Validation of gate Monte Carlo simulations for indium 111 imaging

Accurate quantification of indium 111 ( 111 In) single photon emission computed tomography (SPECT) images is helpful to characterize the distribution of ZEVALINreg labeled with 111 In before therapy using ZEVALINreg labeled with yttrium 90, in patients with non-Hodgkin lymphoma. To optimize acquisition and processing protocols, Monte Carlo simulations of 111 In 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 111 In. 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. 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 from 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%plusmn3.3% 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. Provided an appropriate detector model is developed, GATE enables accurate simulation of 111 In data