A triple energy window scatter subtraction approach for quantitative anger camera imaging of iodine-131
- Univ. of Texas, Houston, TX (United States); and others
Dose estimates for organs and tumor volumes in radioimmunotherapy with I-131 frequently depend on in-vivo quantitation methods using planar Anger camera images. Compton scatter and collimator septal penetration result in overestimation of activity and dose. The objective of this study was to assess the effectiveness of a triple energy window subtraction method for quantitative imaging of I-131. The energy spectrum of I-131 was modeled as a superposition of the spectra of Cr-51 (320 keV) and Cs-137 (662 keV). Images were acquired with three adjacent 15% energy windows--photopeak(PP), upper scatter(US), and lower scatter(LS)--for small sources of these radionuclides. The PP window was centered at 364 keV for I-131 and Cs-137 and 320 keV for Cr-51. Three scatter multipliers were derived from analysis of count profiles of the Cs-137 and Cr-51 images, and used to sequentially remove septal penetration and scatter events included in the 364 keV photopeak of I-131. This method was tested by acquiring images of an abdominal phantom containing a liver, spleen and spherical {open_quotes}tumor{close_quotes} filled with different concentrations of I-131, both with and without background activity in the surrounding phantom. A body thickness attenuation compensation factor was applied to the geometric mean of the conjugate view counts using a narrow beam linear attenuation coefficient of 0.11 cm{sup -1}. With scatter subtraction, the accuracy and reproducibility of activity quantitation was improved because the background count density was more uniformly scored. Also, the influence of different activity concentrations in source organs relative to background on the accuracy of quantitation was removed, and the perimeters of organs were more clearly defined. This method has been used to provide improved dose estimates for I-131 labeled antibody therapy in breast cancer patients.
- OSTI ID:
- 198006
- Report Number(s):
- CONF-940605-; ISSN 0161-5505; TRN: 95:007029-0147
- Journal Information:
- Journal of Nuclear Medicine, Vol. 35, Issue Suppl.5; Conference: 41. annual meeting of the Society of Nuclear Medicine, Orlando, FL (United States), 5-8 Jun 1994; Other Information: PBD: May 1994
- Country of Publication:
- United States
- Language:
- English
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