Bonner sphere spectrometer for characterization of BNCT beam

The characterization of the epithermal beam is performed by different dosimetry techniques that give information on neutron flux as well as neutron and photon doses. One of the possible methods is based on the measurement of thermal neutrons in a moderation environment, which enables the evaluation of neutron flux in a group structure and also neutron dose. The advantage of such a spectrometer consists of the fact that 90% response intervals of the spheres continuously cover the epithermal part of the neutron energy range. The method has been applied to characterize the epithermal neutron beams at several research centers in USA, Finland, the Netherlands and Czech Republic. The comparison of the MIT FCB, HFR HB11, VTT FiR, and LVR-15 beam parameters is presented in this paper.     

15MV医用直线加速器光中子蒙特卡罗模拟

目的 研究高能医用直线加速器运行过程中因光核反应所形成的光中子辐射场。方法 利用蒙特卡罗(MC)程序模拟Clinic 2300CD型医用电子加速器15 MV X射线模式下光中子污染,掌握机头内不同位置光中子能谱和不同照射野下等中心处中子周围剂量当量变化,分析光中子在等中心平面内剂量分布和水模体中剂量衰减。结果 准直器关闭时,加速器机头内靶、主准直器、均整器和多叶准直器下表面的光中子平均能量分别为1.08、1.20、0.35、0.30MeV;等中心处中子周围剂量当量随着照射野的增大先增大后减少,在30 cm × 30 cm照射野下达到最大;随着测点在水模体中的深度增加,中子通量先增加后减小,而中子剂量却在逐渐减小;不同照射野下,光中子剂量率在水模体深度20 cm处,基本都接近本底。结论 探究高能医用直线加速器机头光中子谱和剂量分布特点,以及光中子在水模体内剂量沉积规律,能为进一步研究高能医用直线加速器光中子污染对患者产生的附加剂量提供支持。     

The fixed horizontal neutron therapy beam at Edinburgh: dosimetry and radiation protection.

A compact cyclotron producing 15 MeV deuterons has been installed at the Western General Hospital, Edinburgh, to extend the Medical Research Council's clinical trials of fast neutrons. Two treatment rooms are available one of which has an isocentric unit and the other a fixed horizontal beam which is the subject of this paper. A radiation protection survey has demonstrated safe levels of radiation throughout the building although there is some activation of the fixed horizontal beam cone resulting in doses to radiographers of 10 mrem per week. The calibration of neutron dose is discussed and the measurements of dose distribution described. Isodose and depth-dose data for both the neutron and photon components of the field are presented.     

Cell survival and DNA double-strand break repair following X-ray or neutron irradiation of V79 cells

We have investigated the effects of 250kVp X-rays and 2.3 MeV (mean energy) neutrons on the cell survival, DNA double-strand break (dsb) induction and repair (using the Kohn neutral elution technique) in V79 cells. The lethal effects of neutrons were shown to be significantly greater than for a similar dose of X-rays (RBE = 3.55 at 10 per cent survival). However, the RBE for dsb induction, in a dose range of 10-50 Gy, was 1. On investigating the repair of DNA dsb induced by either X-ray or neutron irradiation, clear differences in the pattern of repair were found. Both a fast and a slow component of repair were seen in both cases; the former, however, was reduced following neutron irradiation and, since the amount of slow repair was similar in both cases, this resulted in proportionally more unrejoined breaks after neutrons. These experiments were carried out with elution buffer at pH 9.6; however, when similar experiments were performed at pH 7.2 the results obtained support our earlier findings. We suggest that these differences in DNA dsb repair reflect basic differences in the nature of the lesions induced by high- and low-LET ionizing radiations.     

