Microdosimetric characteristics of the clinical proton beams at JINR,Dubna

High-energy proton radiotherapy beams give rise to secondary heavy charged particles with elevated linear energy transfer (LET), which contribute to the dose in a patient. This contribution to the characteristics of radiotherapy proton beams was experimentally studied by means of a LET spectrometer based on a track detector. The spectrometer permits LET spectra to be established in the region above 10 keV.micron-1 in tissue. Sets of track detectors were exposed in the various depths of a phantom irradiated with protons of two energies, 150 and 205 MeV. It was observed that the contribution of particles with the values of LET mentioned increases with the depth, representing from about 2 (at the surface) up to few tens% close to Bragg peak region of the total dose. There, some of primary protons contribute also above 10 keV.micron-1. Using the 'biological weighted function' proposed, the clinical RBE was calculated, it could approach 1.3. This effect has to be taken into account during the clinical beam production and the radiotherapy.     

Passive spectrometry of linear energy transfer: development and use

A linear energy transfer (LET) spectrometer based on the evaluation of particle track parameters in a chemically etched polyallyldiglycolcarbonate (PADC) track detector has been developed at our laboratory. It permits us to determine LET spectra between 10 and 700 keV microm(-1) in tissues. The LET spectra obtained permit us to calculate total dose and dose equivalent corresponding to particles with etchable tracks also. We have recently been able to verify the calibration curves used by using C, Mg, Ne, Si and Fe ion beams with different energies. The calibration curves obtained are presented and compared with those originally used, and a good correlation is found. The LET spectrometer with new calibration was used to analyse the radiation quality of the radiotherapy proton beam at the Joint Institute for Nuclear Research (JINR). The radiation quality was studied along the proton's range, particular attention being devoted to the region of the Bragg peak. It was found that the biologically weighted effective dose (BWE) reaches a value of about 1.25 at the Bragg peak region. At the beam entrance this value increases to about 1.02 due to secondary particles created through primary proton nuclear reactions in tissues.     

Dosimetric results from the Mir orbital station

The Mir Orbital Station provided a unique platform on which to carry out a variety of space radiation dosimetry measurements. A number of experiments were conducted using a combination of passive detectors on the interior of the Mir during 1996-97. Thermoluminescent detectors were used to measure absorbed dose. CR-39 plastic nuclear track detectors were used to measure the LET spectra > or =5 keV.microm(-1). Results from TLDs and CR-39 PNTDs were combined to determine total dose and dose equivalent. Mean dose rate was found to decrease while mean dose equivalent rate and average quality factor increased with increasing shielding. Secondary particles from proton-induced target fragmentation interactions, not primary HZE particles, were found to be the largest contributor to the LET spectrum above 100 keV.microm(-1). During the 1997 measurements, mean quality factor was found to vary from 1.7 to 2.1 as a function of location within the Mir.     

Empirical model estimation of relative biological effectiveness for proton beam therapy

A simple model for proton relative biological effectiveness (RBE) is proposed. It describes the RBE as a function of proton depth, the dose and the linear energy transfer (LET) when proton passes through tissue-like materials. Radiobiological parameters were first obtained by fitting the published experimental cell survival data. The dose-averaged LET values were calculated for 250-MeV proton beam in a water phantom by using GEANT4 Monte Carlo simulation code and were then used as input values to calculate the values of RBE as function of depths. The model was also applied to proton spread-out Bragg peak, where the increasing RBE with depth causes an extended RBE-weighted dose in the distal fall-off region. This model was found to be able to reproduce the measured RBE values as a function of LET, depth and dose for a specific cell line.     

Microdosimetric assessment of the radiation quality of a therapeutic proton beam: comparison between numerical simulation and experimental measurements

Using protons for the treatment of ocular melanoma (especially of posterior pole tumours), the radiation quality of the beam must be precisely assessed to preserve the vision and to minimise the damage to healthy tissue. The radiation quality of a therapeutic proton beam at the Centre Antoine Lacassagne in Nice (France) was measured using microdosimetric techniques, i.e. a miniaturised version of a tissue-equivalent proportional counter. Measurements were performed in a 1-μm site at different depths in a Lucite phantom. Experimental data showed a significant increase in the beam quality at the distal edge of the spread-out Bragg peak (SOBP). In this paper, the numerical simulation of the experimental setup is done with the FLUKA Monte Carlo radiation transport code. The calculated microdosimetric spectra are compared with the measured ones at different depths in tissue for a monoenergetic proton beam (E=62 MeV) and for a modulated SOBP. Numerically and experimentally predicted relative biological effectiveness values are in good agreement. The calculated frequency-averaged and dose-averaged lineal energy mean values are consistent with measured data.     

30~160keV单能X射线装置的单色性实验研究

单能X射线光源是由X射线光机、双晶单色器、标准探测器以及准直系统组成。X射线光机产生的连续X射线,通过与双晶单色器发生布拉格衍射完成单色化,调节不同的特定布拉格角度得到能量范围30~160keV的单能X射线。为了研究标定装置的能量展宽,需要对该装置产生的单能X射线的能量分辨率进行研究。结果表明Si(220)晶体产生的单能X射线的能量分辨率为0.91%@30keV和2.3%@70.6keV,Si(551)晶体为1.97%@80.1keV和3.45%@142.6keV。使用这套装置对溴化镧晶体探测器的能量响应进行校准验证,实验发现该装置的能量分辨率良好,可以应用在多种类型探测器的标定实验、X射线质量衰减系数测量以及多层膜反射率测量等领域。     

Responses of TLD Mg2SiO4:Tb and radiophotoluminescent glass to heavy charged particles and space radiation.

The LET dependences of thermoluminescence dosimeters of Mg2SiO4:Tb (TLMS) and radiophotoluminescent glass dosemeters (RPLG) were examined using high energy, heavy ion beams. TLMS kept its efficiency below 10 keV micrometer-1 and decreased almost linearly with the logarithm of LET for higher LET particles. The efficiency of RPLG decreased more gradually than TLMS although its reduction was observed at a lower LET region around 0.5 keV micrometer-1. Accordingly, the ratio of TLMS to RPLG valued showed a maximum peak around 20 keV micrometer-1 of LET. The results obtained with both dosemeters in the 40 day space mission in the Russian space station Mir showed that not only dose level but also radiation quality were varying considerable in the Mir Core Module.     

Contribution of secondary particles to the dose in 12C radiotherapy and other heavy ion beams

The results of experimental studies performed in a radiotherapy (12)C ion beam with a nominal energy of 500 MeV/amu and in (16)O and (56)Fe ion beams with a nominal energy of 1 GeV/amu have been described. Linear energy transfer (LET) spectra have been established by means of an LET spectrometer based on a chemically etched track detector, and the measured results were also compared with theoretical calculations obtained using the program Stopping and Range of Ions in Matter (SRIM). It was observed that with increasing depth in a beam, the LET spectra are shifted towards higher values of LET; one can also observe an important widening of the spectra along the range, as well as an increasing amount of nuclear reaction products and/or of fragments in the spectra. The relative contribution of these secondary particles to the total absorbed dose was assessed.     

Doses and LET spectra in the beam of 12C with energy 500 MeV amu-1

This paper describes the results of experimental studies performed at the Joint Institute for Nuclear Research (JINR) in a (12)C ion beam with the primary nominal energy 500 MeV amu(-1). Data measured by means of a diamond detector and a spectrometer of linear energy transfer (LET) based on chemically etched track detectors are presented, analysed and discussed. LET spectra are also calculated by program SRIM.     

Cellular signal transduction events as a function of linear energy transfer (LET)

In order to obtain a deeper insight into the molecular mechanism controlling the cellular response to high-linear energy transfer (LET) radiation, the number and size of pATM (S1981) and gamma-H2AX foci were compared in cultures of diploid human fibroblasts after exposure to charged particles of varying species, energy and LET at the NIRS-HIMAC-facility (Chiba, Japan). Particle LET ranged from 2.2 to 300 keV/mum, and a low fluence of 7.3 x 10(4) cm(-2) was chosen. Therefore, about 1 out of 7 nuclei was traversed by a particle. Doses and LET were verified with thermoluminescence detectors (LiF:Mg, Ti) evaluated according to the high temperature ratio method. Two hours after irradiation, fibroblasts were fixed and the subcellular distribution of pATM (S1981) and gamma-H2AX was visualised by immunofluorescence or histochemical staining using phosphorylation-specific antibodies. It was found that the number of pATM (S1981) foci per nucleus was higher after exposure to higher-LET particles. Irradiation with the two highest LET beams (Fe-ions, 197 and 300 keV/mum) gave a significant increase in the number of pATM foci, whereas ions with an LET lower than 30 keV/mum yielded similar numbers of pATM foci compared with unirradiated control samples. These data show that the early cellular response to high-LET radiation is modulated by the energy deposition of the particle. Therefore, the correlation between the microdosimetric aspect of energy deposition and biologic consequences at low radiation doses deserves further study.     

