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Sensitivity Study On Two Different Methods for Performing Post-Implant Dosimetry for a Salvage Pd-103 Prostate Implant

R Sheu

R Sheu*, A Powers , R Stock , Y Lo , Mount Sinai Medical Center, New York, NY


TU-RPM-GePD-TT-5 (Tuesday, August 1, 2017) 3:45 PM - 4:15 PM Room: Therapy ePoster Theater

Purpose: To study the sensitivity of two different approaches to perform post-implant dosimetry on a salvage Pd-103 prostate implant case.

Methods: Prior to salvage implant procedure, an AP kV film and CT were acquired to construct 3D positions of 65 seeds from an implant performed 16 years ago. Six needles with twenty-four seeds total were implanted in this procedure to boost the region where the tumor recurred due to a cold spot. Post implant dosimetry was performed with the following two approaches. One method specifically identified salvage implant seeds by excluding pre-existing sources. In-house software NaviSeed, was developed and applied to assist with source localization in VariSeed. The other method used a weighted average source of the source strength (1.947U) without identifying seeds implanted previously or presently.

Results: Since the Pd-103 seeds that were ordered for the salvage case had a similar strength (1.939U previously vs. 1.970U presently) the error for misidentifying previous and current implanted seeds during post-implant dosimetry is minimal. There was no significant difference between the two approaches in terms of prostate coverage (D90, D95, and D100) and OARs sparing (rectum V100, bladder V100, and urethra V150).

Conclusion: Although both approach resulted in a similar post-implant dosimetry for this salvage prostate implant, the methodology established in this study could be useful for future cases, especially when the activity difference is greater or different isotopes are used.

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