Project for the development of the linac based NCT facility in University of Tsukuba

A project team headed by University of Tsukuba launched the development of a new accelerator based BNCT facility. In the project, we have adopted Radio-Frequency Quadrupole (RFQ)+Drift Tube Linac (DTL) type linac as proton accelerators. Proton energy generated from the linac was set to 8 MeV and average current was 10 mA. The linac tube has been constructed by Mitsubishi Heavy Industry Co. For neutron generator device, beryllium is selected as neutron target material; high intensity neutrons are generated by the reaction with beryllium and the 80 kW proton beam.Our team chose beryllium as the neutron target material. At present beryllium target system is being designed with Monte-Carlo estimations and heat analysis with ANSYS. The neutron generator consists of moderator, collimator and shielding. It is being designed together with the beryllium target system. We also acquired a building in Tokai village; the building has been renovated for use as BNCT treatment facility. It is noteworthy that the linac tube had been installed in the facility in September 2012.In BNCT procedure, several medical devices are required for BNCT treatment such as treatment planning system, patient positioning device and radiation monitors. Thus these are being developed together with the linac based neutron source. For treatment planning system, we are now developing a new multi-modal Monte-Carlo treatment planning system based on JCDS. The system allows us to perform dose estimation for BNCT as well as particle radiotherapy and X-ray therapy. And the patient positioning device can navigate a patient to irradiation position quickly and properly. Furthermore the device is able to monitor movement of the patient׳s position during irradiation.     

Interaction between the biological effects of high- and low-LET radiation dose components in a mixed field exposure

Abstract

Purpose: The relative biological effectiveness of two epithermal neutron sources, a reactor based source at Studsvik, Sweden, and a proton accelerator-based source in Birmingham, UK, was studied in relation to the proportional absorbed dose distribution as a function of neutron energy. Evidence for any interactions between the effects of biological damage induced by high- and low-linear energy transfer (LET) dose components, in this ‘mixed field’ irradiation, was also examined

Materials and methods: Clonogenic survival in Chinese Hamster-derived V79 cells was used to assess biological effectiveness in this study. Cells were irradiated in suspension at 4°C at depths of 20, 35, 50 and 65 mm in a water phantom. This prevented the repair of sublethal damage, predominantly that produced by both incident and induced γ-rays in the field, over the variable periods of exposure required to irradiate cells with the same total absorbed dose. Cell survival, as a function of the absorbed radiation dose and depth in the phantom, was compared with Monte Carlo N-Particle (MCNP) calculations of the proportional absorbed dose distribution as a function of neutron energy for the two sources.

Results: In terms of the dose-related reduction in clonogenic cell survival, the epithermal neutron source at Studsvik was more biologically effective than the Birmingham source at all depths considered in the phantom. Although the contribution from the high-LET dose component was greater for the Studsvik source at 20 mm depth in the phantom, at greater depths the dose contribution from the high-LET dose component at Studsvik overlap with those for the Birmingham source. However, the most striking difference is in the fast neutron component to the dose of the two sources, neutron energies > 1 MeV were only associated with the Studsvik source. The relative biological effectiveness (RBE) of both sources declined slightly with depth in the phantom, as the total high-LET dose component declined. The maximum source RBE for Studsvik was 2.70 ± 0.50 at 20 mm; reduced to 2.10 ± 0.35 at depths of 50 and 65 mm. The corresponding values for Birmingham were 1.68 ± 0.25 and 1.31 ± 0.19, all values relate only to the surviving fraction of V79 cells at 37%, since RBE values are only applicable to the selected endpoint. Based on a dose reduction factor (DRF) of 1.0 for the total low-LET component to the absorbed dose, the RBE values for the high-LET dose component (fast neutrons and induced protons from the nitrogen capture reaction) was 14.5 and 7.05 for the Studsvik and Birmingham neutron sources, respectively. This is well outside the range of RBE historically reported values for V79 cells for the same level of cell survival for fast neutrons. The calculation of RBE values, based on the proportional absorbed dose distribution as a function of neutron energy, from historical data, and using a RBE of 1.8 for the dose from the nitrogen capture reaction, suggests RBE values for the total high-LET dose component of 3.1–2.8 and 2.5–2.0 for Studsvik and Birmingham, respectively, values again declining with depth in the phantom.

Conclusions: The overall biological effectiveness of the mixed field irradiation from an epithermal neutron sources depends on the composition and quality of the different dose components. The experimentally derived RBE values for the total high-LET dose components in these ‘mixed field’ irradiations are well in excess of historical data for fast neutrons. The difference between the historically expected and the observed RBE values is attributed to the interactions between the damage produced by high- and low-LET radiation.     

