Gustav K. von Schulthess

Radiation treatment planning with an integrated positron emission and computer tomography (PET/CT): A feasibility study

PURPOSE To investigate the usefulness of hardware coregistered PET/CT images for target volume definition. METHODS AND MATERIALS Thirty-nine patients presenting with various solid tumors were investigated. CT and a FDG-PET were obtained in treatment position in an integrated PET/CT scanner, and coregistered images were used for treatment planning. First, volume delineation was performed on the CT data. In a second step, the corresponding PET data were used as an overlay to the CT data to define the target volume. Delineation was done independently by two investigators. RESULTS Coregistered PET/CT showed good fusion accuracy. The GTV increased by 25% or more because of PET in 17% of cases with head-and-neck (2/12) and lung cancer (1/6), and in 33% (7/21) in cancer of the pelvis. The GTV was reduced > or =25% in 33% of patients with head-and-neck cancer (4/12), in 67% with lung cancer (4/6), and 19% with cancer of the pelvis (4/21). Overall, in 56% (22/39) of cases, GTV delineation was changed significantly if information from metabolic imaging was used in the planning process. The modification of the GTV translated into altered PTV changes exceeding >20% in 46% (18/39) of cases. With PET, volume delineation variability between two independent oncologists decreased from a mean volume difference of 25.7 cm(3) to 9.2 cm(3) associated with a reduction of the standard deviation from 38.3 cm(3) to 13.3 cm(3) (p = 0.02). In 16% of cases, PET/CT revealed distant metastasies, changing the treatment strategy from curative to palliative. CONCLUSION Integrated PET/CT for treatment planning for three-dimensional conformal radiation therapy improves the standardization of volume delineation compared with that of CT alone. PET/CT has the potential for reducing the risk for geographic misses, to minimize the dose of ionizing radiation applied to non-target organs, and to change the current practice to three-dimensional conformal radiation therapy planning by taking into account the metabolic and biologic features of cancer. The impact on treatment outcome remains to be demonstrated.

Positron emission tomography/computed tomography influences on the management of resectable pancreatic cancer and its cost-effectiveness.

Objective:We sought to determine the impact of positron emission tomography/computed tomography (PET/CT) on the management of presumed resectable pancreatic cancer and to assess the cost of this new staging procedure. Summary Background Data:PET using 18F-fluorodeoxyglucose (FDG) is increasingly used for the staging of pancreatic cancer, but anatomic information is limited. Integrated PET/CT enables optimal anatomic delineation of PET findings and identification of FDG-negative lesions on computed tomography (CT) images and might improve preoperative staging. Material and Methods:Patients with suspected pancreatic cancer who had a PET/CT between June 2001 to April 2004 were entered into a prospective database. Routine staging included abdominal CT, chest x-ray, and CA 19-9 measurement. FDG-PET/CT was conducted according to a standardized protocol, and findings were confirmed by histology. Cost benefit analysis was performed based on charged cost of PET/CT and pancreatic resection and included the time frame of staging and surgery. Results:Fifty-nine patients with a median age of 61 years (range, 40–80 years) were included in this analysis. Fifty-one patients had lesions in the head and 8 in the tail of the pancreas. The positive and negative predictive values for pancreatic cancer were 91% and 64%, respectively. PET/CT detected additional distant metastases in 5 and synchronous rectal cancer in 2 patients. PET/CT findings changed the management in 16% of patients with pancreatic cancer deemed resectable after routine staging (P = 0.031) and was cost saving. Conclusions:PET/CT represents an important staging procedure prior to pancreatic resection for cancer, since it significantly improvespatient selection and is cost-effective.

