SU‐FF‐T‐73: An Intra‐Operative Dosimetry System for Prostate Brachytherapy Using Dual‐Modality Imaging

Abstract

Purpose: (1) To develop an intra‐operative dose evaluation and optimization system for prostate brachytherapy using complementary imaging modalities (fluoroscopy for seed localization and ultrasound for prostate delineation). (2) To evaluate the usefulness of the intra‐operative dosimetry system. Method and Materials: Several algorithms were developed to realize the concept of fluoroscopy‐ultrasound based dosimetry. These include automated seed detection, 3D seed reconstruction, patient motion correction, computer‐assisted prostate contouring, and seeds‐prostate registration algorithms. In order to accelerate the seed reconstruction from multiple x‐ray projections, the dimensionality of seed matching process was reduced by strategically forming search restriction sub‐images. Problems of incomplete data due to clustering and superposition of projected seeds were solved by a pseudo‐matching technique. Patient movements between fluoroscopic image acquisitions were corrected through analysis of epipolar‐planes. Registration of seeds and prostate volume was accomplished by establishing a sparse (small subset of seeds detected on ultrasound) to full (seeds reconstructed from fluoroscopy) data set correspondence. Results: Intra‐operative dosimetry was performed on 25 patients implanted with Pd‐ 103 seeds. In nine patients, no additional seeds were implanted after intraoperative dose evaluation. In 16 patients, remedial seed were added based on the intra‐operative evaluation. Subsequently, V100 values improved from 86±8% to 93±4% (p=0.005). For all 25 patients, the post‐implant dosimetry results using our system were compared with Day 0 CT‐study. The V100 and D90 values from the fluoroscopy‐ultrasound based dosimetry were 95±4% and 120±24% while the CT‐based dosimetry computed 95±4% and 122±24%, respectively. Conclusion: We have developed and implemented an intra‐operative dosimetry system that combines the strengths of fluoroscopy and ultrasound. A clinical study has successfully demonstrated its intended utility in intra‐operative setting by significantly improving the quality of seed implant in prostate brachytherapy.