A review of boron neutron capture therapy (BNCT) and the design and dosimetry of a high-intensity, 24 keV, neutron beam for BNCT research

This paper reviews the development of boron neutron capture therapy (BNCT) and describes the design and dosimetry of an intermediate energy neutron beam, developed at the Harwell Laboratory, principally for BNCT research. Boron neutron capture therapy is a technique for the treatment of gliomas (a fatal form of brain tumour). The technique involves preferentially attaching 10B atoms to tumour cells and irradiating them with thermal neutrons. The thermal neutron capture products of 10B are short range and highly damaging, so they kill the tumour cells, but healthy tissue is relatively undamaged. Early trials required extensive neurosurgery to exposure the tumour to the thermal neutrons used and were unsuccessful. It is thought that intermediate-energy neutrons will overcome many of the problems encountered in the early trials, because they have greater penetration prior to thermalization, so that surgery will not be required. An intermediate-energy neutron beam has been developed at the Harwell Laboratory for research into BNCT. Neutrons from the core of a high-flux nuclear reactor are filtered with a combination of iron, aluminium and sulphur. Dosimetry measurements have been made to determine the neutron and gamma-ray characteristics of this beam, and to monitor them throughout the four cycles used for BNCT research. The beam is of high intensity (approximately 2 x 10(7) neutrons cm-2 s-1, equivalent to a neutron kerma rate in water of 205 mGy h-1) and nearly monoenergetic (93% of the neutrons have energies approximately 24 keV, corresponding to 79% of the neutron kerma rate).     

Lack of inverse dose-rate effect on fission neutron induced transformation of C3H/10T1/2 cells

Exponential and density-inhibited cultures of C3H/10T1/2 cells were exposed to a single dose of 0.3 Gy of fission neutrons delivered at rates ranging from 0.005 to 0.1 Gy/min. No discernible effect upon cell survival or transformation was observed by a lowering of the fission neutron dose rate in either exponential or plateau cultures. At the level of 2.3 x 10(-4) transformants per surviving cell, the RBE for neoplastic transformation was three at acute dose rates and ten at the lowest dose rate studied (0.005 Gy/min for neutrons and 0.01 Gy/min for X-rays).     

The RBE of the leakage radiation from the Hiletron neutron therapy unit

The RBE of the leakage radiation from the Hiletron 14.7 MeV neutron therapy unit has been measured using three sensitive biological systems in mice, which differ markedly in their radiobiological characteristics. These systems comprise type A spermatogonia and bone marrow stem cells, which are affected insignificantly by dose rate, and pigment abnormalities in hair follicles which are affected markedly by dose rate. For mice irradiated at 10 cm depth in a water phantom, the leakage radiation up to 40 cm from the beam axis was virtually as effective as the primary beam for the latter two biological systems, and for spermatogonia in mice when irradiated in air. At this distance, the total dose rate was about 0.2 cGy (rad) per minute (3% of that in the primary beam), and the gamma-ray component was about 70%. This equal effectiveness of the total dose for all three systems was considered fortuitous, and it implied high RBE values for equal effect with the small neutron component at far distances. Considering published data on RBE versus neutron energy, the evidence suggested either a positive interaction of neutron and gamma-ray components in killing bone marrow stem cells when the neutron component was less than 40% of the total dose, or an increased efficiency of neutrons when delivered at very low dose rates. However the components were additive in killing spermatogonia.     

Neutron flow measurements in the d(14) + Be neutron radiation field from the cyclotron in Essen

It exists the possibility in the neutron therapy of specific tumours to increase the local energy dose in the tumour by treatment with fast neutrons under use of B-10. Thermal neutrons cause the neutron capture reaction B-10(n, alpha)Li-7 in tissue. A sufficiently high number of thermic neutrons is necessary combined with a possibly selective concentration of B-10 in the tumour as target volume for the clinical application. Gold foils were activated in a water phantom at several depths for the quantitative determination of the thermal neutron fluence. A result of this measurements is a maximal thermal neutron fluence of 1.44 X 10(10) cm-2 at depth of 5 cm with applied total energy dose of 0.8 Gy.     

Neutron fluence depth profiles in water phantom on epithermal beam of LVR-15 research reactor

Horizontal channel with epithermal neutron beam at the LVR-15 research reactor is used mainly for boron neutron capture therapy. Neutron fluence depth profiles in a water phantom characterise beam properties. The neutron fluence (approximated by reaction rates) depth profiles were measured with six different types of activation detectors. The profiles were determined for thermal, epithermal and fast neutrons.     

