Toward a dynamic real-time intraoperative permanent prostate brachytherapy methodology

To evaluate dosimetry and source location relative to CT-based dosimetry when performing real-time dynamic permanent prostate brachytherapy (PPB) with inverse treatment planning.

A treatment algorithm for dynamic PPB was developed using inverse treatment planning. The technique utilizes real-time transrectal ultrasound prostate imaging connected to the treatment planning software. The implementation of the plan with the Mick interstitial gun is monitored with up-to-date dosimetry assessments based on the registration of each seed when placed. Real-time dose assessment is monitored and adjustments can be made during the case, if necessary. A final OR dosimetric (OR-D) assessment based on the registered seed locations is performed. Postoperative CT scans obtained at 3 weeks are used for traditional dosimetry analysis (CT-D). A matrix algorithm was developed to match the seed locations from the ultrasound registration to that of the CT-scan parameters.

Twenty-six consecutive patients with clinically localized prostate cancer underwent PPB using the algorithm designed for dynamic real-time planning. The OR-D identified a mean D90 of 109% (range 100-118%) whereas the mean CT-D D90 at 3 weeks was 105% (range 89-122%) (p=0.894). Analysis of the OR-D V100 and V150 relative to the 3-week CT-dose V100 and V150 were also insignificant (p=0.112 and 0.167, respectively). Assessment of seed locations relative to the intraoperative ultrasound and postimplant CT identified a mean root-mean-square error of 4.6 mm (0-21 mm). The mean error for the x, y, and z coordinates were 2.01 mm, 2.24 mm, and 2.85 mm, respectively.

This study reports the preliminary results of a new treatment algorithm for PPB that incorporates intraoperative inverse planning with dynamic dosimetry assessment during the case. Correlation was seen between the completed intraoperative, postimplant plan and the CT based plan at 3 weeks. Seed to seed deviations between the OR-D matched well with the CT-D. Additional study is necessary to assess whether this approach can assist in improving implant dosimetry and whether it appropriately documents the OR-dose without the need for postimplant dosimetry.