CT-ultrasound fusion prostate brachytherapy: a dynamic dosimetry feedback and improvement method. A report of 54 consecutive cases.

PURPOSE The authors describe a prostate brachytherapy technique with dynamic dosimetry feedback, using coregistered CT and ultrasound (US) images, to map initial dosimetry deficiencies and guide remedial source placement. METHODS AND MATERIALS Fifty-four consecutive patients treated with this method were analyzed for coregistration accuracy and dosimetry outcomes by evaluating the prostate V100, V150, D90, and urethral D50 and D10. Dosimetric improvements created by remedial source placement and preplan/postplan prostate D90 agreement were evaluated. RESULTS Median CT-US coregistration discrepancy with this technique ranged from 0 to 4mm, with the posterior midline prostate and base prostate providing the least consistent and the urethra providing the most consistent coregistration agreement. Final prostate V100 values ranged from 96.1% to 99.8% for all patients. The addition of remedial sources directed by CT-US fusion produced V100 and D90 improvements whose magnitude inversely correlated with the initial result and exceeded the effect of adding quantitatively identical randomly distributed increased millicuries. The final prostate D90 result agreed within (-) 5% to (+) 10% of the preplan result in 98% of all patients. CONCLUSIONS CT-US fusion prostate brachytherapy represents a dynamic dosimetry feedback and remediation method that consistently produced high prostate V100 and D90 values with acceptably low urethra D50 and D10 values in our study. The degree of prostate V100 and D90 dosimetry improvement created by remedial source placement effectively matched the degree of initial dosimetry deficiency. This method produced a high level of correlation between the preplan and final prostate D90 values.