Radiant energy – Calibration or standardization methods
Patent
1977-02-25
1978-11-07
Smith, Alfred E.
Radiant energy
Calibration or standardization methods
250445T, A61B 600, G01D 1800, G01N 2308
Patent
active
041247990
ABSTRACT:
In radiotherapy, for example, a computer-tomogram is to be formed with a conventional relatively low dosage but with sufficient information content to enable the working out of an irradiation plan with a specific selected isodose distribution. Since the normally measured attenuation coefficients are not valid with respect to substantially harder x-radiation or gamma radiation, the present disclosure teaches the introduction of test bodies into the spacial region to be scanned in generating the computer tomograph, such test bodies having the same percentage contents of the same elements as are present in the particular body volume to be examined and having a density which is adapted as far as possible to such body volume, the density however being graduated such that graduated attenuation coefficients are recorded for the test bodies in the resultant computer tomogram. Thus it is possible to find a test body section whose attenuation coefficient is identical with that of the body tissue to be subsequently subjected to radiation therapy. Since this test body section also quantitatively manifests the same elements, the attenuation coefficient of the test body agrees with that of the body tissue to be treated even in the case of radiation energies and types of radiation used in radiotherapy. Thus, by examining the attenuation coefficients of the corresponding section of the test body with the particular type of radiation to be used for radiotherapy, the matrix of attenuation coefficients contained in the computer tomogram may be transcribed into a matrix for the type of radiation to be used for the radiation therapy. This applies not only to x-radiation or gamma radiation, but also any random type of ionizing radiation, such as, for example, electron, proton and neutron radiation. As a further development, two identical test bodies may be arranged on opposite sides of the body during scanning so that the difference between the attenuation coefficients associated with these two test bodies is a measure of the hardening of the x-radiation on passage through the body of the patient. This information enables a refinement in the precision of the remaining attenuation coefficients of the computer tomograph. As a specific example, each test body may contain several hermetically sealed samples of the body substance to be examined, the samples having a known but graduated density.
REFERENCES:
patent: 3778614 (1973-12-01), Hounsfield
patent: 3881110 (1975-04-01), Hounsfield et al.
patent: 4053780 (1977-10-01), Sparks
Grigsby T. N.
Siemens Aktiengesellschaft
Smith Alfred E.
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