Microdosimetric spectra and LET distributions on board the Mir space station obtained with a particle track detector

A spectrometer measuring energy lost (deltaE) was used to determine linear energy transfer (LET) spectra on board the Mir orbital station during the period from 8 October 1997 to 16 June 2000, i.e. during the 24th, 26th, 27th and 28th basic expeditions. It was found that the LET spectra of secondary particles between 10 and 700 keV.microm(-1) in tissue do not depend on the external radiator, with the average quality factors for the region mentioned being about 6.4 with ICRP 26 quality factors or about 7.4 with ICRP 60 quality factors. Both differential and integral LET spectra are presented for some typical cases. The spectra permitted us to calculate the total doses and dose equivalents due to particles with the LET values in the mentioned region. It was found that these doses are higher when the detector was placed in a less shielded area. It was also found that these doses vary from one expedition to another. The correlation of these variations with the solar activity level was studied.     

Low and high LET dose components in carbon beam

Clinical application of light ion beams requires correct understanding of the complex processes of ion interaction with matter and the development of accurate transport methods. Knowledge of the fluence differential in energy of primary and secondary particles is important since it allows evaluation of different linear energy transfer (LET) dose components in the patient. The low LET and high LET particle distributions and the corresponding absorbed doses due to primary and secondary particles were evaluated for different depths in a water phantom using the Monte Carlo code SHIELD-HIT. SHIELD-HIT calculations are compared with the experimental LET distributions for a carbon beam of energy 278 MeV u(-1) from the HIMAC facility in Japan. The capability of the code for the evaluation of particle transport in thin layers of a few micrometres is demonstrated.     

Radiation measured for ISS-Expedition 12 with different dosimeters

Radiation in low Earth orbit (LEO) is mainly from Galactic Cosmic Rays (GCR), solar energetic particles and particles in South Atlantic Anomaly (SAA). These particles’ radiation impact to astronauts depends strongly on the particles’ linear energy transfer (LET) and is dominated by high LET radiation. It is important to investigate the LET spectrum for the radiation field and the influence of radiation on astronauts. At present, the best active dosimeters used for all LET are the tissue equivalent proportional counter (TEPC) and silicon detectors; the best passive dosimeters are thermoluminescence dosimeters (TLDs) or optically stimulated luminescence dosimeters (OSLDs) for low LET and CR-39 plastic nuclear track detectors (PNTDs) for high LET. TEPC, CR-39 PNTDs, TLDs and OSLDs were used to investigate the radiation for space mission Expedition 12 (ISS-11S) in LEO. LET spectra and radiation quantities (fluence, absorbed dose, dose equivalent and quality factor) were measured for the mission with these different dosimeters. This paper introduces the operation principles for these dosimeters, describes the method to combine the results measured by CR-39 PNTDs and TLDs/OSLDs, presents the experimental LET spectra and the radiation quantities.     

Feasibility study of a Superheated Superconducting Granule detector for cold dark matter search

The presented results are part of a feasibility study of a Superheated Superconducting Granule (SSG) device for weakly interacting massive particles (WIMPs) detection. The sensitivity of SSG to nuclear recoils has been explored irradiating SSG detectors with a 70MeV neutron beam proving that energy thresholds of 1keV can be reached in 30µm Zn and 17µm Sn granules. The successful irradiation experiments with neutrons encouraged us to plan a prototype SSG dark matter detector. The status of the project will be presented and the expected counting rate for spin-independent WIMP interactions in SSG detectors will be discussed.     

液体金属和合金的固-气两相流雾化的研究

采用铁粉作为固体雾化介质,研究固-气两相法的雾化工艺。通过对Al-30％Si的研究,结果表明:固-气两相流雾化制粉与普通气体雾化相比,能有效减小雾化粉末的粒度,提高细粉收得率,普通气体雾化制粉得到的粉末平均颗粒尺寸为150μm,固-气两相流雾化粉末的平均颗粒尺寸为50μm;使冷却速度显著提高,达到10~4～10~5K/s,相比普通气体雾化提高了10～100倍,使Al-30％粉末的微观组织明显细化,固-气两相流能量利用率增加。     

Synthesis of gold and silver nanoparticles by electron irradiation at 5-15 keV energy

