Dual-modality PET/CT tomography for clinical oncology.

Diagnosis and follow-up in clinical oncology are traditionally based on computed tomography (CT). In recent years, however, functional imaging using positron emission tomography (PET) has been recognized as an important imaging modality and adjunct to CT that provides complementary metabolic information in many oncology applications. To overcome the challenges of aligning independently acquired PET and CT image sets several ad hoc concepts of integrating PET and CT imaging in a single device have been proposed. This article comments on the development of the first combined dual-modality PET/CT prototype at the University of Pittsburgh, and illustrates commercial advances to dual-modality PET/CT tomography. The current PET/CT designs from the major manufacturers comprise a commercial CT scanner in tandem with a commercial PET scanner. While the level of physical integration is actually less than that of the original prototype it is fair to assume that current PET/CT models may serve as intermediate solutions towards near-future design concepts that aim at greatly reduced costs of the dual-modality tomographs and offer a greater level of physical integration. The goal of the next generation of PET/CT systems is to design and build a device specifically for imaging the function and anatomy of cancer in the most informative and effective way without necessarily conceptualizing it as combined PET and CT scanners. Such a concept of a diagnostic imaging device relates more to a disease management approach rather than the usual division into medical specialities such as radiology and nuclear medicine.     

Role of PET/CT in malignant pediatric lymphoma

Introduction

Malignant pediatric lymphoma accounts for 10–15% of all pediatric cancers, (representing 2–3% of all malignancies), with a peak incidence between 5–9 years. Chemotherapy is usually the first and most common mode of treatment. The choice of treatment and prediction of prognosis depend on the histological type of tumor, initial staging, evaluating treatment response, and detection of early recurrence. Conventional imaging modalities have many limitations. PET/CT is more accurate, however so far the literature lacks the results of a large group of patients.

Aim of study

To report the role of PET/CT in the above-mentioned objectives at the newly established Children’s Cancer Hospital in Cairo, Egypt, which is one of the busiest dedicated pediatric oncology centers of such purposes in the world. All findings were proven by histopathology, clinically, and by clinical follow-up.

Patient population

A total of 152 patients (35 girls and 117 boys) with histologically proven malignant lymphoma (117 HD, 35 NHL) were included in this study. They were divided into four groups. Group I: 41 patients for initial staging. Group II: 51 patients for evaluating early treatment response after two to three cycles of chemotherapy. Group III: 42 patients for evaluating treatment response 4–8 weeks after the end of their treatment. Group IV: 18 patients evaluated for long-term follow-up. Results of PET/CT were compared with the other conventional imaging modalities (CIM).

Results

The sensitivity, specificity, accuracy, and positive and negative predictive values of PET/CT and CIM were as follows: In Group I: PET/CT modified staging and treatment in 11 out of 41 cases (26.8%), upstaged 5(12.2%) patients and down-staged six (14.6%) patients. Group II: 100%, 97.7%, 98%, 85.7%, 100%, respectively, for PET/CT and 83%, 66.6%, 68.6%, 25%, 96.7% for CIM respectively Group III: At the end of chemotherapy 100%, 90.9%, 92.8%, 75%, 100%, respectively, for PET/CT and 55.5%, 57.5%, 57.1%, 26.3%, 82.6% for CIM, respectively. Group IV: For long-term follow-up, all the parameters scored 100% for PET/CT, 100%, 38.4%, 72.2%, 50%, 100% for CIM, respectively.

Conclusion

PET/CT in pediatric lymphoma is more accurate than CIM. We recommend that it should be the first modality for all purposes in initial staging, evaluating treatment response and follow-up.     

A combined PET/CT scanner for clinical oncology.

The availability of accurately aligned, whole-body anatomical (CT) and functional (PET) images could have a significant impact on diagnosing and staging malignant disease and on identifying and localizing metastases. Computer algorithms to align CT and PET images acquired on different scanners are generally successful for the brain, whereas image alignment in other regions of the body is more problematic. METHODS: A combined PET/CT tomograph with the unique capability of acquiring accurately aligned functional and anatomical images for any part of the human body has been designed and built. The PET/CT scanner was developed as a combination of a Siemens Somatom AR.SP spiral CT and a partial-ring, rotating ECAT ART PET scanner. All components are mounted on a common rotational support within a single gantry. The PET and CT components can be operated either separately, or in combined mode. In combined mode, the CT images are used to correct the PET data for scatter and attenuation. Fully quantitative whole-body images are obtained for an axial extent of 100 cm in an imaging time of less than 1 h. When operated in PET mode alone, transmission scans are acquired with dual 137Cs sources. RESULTS: The scanner is fully operational and the combined device has been operated successfully in a clinical environment. Over 110 patients have been imaged, covering a range of different cancers, including lung, esophageal, head and neck, melanoma, lymphoma, pancreas, and renal cell. The aligned PET and CT images are used both for diagnosing and staging disease and for evaluating response to therapy. We report the first performance measurements from the scanner and present some illustrative clinical studies acquired in cancer patients. CONCLUSION: A combined PET and CT scanner is a practical and effective approach to acquiring co-registered anatomical and functional images in a single scanning session.     

