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Experimental animals (mice and rats) were exposed to mixed gamma/neutron radiation. Relative biological effectiveness of a neutron component (RBEn/x) was shown to decrease with decreasing share of neutrons in the combination. This is considered as a manifestation of nonadditivity of the effects of neutrons and sparsely ionizing radiation.
The International Commission on Radiological Protection (ICRP) in its Publication 60 introduced important changes in the concept of risk-related quantities. For external neutron radiation in particular the introduction of the equivalent dose with the radiation weighting factor wR instead of the dose equivalent concept with the quality factor Q(L) has many consequences. The value of wR is defined by the external neutron radiation field, while the radiation quality in the phantom depends on the radiation field at the position of interest and hence on the size of and the position in the phantom. It has been investigated to what extent the size of the phantom influences the mean radiation quality in the phantoms. For incident monoenergetic neutrons, mean photon dose contributions and mean quality factors have been calculated. Results are presented for various phantoms which characterize the conditions for a mouse, a rat, the ICRU sphere and a human body.
At the Massachusetts Institute of Technology (MIT) the first fission converter-based epithermal neutron beam (FCB) has proven suitable for use in clinical trials of boron neutron capture therapy (BNCT). The modern facility provides a high intensity beam together with low levels of contamination that is ideally suited for use with future, more selective boron delivery agents. Prescriptions for normal tissue tolerance doses consist of 2 or 3 fields lasting less than 10 min each with the currently available beam intensity, that are administered with an automated beam monitoring and control system to help ensure safety of the patient and staff alike. A quality assurance program ensures proper functioning of all instrumentation and safety interlocks as well as constancy of beam output relative to routine calibrations. Beam line shutters and the medical room walls provide sufficient shielding to enable access and use of the facility without affecting other experiments or normal operation of the multipurpose research reactor at MIT. Medical expertise and a large population in the greater Boston area are situated conveniently close to the university, which operates the research reactor 24 h a day for approximately 300 days per year. The operational characteristics of the facility closely match those established for conventional radiotherapy, which together with a near optimum beam performance ensure that the FCB is capable of determining whether the radiobiological promise of NCT can be realized in routine practice.
One of the very interesting applications at Munich's New Neutron Source will be neutron tomography. It will be used both for research and industry. The D2O moderated high flux reactor will provide thermal neutrons for the structural analysis of specimen up to the size of 1 m. A central problem is the design of the beam geometry, especially the layout of the collimator and the aperture. Calculations were carried out in order to get an optimal beam geometry, taking into consideration an extended source, low beam divergency and high flux in the detector plane.
Cross sections were measured for the 90Zr(n,alpha)87mSr, 90Zr(n,2n)89m,gZr, 91Zr(n,p)91mY, 92Zr(n,p)92Y, 94Zr(n,alpha)91Sr and 96Zr(n,2n)95Zr reactions over the neutron energy range of 11.4 to 12.4 MeV and for the 94Zr(n,p)94Y reaction from 9.2 to 12.4 MeV. Nuclear model calculations were performed up to 16MeV. The statistical model incorporating precompound effects reproduces excitation functions of the three major threshold reactions, namely (n,p), (n,alpha) and (n,2n), quite well. Spectrum averaged cross sections were measured using a thick target Be(d,n) neutron field at Ed = 14 MeV. For the same neutron field averaged reaction cross sections were deduced using the excitation functions measured in this work as well as those given in the ENDF/B-VI, JEF-2, JENDL-3.2, BROND and ADL-3 data files. A comparison of the experimental and deduced integral data helped validating the differential data.
The pulsed neutron experiment (the variable geometric buckling experiment) in spherical geometry has been simulated using the MCNP code. The time decay of the thermal neutron flux has been observed as a function of the sample size. The thermal neutron diffusion cooling coefficient C with the correction F has been determined for three basic rock minerals (quartz, calcite, dolomite) at the given specific densities. The corresponding density-removed parameters have also been obtained.
The151Sm(n,gamma)152Sm cross section has been measured at the spallation neutron facility n_TOF at CERN in the energy range from 1 eV to 1 MeV. The new facility combines excellent resolution in neutron time-of-flight, low repetition rates, and an unsurpassed instantaneous luminosity, resulting in rather favorable signal/background ratios. The 151Sm cross section is of importance for characterizing neutron capture nucleosynthesis in asymptotic giant branch stars. At a thermal energy of kT=30 keV the Maxwellian averaged cross section of this unstable isotope (t(1/2)=93 yr) was determined to be 3100+/-160 mb, significantly larger than theoretical predictions.
