Improved conjugate view quantitation of I-131 by subtraction of scatter and septal penetration events with a triple energy window method.
The majority of radiation absorbed dose estimates for radioimmunotherapy (RIT) with I-131 labeled antibodies have been calculated based on in vivo quantitation of activity using the conjugate view approach with planar Anger camera images. Scatter and septal penetration events contributed by a small fraction of high-energy photons emitted by I-131 with an energy exceeding 600 KeV lead to a significant degradation of I-131 images acquired with an Anger camera, which blurs the images of uptake sites and complicates the definition of background regions. The objective of this study was to evaluate a triple energy window (TEW) subtraction method that has been used to remove these interfering events from I-131 images. In the method, a primary photopeak image for I-131 is obtained after sequential subtraction of septal penetration and scatter events by using scatter multipliers derived from a photopeak window and two adjacent scatter window images. Qualitative improvement in image contrast was demonstrated with this technique, together with more accurate and reproducible quantitation for I-131 in the organs of an abdominal phantom. This TEW scatter subtraction method can be used to provide more precise dosimetry estimates for radionuclide therapy and RIT with I-131.
Macey
D J
DJ
University of Texas, M.D. Anderson Cancer Center, Houston 77030, USA.
Grant
E J
EJ
Bayouth
J E
JE
Giap
H B
HB
Danna
S J
SJ
Sirisriro
R
R
Podoloff
D A
DA
D000005:Abdomen; D006801:Humans; D007457:Iodine Radioisotopes / Q000627:therapeutic use*; D008433:Mathematics; D008962:Models, Theoretical; D019047:Phantoms, Imaging; D016499:Radioimmunotherapy / Q000295:instrumentation / Q000379:methods*; D011877:Radionuclide Imaging / Q000295:instrumentation / Q000379:methods; D011879:Radiotherapy Dosage; D012542:Scattering, Radiation
D007457:Iodine Radioisotopes