Purpose: To describe a method of creating an intraoperative dosimetric representation of the real-time ultrasound-guided prostate implant.
Materials and methods: An intraoperative dosimetry system (Multi Media Systems [MMS]) captures transverse ultrasound images after peripheral needles have been implanted in the prostate. The prostate contour and needle positions are outlined on the system. The volume of the prostate with needles in place is calculated. As seeds are deposited in the actual implant, the positions of the seeds are marked on the intraoperative system. Following implantation of the peripheral needles, the resulting isodose lines are displayed. The interior needles are inserted into the prostate, and these positions are captured on the system. As seeds are deposited through these needles into the prostate, their positions are captured on the planning system. When the implant is complete, the final dose coverage and dose volume histogram can be visualized.
Results: Ten consecutive patients underwent iodine 125 implants using real-time intraoperative isodose generation. The ratio of the preneedle prostate volume to postneedle prostate volume ranged from 0.89 to 1.0 (median 0.97). The calculated dose delivered to 90% of the prostate volume from the dose volume histogram (D90) ranged from 146.5 to 194 Gy (median 174.75 Gy). The percentage of the prostate covered by 240 Gy ranged from 14.6% to 59% (median 40.75%).
Conclusion: Dosimetric representation of the real-time ultrasound-guided prostate implant can be achieved and demonstrates the efficacy of this brachytherapy technique.