Search

This review paper summarizes the possibilities of the use of therapeutic linear electron accelerators for the production of radioisotopes for nuclear medicine. This work is based on our published results and the thematically similar papers by other authors, directly related to five medical radioisotopes as 99Mo/99mTc, 198Au, 186Re, 188Re, 117mSn, produced using therapeutic linacs. Our unpublished data relating to the issues discussed have also been used here. In the experiments, two types of radiation were included in the analysis of the radioisotope production process, i.e. the therapeutic twenty-megavolt (20 MV) X-rays generated by Varian linacs and neutron radiation contaminating the therapeutic beam. Thus, the debated radioisotopes are produced in the photonuclear reactions and in the neutron ones. Linear therapeutic accelerators do not allow the production of radioisotopes with high specific activities, but the massive targets can be used instead. Thus, the amount of the produced radioisotopes may be increased. Apart from linear accelerators, more and more often, the production of radioisotopes is carried out in small medical cyclotrons. More such cyclotrons are developed, built, and sold commercially than for scientific research. The radioisotopes produced with the use of therapeutic linacs or cyclotrons can be successfully applied in various laboratory tests and in research.

Purpose The field of online monitoring of the beam range is one of the most researched topics in proton therapy over the last decade. The development of detectors that can be used for beam range verification under clinical conditions is a challenging task. One promising possible solution are modalities that record prompt-gamma radiation produced by the interactions of the proton beam with the target tissue. A good understanding of the energy spectra of the prompt gammas and the yields in certain energy regions is crucial for a successful design of a prompt-gamma detector. Monte-Carlo simulations are an important tool in development and testing of detector concepts, thus the proper modelling of the prompt-gamma emission in those simulations are of vital importance. In this paper, we confront a number of GEANT4 simulations of prompt-gamma emission, performed with different versions of the package and different physics lists, with experimental data obtained from a phantom irradiation with proton beams of four different energies in the range 70–230 MeV. Methods The comparison is made on different levels: features of the prompt-gamma energy spectrum, gamma emission depth profiles for discrete transitions and the width of the distal fall-off in those profiles. Results The best agreement between the measurements and the simulations is found for the GEANT4 version 10.4.2 and the reference physics list QGSP_BIC_HP. Conclusions Modifications to prompt-gamma emission modelling in higher versions of the software increase the discrepancy between the simulation results and the experimental data.

In this work, the method of determination of the slow-neutron fluence rate using a gamma-ray spec-troscopy with a high-purity germanium detector (HPGe) and Monte Carlo calculations was presented. The prompt gamma rays with energies of 595.9, 867.9, and 1204.2 keV, originating from the nuclear reaction 73Ge(n, γ)74Ge in the germanium crystal of the HPGe detector, were registered. A special system composed of two neutron sources (Cf-252, PuBe), a lead shield and a HPGe detector was made to find correlations between net areas of the peaks from these prompt gamma rays in the measured spectra and the fluence rate of slow neutrons getting to the germanium crystal. The net areas of the peaks were related to the slow-neutron fluence rate using the Monte Carlo calculations based on the GEANT4 code. The presented method using the gamma-ray spectroscopy can be applied in laborato-ries which do not have detectors for neutron measurements.

Aim This work is focused on the Monte Carlo microdosimetric calculations taking into account the influence of the AuNPs’ shape, size and mass concentration on the radiation dose enhancement for the high-energy 6 MV and 18 MV X-ray therapeutic beams from a medical linac. Background Due to a high atomic number and the photoelectric effect, gold nanoparticles can significantly enhance doses of ionizing radiation. However, this enhancement depends upon several parameters, such as, inter alia, nanoparticles’ shape etc. Method The simulated system was composed of the therapeutic beam, a water phantom with the target volume (with and without AuNPs) located at the depth of the maximum dose, i.e. at 1.5 cm for the 6 MV beam and at 3.5 cm for the 18 MV one. In the study the GEANT4 code was used because it makes it possible to get a very short step of simulation which is required in case of simulating the radiation interactions with nanostructures. Results The dependence between the dose increase and the mass concentration of gold was determined and described by a simple mathematical formula for three different shapes of gold nanoparticles — two nanorods of different sizes and a flat 2D structure. The dose increase with the saturation occurring with the increasing mass concentration of gold was observed. Conclusions It was found that relatively large cylindrical gold nanoparticles can limit the increase of the dose absorbed in the target volume much more than the large 2D gold nanostructure.

