基于蒙特卡罗方法的α粒子细胞S值计算

在放射性免疫治疗以及硼中子俘获治疗（BNCT）等放射性治疗过程中,粒子通过与人体组织材料相互作用产生次级电子将能量传递给人体组织,放射性核素在细胞尺度分布的不均匀性将严重影响靶区剂量分布。为深入了解放射性核素在细胞中不同位置分布对靶区剂量影响,采用基于历史凝聚算法的Monte Carlo 工具包Geant4编写了细胞S值计算程序。计算了2种细胞尺寸,12种粒子能量,3种源分布方式的细胞S值,与医学内照射剂量（MIRD）委员会解析算法的计算结果进行对比,发现两者差异在1%以内。证明了Geant4在m尺度下细胞剂量计算的可行性,并对BNCT治疗过程中产生的粒子(1.47 MeV与1.78 MeV)的细胞S值进行计算。     

Specific energy from Auger and conversion electrons of 131I, 188Re-anti-CD20 to a lymphocyte's nucleus

The typical radionuclides used to label anti-CD20 in the treatment of non-Hodgkin's lymphoma are ⁹⁰Y, ¹³¹I, and ¹⁸⁸Re, with the emission of beta particles, Auger electrons, and conversion electrons for the latter two. The aim of the present work was to calculate the contribution of high linear energy transfer radiation as Auger electrons (AE) and conversion electrons (CE) of ¹³¹I and ¹⁸⁸Re-anti-CD20 to mean specific energy into the cell nucleus by Monte Carlo simulation (MCS), so as to infer therapeutic effectiveness on a dosimetric basis. MCS was used to quantify the frequency–mean specific energy into the cell nucleus, where the cell was modeled by two concentric spheres, considering two cell models. The results showed that 10% and 33% of the mean-specific energies (z¯) per disintegration imparted to the cell nucleus for both geometries are due to AE and CE; on the other hand, if the hit of AE and CE occurs, the contribution to (z¯) is about 64% and 86% for ¹³¹I and ¹⁸⁸Re, respectively. According to the amount of specific energy from AE and CE into the cell nucleus by positive event, they can cause catastrophic effects in the nuclear DNA in the treatment of non-Hodgkin's lymphoma with ¹³¹I, ¹⁸⁸Re-anti-CD20.     

Detection, dosimetry and microdosimetry using high energy C beams

Samples of polyallyldiglycolcarbonate (PADC) track etch detectors (TED) were exposed to high energy ¹²C nuclei at the particle beam of the Dubna synchrophasotron. The energy of ¹²C nuclei varied between 0.1 and 1.5 GeV per amu.

At the low studied energies the linear energy transfer (LET) of these nuclei is higher than the detector threshold value. Then, the primary particle tracks are directly etched in the detector surface. The detection efficiency approaches to 100% at perpendicular incidence. Their LET has been established by means of standard authomatized procedure recently developed. The LET values found here are in good agreement with theoretical ones.

At 1.5 GeV per amu (LET 8.4 KeV μm⁻¹) the secondary particle tracks were evaluated in all the exposed detectors. The energy deposited by these particles was compared to the energy deposited through primary ionization losses. It was found out that its contribution to the total dose is relatively lower than for protons of comparable energies. In some of these samples even the tracks of the primary nuclei were observed. It follows that the detection threshold of the developed LET spectrometer should be below 10 keV μm⁻¹.     

Spectrometry of the LET with track etched detectors—correlation with proportional counter measured spectra

A spectrometer of the linear energy transfer (LET) based on the chemically etched polyallyldiglycolcarbonate (PADC) track etched detector was developed. The LET spectra are determined through the measurements of track parameters, it covers LET range between 10 and 700 keV/μm in tissue. A combined experimental and theoretical approach allowed the estimation of the critical dimensions of the sensitive volume necessary for developing a track to several nm. It seemed interesting to us to compare the LET spectra obtained by this method with the microdosimetric spectra available on the basis of a classical experimental microdosimetry method, a tissue equivalent proportional counter, for which the critical dimensions simulated are of the order of a few μm.

Both methods of experimental microdosimetry were compared in the high energy radiation reference fields and on the subsonic aircraft board. It was found out that the microdosimetric distributions are similar; some differences are, nevertheless, observed. Further studies with the goal to explain them are outlined.