Effect of edema on the post-implant dosimetry of an I-125 prostate implant: A case study

Purpose: To investigate the effect of post-implant edema on the CT-based calculation of the total dose delivered by an I-125 prostate implant. Materials and Methods: CT scans of a transperineal I-125 prostate implant were obtained 1 and 39-days postimplant, Changes in the prostate dimensions were determined from changes in the spatial distribution of the I-125 seeds. The total dose delivered to the target volume was computed from each CT scan, and the results compared. Results: The volume of the prostate decreased by approximately 17% during the 38-day interval between the first and second CT scans, As a result, the radiation dose computed from the second CT scan was 13% higher. Conclusion: Post-implant edema can cause a significant underestimation of the radiation dose delivered by an I-125 prostate implant, Similar analysis should be carried out among a larger cohort of patients to confirm or refute these observations. (C) 1997 Elsevier Science Inc.