An important problem, which is currently overlooked in radiological protection, is the omission of the contribution from low-energy photons when estimating the dose received by persons working in conditions of exposure to ionizing radiation. As shown in this study, this contribution cannot be omitted because it determines the dose in the workplace when an isotropic source of gamma rays (uncollimated beams) and thick shields are used. The omission of the contribution from low-energy photons causes that the gamma-ray attenuation factors, often marked in radiological protection with the letter k, as well as the transmission curves for isotropic gamma-ray beams resemble those for collimated beams without the typical features of uncollimated beams. This causes the estimated doses to be significantly underestimated. In this work the gamma-ray attenuation factors k were determined by Monte Carlo simulations for basic shielding materials, for commonly used isotropic gamma-ray sources. These factors are the basic parameters used to calculate the gamma-ray dose that a person who performs professional activities with gamma rays can receive. Accurate calculation of this dose translates into work safety. Justification for this research is the necessity to apply the exact k-factor values in radiological protection in Poland where doses at workplaces are calculated according to the procedure given in Gostkowska's book based on the old Polish norm (1987). The ground of this norm are transmission curves from NCRP Report 49 (1976) based on data obtained in the 1930's, 40's and 50's, unsuitable for isotropic sources. Although the obtained results refer to the Polish standard, the world's norms based on the NCRP Report 49 also need innovation, because the subsequent versions of this report published in 1991, 1994 and 1998 as well as the NCRP Report No. 151 considered as the new face of the NCRP Report No. 49 do not make the required correction. This work meets these requirements by using the Monte Carlo simulation method based on the GEANT4 code.

The success of proton therapy depends strongly on the precision of treatment planning. Dose distribution in biological tissue may be obtained from Monte Carlo simulations using various scientific codes making it possible to perform very accurate calculations. However, there are many factors affecting the accuracy of modeling. One of them is a structure of objects called bins registering a dose. In this work the influence of bin structure on the dose distributions was examined. The MCNPX code calculations of Bragg curve for the 60 MeV proton beam were done in two ways: using simple logical detectors being the volumes determined in water, and using a precise model of ionization chamber used in clinical dosimetry. The results of the simulations were verified experimentally in the water phantom with Marcus ionization chamber. The average local dose difference between the measured relative doses in the water phantom and those calculated by means of the logical detectors was 1.4% at first 25 mm, whereas in the full depth range this difference was 1.6% for the maximum uncertainty in the calculations less than 2.4% and for the maximum measuring error of 1%. In case of the relative doses calculated with the use of the ionization chamber model this average difference was somewhat greater, being 2.3% at depths up to 25 mm and 2.4% in the full range of depths for the maximum uncertainty in the calculations of 3%. In the dose calculations the ionization chamber model does not offer any additional advantages over the logical detectors. The results provided by both models are similar and in good agreement with the measurements, however, the logical detector approach is a more time-effective method.

Contemporary linear accelerators applied in radiotherapy generate X-ray and electron beams with energies up to 20 MeV. Such high-energy therapeutic beams induce undesirable photonuclear (γ,n) and electronuclear (e,e'n) reactions in which neutrons and radioisotopes are produced. The originated neutron can also induce reactions such as simple capture, (n,γ), reactions that produce radioisotopes. In this work measurements of the non-therapeutic neutrons and the induced gamma radiation were carried out in the vicinity of a new medical accelerator, namely the Varian TrueBeam. The TrueBeam is a new generation Varian medical linac making it possible to generate the X-ray beams with a dose rate higher than in the case of the previous models by Varian. This work was performed for the X-ray beams with nominal potentials of 10 MV (flattening filter free), 15 MV and 20 MV, and for a 22 MeV electron beam. The neutron measurements were performed by means of a helium chamber and the induced activity method. The identification of radioisotopes produced during emission of the therapeutic beams was based on measurements of the energy spectra of gammas emitted in decays of the produced nuclei. The gamma energy spectra were measured with the use of the high-purity germanium detector. The correlation between the neutron field and the mode and nominal potential was observed. The strongest neutron fluence of 3.1 × 10 6 cm −2 Gy −1 and 2.0 × 10 6 cm −2 Gy −1 for the thermal and resonance energies, respectively, was measured during emission of the 20 MV X-ray beam. The thermal and resonance neutron fluence measured for the 15 MV X-rays was somewhat less, at 1.1 × 10 6 cm −2 Gy −1 for thermal neutrons and 6.7 × 10 5 cm −2 Gy −1 for resonance neutrons. The thermal and resonance neutron fluences were smallest for the 10 MV FFF beam and the 22 MeV electron beam and were around two orders of magnitude smaller than those of the 20 MV X-ray beam. This work has shown that the neutron reactions are dominant because of relatively high cross sections for many elements used in the accelerator construction. The detailed analysis of the measured spectra made it possible to identify 11 radioisotopes induced during TrueBeam delivery. In this work the following radioisotopes were identified: 56 Mn, 122 Sb, 124 Sb, 131 Ba, 82 Br, 57 Ni, 57 Co, 51 Cr, 187 W, 24 Na and 38 Cl.

This study provides the first insight into the problem of the induced radioactivity of the construction materials of the new-generation cardiac implantable electronic devices (CIEDs). Its aim was to identify nuclear reactions and the resulting radioisotopes induced in the CIEDs by high-energy X-ray therapeutic beams generated by medical linear accelerators. The presented results allow to verify the rightness of choice of materials for investigated CIEDs. Such analysis is currently available only for the older types of the CIEDs, but not for those of the new generation. Gamma spectrometry measurements have been performed using a high-purity germanium detector (HPGe). The identification and activities of the generated radioisotopes were obtained from the measured spectra of gamma - rays from decays of the produced unstable radioisotopes. 21 radioisotopes originating from 24 nuclear reactions were identified. For all considered models of CIEDs the highest activities are from the tin isomer 117mSn. The induced activities were relatively small, not exceeding 3.1 Bq per a 1 Gy X-ray dose to a target volume.

Acta physica Polonica / B Particle physics and field theory, nuclear physics, theory of relativity B 49(9), 1637-1652 (2018). doi:10.5506/APhysPolB.49.1637, Published by Inst. of Physics, Jagellonian Univ., Cracow

The subject of our investigation was the intensity of the fluorescence of 1,4,5,8-naphtalisoimides subjected to gamma radiation (the absorbed doses were 242 Gy, 1 kGy and 2.242 kGy). Dynamic changes of fluorescence intensity have been observed; the greatest relative increase of fluorescence intensity (and simultaneously, the least durable increase) occurs as a result of structural isomerisation.

There is a lack of extensive data comprising energy spectra of therapeutic beams used in teleradiotherapy, generated by medical linear accelerators. In particular there is a lack of the data for energy spectra in water. However, the spectra in water differ from those in air significantly because of strong photon scattering processes. The aim of this paper was the presentation of the wide range of detailed data for the 6 MV X-ray therapeutic beams from a medical linear accelerator Clinac-2300 by Varian. The presented data were derived by the use of Monte Carlo computer simulations (GEANT4 code). The performed investigations indicate that shapes of the spectra, total number of photon registered in a bin as well as mean energy of the considered beam depend on a depth in water, on a distance from the central-axis of the beam and on a radiation field size. However, shapes of the spectra as well as the beam mean energy does not depend on a bin size, independently of a depth in water and a radiation field whereas total number of photon registered in a bin is related to a bin size. Majority of the presented results were obtained for a cylindrical 1.41 cm3 bin with the radius of 1.5 cm. The obtained data are very useful for the accurate absorbed depth-dose determination particularly outside the reference conditions, for advanced treatment planning systems, for constructors of medical accelerators etc.

A Monte Carlo simulation was used to determine the dependence between the thickness of the cuticle layer of coleoptiles and the spectra of the H? ions (i.e., protons) passing through this layer, which is treated as a potential barrier. The apparently simplistic model of a walled cylinder filled with H? ions propagating through the cuticle layer was solved in silico. We showed that the thickness of the cuticle layer clearly influences the intensity of the efflux of protons, which changes the pH of the surrounding solution. Then, diffusion and cross-correlation data for maize (Zea mays L.) coleoptile growth and H? ion extrusion were probed in an experiment and compared with the Monte Carlo computation results. Ex vivo experiments for the control (APW), auxin (IAA) and fusicoccin (FC) were conducted. The transition from time-delayed pH—(abrasion time) cross-correlation to proton efflux that was not retarded was obtained, thus confirming the canvas that constitutes the acid growth hypothesis and the rationale that was accepted for the derivation of the ‘equation of state’ for plants.

The test of production of the Au-198 radioisotope by means of Varian medical linear accelerators used in teleradiotherapy was carried out. The targets made of the natural gold (100% of the Au-197 isotope) were irradiated with high-energy therapeutic 20 MV X-ray beam. Au-198 was produced in the simple capture reaction Au-197(n, gamma) Au-198. The obtained specific activities in the saturation state are relatively low, not exceeding the value of 510.4 kBq/g, because only the high-energy part of the spectrum of 20 MV X-ray beam covers the energy range of the neutron production cross section. Low activity of the Au-198 radioisotope produced by medical linear accelerators makes this technique not suitable for a massive production of Au-198 for nuclear medicine, but the produced amount of Au-198 is sufficient for laboratory tests of new drugs for possible clinical applications.

We present experimental investigation of cross sections for processes crucial in view of prompt-gamma imaging. The prompt-gamma rays were produced from an interaction of a proton beam with different phantom materials composed of carbon, oxygen and hydrogen. The used target setup allowed precise selection of the investigated depth in the phantom. We studied details of the dependence of prompt-gamma yields on beam energy, detection angle and elemental composition of irradiated phantom. The analysis was focused on the discrete transitions with the largest cross sections: 4.44 MeV in 12C and 6.13 MeV in 16O. The results are presented in form of profiles of the prompt-gamma yield as a function of depth. They are compared to calculations including different cross-section models. Obtained results are in agreement with the model exploiting cross-section data collected from the literature, but the comparison with the TALYS model shows discrepancies. In the latest experiment, special attention was paid to the shape of the distal fall-off. The width of that fall-off is directly linked to the resolution of prompt-gamma based methods of range verification. Preliminary results on the beam-energy dependence of this quantity are presented.

Verification of calculations of the depth-dose distributions in water, using GEANT4 (version of 4.9.3) and MCNPX (version of 2.7.0) Monte Carlo codes, was performed for the scatterer-phantom system used in the dosimetry measurements in the proton therapy of eye tumours. The simulated primary proton beam had the energy spectra distributed according to the Gauss distribution with the cut at energy greater than that related to the maximum of the spectrum. The energy spectra of the primary protons were chosen to get the possibly best agreement between the measured relative depth-dose distributions along the central-axis of the proton beam in a water phantom and that derived from the Monte Carlo calculations separately for the both tested codes. The local depth-dose differences between results from the calculations and the measurements were mostly less than 5% (the mean value of 2.1% and 3.6% for the MCNPX and GEANT4 calculations). In the case of the MCNPX calculations, the best fit to the experimental data was obtained for the spectrum with maximum at 60.8 MeV (more probable energy), FWHM of the spectrum of 0.4 MeV and the energy cut at 60.85 MeV whereas in the GEANT4 calculations more probable energy was 60.5 MeV, FWHM of 0.5 MeV, the energy cut at 60.7 MeV. Thus, one can say that the results obtained by means of the both considered Monte Carlo codes are similar but they are not the same. Therefore the agreement between the calculations and the measurements has to be verified before each application of the MCNPX and GEANT4 codes for the determination of the depth-dose curves for the therapeutic protons.

The detailed analysis of nuclear reactions occurring in materials of the door is presented for the typical construction of an entrance door to a room with a slowed down neutron field. The changes in the construction of the door were determined to reduce effectively the level of neutron and gamma radiation in the vicinity of the door in a room adjoining the neutron field room. Optimisation of the door construction was performed with the use of Monte Carlo calculations (GEANT4). The construction proposed in this paper bases on the commonly used inexpensive protective materials such as borax (13.4 cm), lead (4 cm) and stainless steel (0.1 and 0.5 cm on the side of the neutron field room and of the adjoining room, respectively). The improved construction of the door, worked out in the presented studies, can be an effective protection against neutrons with energies up to 1 MeV.

We present the results of an investigation of the prompt-gamma emission from an interaction of a proton beam with phantom materials. Measurements were conducted with a novel setup allowing the precise selection of the investigated depth in the phantom, featuring three different materials composed of carbon, oxygen and hydrogen. We studied two beam energies of 70.54 and 130.87 MeV and two detection angles: 90° and 120°. The results are presented in form of profiles of the prompt-gamma yield as a function of depth. In the analysis we focused on the transitions with the largest cross sections: 12 C 4.44 → g.s. and 16 O 6.13 → g.s. . We compare the profiles obtained under various irradiation conditions, with emphasis on the shape of the distal fall-off. The results are also compared to calculations including different cross-section models. They are in agreement with the model exploiting published cross-section data, but the comparison with the Talys model shows discrepancies.

The test of production of the 99Mo/99mTc complex by means of Varian medical linear accelerators used in teleradiotherapy was performed. The targets made of the natural molybdenum were irradiated by high-energy therapeutic 20 MV X-ray beam. 99Mo was produced mainly in the photonuclear reaction of 110Mo(; n)99Mo. The obtained specific activities are relatively small in the saturation state (from 155.4 kBq/g to 163.2 kBq/g) because only the high-energetic part of the spectrum of 20 MV X-ray beam covers the energy range of the 110Mo(; n)99Mo reaction cross section. The new application of the 99Mo/99mTc complex of the low activity was suggested using the molybdenum nanoparticle technology.

An experiment investigating gamma emission in hadron therapy was performed at Cyclotron Centre Bronowice (CCB), Cracow, Poland, using two different phantom materials—carbon and poly(methyl methacrylate) PMMA. The measurements were carried out at 70 MeV proton beam energy and the gamma quanta were registered with the use of HP Ge detector with scintillation anti-Compton shielding. Although the primary aim was to establish a solid experimental data base for future applications in prompt gamma imaging, the data have also been analyzed with regards to the position and shape of the spectral line stemming from deexcitation of the carbon excited state 4.44 MeV. Measurements potentially useful to determine the cross section were performed only at 90° laboratory polar angle. However, benefiting from the very good energy resolution it turned out possible to extract information on angular distribution of the C* (4.44 MeV) deexcitation by analyzing the associated line shape. This paper presents the scheme of model calculations assuming the whole process can be divided into two stages: excitation of carbon nuclei by impinging protons and deexcitation of the C* (4.44 MeV) state.

Qualitative and quantitative analysis of radionuclides originating inside a medical linear accelerator during emission of high-energy therapeutic photon beams (15, 18, and 20 MV) is presented. The semiconductor spectrometry method allowed to obtain the fluence rate of photons with defined energy and hence, to quantify the dose at the chosen points in the vicinity of linac, contribution of particular radionuclides and its evolution in time. Typically used materials: copper, tungsten, lead, tantalum and their admixtures: antimony, manganese or bromine, are activated the most.

High-energy therapeutic beams used in the radiotherapy induce photonuclear and electronuclear reactions which are accompanied by generation of undesirable radioisotopes and neutrons inside the treatment room. These neutrons at thermal and resonance energies induce nuclear reactions through the whole accelerator bunker. In consequence various radioisotopes emitting high-energy photons appear. In this paper the correlation between radioactivity induced inside the treatment room and the undesirable thermal and resonance neutron radiation generated by the therapeutic accelerator X-rays was studied. The thermal and resonance neutron fluence determined in chosen places inside the bunkers was 1.0x10(5)-3.4x10(5)cm(-2)Gy(-1) and 1.0x10(5)-1.6x10(6)cm(-2)Gy(-1) at thermal energies (0.1eV) and 3.9x10(4)-1.3x10(5)cm(-2)Gy(-1) and 1.0x10(5)-1.1x10(6)cm(-2)Gy(-1) at epithermal energies (0.1eV-10keV), for the 15MV and 20MV beams, respectively. The gamma energy spectra measured inside the accelerator bunker depended on the neutron radiation level. The net count rates of the gamma peaks from the decays of the excited state (56)Fe* and (28)Si*, the result of the simple capture of the neutron, for the 20MV beam were almost one order of magnitude greater than those for the 15MV beam. Moreover, it turned out that the activation of the wedge - the main accelerator accessory was caused by neutrons.

In this paper, the problem of undesirable photonuclear, electronuclear and neutron capture reactions taking place in the treatment room during emission of the typical high-energy therapeutic beams from two different medical accelerators, i.e. Primus Siemens and Varian Clinac-2300, is presented. The radioisotopes (187)W, (56)Mn, (28)Al, (57)Ni, (38)Cl, (57)Co and (19)Au and the neutron activation of (1)H were identified as a consequence of these reactions. Moreover, the increased photon fluence rate behind the door of the accelerator bunker in the operator console room was observed during emission of the 20 MV X-rays from the Varian Clinac-2300 as well as in the case of the 15 MV X-ray beam from the Primus Siemens. No increased radiation was observed during the 6 MV X-ray beam emission. The performed measurements produced evidences on the presence of neutrons in the operator console room during emission of the 15 MV X-ray beam from the Primus Siemens as well as the 20 MV X-rays and the 22 MeV electrons from the Varian Clinac-2300 accelerator.

Acta physica Polonica / B 46(3), 753- (2015). doi:10.5506/APhysPolB.46.753, Published by Inst. of Physics, Jagellonian Univ., Cracow

The Gamma-CCB experiment is focused on investigation of gamma emission in experiments modeling the course of hadron therapy. The main goal is to search for manifestation of the Bragg peak in the prompt gamma spectra. Experimental program comprises a series of measurements at different proton beam energies and for various phantom materials. In the two beam times performed by the group so far in CCB Cracow and HIT Heidelberg, data were taken with proton beam energy of 70 and 130 MeV and with three phantom materials: graphite, poly(methyl methacrylate) PMMA and polyoxymethylene POM, in order to study effects from different elements forming human tissue. Two different measurement modes were tested. In the first mode the gamma spectrum integrated over the whole beam penetration path in the phantom was registered, in the other mode only the gamma quanta originating in a phantom slice at a certain depth. In both measurement modes we observe strong correlation of the intensity of the carbon and oxygen excitation lines (4.44 and 6.13 MeV, respectively) with the Bragg peak position. Moreover, the correlation was found to be far more pronounced at backward angles than at the 90° polar angle studied so far.

Acta physica Polonica / B 48(3), 675-678 (2017). doi:10.5506/APhysPolB.48.675, Published by Inst. of Physics, Jagellonian Univ., Cracow

The goal of this work was to assess the additional dose from secondary neutrons and γ-rays generated during total body irradiation (TBI) using a medical linac X-ray beam. Nuclear reactions that occur in the accelerator construction during emission of high-energy beams in teleradiotherapy are the source of secondary radiation. Induced activity is dependent on the half-lives of the generated radionuclides, whereas neutron flux accompanies the treatment process only. The TBI procedure using a 18 MV beam (Clinac 2100) was considered. Lateral and anterior–posterior/posterior–anterior fractions were investigated during delivery of 2 Gy of therapeutic dose. Neutron and photon flux densities were measured using neutron activation analysis (NAA) and semiconductor spectrometry. The secondary dose was estimated applying the fluence-to-dose conversion coefficients. The main contribution to the secondary dose is associated with fast neutrons. The main sources of γ-radiation are the following: 56Mn in the stainless steel and 187W of the collimation system as well as positron emitters, activated via (n,γ) and (γ,n) processes, respectively. In addition to 12 Gy of therapeutic dose, the patient could receive 57.43 mSv in the studied conditions, including 4.63 μSv from activated radionuclides. Neutron dose is mainly influenced by the time of beam emission. However, it is moderated by long source–surface distances (SSD) and application of plexiglass plates covering the patient body during treatment. Secondary radiation gives the whole body a dose, which should be taken into consideration especially when one fraction of irradiation does not cover the whole body at once.

Emission of high-energy X-ray and electron therapeutic beams from medical linear accelerators is related to undesirable neutron production and to induction of radioactivity. In this work, measurements of thermal and resonance neutron fluence and induced radioactivity were performed inside two bunkers with medical linacs — Elekta in the Center of Oncology in Opole (Poland). The bunkers differ with a construction of their walls. The neutron measurements were performed by means of the induced activity method during emission of the 18 MV X-ray beam. The investigation of radioactivity induced by neutrons was based on the method of off-line gammaray spectroscopy measurements. This work has shown that the differences in the considered construction of bunkers do not influence significantly on the thermal and resonance neutron fluence as well as on the induced radioactivity. The greatest thermal neutron fluence (1:4 104 cm􀀀2 MU􀀀1) as well as the resonance one (0:7 104 cm􀀀2 MU􀀀1) was measured at the isocenter of a rotation of the accelerator head. The radioisotopes of 187W, 56Mn, 24Na and 82Br originating from the (n;) reactions were identified in the spectral measurements.

Contemporary linear accelerators called often linacs, used in radiation medicine generate electrons and X-rays with energies up to over 20 MeV. Such energies are enough to induce nuclear reactions in which neutrons and radioisotopes are produced. These neutrons and radioisotopes are undesirable in therapy, because they are source of an additional dose to patients and to staff operating the medical accelerators. The therapeutic electrons and X-rays can induce electronuclear (e,e’n) and photonuclear (,n) reactions, respectively. These reactions take place inside the therapeutic beam in massive components of an accelerator head, mainly and in air. In the case of the X-rays the main neutron sources are the collimators of the beam, flattening filter giving the appropriate profile of the beam and the target in which electrons are converted into X-ray radiation. In the case of the electron beams the majority of neutrons are produced in the collimator system and in the scattered foils. The neutrons originated in both mentioned type of reactions have the broad energy spectrum with the high-energy end of more than ten MeV. Majority of the neutrons reach the concrete walls, ceiling and floor of the radiotherapy facility. Concrete is a good moderator. In this medium the neutrons undergo elastic collisions with nuclei of hydrogen, mainly. The slowed down neutrons may get out of concrete and return to air, contributing to the specific distribution of neutron energy inside the radiotherapy facility. Kinetic energies of the slowed down neutrons are distributed according to the Maxwell-Boltzmann distribution law. The neutrons can easy induce the simple capture (n,) reactions in the thermal and resonance energy range and radioisotopes are produced. The neutron field is almost uniform in whole accelerator room. Thus the radioisotopes originating from the neutron reactions can be produced in the accelerator components and accessories as well as in the wall, ceiling and floor of the radiotherapy facility. Moreover, the neutrons can induce simple capture reactions in the entrance door of the radiotherapy facility. The penetrative gammas are emitted as a result of these neutron reactions. Therefore, the gamma radiation can appear close to the radiotherapy facility door in the operator room during emission the high-energy therapeutic beams. In the paper the radioisotopes originating in the accelerator components and in the accessories as well as in the walls, ceiling, floor and door of the radiotherapy facility and in

