Quantitative analysis shows that contrast medium in positron emission tomography/computed tomography may cause significant artefacts

Specific recommendations for accurate and direct use of PET-CT in PET guided radiotherapy for head and neck sites

PURPOSE

To provide specific experience-based guidance and recommendations for centers wishing to develop, validate, and implement an accurate and efficient process for directly using positron emission tomography-computed tomography (PET-CT) for the radiotherapy planning of head and neck cancer patients.

METHODS

A PET-CT system was modified with hard-top couch, external lasers and radiotherapy immobilization and indexing devices and was subject to a commissioning and quality assurance program. PET-CT imaging protocols were developed specifically for radiotherapy planning and the image quality and pathway tested using phantoms and five patients recruited into an in-house study. Security and accuracy of data transfer was tested throughout the whole data pathway. The patient pathway was fully established and tested ready for implementation in a PET-guided dose-escalation trial for head and neck cancer patients.

RESULTS

Couch deflection was greater than for departmental CT simulator machines. An area of high attenuation in the couch generated image artifacts and adjustments were made accordingly. Using newly developed protocols CT image quality was suitable to maintain delineation and treatment accuracy. Upon transfer of data to the treatment planning system a half pixel offset between PET and CT was observed and corrected. By taking this into account, PET to CT alignment accuracy was maintained below 1 mm in all systems in the data pathway. Transfer of structures delineated in the PET fusion software to the radiotherapy treatment planning system was validated.

CONCLUSIONS

A method to perform direct PET-guided radiotherapy planning was successfully validated and specific recommendations were developed to assist other centers. Of major concern is ensuring that the quality of PET and CT data is appropriate for radiotherapy treatment planning and on-treatment verification. Couch movements can be compromised, bore-size can be a limitation for certain immobilization techniques, laser positioning may affect setup accuracy and couch deflection may be greater than scanners dedicated to radiotherapy. The full set of departmental commissioning and routine quality assurance tests applied to radiotherapy CT simulators must be carried out on the PET-CT scanner. CT image quality must be optimized for radiotherapy planning whilst understanding that the appearance will differ between scanners and may affect delineation. PET-CT quality assurance schedules will need to be added to and modified to incorporate radiotherapy quality assurance. Methods of working for radiotherapy and PET staff will change to take into account considerations of both parties. PET to CT alignment must be subject to quality control on a loaded and unloaded couch preferably using a suitable emission phantom, and tested throughout the whole data pathway. Data integrity must be tested throughout the whole pathway and a system included to verify that delineated structures are transferred correctly. Excellent multidisciplinary team communication and working is vital, and key staff members on both sides should be specifically dedicated to the project. Patient pathway should be clearly devised to optimize patient care and the resources of all departments. Recruitment of a cohort of patients into a methodology study is valuable to test the quality assurance methods and pathway.

The clinical use of PET/CT in the evaluation of melanoma

Positron emission tomography combined with computed tomography (PET/CT) has emerged in the last decade as a dominant imaging modality used for staging, monitoring response and surveillance of various cancers, including melanoma. Using 2-deoxy-2-((18)F)fluoro-D-glucose ((18)F-FDG) as the radiopharmaceutical, PET/CT has demonstrated its efficacy and its utility in the management of patients with advanced melanoma. Nonetheless, challenges remain in the early stage evaluation of melanoma and in the development of novel radiotracers to better characterize lesions found on PET/CT. This chapter focuses on the advantages and limitations of this imaging modality in melanoma. We also detail and describe the approach to perform (18)F-FDG PET/CT, the methods to accurately quantify lesions, as well as the pearls/pitfalls of image interpretation. Finally, an overview of preclinical and investigational clinical radiopharmaceuticals is presented.

Evaluation of thymic tumors with 18F-FDG PET-CT: a pictorial review

Thymic tumors represent a broad spectrum of neoplastic disorders and pose considerable diagnostic difficulties. A non-invasive imaging study to determine the nature of thymic lesions can have significant impact on management of such tumors. 18F-flurorodeoxyglucose (18F-FDG) positron emission tomography-computed tomography (PET-CT) has shown promising results in characterization of thymic tumors. The objective of this article is to provide an illustrative tutorial highlighting the clinical utility of 18F-FDG PET-CT imaging in patients with thymic tumors. We have pictorially depicted the 18F-FDG PET-CT salient imaging characteristics of various thymic tumors, both epithelial and non-epithelial. Also discussed is the dynamic physiology of thymus gland which is to be kept in mind when evaluating thymic pathology on 18F-FDG PET-CT, as it can lead to interpretative pitfalls.

Optimizing imaging quality in endourology with the Uro Dyna-CT: contrast agent dilution matters

BACKGROUND AND PURPOSE

The implementation of the Uro Dyna-CT (Siemens Healthcare Solutions, Erlangen, Germany) with interventional 3D- and cross-sectional imaging necessitates the development of new standards for endourologic procedures such as the customized use of diluted contrast agent. Our aim was to find the ideal contrast agent dilution (CAD) for the interventional use of the Uro Dyna-CT in a standardized setting and prove the experimental findings in a clinical case.

MATERIALS AND METHODS

Retrograde pyelographies were performed with 10 different CADs of Imeron 300 (Bracco, Konstanz, Germany) in 10 different pig's urinary tracts. Fluoroscopy, X-ray, 3D- and slice-image reconstruction was performed with the Uro Dyna-CT. Image quality was evaluated, blinded and randomized by 5 observers. Small plastic jars were filled with the CADs and 2 artificial stones (Plaster of paris). Images were evaluated by two observers. The ex vivo findings were transferred to a clinical setting in a complex percutaneous lithotomy procedure. Unweighted and weighted kappa coefficients were calculated to indicate the degree of observers' agreement.

RESULTS

Twenty percent diluted contrast agent provides the best image quality and stone detection when interventional cross-sectional imaging is considered without limitations in fluoroscopy or X-ray quality. This was proved in a percutaneous lithotomy of an obese patient.

CONCLUSIONS

Image quality of the Uro Dyna-CT can be optimized by the use of 20 % diluted contrast agent. This knowledge helps to provide high-quality 3D imaging in the endourological operation room.