Clinical implementation of a digital tomosynthesis-based seed reconstruction algorithm for intraoperative postimplant dose evaluation in low dose rate prostate brachytherapy.

PURPOSE: The low dose rate brachytherapy procedure would benefit from an intraoperative postimplant dosimetry verification technique to identify possible suboptimal dose coverage and suggest a potential reimplantation. The main objective of this project is to develop an efficient, operator-free, intraoperative seed detection technique using the imaging modalities available in a low dose rate brachytherapy treatment room.
METHODS: This intraoperative detection allows a complete dosimetry calculation that can be performed right after an I-125 prostate seed implantation, while the patient is still under anesthesia. To accomplish this, a digital tomosynthesis-based algorithm was developed. This automatic filtered reconstruction of the 3D volume requires seven projections acquired over a total angle of 60 degrees with an isocentric imaging system.
RESULTS: A phantom study was performed to validate the technique that was used in a retrospective clinical study involving 23 patients. In the patient study, the automatic tomosynthesis-based reconstruction yielded seed detection rates of 96.7% and 2.6% false positives. The seed localization error obtained with a phantom study is 0.4 +/- 0.4 mm. The average time needed for reconstruction is below 1 min. The reconstruction algorithm also provides the seed orientation with an uncertainty of 10 degrees +/- 8 degrees. The seed detection algorithm presented here is reliable and was efficiently used in the clinic.
CONCLUSIONS: When combined with an appropriate coregistration technique to identify the organs in the seed coordinate system, this algorithm will offer new possibilities for a next generation of clinical brachytherapy systems.