Procedure for unmasking localization information from ProstaScint scans for prostate radiation therapy treatment planning

Purpose: To demonstrate a method to extract the meaningful biologic information from 111In-radiolabeled capromab pendetide (ProstaScint) SPECT scans for use in radiation therapy treatment planning by removing that component of the 111In SPECT images associated with normal structures. Methods and materials: We examined 20 of more than 80 patients who underwent simultaneous 99mTc/111In SPECT scans, which were subsequently registered to the corresponding CT/MRI scans.A thresholding algorithm was used to identify 99mTc uptake associated with blood vessels and CT electron density associated with bone marrow. Corresponding voxels were removed from the 111In image set. Results: No single threshold value was found to be associated with the 99mTc uptake that corresponded to the blood vessels. Intensity values were normalized to a global maximum and, as such, were dependent upon the quantity of 99mTc pooled in the bladder. The reduced ProstaScint volume sets were segmented by use of a thresholding feature of the planning system and superimposed on the CT/MRI scans. Conclusions: ProstaScint images are now closer to becoming a biologically and therapeutically useful and accurate image set. After known sources of normal intensity are stripped away, the remaining areas that demonstrate uptake may be segmented and superimposed on the treatment-planning CT/MRI volume