CT-based postimplant dosimetry of prostate brachytherapy: Comparison of 1-mm and 5-mm section CT

Purpose. The aim of this study was to compare the outcomes between 1-mm and 5-mm section computed tomography (CT)-based postimplant dosimetry. Materials and methods. A series of 21 consecutive patients underwent permanent prostate brachytherapy. The postimplant prostate volume was calculated using 1-mm and 5-mm section CT. One radiation oncologist contoured the prostate on CT images to obtain the reconstructed prostate volume (pVol), prostate V₁₀₀ (percent of the prostate volume receiving at least the full prescribed dose), and prostate D₉₀ (mean dose delivered to 90% of the prostate gland). The same radiation oncologist performed the contouring three times to evaluate intraobserver variation and subjectively scored the quality of the CT images. Results. The mean ±1 SD postimplant pVol was 20.17 ± 6.66 cc by 1-mm section CT and 22.24 ± 8.48 cc by 5-mm section CT; the difference in the mean values was 2.06 cc (P < 0.01). The mean postimplant prostate V ₁₀₀ was 80.44% ± 7.06% by 1-mm section CT and 77.33% ± 10.22% by 5-mm section CT. The mean postimplant prostate D₉₀ was 83.28% ± 10.81% by 1-mm section CT and 78.60% ± 15.75% by 5-mm section CT. In the evaluation of image quality, 5-mm section CT was assigned significantly higher scores than 1-mm section CT. In regard to intraobserver variation, 5-mm section CT revealed less intraobserver variation than 1-mm section CT. Conclusion. Our current results suggested that the outcomes of postimplant dosimetry using 1-mm section CT did not improved the results over those obtained using 5-mm section CT in terms of the quality of the CT image or reproducibility.