applications external to the field of oncology

Regmentation: A New View of Image Segmentation and Registration

Image segmentation and registration have been the two major areas of research in the medical imaging community for decades and still are. In the context of radiation oncology, segmentation and registration methods are widely used for target structure definition such as prostate or head and neck lymph node areas. In the past two years, 45% of all articles published in the most important medical imaging journals and conferences have presented either segmentation or registration methods. In the literature, both categories are treated rather separately even though they have much in common. Registration techniques are used to solve segmentation tasks (e.g. atlas based methods) and vice versa (e.g. segmentation of structures used in a landmark based registration). This article reviews the literature on image segmentation methods by introducing a novel taxonomy based on the amount of shape knowledge being incorporated in the segmentation process. Based on that, we argue that all global shape prior segmentation methods are identical to image registration methods and that such methods thus cannot be characterized as either image segmentation or registration methods. Therefore we propose a new class of methods that are able solve both segmentation and registration tasks. We call it regmentation. Quantified on a survey of the current state of the art medical imaging literature, it turns out that 25% of the methods are pure registration methods, 46% are pure segmentation methods and 29% are regmentation methods. The new view on image segmentation and registration provides a consistent taxonomy in this context and emphasizes the importance of regmentation in current medical image processing research and radiation oncology image-guided applications

Two-step-fusion 18F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (FDG-PET/CT) based radiotherapy in locally advanced oropharyngeal cancer

Aims. To develop two-step-fusion 18F-fluorodeoxyglucose Positron Emission Tomography/Computed Tomography (FDG-PET/CT) based radiotherapy in locally advanced oropharyngeal cancer at the Beatson West of Scotland Cancer Centre and evaluate the technical and clinical aspect of this multi-modality imaging methodology. Methods. I conducted a radiotherapy service development project at the Beatson. Contrast enhanced radiotherapy simulation CT (CTsim) and FDG-PET/CT were acquired separately with the same set-up and fused using an automatic rigid fusion algorithm (Eclipse, Varian). The fusion accuracy was assessed with the spatial reproducibility index (R=intersection/union ratio) of bony structures. Radiotherapy target volumes for both primary (T) and nodal disease (N) were defined separately on CTsim and FDG-PET/CT using visual assessment (PET/CT-vis) and segmentation with 50% SUVmax (PET/CT-50%). Volumes (cc) and spatial reproducibility (R) were calculated for the various volumes. Changes in TNM staging definition due to FDG-PET/CT were evaluated and compared with the staging based on morphological imaging (CT±MRI) and clinical information (endoscopy). SUVmax was calculated for T and N and correlated with the HPV-status and the oropharyngeal prognostic groups (low risk: HPV+, ≤10 pack years smoking history; intermediate risk: HPV+, >10 pack years smoking history; high risk: HPV-). Patients were treated using the target volumes defined with PET/CT-vis. Volumetric Modulated Arc Therapy (VMAT) was used with 65Gy and 54Gy in 30 fractions to high and low risk volumes respectively. Tumour outcome and late toxicity were recorded and compared with an internal non-PET/CT-based oropharyngeal series. Data were analysed using Stata v14.2 (StataCorp LLC, Texas). Data were summarised using medians (with range or inter-quartile range IQR). P-values were calculated to test for differences. All tests were 2-sided and a p-value <0.05 was considered statistically significant. Results. A total of 30 patients were enrolled. The fusion accuracy of FDG-PET/CT and CTsim was calculated in 14 patients and resulted 0.89 (0.83-0.92). SUVmax was recorded for both primary and nodal disease in 27 patients. Among these patients median SUVmax was significantly higher in the primary tumour compared to the nodal disease (19.0 versus 14.0 g/ml, p=0.0001). Median SUVmax was higher in HPV- compared to HPV+ patients for both primary tumour (21.0 vs 16.9 g/ml) and nodal disease (17.0 vs 10.0 g/ml), however these differences were not statistically significant. Nodal SUVmax was higher in the high risk (i.e. HPV-) compared to the intermediate and low risk (i.e. HPV+) group (17.0 vs 8.8 vs 15.o g/ml) although again these differences were not statistically significant. FDG-PET/CT down-staged and up-staged T and N in 6/30 (20%) and 17/30 (57%) patients. Unsuspected distant metastases were not detected in any of the patients at baseline. The median volume of T and N defined with PET/CTvis and CTsim was 11.5cc vs 16.5cc (p=0.31) and 13.8cc vs 11.1cc (p=0.42), with reproducibility index R=0.49 and R=0.47 respectively. PET/CT50% identified hyper-metabolic sub-volumes inside PET/CTvis for both T and N: 4.6cc vs 11.5cc (p=0.001) and 3.5cc vs 13.8cc (p=0.04), DICE index 1. At median follow-up time of 16 (1-44) months, 74% of the patients had complete response, whilst 22% had progressive disease with median time to progression of 6.1 (3.1-15.9) months. The estimated overall survival (OS) at 2 years was 74% (95%CI, 49%-88%). In the sub-group analysis, the estimated OS at 2 years was 83% (95%CI 27-97%), 87% (39-98%) and 67% (19-90%) in the low, intermediate and high risk category respectively. Grade≥2 late xerostomia, dysphagia, dysgeusia and fatigue were recorded in 36%, 35%, 0% and 14% of the patients. Grade≥2 dysphagia was recorded in 38% of the patients who presented with bilateral and unilateral neck nodes (p=1.0). Conclusions. I developed a 2-step-fusion methodology between FDG-PET/CT and CTsim. PET/CT fusion has been introduced in the routine radiotherapy planning at the Beatson for selected oropharyngeal cancer patients. My data suggest that HPV- are more metabolically active than HPV+ oropharyngeal cancers. My results support the hypothesis of treatment intensification in the high-risk group because more biologically aggressive. Dose intensification to hypermetabolic tumour sub-volumes may improve the outcome especially in the high-risk sub-group. FDG-PET/CT modified tumour staging and radiotherapy target volumes. My outcome and late toxicity results are similar to an internal non-PET-based series and other published studies. A prospective randomised study stratified by risk group would clarify if a true difference exists in outcome and late toxicity between PET-based and non-PET-based radiotherapy

