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High beta and electron dose from 192Ir: implications for "gamma" intravascular brachytherapy
Neil S Patel1, Sou-Tung Chiu-Tsao, Yunsil Ho
1Department of Radiation Oncology, Beth Israel Medical Center and St. Luke's-Roosevelt Hospital Center, New York, NY, USA.
International Journal of Radiation Oncology, Biology, Physics
|October 16, 2002
Summary
Multiple Iridium-192 seeds used in brachytherapy deliver high doses of beta and electron radiation, potentially explaining adverse outcomes. Encapsulation improvements to filter these particles are recommended for intravascular brachytherapy safety.
Area of Science:
- Medical Physics
- Radiation Oncology
- Nuclear Medicine
Background:
- Multiple Iridium-192 (192Ir) seeds are standard in intravascular brachytherapy clinical trials.
- While 192Ir is recognized as a gamma emitter, its significant beta and electron emissions are often overlooked.
- Precise quantification of high-energy beta and electron doses near seed ends is crucial for understanding brachytherapy complications.
Purpose of the Study:
- To quantify the dose distribution from multiple 192Ir seeds, focusing on beta and electron energies.
- To investigate the contribution of these emissions to the overall dose in the submillimeter range.
- To correlate dose findings with potential adverse outcomes in clinical trials.
Main Methods:
- Monte Carlo simulations using MCNP4C code for a 5-seed 192Ir model.
- Dose distribution measurements using radiochromic film stacks for a 6-seed 192Ir train.
- Evaluation of dose-volume histograms (DVH) for lumen surfaces.
Main Results:
- Betas and electrons deposit higher doses than photons in the submillimeter range, especially in interseed gaps.
- Combined 192Ir emissions can deliver high luminal doses, reaching 160 Gy at 0.5 mm when prescribed at 15 Gy/2 mm.
- Significant dose variations and hot spots were observed, influenced by seed positioning and activity uniformity.
Conclusions:
- 192Ir seed trains deliver substantial doses to the luminal wall, particularly from beta and electron emissions.
- Non-centered seeds exacerbate high localized doses near interseed gaps.
- Improved encapsulation to filter beta and electron radiation is essential for mitigating adverse events in 192Ir brachytherapy.