RT Journal Article
SR Electronic
T1 Impact of CT image quality on the accuracy of absorbed dose computations in nuclear medicine
JF Journal of Nuclear Medicine
JO J Nucl Med
FD Society of Nuclear Medicine
SP 54
OP 54
VO 55
IS supplement 1
A1 Poul-Erik Braad
A1 Poul Høilund-Carlsen
YR 2014
UL http://jnm.snmjournals.org/content/55/supplement_1/54.abstract
AB 54 Objectives Radionuclide patient specific 3D absorbed dose estimates are obtainable by Monte Carlo methods. Inputs are radionuclide biodistributions and tissue and density compositions of the patient. CT images are used for tissue segmentation and affect quantitation through scatter and attenuation correction of PET or SPECT images. We investigated the potential errors from CT on absorbed dose estimates in radioiodine therapy. Methods An extendable anthropomorphic thorax phantom (diameters ranging from 300 to 600 mm) with 3 radioactive [18F]-FDG central concentric spheres (diameters 10, 22 and 37 mm) was PET/CT-scanned. CT scans were acquired with varying tube modulation settings. CT-number variation of lung, bone, and soft tissue equivalent materials was assessed on reconstructed images. The recovery of 18F-activity was measured in the spheres as a function of phantom size and the CT acquisition parameters. Total 131I dose point kernels were Monte Carlo computed in water, lung, bone, and soft ICRU-tissues. A biokinetic model for 131I with 15% thyroid uptake was Monte Carlo simulated in the ICRP 110 computational male reference phantom and target average organ doses computed. Artificial CT images were created of the phantom and the impact of CT number variation on organ absorbed doses was assessed. Results In the three smallest phantoms, the CT number variation was below 20 Hounsfield units (HU) and the accuracy of the PET quantitation across lesion sizes was correct within 5%. In the huge phantom, CT number variations were above 100 HU and quantitation errors up to 10%. Correct quantitation was feasible for CT scans giving an estimated whole-body CT dose of 2 mSv. CT number variations of 20 HU and below led to changes in phantom absorbed doses of less than 2% except in spongious bone where the absorbed doses changed up to 11%. The larger value was caused by spongious bone being segmented as soft tissue by the CT conversion ramp. Conclusions CT number variations on a modern PET/CT system only have a small impact on absorbed dose estimates and PET image quantitation.