The value of simultaneous co-registration of 99mTc- MDP and 131Iodine in metastatic differentiated thyroid carcinoma

BACKGROUND: The lack of anatomical details in standard 131Iodine whole body scanning (131I WBS) interferes with the proper localization of metastatic differentiated thyroid carcinoma (DTC) lesions. In addition, nearby or overlapping variable physiological distribution of 131I may affect the specificity of 131I uptake, giving indeterminate results. The aim of this study was to demonstrate the clinical usefulness of simultaneous co-registration of 99mTc MDP bone scanning as an anatomical landmark with 131I scanning in the evaluation of metastatic DTC. MATERIAL AND METHODS: Twenty-five patients (16 females and 9 males, mean age &#177; SD = 52 &#177; 13 years) with metastatic DTC (17 papillary, 8 follicular), were included. Whole body scanning using a 256 x 1024 matrix and an 8 cm/min scan rate were obtained 48 hours after oral administration of 185-370 MBq 131I and 2 hours after IV administration of 185-370 MBq 99mTc MDP using a dual head gamma camera equipped with high energy parallel hole collimators. Occasionally, additional simultaneous co-registration of localised detailed images was also performed using a 256 x 256 matrix size. The two planar images were fused with optional fusion of SPECT images. The data from standard 131I scanning and fused 131I/ 99mTc-MDP scanning were separately assessed by two nuclear medicine physicians. Fusion images were considered to improve image interpretation in comparison with standard 131I scanning when they provided better localization of lesions. RESULTS: All lesions in the present study were validated by radiological images and clinical follow up for at least 12 months. Forty-eight metastatic lesions were confirmed as follows: 2 in the skull, 10 in the neck, 20 in the thorax, 12 in the pelvic-abdominal region and 4 in the extremities. Standard 131I WBS showed 54 extra-thyroidal foci with 8 false positive lesions of which 2 were located in the scalp and 6 in the pelvic-abdominal region extra-skeleton (i.e. sensitivity 100%, specificity 86%). Out of the 48 validated lesions, 16 were indeterminately localized: 10 in the thorax (3 mediastinal nodal lesions, 5 vertebral lesions and 2 ribs) and 6 in the pelvic-abdominal region (2 upper sacral, 2 sacroiliac region and 2 ischial bone). Fusion images confirmed the precise localization of the pathological uptake in the validated 48 lesions (sensitivity 100%, specificity 100%). There were 2 (4%) indeterminate lesions in fused planar imaging that were clearly localized via fused SPECT images. CONCLUSIONS: Fusion images using simultaneous co-registration of 131I and 99mTc MDP scanning is a simple and feasible technique that improves the anatomically limited interpretation of scintigraphy using 131I alone in patients with metastatic differentiated thyroid carcinoma. The diagnostic advantage of this technique seems to be more apparent in the thoracic and pelvic- abdominal regions in contrast to the neck and extremities

