Radiant energy – Invisible radiation responsive nonelectric signalling – Optical change type
Reexamination Certificate
1997-09-05
2001-04-17
Ham, Seungsook (Department: 2878)
Radiant energy
Invisible radiation responsive nonelectric signalling
Optical change type
C250S473100
Reexamination Certificate
active
06218673
ABSTRACT:
TECHNICAL FIELD
This invention relates to an optical tomographic system that permits the accurate reconstruction in a series of two-dimensional images of three-dimensional dose distributions or energy fields represented using polymer gels.
BACKGROUND OF THE INVENTION
It has been previously suggested (Maryanski, et al., 1994) that three-dimensional aspects of tissue-equivalent, polymer-gel dosimeters, combined with the flexibility and high resolution inherent in magnetic resonance imaging, can provide radiation dose distributions in a manner that is unique to the field of radiation oncology. Tomographic analysis of an irradiated polymer gel can yield important dosimetry data for the new and highly complex treatment modalities which are being introduced into radiation oncology such as stereotactic radiosurgery, conformal radiation therapy, the dynamic wedge, scanning electron beams and energy-modulated proton beams. While MRI will likely remain the method of choice at some institutions for specific types of studies, for many institutions there will be significant financial, administrative and logistical advantages to have a relatively low-cost tomographic dosimetry system located in the radiation oncology department which can readily provide the bulk of the clinical and research data required by the radiation oncology physicists.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a tomographic system which accurately reconstructs three-dimensional energy fields as a series of two-dimensional images.
It is another object of the invention to provide a tomographic system of the above character which optically scans dose distributions represented in translucent media.
It is a further object of the invention to provide tomographic systems of the above character which are useful for the determination of three-dimensional dose distributions in irradiated translucent media, including measurements of the complex distributions produced by multi-leaf collimators, dynamic wedge and stereotactic treatments, and for quality-assurance procedures.
These and other objects are accomplished by the present invention, which provides an optical scanner for measuring three dimensional dosimetric data comprising a translucent medium exhibiting optical properties, e.g., optical density, light scattering, emitted light intensities, and combinations thereof, which change upon receipt of radiant energy representing a dose distribution of the energy; at least one light beam such as a laser beam or a series of divergent rays for scanning the translucent medium; and at least one detector, and in some embodiments, multiple detectors, for receiving and measuring data indicative of changes in the optical properties of the medium after scanning from multiple directions to provide a representation of the optical properties in sections through the medium. In the practice of the invention, the space accommodating the medium, a light source, mirrors to deflect beams, and/or a detector may be moved to provide scanning in multiple directions. One embodiment employs moving mirrors to deflect light beams.
In one embodiment, an optical scanner incorporates a He—Ne laser, photodiode detectors, and a rotating translucent media platform to measure dosimetric data stored within tissue-equivalent translucent media such as polymeric gels. Using mirrors mounted on a translating stage, the laser beam scans across the translucent media between each incremental rotation of the platform. Using the set of optical-density projections obtained, a cross-sectional image of the radiation field is then reconstructed. Doses in the range 0-10 Gy can be measured to better than 5% accuracy with a spatial resolution ≈2 mm.
The invention further provides a method of reconstructing a three-dimensional energy field as a series of two-dimensional images by applying an energy field to a translucent medium having distinct optical properties that change upon receipt of the energy field; optically scanning the translucent medium at various angles; detecting and measuring data indicative of optical changes such as those mentioned above in the medium; and preparing a two-dimensional image of the energy field by analyzing the changes in the optical properties. The depth of the translucent medium at which the optical scanning step occurs may be changed, and the optical scanning and detecting steps, repeated, to provide different two-dimensional images in the series. The two-dimensional images may be reviewed in consideration of altering or confirming radiant energy treatment.
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Gore John C.
Maryanski Marek J.
Schulz Robert J.
Ham Seungsook
Haniq Richard
Krinsky Mary M.
Yale University
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