added 6 research items
The Development of Criteria for Limiting the Non-Uniform Irradiation of Skin
Has anyone used plucked (or waxing-derived) hair follicles, as extracted, to successfully facilitate wound healing? ORIGINAL TEXT: https://www.linkedin.com/pulse/repopulation-damaged-skin-using-freshly-plucked-hair-wells-frsb-fsrp/ and PHOTOS: https://www.linkedin.com/feed/update/urn:li:activity:6738045894437953536?commentUrn=urn%3Ali%3Acomment%3A%28activity%3A6738045894437953536%2C6747526052072960000%29 (see the first comment).
Late radiation damage to pig skin has been assessed at 104 weeks after exposure to sources of 90Sr/90Y (Emax 2.2 MeV) and 170Tm (Emax 0.9 MeV). Damage was assessed from measurements of dermal thickness in histological sections of irradiated skin and was compared with that of unirradiated skin to establish the relative reduction in dermal thickness. The size of the source varied from 0.1 to 40.0 mm in diameter; this covered the range of source sizes designed to simulate exposure to radioactive "hot" particles (< or = 1.0 mm diameter) up to the lower range of field size that patients may be exposed to in radiotherapy treatments. Radiation doses were measured using an extrapolation chamber with a collecting electrode of 1.1 mm2, and thus the quoted doses represent an average dose over this area. For the larger 90Sr/90Y sources of > or = 5 mm diameter and the larger 170Tm sources of > or = 2 mm diameter there was no evidence, based on levels of damage consistent with a > or = 10, > or = 20, > or = 30, and > or = 40% reduction in relative dermal thickness, for any effect of source size on the ED50 value for each of these specified levels of effect. However, there was a marked effect of beta-particle energy; the skin surface doses associated with the ED50 values (+/- SE) for a > or = 20% reduction in relative dermal thickness were approximately 12 and approximately 40 Gy for 90Sr/90Y and 170Tm, respectively. This difference in skin surface dose for an equivalent level of dermal injury reflects the variation in the depth dose from these two beta-particle emitters. These skin surface doses, for what was considered to be a clinically detectable dermal effect, were below the ED10 for the early skin response of moist desquamation. This supports the selection of late dermal thinning as the effect on which to base dose limits in radiation protection for more generalized larger area skin exposures. In comparison, single exposures to a small area, from sources designed to simulate those from hot particles, reinforced the view that acute ulceration should be the effect on which dose limitation is based. Either the isoeffect doses for a clinically detectable reduction in relative dermal thickness of > or = 20%, following a single exposure to a small area, were higher than the ED10 for acute ulceration or the area of skin showing dermal thinning was so small that it was not considered to be detrimental.
A Loevinger extrapolation chamber has been automated and used to determine detailed dose distributions around beta emitting sources of varied geometry. The absolute dose estimates provided by the extrapolation chamber have been compared with those obtained from radiochromic dye film dosemeters. For large area planar sources, extrapolation chamber estimates obtained by conventional linear extrapolation of the ionisation current/electrode spacing characteristic are in reasonable agreement with the radiochromic film values. The shape of the curve for punctiform sources, however, indicates that significant curvature may still be present at the smallest practically attainable electrode separations. In such situations non-linear extrapolation of the current/spacing curve appears to provide estimates which are in better agreement with those obtained using radiochromic film. This is in accord with the predictions of a simple theoretical model for an idealised point source.