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Postimplant dosimetry for (125)I prostate implants: definitions and factors affecting outcome
1Department of Radiation Oncology, Mount Sinai School of Medicine, New York, NY, USA.
International Journal of Radiation Oncology, Biology, Physics
|October 6, 2000
Summary
CT-based dosimetry confirms real-time prostate implants are effective. Factors like CT/US volume ratio, prostate size, and seed count significantly impact D90 dose delivery, with newer technology improving outcomes.
Area of Science:
- Medical Physics
- Radiation Oncology
- Urology
Background:
- Real-time prostate implantation is a common treatment for prostate cancer.
- Accurate dosimetry is crucial for treatment efficacy and minimizing side effects.
- CT-based dosimetry offers a method for assessing implant quality post-procedure.
Purpose of the Study:
- To evaluate the effectiveness of real-time prostate implantation using CT-based dosimetry.
- To analyze relationships between different dose metrics and identify factors influencing prostate implant outcomes.
- To determine the impact of implant parameters on dose distribution.
Main Methods:
- CT-based dosimetry (TG43 formalism) was performed on 297 patients with T1-T2 prostate cancer post-(125)I implantation.
- Dose-volume histogram analysis reported doses to 100%, 95%, 90%, and 80% of the prostate (D100, D95, D90, D80) and volumes receiving specific doses (V240, V160, V140).
- Correlations and stepwise regression analyzed relationships between dose parameters and factors including seed number, prostate volume, and CT/US volume ratio.
Main Results:
- Median D90 was 17,578 cGy, with V140 and V160 at 98% and 94% respectively.
- Strong correlations were observed between D90 and D95, D80, V240, V160, and V140.
- CT/US volume ratio, prostate volume, and seed number were significant predictors of D90; dual-phased electronic probes resulted in fewer suboptimal D90 values compared to mechanical sector probes.
Conclusions:
- CT-based dosimetry validates the efficacy of real-time prostate implantation.
- Achieving higher D90 values is associated with precise implantation factors, including reduced post-implant edema, advanced technology, and increased seed density.