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Biomedical subjects

M Kartha

Publications and source records attributed to M Kartha.

18 recordsLinked to original sources
PubMed1983

Determination of hydroxyl radical production in aqueous solutions irradiated to clinically significant doses.

Decarboxylation of 14C-carboxylbenzoic acid in aqueous solutions after low-dose irradiation has been used to determine the relative magnitude of oxidation reactions and estimate the hydroxyl radicals produced. The G CO2 values determined from these measurements of 0.4 to 1.0 mM solutions of benzoic acid after x-ray doses of 1000 rads ranged from 0.72 to 0.77, in excellent agreement with values reported by authors using much higher doses of radiation. Superoxide dismutase and catalase, known scavengers of superoxide and hydrogen peroxide, respectively, did not show impairment of the oxidation of benzoic acid. On the other hand, biologically significant concentrations of phenol and mannitol appear to impair the radiation-induced oxidation of benzoic acid, indicating that the process is secondary to a reaction with OH . . We found that serum and glucose, common cell media contents, are potent OH . scavengers. These observations indicate that the oxidation of benzoic acid can be as a reliable method to estimate OH . with radiation doses of clinically significant magnitudes. In addition, these results suggest that the radiation induced by OH . in cell systems can be significantly modified by the type of buffer used.

Benzoates↗
PubMed1981

Dosimetry disparities resulting from two accepted methods of calibration of cobalt-60 teletherapy machines.

The primary concern of all involved in the management of radiotherapeutic patients is that the tumor dose delivered to each and every patient in one institution is identical to that delivered anywhere else. Despite the advocacy 1,2,3,4 for the calibration of high energy photon beams at 5 cm depth or beyond in a water phantom to reduce the effect of electron "contamination" from collimators, filters, applicators, etc., the "in-air" method of calibration is still in vogue in many institutions in the United States and elsewhere. The introduction of S.I. units in radiology is likely to create ambiguity in proper conversion factors from exposure to absorbed dose which can be avoided if field instruments are calibrated in terms of absorbed dose in water under specified conditions. The present study shows that the estimated error can be as much as 7% low when the "in-air" method of calibration is used instead of measurements in a large water phantom at 5 cm depth for cobalt-60 photon beams and hence recommends that the procedure for "in-air" calibration for high energy photon beam should be discontinued.

Air↗
PubMed1979

An analysis of the dosimetry for mantle field therapy using 4 MV X-rays and its routine application.

There are several different methods in vogue at present in determining patient midplane doses in the "mantle" treatment for Hodgkin's disease and malignant lymphomas. A method of determining midplane doses in individual cases using thermoluminescent dosimetry is presented. It shows excellent agreement with the midplane doses measured in an Alderson-Rando phantom treated as a hypothetical "mantle" patient.

Hodgkin Disease↗
PubMed1978

A study of dose distribution patterns from cobalt-60 and Varian Clinac-4 beams.

Dose distribution patterns of 4 MV x-rays from a Varian Clinac 4 linear accelerator are compared with those from a 60Co teletherapy machine. Field flatteners of lead and depleted uranium were used. Dose distribution maps display the off-axis high dose or "horns" with lead filters and circular dose distribution patterns. The uranium field flattener clearly "clipped the horns" and eliminated circular dose distribution patterns with larger fields.

Cobalt Radioisotopes↗