Dose calculation in biological samples in a mixed neutron-gamma field at the TRIGA reactor of the University of Mainz (original) (raw)
Related papers
Acta Oncologica, 2011
Boron Neutron Capture Therapy for liver malignancies is being investigated at the University of Mainz. One important aim is the set-up of a reliable dosimetry system. Alanine dosimeters have previously been applied for dosimetry of mixed radiation fi elds in antiproton therapy, and may be suitable for measurements in mixed neutron and gamma fi elds. Material and methods. Two experiments have been carried out in the thermal column of the TRIGA Mark II reactor at the University of Mainz. Alanine dosimeters have been irradiated in a phantom and in liver tissue. Results . For the interpretation and prediction of the dose for each pellet, beside the results of the measurements, calculations with the Monte Carlo code FLUKA are presented here. For the phantom, as well as for the liver tissue, the measured and calculated dose and fl ux values are in good agreement. Discussion . Alanine dosimeters, in combination with fl ux measurements and Monte Carlo calculations with FLUKA, suggest that it is possible to establish a system for monitoring the dose in a mixed neutron and gamma fi eld for BNCT and other applications in radiotherapy.
Neutron Dosimetry for In Vitro Biomedical Sample Irradiations
HNPS Advances in Nuclear Physics
The absorbed dose in vials containing photo-sensitizer solutions irradiated under neutron beams produced by the p-Li, D-D and D-T reactions was calculated. Monte Carlo simulations were performed by coupling the NeuSDesc and MCNP codes in order to derive the neutron energy spectrum, fluence and absorbed dose with depth in the samples. The absorbed dose was estimated taking into account the contributions of all particles (photons, electrons, protons and alpha particles). This study provides important information for the interpretation of in vitro irradiation experiments to be performed under the research program FRINGE aiming to investigate neutron generated electronic excitation as a foundation for a radically new cancer therapy.
The current Boron Neutron Capture Therapy (BNCT) experiments performed at the University of Pavia, Italy, are focusing on the in vivo irradiations of small animals (rats and mice) in order to evaluate the effectiveness of BNCT in the treatment of diffused lung tumors. After the irradiation, the animals are manipulated, which requires an evaluation of the residual radioactivity induced by neutron activation and the relative radiological risk assessment to guarantee the radiation protection of the workers. The induced activity in the irradiated animals was measured by high-resolution open geometry gamma spectroscopy and compared with values obtained by Monte Carlo simulation. After an irradiation time of 15 min in a position where the in-air thermal flux is about 1.2 1010 cm−2 s −1, the specific activity induced in the body of the animal is mainly due to 24Na, 38Cl, 42K, 56Mn, 27Mg and 49Ca; it is approximately 540 Bq g−1 in the rat and around 2,050 Bq g−1 in the mouse. During the irradiation, the animal body (except the lung region) is housed in a 95% enriched 6Li shield; the primary radioisotopes produced inside the shield by the neutron irradiation are 3H by the 6Li capture reaction and 18F by the reaction sequence 6Li(n,α)3H → 16O(t,n)18F. The specific activities of these products are 3.3 kBq g−1 and 880 Bq g−1, respectively.
Health Physics, 2014
The current Boron Neutron Capture Therapy (BNCT) experiments performed at the University of Pavia, Italy, are focusing on the in vivo irradiations of small animals (rats and mice) in order to evaluate the effectiveness of BNCT in the treatment of diffused lung tumors. After the irradiation, the animals are manipulated, which requires an evaluation of the residual radioactivity induced by neutron activation and the relative radiological risk assessment to guarantee the radiation protection of the workers. The induced activity in the irradiated animals was measured by high-resolution open geometry gamma spectroscopy and compared with values obtained by Monte Carlo simulation. After an irradiation time of 15 min in a position where the in-air thermal flux is about 1.2 × 10(10) cm(-2) s(-1), the specific activity induced in the body of the animal is mainly due to 24Na, 38Cl, 42K, 56Mn, 27Mg and 49Ca; it is approximately 540 Bq g(-1) in the rat and around 2,050 Bq g(-1) in the mouse. During the irradiation, the animal body (except the lung region) is housed in a 95% enriched 6Li shield; the primary radioisotopes produced inside the shield by the neutron irradiation are 3H by the 6Li capture reaction and 18F by the reaction sequence 6Li(n,α)3H → 16O(t,n)18F. The specific activities of these products are 3.3 kBq g(-1) and 880 Bq g(-1), respectively.
IFMBE proceedings, 2009
A project has been set up to study the effect on a radiotherapy patient of the neutrons produced around the LINAC accelerator head by photonuclear reactions induced by photons above w8 MeV. These neutrons may reach directly the patient, or they may interact with the surrounding materials until they become thermalised, scattering all over the treatment room and affecting the patient as well, contributing to peripheral dose. Spectrometry was performed with a calibrated and validated set of Bonner spheres at a point located at 50 cm from the isocenter, as well as at the place where a digital device for measuring neutrons, based on the upset of SRAM memories induced by thermal neutrons, is located inside the treatment room. Exposures have taken place in six LINAC accelerators with different energies (from 15 to 23 MV) with the aim of relating the spectrometer measurements with the readings of the digital device under various exposure and room geometry conditions. The final purpose of the project is to be able to relate, under any given treatment condition and room geometry, the readings of this digital device to patient neutron effective dose and peripheral dose in organs of interest. This would allow inferring the probability of developing second malignancies as a consequence of the treatment. Results indicate that unit neutron fluence spectra at 50 cm from the isocenter do not depend on accelerator characteristics, while spectra at the place of the digital device are strongly influenced by the treatment room geometry.
