Radiotherapy planning of lymphomas: role of metabolic imaging with PET/CT.

Accurate target delineation is an absolute requirement for modern radiotherapy planning. Historically, structural imaging modalities have been used for this purpose, but there is a considerable role for functional imaging with PET/CT to contribute in this area. PET/CT's role in radiotherapy planning is well established and its use is indispensable in the clinical management of the lymphomas, particularly Hodgkin Lymphoma. A crucial use of PET/CT is as a baseline scan for delineation of the initial lymphomatous involvement, since this will determine the contouring of the gross-, clinical- and planning-target volumes (GTV, CTV, PTV). This article reviews the principles of contemporary radiotherapy, examines the evidence for the contribution of PET/CT to radiotherapy planning in lymphoma and the practicalities and challenges of applying this powerful technology to this situation.

Pulmonary emboli imaging with (99m)Tc-labelled anti-D-dimer (DI-80B3) Fab' followed by SPECT.

OBJECTIVES: Pre-clinical experiments demonstrated that intravenous (99m)Tc labelled DI-DD-3B6/22-80B3 humanised anti-fibrin-D-dimer Fab' fragments ((99m)Tc-DI-80B3) allowed scintigraphic imaging of acute pulmonary emboli (PE). The aims of this clinical study were to determine the safety of (99m)Tc-DI-80B3 in patients with PE and evaluate the resulting scintigraphic images for the localisation of acute PE. MATERIALS/PATIENTS AND METHODS: (99m)Tc-DI-80B3 (0.5mg, 710-850MBq) was administered intravenously to subjects (n=14) with segmental or larger PE on recent contrast-enhanced helical CT scans. Thoracic SPECT scans were acquired 15 minutes, 2 hours and 4 hours afterwards. Subjects were followed for 90 days subsequently. RESULTS: There were no serious adverse events or antibody responses associated with (99m)Tc-DI-80B3 administration. Focal accumulations of (99m)Tc-DI-80B3 on the SPECT images of the thorax acquired at four hours corresponded to pulmonary emboli detected by CT. Two independent "blinded" SPECT readers identified 79% and 71% (respectively) of the right lung and 79% and 64% (respectively) of the left lung in which CT scans disclosed PE. CONCLUSIONS: (99m)Tc-DI-80B3 is well-tolerated in patients with acute PE and does not induce an immune response. (99m)Tc-DI-80B3 may offer a novel approach to imaging PE in a clinically acceptable timeframe without exposure to potentially nephrotoxic radiographic contrast agents.

Prevalence of non 18 F-fluorodeoxyglucose-avid incidental findings of clinical significance on whole body positron emission tomography/computed tomography: A review of 500 consecutive cases.

INTRODUCTION: The prevalence of incidental 18 F-fluorodeoxyglucose (FDG)-avid findings on positron emission tomography-computed tomography (PET/CT) has been extensively described. Few studies, however, have assessed the prevalence and significance of non-FDG-avid findings; pathology that is identified on review of the low-dose, non-contrast CT. The aim of this study was to determine the overall prevalence of non FDG-avid incidental findings on PET/CT and the prevalence of 'clinically significant' non FDG-avid pathology. METHODS: Five hundred consecutive whole body PET/CT studies performed in 2016 at a university affiliated tertiary hospital were retrospectively reviewed by two radiologists experienced in reporting PET/CT. Findings were categorized according to potential clinical relevance, and a targeted follow-up of clinically significant incidental findings was performed. RESULTS: Incidental findings were encountered in 463 of 500 (92.6%) patients. In 226 patients, these findings had been detected on previous imaging studies, with unknown incidental findings present in 237 of 500 (47.4%) patients. 113 of 500 (22.6%) patients had non-avid incidental findings of potentially major clinical significance, and in 35 patients (7.0%) these findings were considered previously unknown. The most common non-avid findings of potentially major significance were pulmonary nodules (6 mm or larger), moderate or large size pleural effusions, and vascular aneurysms. Unknown incidental findings of potentially major clinical significance were significantly higher in patients imaged for melanoma staging (P= 0.004). CONCLUSION: The prevalence of incidental findings of clinical significance that do not accumulate FDG in PET/CT is not insignificant. Routine systematic review of the low-dose CT is required to avoid missing potentially clinically important findings, in particular pleural effusions, vascular aneurysms and metastatic pulmonary nodules.

Molecular Imaging Using PET/CT for Radiation Therapy Planning for Adult Cancers: Current Status and Expanding Applications.

Accurate tumor delineation is a priority in radiation therapy (RT). Metabolic imaging has a key and evolving role in target volume selection and delineation. This is especially so for non-small cell lung cancer, squamous cell cancer of the head and neck, and lymphoma, for which positron emission tomography/computed tomography (PET/CT) is complimentary to structural imaging modalities, not only in delineating primary tumors, but also often in revealing previously undiagnosed regional nodal disease. At some sites, PET/CT has been confirmed to enable target size reduction compared with structural imaging alone, with enhanced normal tissue sparing and potentially allowing for dose escalation. These contributions often dramatically affect RT strategies. However, some limitations exist to the use of fluorodeoxyglucose-PET in RT planning, including its relatively poor spatial resolution and partial voluming effects for small tumors. A role is developing for contributions from metabolic imaging to RT planning at other tumor sites and exciting new applications for the use of non-fluorodeoxyglucose metabolic markers for RT planning.