TY - JOUR T1 - Comparison of Medium- and High-Energy Collimators for <sup>131</sup>I-Tositumomab Dosimetry JF - Journal of Nuclear Medicine Technology JO - J. Nucl. Med. Technol. SP - 148 LP - 153 DO - 10.2967/jnmt.106.038174 VL - 35 IS - 3 AU - Eugene Mah AU - Ken M. Spicer Y1 - 2007/09/01 UR - http://tech.snmjournals.org/content/35/3/148.abstract N2 - Residence time measurements obtained by serial whole-body conjugate-view imaging are commonly used in patient-specific dosimetry for radioimmunotherapy applications. In order to determine the effect of collimator selection on residence time measurements for 131I, the accuracies of 131I half-life measurements obtained with multiple γ-camera and collimator combinations were investigated. Methods: Serial anterior and posterior whole-body images were acquired over a period of 15 d with 4 different γ-cameras and medium- or high-energy collimators. Background-corrected geometric mean counts from the images were fitted to a monoexponential curve to determine the half-life of 131I obtained with the different γ-camera and collimator combinations. Results: An average half-life of 8.15 d (SD, 0.07 d) was obtained with all γ-camera and collimator combinations. A half-life of 8.12 d (SD, 0.11 d) was obtained with the high-energy collimators, and a half-life of 8.18 d (SD, 0.04 d) was obtained with the medium-energy collimators. These values are all very close to the 131I physical half-life of 8.02 d and were not found to be statistically significantly different (P = 0.44). Similar results were obtained for the half-life obtained with single-head γ-camera configurations (mean half-life, 8.15 d; SD, 0.12 d). The therapeutic 131I-tositumomab dose resulting from the differences in the measured half-life ranged from 2.58 to 2.6 GBq (69.8–70.4 mCi). Conclusion: There is no significant difference in 131I half-life and residence time measurements obtained with medium- or high-energy collimators in dual-head or single-head imaging configurations. ER -