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Biomedical subjects

R H Thomas

Publications and source records attributed to R H Thomas.

At least 91 records · Page 5Linked to original sources
PubMed1976

Reducing patient exposure to ionizing radiation--is it really necessary?

The thesis that medical radiation exposures to the general population in the United States are excessive and that urgent steps need to be taken to reduce them is examined. At the present time, no evidence is found that deleterious effects result from radiation exposures at the level of a few rads or less. Nevertheless it is prudent that we assume the possibility of harmful effects of radiation exposure. However, because medical radiology is clearly so beneficial, and the harmful effects are problematical, it is doubtful whether the public should be alarmed by the suggestion of any crisis. A balancing of risks and benefits in the medical uses of radiology supports this latter contention.

Dose-Response Relationship, Radiation↗
PubMed1975

Compartmental evaluation of osteoarthritis of the knee. A comparative study of available diagnostic modalities.

The distribution and severity of osteoarthritis were investigated in 56 knees by history and physical examination, assessment of knee function, radiography with and without weight-bearing, double-contrast arthrography, and 99mTc-polyphosphate bone imaging. Compartmental involvement (medial, lateral, patellofemoral) was graded independently by 2 or 3 observers for each modality and was correlated with that observed during arthroscopy or direct surgical inspection. The more involved compartments were graded abnormal by all methods. In the less involved compartments, the gamma camera image was most sensitive to pathology, followed by arthrography. The choice of surgical technique and the prognosis depend upon accurate preoperative knowledge of the extent of disease.

Adult↗
PubMedDate not supplied

Neutron flux-density and secondary-particle energy spectra at the 184-inch synchrocyclotron medical facility.

We have identified the sources of neutron production in the beam transport system of the 720-MeV helium beam used for radiation therapy at the 184-in synchrocyclotron of the Lawrence Berkeley Laboratory, and determined their magnitude. Measurements with activation detectors of differing energy response were used to unfold secondary particle spectra at various locations on the patient table. The effect of charged particles was estimated using a calculation of neutron-flux densities derived from published cross sections. The absorbed dose, as a function of distance from the beam axis, was calculated using the unfolded spectra and evaluated fluence-to-dose conversion factors. The values of absorbed dose obtained from the unfolding of experimental data agree with the values obtained from the calculated spectra within the estimated uncertainty of +/- 25%. These values are approximately 5 X 10(-3) rad on the beam axis and approximately 1 X 10(-3) rad at distances greater than 20 cm, perpendicular to the beam axis, per rad deposited by the incident alpha-particle beam in the plateau. Estimates of upper limits of dose to two critical organs, the lens of the eye and red bone marrow, are approximately 25 rad and approximately 5 rad, respectively, for a typical treatment plan.

Alpha Particles↗