FDG-PET/CT imaging for staging and radiotherapy treatment planning of head and neck carcinoma

<p>Abstract</p> <p>Background</p> <p>Positron emission tomography (PET) has a potential improvement for staging and radiation treatment planning of various tumor sites. We analyzed the use of ¹⁸F-fluorodeoxyglucose (FDG)-PET/computed tomography (CT) images for staging and target volume delineation of patients with head and neck carcinoma candidates for radiotherapy.</p> <p>Methods</p> <p>Twenty-two patients candidates for primary radiotherapy, who did not receive any curative surgery, underwent both CT and PET/CT simulation. Gross Tumor Volume (GTV) was contoured on CT (CT-GTV), PET (PET-GTV), and PET/CT images (PET/CT-GTV). The resulting volumes were analyzed and compared.</p> <p>Results</p> <p>Based on PET/CT, changes in TNM categories and clinical stage occurred in 5/22 cases (22%). The difference between CT-GTV and PET-GTV was not statistically significant (p = 0.2) whereas the difference between the composite volume (PET/CT-GTV) and CT-GTV was statistically significant (p < 0.0001).</p> <p>Conclusion</p> <p>PET/CT fusion images could have a potential impact on both tumor staging and treatment planning.</p

Comparative Study With New Accuracy Metrics for Target Volume Contouring in PET Image Guided Radiation Therapy

[EN] The impact of positron emission tomography (PET) on radiation therapy is held back by poor methods of defining functional volumes of interest. Many new software tools are being proposed for contouring target volumes but the different approaches are not adequately compared and their accuracy is poorly evaluated due to the ill-definition of ground truth. This paper compares the largest cohort to date of established, emerging and proposed PET contouring methods, in terms of accuracy and variability. We emphasize spatial accuracy and present a new metric that addresses the lack of unique ground truth. Thirty methods are used at 13 different institutions to contour functional volumes of interest in clinical PET/CT and a custom-built PET phantom representing typical problems in image guided radiotherapy. Contouring methods are grouped according to algorithmic type, level of interactivity and how they exploit structural information in hybrid images. Experiments reveal benefits of high levels of user interaction, as well as simultaneous visualization of CT images and PET gradients to guide interactive procedures. Method-wise evaluation identifies the danger of over-automation and the value of prior knowledge built into an algorithm.For retrospective patient data and manual ground truth delineation, the authors wish to thank S. Suilamo, K. Lehtio, M. Mokka, and H. Minn at the Department of Oncology and Radiotherapy, Turku University Hospital, Finland. This study was funded by the Finnish Cancer Organisations.Shepherd, T.; Teräs, M.; Beichel, RR.; Boellaard, R.; Bruynooghe, M.; Dicken, V.; Gooding, MJ.... (2012). Comparative Study With New Accuracy Metrics for Target Volume Contouring in PET Image Guided Radiation Therapy. IEEE Transactions on Medical Imaging. 31(12):2006-2024. doi:10.1109/TMI.2012.2202322S20062024311