Neutron Generator (HIRRAC) and Dosimetry Study
Journal of Radiation Research, 1999
Dosimetry studies have been made for neutrons from a neutron generator at Hiroshima University (HIRRAC) which is designed for radiobiological research. Neutrons in an energy range from 0.07 to 2.7 MeV are available for biological irradiations. The produced neutron energies were measured and evaluated by a 3 He-gas proportional counter. Energy spread was made certain to be small enough for radiobiological studies. Dose evaluations were performed by two different methods, namely use of tissue equivalent paired ionization chambers and activation of method with indium foils. Moreover, energy deposition spectra in small targets of tissue equivalent materials, so-called lineal energy spectrum, were also measured and are discussed. Specifications for biological irradiation are presented in terms of monoenergetic beam conditions, dose rates and deposited energy spectra.
Neutron spectra and dose equivalents calculated in tissue for high-energy radiation therapy
Medical Physics, 2009
Neutrons are by-products of high-energy radiation therapy and a source of dose to normal tissues. Thus, the presence of neutrons increases a patient's risk of radiation-induced secondary cancer. Although neutrons have been thoroughly studied in air, little research has been focused on neutrons at depths in the patient where radiosensitive structures may exist, resulting in wide variations in neutron dose equivalents between studies. In this study, we characterized properties of neutrons produced during high-energy radiation therapy as a function of their depth in tissue and for different field sizes and different source-to-surface distances ͑SSD͒. We used a previously developed Monte Carlo model of an accelerator operated at 18 MV to calculate the neutron fluences, energy spectra, quality factors, and dose equivalents in air and in tissue at depths ranging from 0.1 to 25 cm. In conjunction with the sharply decreasing dose equivalent with increased depth in tissue, the authors found that the neutron energy spectrum changed drastically as a function of depth in tissue. The neutron fluence decreased gradually as the depth increased, while the average neutron energy decreased sharply with increasing depth until a depth of approximately 7.5 cm in tissue, after which it remained nearly constant. There was minimal variation in the quality factor as a function of depth. At a given depth in tissue, the neutron dose equivalent increased slightly with increasing field size and decreasing SSD; however, the percentage depth-dose equivalent curve remained constant outside the primary photon field. Because the neutron dose equivalent, fluence, and energy spectrum changed substantially with depth in tissue, we concluded that when the neutron dose equivalent is being determined at a depth within a patient, the spectrum and quality factor used should be appropriate for depth rather than for in-air conditions. Alternately, an appropriate percent depthdose equivalent curve should be used to correct the dose equivalent at the patient surface.
Radiation Measurements, 2010
A project has been set up to study the effect on a radiotherapy patient of the neutrons produced around the LINAC accelerator head by photonuclear reactions induced by photons above w8 MeV. These neutrons may reach directly the patient, or they may interact with the surrounding materials until they become thermalised, scattering all over the treatment room and affecting the patient as well, contributing to peripheral dose. Spectrometry was performed with a calibrated and validated set of Bonner spheres at a point located at 50 cm from the isocenter, as well as at the place where a digital device for measuring neutrons, based on the upset of SRAM memories induced by thermal neutrons, is located inside the treatment room. Exposures have taken place in six LINAC accelerators with different energies (from 15 to 23 MV) with the aim of relating the spectrometer measurements with the readings of the digital device under various exposure and room geometry conditions. The final purpose of the project is to be able to relate, under any given treatment condition and room geometry, the readings of this digital device to patient neutron effective dose and peripheral dose in organs of interest. This would allow inferring the probability of developing second malignancies as a consequence of the treatment. Results indicate that unit neutron fluence spectra at 50 cm from the isocenter do not depend on accelerator characteristics, while spectra at the place of the digital device are strongly influenced by the treatment room geometry.
Radiotherapy and Oncology, 1991
Incorporation of ~°B in human tumours treated with fast neutrons would increase the local dose in the tumour. In tissue the neutrons are thermalized mainly causing the neutron capture reaction ~°B (n,a) 7Li. The dose enhancement can be calculated using the thermal neutron fluence measured by activation of gold foils in a phantom. At a phantom depth of 5 cm a dose enhancement of (0.056 + 0.0028)% for each #g of ~°B per gram of tissue was determined in the tumour. A therapeutic gain by this dose enhancement in fast neutron therapy should be examined for a solid tumour in a mouse. The feasibility for neutron capture therapy of tumours in mice depends on the distribution of the tumour dose and on the effective shielding of the bodies of the mice. Therefore, a special holding device for simultaneous irradiation of four turnouts was developed. The dose distribution in the tumours and in the surrounding bodies of mice was measured with TLD-300 in a special mouse phantom.