Laser-scanned agarose gel sections for radiation field mapping.

PURPOSE: A dedicated laser scanning system has been applied to the measurement of optical density change in ferrous sulphate-xylenol orange dye-agarose gel mixtures for applications in radiation field mapping. METHODS AND MATERIALS: The gels were poured, irradiated, and optically scanned in Lucite casts providing a uniform gel section thickness of 1 cm. The gel sections were optically scanned both pre- and postirradiation to determine the optical density change in the gel and consequently the absorbed dose. Irradiations of the gel sections were performed with an orthovoltage unit and a linear accelerator. RESULTS: For linear dose response up to 10 Gy, an appropriate gel mixture was found to be 0.4 mM Fe2+, 0.2mM xylenol orange dye, 25 mM sulphuric acid, and 1% by weight agarose gel with a mixing temperature of 60 degrees C. In dosimetry of a 20 x 10 cm 6 MV wedged x-ray field, good agreement in terms of relative dose was found between the gel values and ionization chamber readings. However, in repeated experiments with the gel dosimeter involving calculation of absolute dose at various points in the wedged field, variations in absolute dose measurements of up to +/- 5% were observed. CONCLUSION: The dosimetry technique involving laser scanning of agarose gel sections has potential for further applications in radiotherapy dosimetry.

Development of a CCD array imaging system for measurement of dose distributions in doped agarose gels.

An imaging system for agarose gel sections has been investigated for applications in rapid two-dimensional radiation dosimetry. The imaging system, with white light illumination and CCD camera detection, was designed for measurement of the radiation-induced optical density changes in iron- and xylenol orange dye-doped agarose gels. The performance of the imaging system was compared with that of a laser scanning system for the gels and with the accepted dosimetry standard, the ionization chamber. In measurement of beam profiles of two therapeutic radiation fields, relative dose values from the CCD camera imaging system were on average within 3% ranging from 0.005% to 7.5%) of values recorded with a parallel plate ionization chamber. In comparison with the laser scanner, the CCD camera imaging system provided comparable spatial resolution and an increased rate of data acquisition, although a consistently reduced signal to noise ratio was observed. Suggestions for improving the camera imaging technique include noise reduction through camera cooling and further frame averaging.

Preclinical pharmacology of CP-424,391, an orally active pyrazolinone-piperidine [correction of pyrazolidinone-piperidine] growth hormone secretagogue.

Growth hormone secretagogues (GHSs) represent attractive therapeutic alternatives to recombinant growth hormone (GH), given their ability to amplify pulsatile hormone secretion in a relatively physiologic manner. CP-424,391 (391) is a novel, orally active pyrazolinone-piperidine [corrected] GHS. In rat pituitary cell cultures, 391 stimulated GH release with an EC50 = 3 nM. The addition of 391 to rat pituitary cells activated intracellular calcium signaling but did not elevate intracellular cyclic adenosine monophosphate (cAMP). 391 also modulated the effects of GH-releasing hormone and somatostatin on pituitary cell GH-release and intracellular signaling. In nonpituitary cell lines, the ability of 391 to stimulate intracellular signaling was dependent on the expression of recombinant human GHS receptor. Acute administration of 391 to anesthetized rats or to conscious dogs induced pulsatile release of G H in a dose-dependent manner. Plasma insulin-like growth factor-I (IGF-I) was elevated progressively over a 5-d course of daily oral dosing in dogs. Chronic oral administration of 391 augmented body weight gain in rats and dogs. Thus, the peptidomimetic GHS 391 has potential utility for the treatment of clinical conditions that could benefit from systemic augmentation of GH and IGF-I levels.