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Dose anisotropy around an Au-198 seed source.
S K Jani1, E C Pennington, B M Knosp
1Division of Radiation Oncology, University of Iowa College of Medicine, Iowa City 52242.
Medical Physics
|July 1, 1989
Summary
This study investigated dose anisotropy around gold-198 (Au-198) seeds used in interstitial implants. While measurable dose anisotropy exists, it is too small for significant clinical impact.
Area of Science:
- Medical Physics
- Radiotherapy
- Nuclear Medicine
Background:
- Interstitial implants with radioactive gold-198 (Au-198) seeds commonly use point source approximations for dosimetric calculations, assuming isotropic dose distribution.
- Measured radiation fluence from Au-198 seeds indicates anisotropy, suggesting potential dose anisotropy in surrounding tissues.
Purpose of the Study:
- To experimentally measure and characterize the dose anisotropy around Au-198 seeds in a phantom.
- To compare experimental findings with theoretical assumptions and reported radiation fluence data.
Main Methods:
- Utilized Kodak X-OMAT XV-2 films in direct contact with Au-198 seeds within a phantom to measure dose anisotropy.
- Digitized autoradiographs using an image analysis computer network with a spatial resolution of approximately 0.01 cm.
- Analyzed optical isodensity contours within a useful optical density range (1-2 OD units) to infer isodose contours.
Main Results:
- Observed elliptical optical isodensity contours proximal to the seed, elongated along the seed axis.
- Further from the source, contours showed elongation in the direction perpendicular to the seed axis.
- Experimental results aligned with previously reported anisotropic radiation fluence data for Au-198 seeds.
Conclusions:
- Confirmed the existence of measurable dose anisotropy around Au-198 seeds.
- Concluded that the observed dose anisotropy is of negligible clinical significance in interstitial implant therapy.