Purpose: To evaluate the image quality of retrospectively attenuation corrected Positron Emission Tomography (PET) scans used for gross tumor volume (GTV) delineation in lung cancer patients. Materials and methods: Data of 13 lymph node positive lung cancer patients were acquired on separate CT and PET scanners under free breathing conditions (for radiotherapy planning). First we determined a protocol for CT/PET registration. Second, we compared the image quality of attenuation-corrected PET images using positron transmission images and CT images, in terms of signal-to-noise ratio (SNR) and lesion-to-background ratio (contrast). Results: The largest differences between manual and automatic CT/PET registration were found in the anterior-posterior direction with a mean of 1.8 mm (SD 1.0 mm). Differences in rotations were always smaller than 1.0°. The attenuation-corrected images using CT showed a larger SNR (mean 30%, SD 17%) and larger contrast (mean 14.0%, SD 8.5%) compared to attenuation-corrected images using positron transmission. For lymph nodes, the mean contrast was 16% (SD 6.4%) larger. Conclusions: This study demonstrated that attenuation correction based on CT provides a better image quality for GTV delineation than when using positron transmission for attenuation correction. Retrospective attenuation correction of PET scans based on registered CT is a good alternative for a dedicated PET/CT scanner if a free-breathing CT is available, e.g., for radiotherapy planning, and allows the use of CT with diagnostic quality for attenuation correction.

Attenuation correction, Lung cancer, Target delineation
dx.doi.org/10.1016/j.radonc.2007.02.010, hdl.handle.net/1765/35825
Radiotherapy & Oncology
Erasmus MC: University Medical Center Rotterdam

Fitton, I, Steenbakkers, R.J.H.M, Zijp, L, Duppen, J.C, Comans, E.F.I, Muller, S.H, … Herk, M. (2007). Retrospective attenuation correction of PET data for radiotherapy planning using a free breathing CT. Radiotherapy & Oncology, 83(1), 42–48. doi:10.1016/j.radonc.2007.02.010