Infection imaging using whole-body FDG-PET

Abstract.The purpose of this study was to evaluate fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) for the detection of soft tissue and bone infections. Forty-five PET examinations in 39 patients (26 male, 13 female, age range 27–86 years) with suspected infectious foci were examined with whole- or partial-body PET scans using FDG. Twenty-seven scans were done in patients with soft tissue and 18 in patients with bone infections. Corrected and uncorrected transaxial PET images were acquired. Seven hundred and twelve body regions in these 45 PET scans were evaluated. Pathological findings were graded using a confidence scale from A to E (A, definitive infection; E, no infection). Disease status was defined in all patients by culture, biopsy or surgery and clinical follow-up. In 45 PET scans there were 40 true-positive, four false-positive and one false-negative findings. Twelve foci suspected to be infectious in nature on the basis of other imaging examinations were identified as negative by PET, thus representing true-negative findings. Sensitivities for the patients with soft tissue (STI) and bone infections (BI) and for the pooled data were 96%, 100% and 98%, respectively. As the calculation of specificity is not straightforward, it was calculated on a per lesion as well as on a per body region basis to permit estimation of an upper and a lower limit. On a per lesion basis, specificities were 70% (STI), 83% (BI) and 75% for the pooled data and on a per body region basis (dividing the body into 22 regions) they were 99% (STI), 99% (BI) and 99% for the pooled data. One false-negative result was found in a patient with cholangitis. It is concluded that PET appears to be a highly sensitive method to detect infectious foci. Specificity is more difficult to estimate, but is probably in the range from 70% to above 90%.

Detection of extrathoracic metastases by positron emission tomography in lung cancer

BACKGROUND Accurate staging of non-small cell lung cancer is essential for treatment planning. We evaluated in a prospective study the role of whole-body 2-[18F]fluoro-2-deoxy-D-glucose (FDG) positron emission tomography (PET) in mediastinal nodal staging with a positive predictive value of 96%. The study was continued to further evaluate the value of whole-body FDG PET in detecting unexpected extrathoracic metastases (ETMs) in patients qualifying for surgical treatment by conventional staging. METHODS One hundred patients underwent clinical evaluation, chest and upper abdominal computed tomography scan, mediastinoscopy (lymph nodes greater than 1 cm on computed tomography), and routine laboratory tests. In 94 patients with stage IIIa or less and 6 with suspected N3 a whole-body FDG PET was performed. If clinical signs of ETMs were present additional diagnostic methods were applied. All findings in the FDG PET were confirmed histologically or radiologically. RESULTS Unexpected ETMs were detected in 13 (14%) of 94 patients (stage IIIa or less) at 14 sites. In addition 6 of 94 patients were restaged up to N3 after PET. The suspected N3 disease (stage IIIb) on computed tomography was confirmed by PET in all 6 patients. There was no false positive finding of ETM. Weight loss was correlated with the occurrence of ETM: more than 5 kg, 5 of 13 patients (38%); more than 10 kg, 4 of 6 patients (67%). Pathologic laboratory findings were not predictive for ETM. CONCLUSIONS Whole-body FDG PET improves detection of ETMs in patients with non-small cell lung cancer otherwise elegible for operation. In 14% of patients (stage IIIa or less), ETMs were detected, and in total, 20% of the patients were understaged.

Characterization of Dysfunctional Myocardium by Positron Emission Tomography and Magnetic Resonance Relation to Functional Outcome After Revascularization

Background—Metabolic assessment of dysfunctional myocardium by PET allows prediction of functional recovery after revascularization. Contrast-enhanced MR (ce-MR) discriminates transmural distribution of viable and scar tissue with excellent spatial resolution. Both techniques were applied in ischemic chronic left ventricular dysfunction to relate metabolism and tissue composition to changes of contractile function after revascularization. Methods and Results—Nineteen patients with myocardial infarctions (>3 months) were studied by MR and PET, and 10 patients were followed by MR 11±2 months after revascularization. In 56 to 64 segments/heart, systolic wall thickening, viable mass, and thickness of viable rim tissue were determined by MR (inversion-recovery MR with 0.25 mmol/kg Gd-chelate). [18F]Fluorodeoxyglucose (FDG) uptake and resting perfusion (13N-ammonia) were determined by PET. Viable tissue per segment on ce-MR correlated with FDG uptake per segment (r =0.62 and 0.82 for segments with and without flow metabolism mismatch, P <0.0001). FDG uptake ≥50% (a predictor of functional recovery) corresponded to a viable rim thickness of 4.5 mm on ce-MR. Thick (>4.5 mm) and metabolically viable segments (≥50% FDG uptake) showed functional recovery in 85%, whereas thin metabolically nonviable segments improved function in 13% (P <0.0005). Metabolically viable segments with a thin viable rim and thick segments with reduced FDG uptake improved function in only 36% and 23% of segments, respectively (NS versus thin metabolically nonviable). In these 2 classes of segments, scar per segment was higher than in thick viable segments (P <0.0001). Conclusions—Metabolism and tissue composition discriminate various classes of dysfunctional myocardium. Most metabolically viable segments with a thick viable rim on ce-MR recover function after revascularization, whereas all other classes showed low recovery rates of contractile function.

