Application of a medium-energy collimator for I-131 imaging after ablation treatment of differentiated thyroid cancer.
OBJECTIVE
High-energy (HE) collimators are usually applied for I-131 imaging after ablation treatment of differentiated thyroid cancer (DTC). However, purchase of HE collimators has been avoided in many nuclear medicine departments because the HE collimators are more expensive than other collimators. In this study, we compared the I-131 imaging using HE- and medium-energy (ME) collimators, which is more versatile than HE collimators.


METHODS
To simulate DTC patients with extra-thyroid beds, a phantom of acrylic containers containing I-131 was used. To simulate patients with thyroid beds, four phantoms representing extra-thyroid beds were arranged around the phantom representing normal thyroid tissues. Patients administered 1.11 or 3.70 GBq NaI-131 were also evaluated. Whole-body imaging and SPECT imaging of the phantoms and patients performed using HE-general-purpose (HEGP) and ME-low-penetration (MELP) collimators, and full-width at half maximum (FWHM) and percent coefficient of variation (%CV) were measured.


RESULTS
In the extra-thyroid beds, FWHM and %CV with MELP were negligibly different from those with HEGP in whole-body imaging. Although FWHM with MELP was a little different from that with HEGP in SPECT imaging, %CV with MELP was significantly higher than that with HEGP. In the thyroid beds, only an extra-thyroid bed including higher radioactivity was identified in whole-body imaging with both collimators. Although SPECT images with MELP could not clarify extra-thyroid beds with low radioactivity, HEGP could identify them. In patients, although some whole-body images with MELP could not detect extra-thyroid beds, whole-body imaging with HEGP and SPECT imaging with both collimators could detect them.


CONCLUSIONS
Although HEGP is the best collimator for I-131 imaging, MELP is applicable for not only whole-body imaging but also SPECT imaging.
School of Health Sciences, College of Medical, Pharmaceutical and Health Sciences, Kanazawa University, 5-11-80 Kodatsuno, Kanazawa, 920-0942, Japan, kobayasi@mhs.mp.kanazawa-u.ac.jp.
Masato
M
Kobayashi
Hiroshi
H
Wakabayashi
Daiki
D
Kayano
Takahiro
T
Konishi
Hironori
H
Kojima
Hiroto
H
Yoneyama
Koichi
K
Okuda
Hiroyuki
H
Tsushima
Masahisa
M
Onoguchi
Keiichi
K
Kawai
Seigo
S
Kinuya
D055011:Ablation Techniques; D000368:Aged; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D019047:Phantoms, Imaging; D019275:Radiopharmaceuticals; D013964:Thyroid Neoplasms / Q000175:diagnosis* / Q000601:surgery*; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation* / Q000379:methods; D051598:Whole Body Imaging / Q000295:instrumentation* / Q000379:methods
D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals