Mijnheer B J, Haringa H, Nolthenius H J, Zijp W L
Phys Med Biol. 1981 Jul;26(4):641-55. doi: 10.1088/0031-9155/26/4/008.
Neutron spectra at different positions in a phantom have been derived from activation foil and fission counter measurements for the collimated beam of the Amsterdam d+T fast-neutron therapy facility. The spectra show that the fraction of lower-energy neutrons increases with increasing depth in the phantom as well as with increasing distance from the central axis of the beam. Calculation of the ratios of kerma values in tissue and tissue-equivalent (TE) plastic and of WN values for the spectra at five positions in the phantom, showed that the variations in these quantities are less than 0.5%. Kerma values have been derived from the neutron spectra and from the fission counter measurements separately. These neutron kerma values were compared with the neutron absorbed dose values derived from combined TE ionisation chamber and GM counter measurements. The dose values have been obtained applying recommendations given in the European protocol for neutron dosimetry for external beam therapy. At 50 mm and 100 mm depth along the central axis of the beam in the phantom, the agreement between the three methods was within 2%. In the penumbra regions a maximum difference of about 7% has been observed between the three methods. The contribution from thermal neutrons to the total kerma is less than 1% in the beam as well as in the penumbra.
已通过活化箔和裂变计数器测量，得出了阿姆斯特丹氘 - 氚快中子治疗设施准直束在体模不同位置处的中子能谱。能谱表明，较低能量中子的份额随着在体模中深度的增加以及与束中心轴距离的增加而增大。对体模中五个位置处的能谱计算组织和组织等效（TE）塑料中的比释动能值之比以及WN值，结果表明这些量的变化小于0.5%。比释动能值已分别从中子能谱和裂变计数器测量中得出。将这些中子比释动能值与通过组合TE电离室和GM计数器测量得出的中子吸收剂量值进行了比较。剂量值是按照欧洲外照射束中子剂量测定协议中的建议获得的。在体模中沿束中心轴50毫米和100毫米深度处，三种方法之间的一致性在2%以内。在半影区，三种方法之间观察到的最大差异约为7%。热中子对总比释动能的贡献在束区以及半影区均小于1%。