Head and neck imaging with PET and PET/CT: artefacts from dental metallic implants

Abstract. Germanium-68 based attenuation correction (PETGe68) is performed in positron emission tomography (PET) imaging for quantitative measurements. With the recent introduction of combined in-line PET/CT scanners, CT data can be used for attenuation correction. Since dental implants can cause artefacts in CT images, CT-based attenuation correction (PETCT) may induce artefacts in PET images. The purpose of this study was to evaluate the influence of dental metallic artwork on the quality of PET images by comparing non-corrected images and images attenuation corrected by PETGe68 and PETCT. Imaging was performed on a novel in-line PET/CT system using a 40-mAs scan for PETCT in 41 consecutive patients with high suspicion of malignant or inflammatory disease. In 17 patients, additional PETGe68 images were acquired in the same imaging session. Visual analysis of fluorine-18 fluorodeoxyglucose (FDG) distribution in several regions of the head and neck was scored on a 4-point scale in comparison with normal grey matter of the brain in the corresponding PET images. In addition, artefacts adjacent to dental metallic artwork were evaluated. A significant difference in image quality scoring was found only for the lips and the tip of the nose, which appeared darker on non-corrected than on corrected PET images. In 33 patients, artefacts were seen on CT, and in 28 of these patients, artefacts were also seen on PET imaging. In eight patients without implants, artefacts were seen neither on CT nor on PET images. Direct comparison of PETGe68 and PETCT images showed a different appearance of artefacts in 3 of 17 patients. Malignant lesions were equally well visible using both transmission correction methods. Dental implants, non-removable bridgework etc. can cause artefacts in attenuation-corrected images using either a conventional 68Ge transmission source or the CT scan obtained with a combined PET/CT camera. We recommend that the non-attenuation-corrected PET images also be evaluated in patients undergoing PET of the head and neck.

Impact of positron emission tomography on the initial staging and therapy in locoregional advanced squamous cell carcinoma of the head and neck.

Objective To evaluate the impact of 18F‐fluoro‐deoxy‐glucose positron emission tomography after standard diagnostic workup in patients with advanced head and neck squamous cell carcinoma on staging and radiation treatment planning.

Etiology of solitary extrapulmonary positron emission tomography and computed tomography findings in patients with lung cancer

PURPOSE The aim of this prospective study was to assess the incidence and the nature of solitary extrapulmonary [18F] fluorodeoxyglucose (FDG) accumulations in patients with non-small-cell lung cancer (NSCLC) staged with integrated positron emission tomography and computed tomography (PET/CT) and to evaluate the impact on management. PATIENTS AND METHODS A total of 350 patients with NSCLC underwent whole-body PET/CT imaging. All solitary extrapulmonary FDG accumulations were evaluated by histopathology, further imaging, or clinical follow-up. RESULTS PET/CT imaging revealed extrapulmonary lesions in 110 patients. In 72 patients (21%), solitary lesions were present. A diagnosis was obtained in 69 of these patients, including 37 (54%) with solitary metastases and 32 (46%) with lesions unrelated to the lung primary. Histopathologic examinations of these 32 lesions revealed a second clinically unsuspected malignancy or a recurrence of a previous diagnosed carcinoma in six patients (19%) and a benign tumor or inflammatory lesion in 26 patients (81%). The six malignancies consisted of carcinoma of the breast in two patients, and carcinoma of the orbit, esophagus, prostate, and non-Hodgkins lymphoma in one patient each. Benign tumors and inflammatory lesions included eight colon adenomas, four Warthins tumors, one granuloma of the lower jaw, one adenoma of the thyroid gland, one compensatory muscle activity due to vocal chord palsy, two occurrences of arthritis, three occurrences of reflux esophagitis, two occurrences of pancreatitis, two occurrences of diverticulitis, one hemorrhoidal inflammation, and one rib fracture. CONCLUSION Solitary extrapulmonary FDG accumulations in patients with newly diagnosed lung cancer should be analyzed critically for correct staging and optimal therapy, given that up to half of the lesions may represent unrelated malignancies or benign disease.

