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Query: UNIPROT:P50583 (asymmetrical)
 12,197 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Irradiation of target volumes within the ethmoid sinus and nasal cavity region has, at our institution, been performed using one anterior electron beam, abutted to two opposing lateral photon beams, in order to exclude the orbit from the irradiated volume. However, this technique give rise to larger dose hetereogeneities within the target volume, as well as undesired hot spots in the chiasma region. To reduce the inhomogenious distribution, we have introduced asymmetrical photon beam edges to broaden the penumbra of the two opposing photon beams resembling the dose gradient of the perpendicular electron beam. The achieved reduction in dose heterogeneity, measured from the differential dose-volume-histogram, is in the order of 30-40% when applying the asymmetrical abutting technique compared with the conventional two opposing photon beam technique. As demonstrated by calculating the tumour control probability (TCP), the increase in dose homogeneity within the target volume, may be of clinical significance.
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PMID:Abutting orthogonal electron and photon beams in the head and neck region using asymmetrical photon beam edges. 940 48

We propose and analyze in detail a method to measure the in-air spatial spread parameter of clinical electron beams. Measurements are performed at the center of the beam and below the adjustable collimators sited in asymmetrical configuration in order to avoid distortions due to the presence of the applicator. The main advantage of our procedure lies in the fact that the dose profiles are fitted by means of a function which includes, in addition to the Gaussian step usually considered, a background which takes care of the dose produced by different mechanisms for which the Gaussian model does not account. As a result, the spatial spread is obtained directly from the fitting procedure and the accuracy permits a good determination of the angular spread. The way the analysis is done is alternative to that followed by the usual methods based on the evaluation of the penumbra width. Besides, the spatial spread found shows quadratic-cubic dependence with the distance to the source predicted by the Fermi-Eyges theory. However, the corresponding values obtained for the scattering power are differing from those quoted by ICRU nr. 35 by a factor of approximately 2 or larger, which requires of a more detailed investigation.
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PMID:A method to determine the in-air spatial spread of clinical electron beams. 1022 58

Several methods have been developed for the dosimetry of asymmetric radiation fields formed by independently moving collimator jaws. Three of these methods, based on different principles and modified to comply with our set of available data, are utilized for the calculation of asymmetric field dose profiles. All three methods use output factors and per cent depth doses or tissue maximum ratios of symmetric fields. In the first method, calculation of the off-centre ratio (OCR) of the asymmetric field is based on the symmetric field from which the asymmetric is originated, by setting the one jaw in an asymmetrical position. In the second method the OCR of the symmetric field is used for the OCR calculation of the asymmetric field of the same size; whereas the third method does not allow for the asymmetric OCR calculation. The results obtained using data for the 6 MV photon beam of a Philips SL-20 linear accelerator indicate that both the first and second method can accurately reproduce asymmetric field profiles from symmetric field data; the third method does not allow for penumbra reproduction, but it is accurate at the central part of the asymmetric field. The problems encountered in the application of the three methods are reported and their accuracy is compared.
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PMID:Dose calculations for asymmetric fields defined by independent collimators using symmetric field data. 1084 66