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Biomedical subjects

J F Malone

Publications and source records attributed to J F Malone.

At least 55 records · Page 3Linked to original sources
PubMed1979

High thyroid radiation dose associated with 131-I-19-iodocholesterol adrenal scanning.

We have examined two patients undergoing 131I-19-iodocholesterol adrenal scans in order to assess thyroidal radiation dose. Thyroid uptakes of 3--5% of the administered 2 mCi dose were found despite prior administration of Lugol's iodine. Analysis of serum samples over a ten day period after iodocholesterol injection indicated that less than 10% of the radioactivity was free iodide. Kinetic results showed a high value for the thyroid/plasma 131I ratio indicating thyroid retention of 131I. This was substantiated by thyroid scintigrams. The thyroid radiation dose was estimated to be 200--250 rad for the two patients. The associated carcinogenic risk is of sufficient magnitude, in our opinion, to warrant regular follow-up of all patients who have undergone 131I-19-iodocholesterol adrenal scanning.

19-Iodocholesterol↗
PubMed1979

The value of a tracer dose in predicting the kinetics of therapeutic doses of 131I in thyrotoxicosis.

The kinetics of tracer doses of 131I, assessed by measuring uptake and effective half-life, correlate well with the kinetics of therapy doses. The effective half-life was measured using thermoluminescent discs fixed to the patients' anterior neck surface. This method gives results comparable with those obtained using an uptake probe, and met with a good response by the patients. Using the kinetics of the tracer dose to assist prescription of radioiodine therapy would considerably reduce the spread of absorbed doses to the glands of a group of patients. The case for attempting more exact dosimetry in this field is reviewed.

Half-Life↗
PubMed1978

The influence of thyroid geometry on the response of LiF and CaSO4 thermoluminescent discs to 131I and 125I irradiation.

Recent work has demonstrated that LiF and CaSO4 thermoluminescent discs may be used to monitor the effective half-life of radioiodine in the thyroid in man. To provide a firm basis for this work, the radiation field presented by model thyroids to thermoluminescent discs on the surface of a neck phantom has been examined in detail. The influence of thyroid mass, depth and lobe separation, factors which in practice are highly variable, has also been determined. The results demonstrate that the method is sufficiently sensitive to measure less than 0.5 muCi of 131I or 125I in the human thyroid, and that effective half-life determinations should not be influenced by minor positioning errors which may be encountered when placing thermoluminescent discs on the neck surface.

Calcium↗
PubMed1978

Thyroid uptake measurements: the influence of gland depth, gland mass and lobe separation.

Phantom measurements were carried out to define the dependence of standard thyroid uptake measurements on gland depth, gland mass and lobe separation. In the case of 99Tcm and 131I, depth can cause a variation of up to a factor of two in the apparent uptake, while in the case of 125I the variation due to depth is a factor of about four. By contrast, gland mass and lobe separation cause only small errors, of the order of 2 and 10% respectively for medium energy isotopes. These errors are particularly important when the uptake value is used to guide prescription of 131I for therapy of thyrotoxicosis.

Humans↗
PubMed1977

A radioprotective effect of vitamin C observed in Chinese hamster ovary cells.

Vitamin C at high concentrations was found to inhibit the growth of CHO clone A cells in culture. It had a radioprotective effect, giving a maximum increase in cell survival of a factor of seven under the experimental conditions used. The protective effect was mainly but not exclusively attributable to an increase in the Do, the maximum increase observed being the order of 1.4.

Ascorbic Acid↗
PubMed1976

Two mechanisms for hypothyroidism after 131I therapy.

It is proposed that the incidence of hypothyroidism after radioiodine therapy of thyrotoxicosis has two distinct mechanism. One operates in the first two years after therapy and depends on radiation dose. The other operates in later years, and is not, to any significant extent, dose dependent. Possible canidates for each mechanism are explored.

Dose-Response Relationship, Radiation↗
PubMed1975

The radiation biology of the thyroid.

The structure and function of the thyroid gland are described. A detailed analysis of population kinetics in the gland suggests a method of measuring cell survival after irradiation that has many features in common with methods used in other mammalian cell systems. This method is used to obtain survival curves for thyroid cells afer irradiation. The effects on survival of splitting the radiation dose into two or multiple fractions, radiation type, and radioprotective agents are also examined. In the light of these data the tolerance of thyroid tissue to radiation exposure under various conditions is discussed. The dosimetry and biological effects of 125I and 131I are described in detail, and compared with X-rays. Radioiodine treatment of thyrotoxicosis is presented in relation to the known biological effects of the isotopes on the gland. Carcinogenic action of ionizing radiations in the thyroid are reviewed with particular reference to the clinical consequences of observations in this field.

Age Factors↗