Mellenberg D E, Hogstrom K R, White R A
Department of Radiation Physics, University of Texas MD Anderson Hospital and Tumor Institute, Houston 77030.
Phys Med Biol. 1987 Dec;32(12):1559-67. doi: 10.1088/0031-9155/32/12/003.
In order to establish the feasibility of performing blood flow measurements following therapeutic neutron irradiation by determining increased 15O disappearance rate from a volume of tissue, knowledge of the probabilities of 15O, 11C and 13N production in tissue by a p(42)Be neutron-beam irradiation is required. Isotope production probability per unit dose (defined as the isotope-yield coefficient) is determined from the measured production of 15O, 13N and 11C in irradiated H2O. Measured isotope-yield coefficients average 1.20 x 10(-16), 2.85 x 10(-18) and 5.56 x 10(-18) Gy-1 per 16O nucleus, respectively, at depths between 1 and 15 cm in a water phantom. The isotope yield coefficients for 11C production from 12C (polyethylene) average 1.04 x 10(-16) Gy-1 per 12C nucleus at depths between 1 and 15 cm in a water phantom. From these yield coefficients, the creation of 9700 Bq 15O and 450 Bq 11C per cubic centimetre of human soft tissue (chemical composition of soft tissue of Reference Man) is calculated assuming a 0.65 Gy neutron irradiation given at a dose rate of 40 cGy min-1 and assuming no perfusion of the activity. These results agree with those calculated using published neutron cross sections and neutron energy spectra, indicating that (n, 2n) reactions are the predominant activation mechanisms.
为了通过测定一定体积组织中(^{15}O)消失率的增加来确定治疗性中子辐照后进行血流测量的可行性，需要了解(p(42)Be)中子束辐照在组织中产生(^{15}O)、(^{11}C)和(^{13}N)的概率。单位剂量的同位素产生概率（定义为同位素产额系数）由辐照水中(^{15}O)、(^{13}N)和(^{11}C)的测量产生量确定。在水模体中深度为(1)至(15)厘米处，每(^{16}O)核的测量同位素产额系数分别平均为(1.20×10^{-16})、(2.85×10^{-18})和(5.56×10^{-18} Gy^{-1})。在水模体中深度为(1)至(15)厘米处，由(^{12}C)（聚乙烯）产生(^{11}C)的同位素产额系数平均为每(^{12}C)核(1.04×10^{-16} Gy^{-1})。根据这些产额系数，假设以(40 cGy min^{-1})的剂量率给予(0.65 Gy)的中子辐照且假设放射性无灌注，计算出每立方厘米人体软组织（参考人软组织的化学成分）产生(9700 Bq)的(^{15}O)和(450 Bq)的(^{11}C)。这些结果与使用已发表的中子截面和中子能谱计算的结果一致，表明((n, 2n))反应是主要的活化机制。
