Static and moving phantom studies for radiation treatment planning in a positron emission tomography and computed tomography (PET/CT) system

• Published in: Annals of nuclear medicine 2008-08, Vol.22 (7), p.579-586
• Main Authors: Okubo, Mitsuru, Nishimura, Yasumasa, Nakamatsu, Kiyoshi, Okumura, Masahiko, Shibata, Toru, Kanamori, Shuichi, Hanaoka, Kouhei, Hosono, Makoto
• Format: Article
• Language: English
• Subjects: Fluorodeoxyglucose F18 - therapeutic use; Humans; Imaging; Imaging, Three-Dimensional - methods; Medicine; Medicine & Public Health; Motion; Nuclear Medicine; Original Article; Patient Care Planning; Phantoms, Imaging; Positron-Emission Tomography - instrumentation; Positron-Emission Tomography - methods; Positron-Emission Tomography - standards; Radiology; Radiopharmaceuticals - therapeutic use; Radiotherapy Planning, Computer-Assisted - methods; Radiotherapy Planning, Computer-Assisted - standards; Reference Standards; Subtraction Technique; Tomography, X-Ray Computed - instrumentation; Tomography, X-Ray Computed - methods; Tomography, X-Ray Computed - standards
• ISSN: 0914-7187; 1864-6433
• DOI: 10.1007/s12149-008-0166-8

Objective To determine an appropriate threshold value for delineation of the target in positron emission tomography (PET) and to investigate whether PET can delineate an internal target volume (ITV), a series of phantom studies were performed. Methods An ellipse phantom (background) was filled with 1028 Bq/ml of [ 18 F] fluoro-2-deoxyglucose ( 18 FDG), and six spheres of 10 mm, 13 mm, 17 mm, 22 mm, 28 mm, and 37 mm in diameter inside it were filled with 18 FDG activity to achieve source-to-background (S/B) ratios of 10, 15, and 20. In static phantom experiments, an appropriate threshold value was determined so that the size of PET delineation fits to an actual sphere. In moving phantom experiments with total translations of 10 mm, 20 mm, and 30 mm and a period of oscillation of 4 s, the maximum size of PET delineation with the appropriate threshold value was measured in both the axial and sagittal planes. Results In the static phantom experiments, the measured maximum 18 FDG activities of spheres of less than 22 mm were lower than 80% of the injected 18 FDG activity, and those for the larger spheres ranged from 90% to 110%. Appropriate threshold values determined for the spheres of 22 mm or more ranged from 30% to 40% of the maximum 18 FDG activity, independent of the S/B ratio. Therefore, we adopted an appropriate threshold value as 35% of the measured maximum 18 FDG activity. In moving phantom experiments, the maximum 18 FDG activity of spheres decreased significantly, dependent on the movement distance. Although the sizes of PET delineation with 35% threshold value tended to be slightly smaller (