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

The aim of this study was to compare the outcomes between 1-mm and 5-mm section computed tomography (CT)-based postimplant dosimetry.

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 V(100) (percent of the prostate volume receiving at least the full prescribed dose), and prostate D(90) (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.

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 D(90) 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.

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.