PURPOSE: The method of an evaluation for the dose characteristics of BNCT is presented, and an eccentric core design for the TRIGA-II reactor is proposed. METHODS AND MATERIALS: We have defined the "irradiation time" as the time of irradiation in which the "maximum 1 microgram/g dose" becomes 3,000 RBE-cGy, because we assumed that the normal tissue contained 1 microgram/g 10B. We have also changed the RBE values and calculated the absorbed dose in the "irradiation time" by using an arrangement including both a facility structure and a body phantom. Moreover, we have modified the dose criteria for BNCT as follows: The "eye dose," "total body dose," and "except-head dose" should be less than 200, 100, and 50 RBE-cGy, respectively. We have added one more criteria for BNCT-that the thermal neutron fluence at the tumor position (5 cm from the surface) should be over 2.5 x 10(12) n/cm2 in the "irradiation time." RESULTS: The distance from the core side to the irradiation port is a very important factor to design a neutron irradiation field for BNCT. CONCLUSION: We can get the acceptable dose for BNCT with only 1-h irradiation by using a 100 kW reactor if we can get the irradiation port at the distance of 120 cm from the core side.
A modeling investigation was performed to choose moderator material and size for creating optimal epithermal neutron beams for BNCT based on a proton accelerator and the (7)Li(p,n)(7)Be reaction as a neutrons source. An optimal configuration is suggested for the beam shaping assembly made from polytetrafluoroethylene and magnesium fluorine to be placed on high current IPPE proton accelerator KG-2.5. Results of calculation were experimentally tested and are in good agreement with measurements.
The in vitro characteristics of enteric coated acetylsalicylic acid tablets and cores were compared before and after irradiation with thermal neutrons, 2, 4, 7 or 15 min at 1.1.1013 neutrons cm-2s-I. The irradiation procedure affected the coated formulation to a greater extent than the cores. Drug release from tablets was already affected after 2 min of exposure, whereas the cores showed no significant inhibition of release until after 15 min of irradiation, leading to the conclusion that the effects of irradiation were caused by a combination of changes both in the core and the coating. Both tablets and cores showed an increase in the disintegration time following irradiation. Scanning electron micrographs (SEM) of non-irradiated cores/tablets and cores/tablets irradiated for 15 min, showed clear differences in the structure of the surface. SEM of the tablets irradiated for 15 min, showed that the irradiation had caused the film to loosen from the core in several places. SEM of the cross-sections of both irradiated tablets and cores showed a partially melted surface above stacked layers with reduced porosity.
A Phase I/II clinical trial of boron neutron capture therapy (BNCT) for glioblastoma multiforme is underway using the amino acid analog p-boronophenylalanine (BPA) and the epithermal neutron beam at the Brook-haven Medical Research Reactor. Biodistribution studies were carried out in 18 patients at the time of craniotomy using an i.v. infusion of BPA, solubilized as a fructose complex (BPA-F). There were no toxic effects related to the BPA-F administration at doses of 130, 170, 210, or 250 mg BPA/kg body weight. The tumor/ blood, brain/blood and scalp/blood boron concentration ratios were approximately 3.5:1, 1:1 and 1.5:1, respectively. Ten patients have received BNCT following 2-hr infusions of 250 mg BPA/kg body weight. The average boron concentration in the blood during the irradiation was 13.0 +/- 1.5 micrograms 10B/g. The prescribed maximum dose to normal brain (1 cm3 volume) was 10.5 photon-equivalent Gy (Gy-Eq). Estimated maximum and minimum doses (mean +/- sd, n = 10) to the tumor volume were 52.6 +/- 4.9 Gy-Eq (range: 64.4-47.6) and 25.2 +/- 4.2 Gy-Eq (range: 32.3-20.0), respectively). The estimated minimum dose to the target volume (tumor +2 cm margin) was 12.3 +/- 2.7 Gy-Eq (range: 16.2-7.8). There were no adverse effects on normal brain. The scalp showed mild erythema, followed by epilation in the 8 cm diameter field. Four patients developed recurrent tumor, apparently in the lower dose (deeper) regions of the target volume, at post-BNCT intervals of 7,5,3.5 and 3 months, respectively. The remaining patients have had less than 4 months of post-BNCT follow-up. BNCT, at this starting dose level, appears safe. Plans are underway to begin the dose escalation phase of this protocol.
Lineal energy spectra of fast neutrons, produced by bombarding a thick beryllium target with 14 MeV deuterons, were measured with a proportional counter simulating a sensitive diamter of 2 micrometers. The mean neutron energy of the collimated beam was 6 MeV. The total lineal energy spectra, measured at different positions within a water phantom were separated into three different components: the gamma component, the recoil-proton component, and the component of heavier recoil ions. It is shown mathematically that the components of a linear energy spectrum thus derived allow the calculation of their fractional dose contributions. These dose fractions i.e. the gamma dose, the recoil-proton dose, and the dose fraction of heavier recoil ions, are shown as a function of the spatial position in the phantom.
