Outdoor solar UVA dose assessment with EBT2 radiochromic film using spectrophotometer and densitometer measurements.

Direct measurements of solar ultraviolet radiations (UVRs) have an important role in the protection of humans against UVR hazard. This work presents simple technique based on the application of EBT2 GAFCHROMIC(®) film for direct solar UVA dose assessment. It demonstrates the effects of different parts of the solar spectrum (UVB, visible and infrared) on performed UVA field measurements and presents the measurement uncertainty budget. The gradient of sunlight exposure level permitted the authors to establish the mathematical relationships between the measured solar UVA dose and two measured quantities: the first was the changes in spectral absorbance at the wavelength 633 nm (A633) and the second was the optical density (OD). The established standard relations were also applied to calculate the solar UVA dose variations during the whole day; 15 min of exposure each hour between 8:00 and 17:00 was recorded. Results show that both applied experimental methods, spectrophotometer absorbance and densitometer OD, deliver comparable figures for EBT2 solar UVA dose assessment with relative uncertainty of 11% for spectral absorbance measurements and 15% for OD measurements.

A CCD-based optical CT scanner for high-resolution 3D imaging of radiation dose distributions: equipment specifications, optical simulations and preliminary results.

Methods based on magnetic resonance imaging for the measurement of three-dimensional distributions of radiation dose are highly developed. However, relatively little work has been done on optical computed tomography (OCT). This paper describes a new OCT scanner based on a broad beam light source and a two-dimensional charge-coupled device (CCD) detector. A number of key design features are discussed including the light source; the scanning tank, turntable and stepper motor control; the diffuser screen onto which images are projected and the detector. It is shown that the non-uniform pixel sensitivity of the low-cost CCD detector used and the granularity of the diffuser screen lead to a serious ring artefact in the reconstructed images. Methods are described for eliminating this. The problems arising from reflection and refraction at the walls of the gel container are explained. Optical ray-tracing simulations are presented for cylindrical containers with a variety of radii and verified experimentally. Small changes in the model parameters lead to large variations in the signal intensity observed in the projection data. The effect of imperfect containers on data quality is discussed and a method based on a 'correction scan' is shown to be successful in correcting many of the related image artefacts. The results of two tomography experiments are presented. In the first experiment, a radiochromic Fricke gel sample was exposed four times in different positions to a 100 kVp x-ray beam perpendicular to the plane of imaging. Images of absorbed dose with slice thickness of 140 microm were acquired. with 'true' in-plane resolution of 560 x 560 microm2 at the edge of the 72 mm field of view and correspondingly higher resolution at the centre. The nominal doses measured correlated well with the known exposure times. The second experiment demonstrated the well known phenomenon of diffusion in the dosemeter gels and yielded a value of (0.12 +/- 0.02) mm2 s(-1) for the diffusion coefficient of the xylenol orange/iron complex. Finally, the overall implications of the above findings for dosimetry using OCT are discussed.

An optical method for three-dimensional dosimetry.

Accurate determination of the spatial distribution of the absorbed dose of ionising radiation plays an important role in radiotherapy, industrial radiation processing and many other applications. Computer calculations have frequently been used to estimate three-dimensional (3D) dose distributions in complex geometries and it becomes important to validate these by accurate 3D measurements. For this purpose we have been investigating the use of gelatin gels loaded with a modified Fricke solution which are pale orange in appearance and which, upon irradiation, become increasingly purple when viewed in normal light. This ferrous sulphate xylenol orange in gelatin gel (FXG) system displays very good properties, such as sensitivity, linearity and dynamic range, that make it suitable for 3D dosimetry applications. A high-speed optical tomography readout technique has been developed enabling two-dimensional projections of optical absorption data to be recorded rapidly. From these data the 3D absorbed dose distribution can quickly be derived with minimal degradation due to ion diffusion.

Kinetics of a nucleoside release from lactide-caprolactone and lactide-glycolide polymers in vitro.

We assessed the rate of release of a model nucleoside (adenosine, 5%, w/w) from nine different lactide-glycolide or lactide-caprolactone polymers. The polymer discs were eluted every second day with an artificial cerebrospinal fluid at the elution rate roughly approximating the brain extracellular fluid formation rate. Adenosine in eluate samples was assayed by HPLC. Three polymers exhibited a relatively constant release of adenosine for over four weeks, resulting in micromolar concentrations of nucleoside in the eluate. This points to the necessity of further development of polymers of this types as intracerebral nucleoside delivery systems for local treatment of brain tumors.

The application of microspheres from the copolymers of lactide and epsilon-caprolactone to the controlled release of steroids.

The microspheres made of the copolymers of lactide and epsilon-caprolactone were used for the controlled release of progesterone and beta-estradiol. The copolymers contained 83-94% of l or d,l-lactide. The influence of the microstructure of lactidyl blocks in the copolymer chains on the drug release rate was studied. More uniform release rate was observed in the case of the copolymer derived from d,l-lactide as composed to l-lactide. For the copolymer containing 83-94% of d,l-lactide units the progesterone and beta-estradiol release rate in vitro was found to be practically constant within over 40 days. The in vivo studies performed on rats revealed that the period of constant release rate of beta-estradiol can be prolonged to about 70 days. The microspheres made of the applied poly-(d,l-lactide-co-epsilon-caprolactone) are the convenient system for long time release of steroids.

Estradiol and progesterone release form biodegradable d,l-lactide and epsilon-caprolactone copolymer.

A study on the release of 17 beta-estradiol and progesterone from d,l-lactide and epsilon-caprolactone copolymer was performed. The copolymer was used in the form of microsphere, d,l-lactide content in the copolymer was 83%. It was found that nearly constant rate of hormone release during 100 days of experiment can be achieved by using this biodegradable material as a drug carrier.

[Evaluation of selected parameters of collagen metabolism in rats after implantation of copolymer d,l-lactide and E-caprolacton with cortisol and progesterone]. / Ocena wybranych parametrów metabolizmu kolagenu u szczurów po implantacji d,l-laktydu i E-kaprolaktonu z kortyzolem i progesteronem.

Tests were carried out on the possibility of biodegradable copolymer d, l-lactide and E-caprolacton as a carrier system for a long-term substitution of progesterone and cortisole. During 120 days of the experiment almost linear profile of freeing of progesterone with average rate 0.5% of the initial amount of hormone (24 hours, what indicates a practical possibility of its application in hormonal substitution) was obtained. Simultaneously the influence of copolymer implants on the metabolism of collagen was tested marking the concentrations P I CP and P III NP in particular periods of the experiment. We did not notice any permanent changes of metabolism of collagen under the influence of the tested carrier system of the hormonal medicaments and the obtained changes of concentrations P I CP and P III NP are probably caused by the hormones freeing from the subgrade.