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J Nucl Med. 2008; 49 (Supplement 1):335P
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Oncology-Basic Science: Therapy, Metrics & Intervention

Therapy, Metrics & Intervention Posters

Effects of metallic implant artifacts on FDG-PET-CT three dimensional brachytherapy target definition

S. Morzenti4, E. De Ponti1, C. Pasquali1, N. Paruccini1, G. Montanari1, L. Guerra2, C. Messa3 and A. Crespi1

1 Medical Physics; 2 Nuclear Medicine, San Gerardo Hospital, Monza, Italy; 3 University of Milan Bicocca, Milan, Italy; 4 University of Milan, Milan, Italy

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Objectives: In 3D brachytherapy treatment planning the accuracy of target definition is central to treatment success. When using PET-CT images in target definition, the metallic brachytherapy implant creates CT image artifacts that could influence 18F quantification; this is mainly true in low dose CT images. We evaluated the effects of CT parameters on artifacts and the relation between artifacts and radioactivity quantification.

Methods: We built a cylindrical phantom to simulate a cervical cancer filled with 18F and with a brachitherapy probe placed in the centre. Target to background ratio was 7:1 with a concentration of 0.5 MBq/ml in the target. The effect of different 8 slices MDCT acquisitions, used as attenuation map, on 18F quantification was evaluated by changing mAs (60-200 mA) and pitch (0.625-1.675). The different PET and CT images were compared both by visual inspection and quantitatively (eg. SUV, counts and noise).

Results: CT artifacts are substantially reduced by decreasing the pitch value independently on the mAs changes; this effect is greater when the phantom axis is not aligned to the gantry axis. Artifacts are asymmetrical in helical CT acquisition but they do not alter 18F quantification on PET images. Low dose protocols obtained with small pitch and mAs values do not show artifacts.

Conclusions: Small noise images are obtained using different combination of pitch and mAs. Artifacts on CT images does not influence 18F quantification; acquisitions with lower pitch and mAs allow to obtain better quality CT images for anatomical volume definition without increasing CTDIvol.





This Article
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Right arrow Email this article to a friend
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Right arrow Alert me to new issues of the journal
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Right arrow Articles by Morzenti, S.
Right arrow Articles by Crespi, A.
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Right arrow Articles by Morzenti, S.
Right arrow Articles by Crespi, A.