Microdosimetric single event spectrum in a human body simulated by an acrylic phantom has been measured for the clinical BNCT field at the Kyoto University Reactor (KUR). The recoil particles resulting from the initial reaction and subsequent interactions, namely protons, electrons, alpha particles and carbon nuclei are identified in the microdosimetric spectrum. The relative contributions to the neutron dose from proton, alpha particles and carbon are estimated to be about 0.9, 0.07 and 0.3, respectively, four depths between 5 and 41 mm. We estimate that the dose averaged lineal energy, yD decreased with depth from 64 to 46 keV microm(-1). Relative biological effectiveness (RBE) of this neutron field using a response function for the microdosimetric spectrum was estimated to decrease from 3.6 to 2.9 with increasing depth.
This paper is concerned with the proposed Birmingham accelerator-based epithermal neutron beam for boron neutron capture therapy (BNCT). Details of the final moderator design, such as beam delimiter, shield, and beam exit surface shape are considered. Monte Carlo radiation transport simulations with a head and body phantom have shown that a simple flat moderator beam exit surface is preferable to the previously envisioned spherical design. Dose rates to individual body organs during treatment have been calculated using a standard MIRD phantom. We have shown that a simple polyethylene shield, doped with natural lithium, is sufficient to provide adequate protection to the rest of the body during head irradiations. The effect upon the head phantom dose distributions of the use of such a shield to delimit the therapy beam has been evaluated.
We reviewed retrospectively a series of 58 patients with deeply invasive bladder cancer treated with fast neutron therapy (p(65) + Be) in order to evaluate its tolerance and side effects. Patients were divided into three groups according to treatment technique. Patients of group A received whole pelvis irradiation up to 50 Gy photon equivalent followed by a boost to the bladder up to 57-66 Gy photon equivalent (40-56 days). Group B patients were treated by a split course regimen of 30 Gy photon equivalent on the whole pelvis at 3-4 weeks interval (66-108 days). Group C patients, not suitable for radical treatment, received only 40-54 Gy photon equivalent (26-70 days). The overall 5-year actuarial survival rate was 30% (SE 8%). As expected, T stage was a statistically significant prognostic factor. The overall local control rate reached 21% at 4 years. Acute and late side effects were minimal to moderate. These results suggest that high-energy neutron beam treatment is at least as effective as photon beam treatment for bladder carcinoma, without a higher incidence of major side effects.
Between 1977 and 1987, 30 patients with adenoid-cystic carcinomas of the head and neck region were treated, at the Hamburg-Eppendorf neutron therapy facility, with a 14 MeV-DT-generator. The present review deals with 15 patients treated before October 1986 e.g. with follow up longer than one year. These results, although preliminary, tend to confirm that fast neutrons is the best irradiation modality of adenoid-cystic carcinomas of the head and neck region, especially when surgery is not possible, or cannot be radical.
The neutron irradiation facility developed at the McMaster University 3 MV Van de Graaff accelerator was employed to assess in vivo elemental content of aluminum and manganese in human hands. These measurements were carried out to monitor the long-term exposure of these potentially toxic trace elements through hand bone levels. The dose equivalent delivered to a patient during irradiation procedure is the limiting factor for IVNAA measurements. This article describes a method to estimate the average radiation dose equivalent delivered to the patient's hand during irradiation. The computational method described in this work augments the dose measurements carried out earlier [Arnold et al., 2002. Med. Phys. 29(11), 2718-2724]. This method employs the Monte Carlo simulation of hand irradiation facility using MCNP4B. Based on the estimated dose equivalents received by the patient hand, the proposed irradiation procedure for the IVNAA measurement of manganese in human hands [Arnold et al., 2002. Med. Phys. 29(11), 2718-2724] with normal (1 ppm) and elevated manganese content can be carried out with a reasonably low dose of 31 mSv to the hand. Sixty-three percent of the total dose equivalent is delivered by non-useful fast group (> 10 keV); the filtration of this neutron group from the beam will further decrease the dose equivalent to the patient's hand.
PURPOSE: To clarify the correlation between the radiation dose and clinical outcome of sodium borocaptate-based intraoperative boron neutron capture therapy in patients with malignant glioma. METHODS AND MATERIALS: The first protocol (P1998, n = 8) prescribed a maximal gross tumor volume (GTV) dose of 15 Gy. In 2001, a dose-escalated protocol was introduced (P2001, n = 11), which prescribed a maximal vascular volume dose of 15 Gy or, alternatively, a clinical target volume (CTV) dose of 18 Gy. RESULTS: The GTV and CTV doses in P2001 were 1.1-1.3 times greater than those in P1998. The maximal vascular volume dose of those with acute radiation injury was 15.8 Gy. The mean GTV and CTV dose in long-term survivors with glioblastoma was 26.4 and 16.5 Gy, respectively. A statistically significant correlation between the GTV dose and median survival time was found. In the 11 glioblastoma patients in P2001, the median survival time was 19.5 months and 1- and 2-year survival rate was 60.6% and 37.9%, respectively. CONCLUSION: Dose escalation contributed to the improvement in clinical outcome. To avoid radiation injury, the maximal vascular volume dose should be <12 Gy. For long-term survival in patients with glioblastoma after boron neutron capture therapy, the optimal mean dose of the GTV and CTV was 26 and 16 Gy, respectively.