Hopewell J W, Sieber V K, Heryet J C, Wells J, Charles M W
Research Institute (University of Oxford), Churchill Hospital, United Kingdom.
Radiat Res. 1993 Mar;133(3):303-11.
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.
在暴露于90Sr/90Y（最大能量2.2 MeV）和170Tm（最大能量0.9 MeV）源后104周，对猪皮肤的晚期辐射损伤进行了评估。通过测量受辐照皮肤组织切片中的真皮厚度来评估损伤，并与未受辐照皮肤的真皮厚度进行比较，以确定真皮厚度的相对减少量。源的尺寸直径从0.1到40.0毫米不等；这涵盖了旨在模拟暴露于放射性“热”粒子（直径≤1.0毫米）的源尺寸范围，直至患者在放射治疗中可能暴露的较低野尺寸范围。使用具有1.1平方毫米收集电极的外推电离室测量辐射剂量，因此所引用的剂量代表该区域的平均剂量。对于直径≥5毫米的较大90Sr/90Y源和直径≥2毫米的较大170Tm源，基于与相对真皮厚度减少≥10%、≥20%、≥30%和≥40%相一致的损伤水平，没有证据表明源尺寸对这些特定效应水平的半数有效剂量（ED50）值有任何影响。然而，β粒子能量有显著影响；对于相对真皮厚度减少≥20%的情况，与ED50值（±标准误差）相关的皮肤表面剂量，90Sr/90Y和170Tm分别约为12 Gy和约40 Gy。在同等程度的真皮损伤下，这种皮肤表面剂量的差异反映了这两种β粒子发射体深度剂量的变化。对于被认为是临床可检测的真皮效应而言，这些皮肤表面剂量低于湿性脱屑早期皮肤反应的ED10。这支持选择晚期真皮变薄作为在更广泛的大面积皮肤暴露的辐射防护中确定剂量限值所依据的效应。相比之下，单次小面积暴露于旨在模拟热粒子源的辐射中，强化了这样一种观点，即急性溃疡应作为剂量限制所依据的效应。单次小面积暴露后，相对真皮厚度临床可检测减少≥20%的等效应剂量，要么高于急性溃疡的ED10，要么显示真皮变薄的皮肤面积太小，以至于不被认为有害。
