Validation of gate Monte Carlo simulations for indium 111 imaging

Accurate quantification of indium III (In-III) Single Photon Emission Computed Tomography (SPECT) images is helpful to characterize the distribution of ZEVALIN (R) labeled with In-III before therapy using ZEVALIN (R) labeled with yttrium 90, in patients with non-Hodgkin lymphoma, To optimize acquisition and processing protocols, Monte Carlo simulations of In-III SPECT data should be useful. In that context, we studied the validity of the Monte Carlo simulation code GATE for simulations of SPECT acquisitions involving In-III. Methods Acquisitions of line sources and of a cylindrical phantom including spheres were performed using a DST-Xli camera equipped with MEHR collimators, together with the corresponding simulations. The simulation model included photon tracking in the camera collimator, NaI crystal, back-compartment, and camera shielding. Energy spectra, spatial resolution, sensitivity values, images and count profiles obtained for real and simulated data were compared Results: The simulated and real spectra agreed well for all configurations. The simulated spatial resolutions differed by less than 0.1 mm from the measured values, for line sources in air at 0 to 15 cm front the collimator. In water, the simulated and measured full width at tenth maximum differed by about 10% at 6 6 cm from the collimator. The simulated sensitivity values were within 4.7% +/- 3.3% of the experimental values for line sources at 0 to 20 cm from the collimator. The simulation of the cylindrical phantom reproduced well the experimental results. Conclusion: Provided an appropriate detector model is developed, GATE enables accurate simulation of In-III data.