A look ahead: PET/MR versus PET/CT

IntroductionIntegration of positron emission tomography (PET) and magnetic resonance (MR) has become a topic of increasing interest to the imaging community over the past two years.ObjectivesIn this text, the authors attempt to distinguish facts from fiction concerning such integrated systems. Analysis of existing information of combined imaging on existing brain PET/MR systems and imaging experience with PET-computed tomography (CT) is reviewed. Various types of system integration of PET and MR are discussed with completely independent systems on one hand and completely integrated systems with the possibility of simultaneous data acquisition on the other hand. Furthermore, it is discussed, what simultaneous data acquisition with nuclear imaging systems combined with MR or CT really means, as technical simultaneity may not be relevant in light of the pharmacokinetics of the nuclear tracers used.DiscussionThe authors conclude that combining PET/MR is an interesting research endeavor with uncertain outcome. They argue that, while completely simultaneous brain applications are of research interest immediately, clinical applications do not currently warrant the construction of fully integrated systems. Systems adjacent to each other, where imaging tables are linked with a patient “shuttle” thereby requiring only patient translation but no repositioning, may be a good start to assess the value of integrated PET/MR.

Absolute quantification of cerebral blood flow with magnetic resonance, reproducibility of the method, and comparison with H215O positron emission tomography

While H215O positron emission tomography (PET) is still the gold standard in the quantitative assessment of cerebral perfusion (rCBF), its technical challenge, limited availability, and radiation exposure are disadvantages of the method. Recent work demonstrated the feasibility of magnetic resonance (MR) for quantitative cerebral perfusion imaging. There remain open questions, however, especially regarding reproducibility. The main purpose of this study was to assess the accuracy and reproducibility of MR-derived flow values to those derived from H215O PET. Positron emission tomography and MR perfusion imaging was performed in 20 healthy male volunteers, who were chronic smokers, on day 1 and day 3 of a 4-day hospitalization. Subjects were randomly assigned to one of two groups, each with 10 subjects. One group was allowed to smoke as usual during the hospitalization, while the other group stopped smoking from day 2. Positron emission tomography and MR images were coregistered and rCBF was determined in two regions of interest, defined over gray matter (gm) and white matter (wm), yielding rCBFPETgm, rCBFMRgm, rCBFPETwm, and rCBFMRwm. Bland-Altman analysis was used to investigate reproducibility by assessing the difference rCBFday3 - rCBFday1 in eight continual-smoker volunteers. The analysis showed a good reproducibility for PET, but not for MR. Mean ± SD of the difference rCBFday3 - rCBFday1 in gray matter was 6.35 ± 21.06 and 0.49 ± 5.27 mL · min−1 · 100 g−1 for MR and PET, respectively; the corresponding values in white matter were 2.60 ± 15.64 and −1.14 ± 4.16 mL · min−1 · 100 g−1. The Bland-Altman analysis was also used to assess MRI and PET agreement comparing rCBF measured on day 1. The analysis demonstrated a reasonably good agreement of MR and PET in white matter (rCBFPETwm - rCBFMRwm; −0.09 ± 7.23 mL · min−1 · 100 g−1), while in gray matter a reasonable agreement was only achieved after removing vascular artifacts in the MR perfusion maps (rCBFPETgm - rCBFMRgm; −11.73 ± 14.52 mL · min−1 · 100 g−1). In line with prior work, these results demonstrate that reproducibility was overall considerably better for PET than for MR. Until reproducibility is improved and vascular artifacts are efficiently removed, MR is not suitable for reliable quantitative perfusion measurements.