Preliminary study of correction of original metal artifacts due to I-125 seeds in postimplant dosimetry for prostate permanent implant brachytherapy

Purpose: We investigated a subtraction-based reprojection approach to reduce CT metal artifacts due to 1-125 seeds and evaluated the clinical implications in postimplant dosimetry for prostate permanent implant brachytherapy. Materials and Methods: The raw projection data were used to reduce metal artifacts due to I-125 seeds. CT images of the metal parts only were separated from the original CT images by setting the threshold for pixel value to that of the I-125 seeds. Using these images, sinograms of CT images with and without seeds were obtained by inverse Radon transform (iRT), and the sinogram of the metal image was subtracted from that of the original image. Finally, the image was reconstructed using the sinogram by Radon transform (RT). This technique was applied to a prostate phantom and to a patient undergoing prostate permanent implant brachytherapy. Results: Metal artifacts from I-125 seeds were reduced in both the phantom and patient studies. This technique decreased the density of the inner region of seeds but enhanced the density of the seed edge, thereby facilitating the identification of seed number, orientation, and location. Conclusion: This method reduces metal artifacts from I-125 seeds, and has potential for decreasing the time required for and improving the accuracy of postimplant dosimetry.