PET/CT在儿科恶性肿瘤中的应用进展

自PET/CT进入临床以来,主要应用于成人肿瘤的良恶性鉴别、原发灶寻找、临床分期和再分期、疗效评估、指导手术和放化疗计划以及预测生存期等方面,在儿童中的应用相对较少。从国内外相关的文献来看,PET/CT在国内儿科肿瘤诊断中的应用与国外有一定的差距。究其原因,主要与医用放射性核素知识的普及程度低,以及临床对PET/CT在儿科恶性肿瘤中的应用认知度不够相关,以致国内儿科PET/CT工作开展少,缺乏经验,从而形成一种恶性循环。该文主要从以上两方面分别进行阐述,希望促进PET/CT在儿科恶性肿瘤中的应用。     

Molecular imaging in oncology: the acceptance of PET/CT and the emergence of MR/PET imaging

In the last decade, PET-only systems have been phased out and replaced with PET-CT systems. This merger of a functional and anatomical imaging modality turned out to be extremely useful in clinical practice. Currently, PET-CT is a major diagnostic tool in oncology. At the dawn of the merger of MRI and PET, another breakthrough in clinical imaging is expected. The combination of these imaging modalities is challenging, but has particular features such as imaging biological processes at the same time in specific body locations.     

肿瘤分子成像:对PET/CT的认可及MR/PET的出现

在过去的10年中,单纯的PET系统已淘汰并被PET/CT系统所替代,这种功能与解剖相结合的成像方式在临床实践中非常有用。当前,PET/CT是一种主要的肿瘤诊断方法。PET与MRI的联合应用,预示了临床成像的另一突破。     

PET/CT and SPECT/CT dosimetry in children: the challenge to the pediatric imager

Both positron emission tomography (PET) and computed tomography (CT) contribute significantly to the effective dose from PET/CT imaging. For PET imaging, the effective dose is related to the administered activity and age of patient. For CT, there are many factors that determine effective dose. Effective dose is dependent on tube current (mA), tube potential (kVp), rotation speed, pitch, slice thickness, patient mass, and the exact volume of the patient that is being imaged. The CT scan may be acquired at exposure parameters similar to those used for diagnostic CT, but more commonly, the tube current is reduced and a localization CT scan of somewhat less than optimal diagnostic quality is obtained. A very low dose CT scan for attenuation correction may also be considered.     

18F-FDG PET/CT in evaluating non-CNS pediatric malignancies.

We reviewed our experience of (18)F-FDG PET/CT in noncentral nervous system (CNS) pediatric malignancies and evaluated if PET/CT provided additional information to conventional imaging (CI) examinations to determine the efficacy of this new imaging modality in the clinical setting. METHODS: One-hundred fifty-one consecutive FDG PET/CT examinations in 55 pediatric patients with non-CNS malignant tumors were reviewed. Among them, 108 PET/CT examinations were accompanied by CI, such as contrast CT or MRI, performed within a month of PET/CT in our hospital. Two radiologists reviewed the indication, purpose, and PET/CT findings and compared the findings with those of CI, if available, on the representative lesion in each of the 6 separate body regions. Positive findings included abnormal findings related to malignant lesions (suspected) as well as equivocal findings, in which the presence of malignancy could not be denied, but excluded findings considered to relate to past treatment. Accuracy of the findings was determined on the basis of the reference standard comprising histopathologic findings or informative follow-up of >1 y. An examination-based analysis was also performed in terms of additional information of PET/CT to CI. RESULTS: There were 56 PET/CT-positive-CI-positive, 26 PET/CT-positive-CI-negative, and 54 PET/CT-negative-CI-positive lesions in 108 PET/CT examinations accompanied by CI, of which 54, 20, and 52 exhibited accurate PET/CT findings, respectively. Seventeen of the 20 PET/CT true-positive-CI false-negative lesions represented small lymph nodes diagnosed as negative on CI. All 52 PET/CT true-negative-CI false-positive findings were observed in lesions in a posttreatment status including 30 mediastinal masses in lymphoma. Examination-based analysis revealed that additional information of PET/CT to CI was found in 37 (34%) of the 108 examinations: 23 (21%) as negative and 14 (13%) as positive PET/CT findings. CONCLUSION: PET/CT exhibited better diagnostic performance than CI and showed accurate findings in 90% (72/80) of lesions with discordant findings between them. Additional information of PET/CT to CI was observed in more than one third of examinations compared. PET/CT was demonstrated to be an accurate imaging modality in evaluating pediatric patients with non-CNS malignancies.     

PET/CT for staging and follow-up of pediatric nasopharyngeal carcinoma

Purpose

While FDG PET/CT for the evaluation of nasopharyngeal carcinoma (NPC) in adult patients has documented advantages and disadvantages compared with conventional imaging, to our knowledge, no studies of FDG PET/CT for the evaluation of NPC in pediatric patients have been performed. In this investigation, we studied the utility of FDG PET/CT in children with NPC.

Methods

The study group comprised 18 children with biopsy-proven NPC who underwent FDG PET/CT and MRI (total 38 pairs of images). All baseline and follow-up FDG PET/CT and MRI studies were independently reviewed for restaging of disease.

Results

The concordance between FDG PET/CT and MRI in T, N, and overall staging was 29%, 64%, and 43%, respectively. Compared with MRI, FDG PET/CT yielded lower T and overall staging and showed less cervical and retropharyngeal lymphadenopathy. The concordance between follow-up FDG PET/CT and MRI was 79% overall and 100% 9?months after therapy. In patients who achieved complete remission, FDG PET/CT showed disease clearance 3–6?months earlier than MRI. There were no false-positive or false-negative FDG PET/CT scans during follow-up.

Conclusion

FDG PET/CT may underestimate tumor extent and regional lymphadenopathy compared with MRI at the time of diagnosis, but it helps to detect metastases and clarify ambiguous findings. FDG PET/CT is sensitive and specific for follow-up and enables earlier determination of disease remission. FDG PET/CT is a valuable imaging modality for the evaluation and monitoring of NPC in pediatric patients.