High accuracy dosimetry with small pieces of Gafchromic films.

AIM: To investigate the influence of several factors on the accuracy of dose measurements and feasibility of application of small Gafchromic detectors for postal audit. BACKGROUND: Our experience showed that precision of dose measurements with small pieces of Gafchromic films may be significantly improved. MATERIALS AND METHODS: Gafchromic films with dimensions of 1 × 1, 2 × 2 and 3 × 3 cm2 were exposed to 6 MV X-rays at dose levels of 50 cGy-210 cGy. The single- and multichannel methods (MM) were used for dose measurements. Detectors were scanned with an Epson V750PRO flatbed colour scanner. For 1 × 1 and larger detector sizes, separate calibration curves were established. The influence of the following factors was investigated: the heterogeneity of Gafchromic detectors group for single- and MM, ambient thermal detector conditions, the dose delivered on the measurement accuracy, application of two separate calibration curves for the smallest and larger pieces of films. RESULTS: The MM improves significantly the precision of dose measurement. The uncertainty attributed to detector active layer differences and scanner instabilities was about 1 cGy (1 StDev) regardless of dose and detector size. The ambient temperature of the environment in which films were stored after irradiation influenced the dose reading. Significant difference of transmission for detectors sized 1 × 1 and 2 × 2cm2 was observed. The maximal difference between applied dose and dose reading performed was 1.1%. CONCLUSIONS: The MM with a scaling protocol leads to a very high precision of dose measurements. The ambient thermal detector environment causes significant changes of measured signal. The detector size has relevant impact on dose reading.

Regulatory influence of melatonin on collagen accumulation in the infarcted heart scar.

The regulatory influence of the pineal gland on superficial wound healing and collagen content is documented. The aim of the present study was to determine whether the pineal gland and its secretory product melatonin regulate collagen accumulation in the scar of the infarcted heart and to explain the mechanisms of its action. To induce myocardial infarction in rats the left coronary artery was ligated. Metoprolol at the dose of 0.2 mg/100 g body weight (b.w.) was injected intraperitoneally to inhibit melatonin secretion. Pinealectomy was performed on some animals. For the in vitro study, cells were isolated from the heart scar and cultured in Dulbecco's modified Eagle medium with 3% fetal calf serum and antibiotics. Collagen content was evaluated as hydroxyproline content according to the Woessner method. Melatonin subcutaneously injected into the rats at the doses of 30 microg/100 g or 60 microg/100 g b.w. increased collagen accumulation in the heart scar. The doses of 3 microg/100 g b.w. and 300 microg/100 g b.w. were not effective. Surgical and pharmacological pinealectomies had opposite effects and reduced collagen content in the scar. However, melatonin administration (60 microg/100 g b.w.) to pinealectomized rats reversed the effect of pinealectomy and normalized collagen levels in heart after infarction. Cells isolated from the heart scar were identified as myofibroblasts. Melatonin (10(-7)-10(-8) m) increased collagen accumulation in the cultures. Collagen accumulation in the scar of the infarcted heart is regulated by melatonin and it exerts effects directly on the myofibroblasts of the infarcted area. Therefore, melatonin-induced collagen accumulation in the infarcted heart could be considered as the event improving the tensile strength of the scar and retarding the development of complications.

The opposite effect of morning or afternoon application of melatonin on collagen accumulation in the sponge-induced granuloma.

OBJECTIVES: Collagen accumulation in the sponge-induced granuloma is under inhibitory influence of melatonin. This effect was observed when the pineal hormone was injected late in the afternoon. DESIGN: The present study was conducted to compare the afternoon and morning melatonin application and to answer the question whether melatonin effect on the collagen accumulation in wounds is dependent on tissue circadian sensitivity to the pineal hormone. METHODS: In order to induce granulation tissue development, the Ivalon sponge was implanted subcutaneously in the Wistar rats. Then the animals were divided into 5 groups: intact controls, rats injected with vehicle in the morning or in the late afternoon, as well as animals receiving melatonin (30 &mgr;g/100g body wt) in the morning or late afternoon. After 4 weeks, the sponges were removed for the analysis of both soluble and total collagen content. Collagen was analyzed as hydroxyproline content in the tissue. Insoluble collagen was calculated. RESULTS: The afternoon application of melatonin was seen to decrease the total and insoluble collagen content in the sponge-induced granuloma (p<0.05). However, morning administration of the pineal hormone increased collagen capacity in the granulation tissue (p<0.01). CONCLUSION: Therefore, contradictory effect of morning or afternoon melatonin application on the collagen content in the granulation tissue has been shown. This phenomenon is supposed to be due to various circadian sensitivity of tissues to melatonin and may suggest that the mechanism of melatonin regulatory action on collagen accumulation in wounds is complex.