We aimed to investigate whether gold marker implantation in the tissue surrounding the prostate could accurately monitor setup errors during external beamradiation therapy (EBRT) following low-dose-rate (LDR) brachytherapy. Thirty-eight patients had confirmed intermediate- or high-risk prostate cancer and received EBRT following LDR brachytherapy. In>175 computed tomography imaging sessions, the average values of the weekly setup error during EBRT to the prostate centroid at the time of gold marker matching in the surrounding tissue of the prostate and pelvic bonematching were measured and then compared using theWilcoxon signed-rank test.Goldmarkermatching in the surrounding tissue of the prostate estimated setup errors better than those estimated by bone matching (3D displacement=2.7±2.0 vs 3.8±2.6 mm, P<0.01).Overall, the standard deviation of systematic (Σ) and random (σ) setup error was lower with goldmarkermatching than with bonematching (3D displacement=1.8 and 1.1mm vs 2.1 and 1.6 mm, respectively). With gold marker matching, the setup error of the position of the prostate centroid was smaller, and the optimal setup margin was lower than that with bone matching (2Σ + 0.7σ and 2.5_ + 0.7σ of 3D displacement = 4.3 and 5.2 mm vs 5.3 and 6.4 mm, respectively). This high-precision radiotherapy approach placing gold markers in the surrounding tissue of the prostate can allow more accurate setup during EBRT following LDR brachytherapy.
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