Analysis of neutron and gamma-ray streaming along the maze of NRCAM thallium production target room.

Study of the shield performance of a thallium-203 production target room has been investigated in this work. Neutron and gamma-ray equivalent dose rates at various points of the maze are calculated by simulating the transport of streaming neutrons, and photons using Monte Carlo method. For determination of neutron and gamma-ray source intensities and their energy spectrum, we have applied SRIM 2003 and ALICE91 computer codes to Tl target and its Cu substrate for a 145 microA of 28.5 MeV protons beam. The MCNP/4C code has been applied with neutron source term in mode n p to consider both prompt neutrons and secondary gamma-rays. Then the code is applied for the prompt gamma-rays as the source term. The neutron-flux energy spectrum and equivalent dose rates for neutron and gamma-rays in various positions in the maze have been calculated. It has been found that the deviation between calculated and measured dose values along the maze is less than 20%.     

A Monte Carlo study on neutron and electron contamination of an unflattened 18-MV photon beam

Recent studies on flattening filter (FF) free beams have shown increased dose rate and less out-of-field dose for unflattened photon beams. On the other hand, changes in contamination electrons and neutron spectra produced through photon (E>10 MV) interactions with linac components have not been completely studied for FF free beams. The objective of this study was to investigate the effect of removing FF on contamination electron and neutron spectra for an 18-MV photon beam using Monte Carlo (MC) method. The 18-MV photon beam of Elekta SL-25 linac was simulated using MCNPX MC code. The photon, electron and neutron spectra at a distance of 100 cm from target and on the central axis of beam were scored for 10×10 and 30×30 cm² fields. Our results showed increase in contamination electron fluence (normalized to photon fluence) up to 1.6 times for FF free beam, which causes more skin dose for patients. Neuron fluence reduction of 54% was observed for unflattened beams. Our study confirmed the previous measurement results, which showed neutron dose reduction for unflattened beams. This feature can lead to less neutron dose for patients treated with unflattened high-energy photon beams.     

The munich fission neutron therapy facility MEDAPP at the research reactor FRM II

Purpose

At the new research reactor FRM II of the Technical University of Munich (TUM), the facility for Medical Applications (MEDAPP) was installed where fast neutrons are available as a beam for medical use.

Material and Methods

Thermal neutrons induce fission in a pair of uranium converter plates and generate fast neutrons which are guided to the patient by a beam tube. The maximum opening of the multi leaf collimator (MLC) is 30 × 20 cm² W × H. The beam is characterized by neutron-photon mixed beam phantom dosimetry. Specific safety measures are outlined.

Results

The neutron and gamma dose rates are 0.52 Gy/min and 0.20 Gy/min, respectively, in 2 cm depth of a water phantom. The half maximum depth of the neutron dose rate in water is 5.4 cm (mean neutron energy 1.9 ± 0.1 MeV). Conformity with the European Medical Devices Directive (MDD) 93/42/EEG, was proven so that MEDAPP has a CE mark and since February 2007 also the license for clinical operation.

Conclusion

The clinical neutron irradiations of malignant tumors, which were performed at the former research reactor FRM until 2000, can be continued at FRM II under improved conditions. First patients were irradiated in June 2007.     

Monte Carlo simulation of surface percent depth dose.

This work studied the surface percent depth dose of 6 and 15 MV X-rays, 10 x 10 cm2 and 20 x 20 cm2 fields by Monte Carlo simulation. The OMEGA/BEAM code, an EGS4 user code developed by the NRCC, was used. The linac, Siemens PRIMUS, was accurately modeled according to the ion chamber and CEA film measurement, and the phase space data generated from this linac were collected to simulate dose distribution in water. The water phantom had radius 30 cm and thickness 10 cm. The percent depth doses at zero depth, PDDsurface, for 6 MV X-rays were 13.85 +/- 0.11% and 23.21 +/- 0.20% for the 10 x 10 cm2 and 20 x 20 cm2 fields, respectively. For 15 MV X-rays, PDDsurface values were 8.83 +/- 0.07% and 18.60 +/- 0.12% for the 10 x 10 cm2 and 20 x 20 cm2 fields, respectively.     

