Estimation of radioactivity in single-photon emission computed tomography for sentinel lymph node biopsy in a torso phantom study.
OBJECTIVE
The number of lymph nodes to be removed is determined from residual counts. Advance estimation of residual radioactivity in lymphatic nodes before a biopsy is useful for reducing surgical operation time. The purpose of this study was to estimate the total radioactivity of a small hotspot in single-photon emission computed tomography (SPECT) of a torso phantom.


METHODS
A cross-calibration study was performed to convert counts in SPECT images to radioactivity. A simulation study was performed to estimate the size of the volume of interest (VOI) covering a hotspot corrupted with full-width at half-maximum between 8 and 16 mm. The estimation of total radioactivity was validated in a torso phantom study using small sources.


RESULTS
True radioactivity was approximately equal to integrated values of hotspots using the VOI with a diameter of 40 mm in our simulation study. The difference was less than 18% in cases of more than 9.4 kBq.


CONCLUSIONS
The total radioactivity in small sources simulating a typical sentinel node was estimated from SPECT images using a VOI of 40 mm in a torso phantom study. Because the difference from actual values was less than 10% on average when radioactivities were more than 9.4 kBq, the total radioactivity of a lymph node can be estimated in a clinical examination.
aDiagnostics Radiology Division, National Cancer Center Hospital bGraduate School of Human Health Sciences, Tokyo Metropolitan University, Tokyo, Japan.
Hideaki
H
Kitamura
Yuzuru
Y
Kono
Takeshi
T
Murano
Kenta
K
Hiroi
Kanyu
K
Ihara
Tomohiko
T
Aso
Kazumasa
K
Inoue
Masahiro
M
Fukushi
D002138:Calibration; D006801:Humans; D019047:Phantoms, Imaging; D021701:Sentinel Lymph Node Biopsy; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation*; D060726:Torso / Q000000981:diagnostic imaging*