Thin coatings (～10?μm) made from a mixture of polyvinyl alcohol (PVA) and HAuCl(4) or PVA and AgNO(3) on quartz plates were irradiated with 5-15?keV electrons, at room temperature. The electron energy was varied from coating to coating in the range of 5-15?keV, but electron fluence was kept constant at ～10(15)?e?cm(-2). Samples were characterized by the UV-vis, XRD, SEM and TEM techniques. The plasmon absorption peaks at ～511 and ～442?nm confirmed the formation of gold and silver nanoparticles in the respective electron-irradiated coatings. The XRD, SEM and TEM measurements reveal that the average size of the particles could be tailored in the range of 130-50?nm for gold and from 150-40?nm for silver by varying the electron energy in the range of 5-15?keV. These particles of gold and silver embedded in the polymer could also be separated by dissolving the coatings in distilled water.     

Radiation dosimetry for microbial experiments in the International Space Station using different etched track and luminescent detectors

The laboratory of Microbiology at SCK.CEN, in collaboration with different universities, participates in several ESA programmes with bacterial experiments that are carried out in the International Space Station (ISS). The main objective of these programmes is to study the effects of space flight conditions such as microgravity and cosmic radiation on the general behaviour of model bacteria. To measure the radiation doses received by the bacteria, different detectors accompanied the microbiological experiments. The results obtained during two space flight missions are discussed. This dosimetry experiment was a collaboration between different institutes so that the doses could be estimated by different techniques. For measurement of the high linear energy transfer (LET) doses (>10 keV microm(-1)), two types of etched track detectors were used. The low LET part of the spectrum was measured by three types of thermoluminescent detectors ((7)LiF:Mg,Ti; (7)LiF:Mg,Cu,P; Al(2)O(3):C) and by the optically stimulated luminescence technique using Al(2)O(3):C detectors.     

LET dependence of bubble detector response to heavy ions

A series of experiments have been recently performed at the Heavy Ion Medical Accelerator in Chiba (HIMAC) laboratory to study the response of bubble detectors to high-mass high-energy (HZE) particles. The motivation for this study was to improve our ability to interpret measurements of neutron energy spectra in space. A recent analysis showed that emulsions of light halocarbons display common properties when they are characterised by a quantity called 'reduced superheat'. This quantity evolved from the examination of neutron and gamma responses of many types of detectors. In this study, we describe direct irradiations with N, Ar and Kr charged particles at HIMAC. It was observed that when the linear energy transfer (LET) corresponding to bubble formation was plotted vs. reduced superheat, different curves were obtained for a particular ion for detectors at different temperatures. Different curves were also obtained when data from different ions were plotted. These results confirm that bubble nucleation is not a simple function of particle LET and that an analysis based on track-structure appears warranted.     

Comparison of the cathodo- and γ-luminescence spectra of scintillation crystals

The spectra of pulsed cathodoluminescence (PCL) of CsI:Tl, YAG:Ge³⁺,Tb³⁺, and LFS-3 crystals excited by high-power (～10 MW) short-time (～2 ns) action of an electron beam with an average particle energy of ～150 keV have been compared to the spectra of steady-state luminescence of the same crystals under the action of γ-photons with an energy of 511 keV emitted from a radioactive ²²Na sample. It is established that the two spectra are identical, which allows the PCL method to be used for rapid analysis of scintillation crystals.     

A database of frequency distributions of energy depositions in small-size targets by electrons and ions

Linear energy transfer (LET) is an average quantity, which cannot display the stochastics of the interactions of radiation tracks in the target volume. For this reason, microdosimetry distributions have been defined to overcome the LET shortcomings. In this paper, model calculations of frequency distributions for energy depositions in nanometre size targets, diameters 1-100 nm, and for a 1 μm diameter wall-less TEPC, for electrons, protons, alpha particles and carbon ions are reported. Frequency distributions for energy depositions in small-size targets with dimensions similar to those of biological molecules are useful for modelling and calculations of DNA damage. Monte Carlo track structure codes KURBUC and PITS99 were used to generate tracks of primary electrons 10 eV to 1 MeV, and ions 1 keV μm(-1) to 300 MeV μm(-1) energies. Distribution of absolute frequencies of energy depositions in volumes with diameters of 1-100 nm randomly positioned in unit density water irradiated with 1 Gy of the given radiation was obtained. Data are presented for frequency of energy depositions and microdosimetry quantities including mean lineal energy, dose mean lineal energy, frequency mean specific energy and dose mean specific energy. The modelling and calculations presented in this work are useful for characterisation of the quality of radiation beam in biophysical studies and in radiation therapy.