Development of a low-energy monoenergetic neutron source for applications in low-dose radiobiological and radiochemical research

The McMaster University 3 MV KN Van de Graff accelerator facility primarily dedicated to in vivo neutron activation measurements has been used to produce moderate dose rates of monoenergetic fast neutrons of energy ranging from 150 to 600 keV with a small energy spread of about 25 keV (1σ width of Gaussian) by bombarding thin lithium targets with 2.00–2.40 MeV protons. The calculated dose rate of the monoenergetic neutrons produced using thin lithium targets as functions of beam energy, target thickness, lab angle relative to beam direction, and the solid angle subtended by the sample with the target has also been reported.     

A fast neutron source for cultured cell irradiation.

Because of recent interest in the use of neutrons for radiotherapy, there has been an increased interest in the radiology of neutrons. In this irradiated cell study, a 1.3 MeV accelerator produced beam currents over 100 muA on the water-cooled 3-mm thick beryllium disk target. The monolayer of irradiated cells was neutron-shielded by about 700 kg of paraffin. The neutron energy spectrum for the 9Be(d,n)10B reaction was obtained, with an average neutron energy calculated to be between 3.3 and 3.5 MeV, and an average linear energy transfer calculated at more than 30 keV/micron.     

Characteristics of the new THOR epithermal neutron beam for BNCT.

A characterization of the new Tsing Hua open-pool reactor (THOR) epithermal neutron beam designed for boron neutron capture therapy (BNCT) has been performed. The facility is currently under construction and expected in completion in March 2004. The designed epithermal neutron flux for 1 MW power is 1.7x10(9)n cm(-2)s(-1) in air at the beam exit, accompanied by photon and fast neutron absorbed dose rates of 0.21 and 0.47 mGys(-1), respectively. With (10)B concentrations in normal tissue and tumor of 11.4 and 40 ppm, the calculated advantage depth dose rate to the modified Snyder head phantom is 0.53RBE-Gymin(-1) at the advantage depth of 85 mm, giving an advantage ratio of 4.8. The dose patterns determined by the NCTPlan treatment planning system using the new THOR beam for a patient treated in the Harvard-MIT clinical trial were compared with results of the MITR-II M67 beam. The present study confirms the suitability of the new THOR beam for possible BNCT clinical trials.     

RBE and OER measurements on the p(66) + Be neutron beam at Faure, South Africa.

Results reported are for single dose exposures and refer to 60Co-gamma-irradiation. The RBE determined by V79 cell survival and based on the Do ratio was found to be 1.70 +/- 0.4 ranging from 1.5 to 1.8. In the case of the regeneration of mouse jejunal crypts the RBE was calculated at ten cell survival and was found to be 1.68. The maximum acute mouse skin reaction at a skin score of 2.0 was found to be 2.1 while the average skin reaction was 1.7. Growth retardation of Vicia faba bean roots measured at the level of 50% indicated an average RBE of 3.0 and a range of 2.7 to 3.7. The OER obtained for V79 cell survival was found to be 1.7 to 1.8. Comparison is made with the RBE and OER measurements for the neutron facilities at Clatterbridge, Fermilab and Louvain-la-Neuve which produce neutrons by the same nuclear reaction and whose physical specifications closely resemble those of the Faure neutrons. This comparison indicates that the Faure beam shows no unusual biological features and that its biological effectiveness is in line with that expected from its physical characteristics.     

Neutron spectra at two beam ports of a TRIGA Mark III reactor loaded with HEU fuel

The neutron spectra have been measured in two beam ports, one radial and another tangential, of the TRIGA Mark III nuclear reactor from the National Institute of Nuclear Research in Mexico. Measurements were carried out with the reactor core loaded with high enriched uranium fuel. Two reactor powers, 5 and 10 W, were used during neutron spectra measurements using a Bonner sphere spectrometer with a ⁶LiI(Eu) scintillator and 2, 3, 5, 8, 10 and 12 in.-diameter high-density polyethylene spheres. The neutron spectra were unfolded using the NSDUAZ unfolding code. For each spectrum total flux, mean energy and ambient dose equivalent were determined. Measured spectra show fission, epithermal and thermal neutrons, being harder in the radial beam port.