PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Scattering, Radiation”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 163 records · Page 9Linked to original sources
PubMedDate not supplied

[An in-vivo dosimetric study of the scattered radiation during the treatment of breast carcinoma].

In the last decade, radiation therapy has been increasingly used to treat breast cancer conservatively and some authors showed their concern about the radiogenic effects of irradiation outside the treated area. Our aim was to measure the scattered dose to the contralateral breast, thyroid and gonads during radiation therapy after conservative breast surgery. Thermoluminescent dosimeters, LiF Mn Ti (3 x 3 x 0.9 mm3), were used to measure scattered radiations outside the treated area. They were positioned on the skin of the patients in small (2 cm in diameter and 1 cm thick) perspex holders. Each measurement was performed once per treatment and six dosimeters were used--two on the contralateral breast, one on the midpoint of the medial side and one on the midpoint of the lateral side; two on thyroid lobes and two on the pelvis. The minimum dose to the contralateral breast (p < 0.002) and the maximum dose to the gonads (p < 0.003) were significantly higher in the 60Co group than in the LINAC6 group. The mean values of the minimum doses to the contralateral breast were significantly different (p < 0.007) in the whole series when beam area values were lower or higher than the median value (176 cm2). In the whole series the beam area and the minimum dose to the contralateral breast were correlated (Pearson, p < 0.001); the beam area and the minimum dose to the contralateral breast (p < 0.005), the gantry angle for the lateral beam and the minimum dose to the contralateral breast (Spearman, p < 0.001) exhibited statistically significant correlations. Of 30 patients, 16 were irradiated with 60Co (group A) and 14 with LINAC6 (group B). In group A the average scattered dose to the contralateral breast ranged 0.53-2.15 Gy, 0.66-1.91 Gy in the thyroid, 0.14-0.19 Gy in the gonads. In group B the average scattered dose to the contralateral breast ranged 0.36-2.07 Gy, 0.53-0.98 Gy in the thyroid and 0.08-0.12 Gy in the gonads. In the LINAC6 group the beam area and the minimum dose to the thyroid exhibited a statistically significant correlation (p < 0.009), as well as the beam area and the maximum dose to the gonads (p < 0.006), the beam area and the minimum dose to the gonads (p < 0.02), the gantry angle of the lateral beam and the minimum dose to the contralateral breast (p < 0.02). In the 60Co group no correlation was statistically significant, except for the correlation between the beam area and the minimum dose to the gonads (p < 0.001). Our experience confirms the scattered dose to depend on head treatment, beam area, gantry angle and wedge angle. Finally, the literature on this subject is reviewed.

Breast Neoplasms↗
PubMed2006

Scatter radiation in cephalometric radiography: the effects of grid and collimation.

OBJECTIVES: To measure the scatter fraction in cephalometric radiography with and without a grid and to estimate the patient's dose reduction by using a specially fabricated collimator without a grid. METHODS: A 16 cm thick water-equivalent phantom was used to measure the scatter fraction. The projection geometry was the same as our conventional one, i.e. the distance from the X-ray source to the centre of the phantom was 200 cm. A photostimulable phosphor plate was used as an X-ray sensor and was 20 cm from the centre of the phantom. The measurements were performed in four combinations: with an antiscatter grid in place, with a specially fabricated collimator in place, with neither in place, and with both in place. The images of a human dried skull were obtained by using the above parameters and were subjectively assessed for a visibility of several reference points. RESULT: The scatter fraction in the regularly collimated geometry with the antiscatter grid in place was 0.35 for a relative exposure of 1. With the antiscatter grid removed, the scatter fraction increased to 0.68, but the relative exposure was reduced to 0.3. With a special collimator, the scatter fraction was reduced to some extent in all instances, but the exposure was reduced to 0.45. The visibility of the reference points was acceptable in all conditions. CONCLUSION: In cephalometric radiography, removal of the antiscatter grid yields a significant reduction in exposure with no significant loss of information.

Cephalometry↗
PubMed2003

Modeling of thin-film slurry photocatalytic reactors affected by radiation scattering.

Photocatalytic oxidation over titanium dioxide is a "green" sustainable process for treatment and purification of water and wastewater. A dimensionless model for steady-state, continuous flow, thin-film, slurry (TFS) photocatalytic reactors for water purification using solar radiation and UV lamps is presented and validated. The model is applicable to TFS flat plate and annular photoreactors of (a) falling film or (b) double-skin designs, operating with three ideal flows: (1) falling film laminar flow (FFLF), (2) plug flow (PF) and (3) slitflow (SF). Model parameters can be estimated easily from real systems, and solutions can be obtained with modest computational efforts. A modified two-flux absorption-scattering model models the radiation field in the photoreactor. Model simulations show that at a scattering albedo higher than 0.3, radiation scattering can significantly affect conversions obtained at different values of optical thickness. However, at lower values, the effect of scattering on conversions is negligible. The conversions with the idealized flow systems follow the sequence FFLF > PF > SF. SF operation should always be avoided. The model estimates the optimum value of optical thickness that maximizes conversion in a photocatalytic reactor. Optimal design of TFS photocatalytic reactors using the photocatalyst TiO2 Degussa P25 requires an optical thickness in the range from 1.8 to 3.4 depending on flow conditions and reaction kinetics.

Coloring Agents↗
PubMed1987

Reduction of radiation scatter with a multiple pencil-beam imaging device.

A prototype device consisting of a focused array of several scanning collimator plates that produce multiple pencil beams has been constructed for radiographic imaging. Under normal imaging conditions, the scatter-to-primary ratio resulting from this device is less than 10%. High-contrast radiographs can be produced without increasing patient radiation dose.

Equipment Design↗
PubMedDate not supplied

The photon-fluence scaling theorem for Compton-scattered radiation.

This paper concerns a method of scaling photon fluence from one scattering material to another when the photon energies are such that the dominant mode of interaction is Compton scattering. The theorem establishes a one-to-one correspondence between points in the two scattering media where the spectra of primary and scattered photons have the same distribution in energy and angle, and where the fluence ratio equals the square of the electron density ratio. Experimental tests were made with cobalt-60 gamma radiation using ionization-chamber measurements in graphite, acrylic plastic, polystyrene, and water phantoms. The experimental results are consistent with the equality of photon spectral shapes and angular distributions at corresponding points. The fluence ratios may differ by a few percent from the predicted values, depending on distance from the source.

Acrylic Resins↗