A nomogram to compensate for intraoperative prostate edema during transperineal brachytherapy.

Purpose: Prostate edema during and following prostate brachytherapy may have a negative impact on implant dosimetry. The purpose of this study was to assess the magnitude of prostate edema during the operative procedure and to develop a nomogram of isotope activity required for compensation of such intraoperative prostate volume changes.

Materials and methods: Twenty-five consecutive patients with early-stage, localized adenocarcinoma of the prostate underwent ultrasound-guided transperineal interstitial permanent prostate brachytherapy with either iodine 125 or palladium 103. Transrectal ultrasound volume studies of the prostate were performed before and during the implant procedure. Computed tomography-based postimplant dosimetry was performed 3-4 weeks after surgery.

Results: A median intraoperative prostate volume increase after insertion of applicator needles of 10.4% (range 1.2-32.5%) was identified. A correlation of -0.55 (95% confidence interval -0.78 to -0.19) between the minimum dose covering 90% of the prostate volume (%D90) and the amount of edema was identified. An algorithm and nomogram was developed to calculate the extra isotope activity necessary to compensate for intraoperative edema.

Conclusions: Prostate edema occurs at the time of transperineal needle placement. A negative correlation was found between the amount of edema and dose coverage of the prostate (%D90). Therefore, to cover the prostate volume adequately, additional isotope activity is required when preoperative treatment planning is performed. This nomogram can be used to compensate for such volume changes.