The penombra in roe-therapeutic machines

The evaluation of penombra and its elimination of its negative effects in roe-therapy, is an important question, linked directly with the amount of doses given to the tumors. The goal of this paper is to study the parameters from which depends the quality and quality of penombra's irradiation for ro-therapeutical machines and to give the methods for protection of patients from it. Penombra is the irradiation propagated outside the primary beam. It is composed by geometrical and physical penombra, originated respectively by the geometry of X-ray tube (target, diaphragm, source-skin distance SSD etc.) and by the diffusion of secondary X-rays produced by interaction of primary X-rays with matter. Because the geometrical penombra is linked with the dimensions of target diaphragm and SSD, it is not difficult to find its size and apperture. In our X-ray machines the value of geometrical penombra's dose is about 5-7 % of primary beam's dose, when the value of dose at external part (outside of geometrical penombra) of physical penombra is about I-2% of primary beam's dose. The H.V.L. in percentage of that of primary beam is respectively about 20% and 12%; that means much more softer than primary irradiation. This fact constitute a big abstracte for delivering high doses The size of primary beam is about two times less than that of penombra. So for the primary beam 82 cm2, the geometrical penombra is about 90 cm2, the physical-90 cm2