Feasibility of renal dosimetry after a first 90Y-DOTATOC cycle: Bremsstrahlung pinhole SPECT acquisition of a renal phantom modeling the intra-cortex uptake pattern

1493 Objectives Evaluate whether pinhole collimator is well adapted to bremsstrahlung SPECT after 90Y-DOTATOC therapy as recently shown in liver-SIRT. Methods A hand-made plexiglas realization of the mathematical dosimetric renal phantom proposed by Konijnenberg et al. (2007) was investigated. This phantom implements, in the MIRD Pamphlet No. 19 mathematical renal phantom, an intra-cortex uptake pattern derived from human kidney autoradiography. The kidney phantom was set into an abdominal shaped water container (20cmx30cm section) and was filled with 35MBq of 90Y that corresponded to a typical kidney uptake after a 4.4GBq Y90-DOTATOC cycle. One-hour helical non-circular SPECT using the energy window [50,150]keV was performed on a single head camera equipped with a medium energy pinhole collimator having a 10mm-diameter tungsten insert. The OSEM reconstruction included an analytical model of the collimator PSF and of the x-rays scatter occurring in the phantom. A 90Y aliquot was acquired in order to determine the system sensitivity. VOIs around the different kidney compartments were drawn on a co-registered CT image. Results The mean measured cortex/kidney ratio on the SPECT was 64.9% corresponding to a relative deviation of -11%. An under-estimation of 6% was obtained on the total kidney activity. Conclusions Renal dosimetry can be derived from bremsstrahlung pinhole SPECT after a first 90Y-DOTATOC cycle. The design (pinhole collimator is almost an empty volume in which the high-energy bremsstrahlung X rays cannot scatter down into the acquisition energy window) and the good attenuating material used for the collimation (tungsten instead of lead) explain that pinhole collimator is well adapted to bremsstrahlung imaging