Entrance doses measured in 50 patients treated by electron beams were compared with planned values as the percentage difference between the given dose and its planned value. Electron beams of energy 6, 9, 12, 15, 18 and 22 MeV were generated by the Clinac 2300 C/D linear accelerator (Varian). Semiconductor EDE-5 diodes connected to a DPD-510 (Scanditronix) electrometer were applied for entrance dose measurements. In our investigations, the mean values of doses administered agreed well with the values of planned doses. The observed relatively large discrepancies in a few patients (up to 12%) should be carefully investigated.

BackgroundHigh-energy photon and electron therapeutic beams generated in medical linear accelerators can cause the electronuclear and photonuclear reactions in which neutrons with a broad energy spectrum are produced. A low-energy component of this neutron radiation induces simple capture reactions from which various radioisotopes originate and in which the radioactivity of a linac head and various objects in the treatment room appear.AimThe aim of this paper is to present the results of the thermal/resonance neutron fluence measurements during therapeutic beam emission and exemplary spectra of gamma radiation emitted by medical linac components activated in neutron reactions for four X-ray beams and for four electron beams generated by various manufacturers’ accelerators installed in typical concrete bunkers in Polish oncological centers.Materials and methodsThe measurements of neutron fluence were performed with the use of the induced activity method, whereas the spectra of gamma radiation from decays of the resulting radioisotopes were measured by means of a portable high-purity germanium detector set for field spectroscopy.ResultsThe fluence of thermal neutrons as well as resonance neutrons connected with the emission of a 20MV X-ray beam is ∼106neutrons/cm2 per 1Gy of a dose in water at a reference depth. It is about one order of magnitude greater than that for the 15MV X-ray beams and about two orders of magnitude greater than for the 18–22MeV electron beams regardless of the type of an accelerator.ConclusionThe thermal as well as resonance neutron fluence depends strongly on the type and the nominal potential of a therapeutic beam. It is greater for X-ray beams than for electrons. The accelerator accessories and other large objects should not be stored in a treatment room during high-energy therapeutic beam emission to avoid their activation caused by thermal and resonance neutrons. Half-lives of the radioisotopes originating from the simple capture reaction (n,γ) (from minutes to hours) are long enough to accumulate radioactivity of components of the accelerator head. The radiation emitted by induced radioisotopes causes the additional doses to staff operating the accelerators.

Aim The aim of the investigation was to determine the undesirable dose coming from neutrons produced in reactions (p,n) in irradiated tissues represented by water. Background Production of neutrons in the system of beam collimators and in irradiated tissues is the undesirable phenomenon related to the application of protons in radiotherapy. It makes that proton beams are contaminated by neutrons and patients receive the undesirable neutron dose. Materials and methods The investigation was based on the Monte Carlo simulations (GEANT4 code). The calculations were performed for five energies of protons: 50 MeV, 55 MeV, 60 MeV, 65 MeV and 75 MeV. The neutron doses were calculated on the basis of the neutron fluence and neutron energy spectra derived from simulations and by means of the neutron fluence–dose conversion coefficients taken from the ICRP dosimetry protocol no. 74 for the antero-posterior irradiation geometry. Results The obtained neutron doses are much less than the proton ones. They do not exceed 0.1%, 0.4%, 0.5%, 0.6% and 0.7% of the total dose at a given depth for the primary protons with energy of 50 MeV, 55 MeV, 60 MeV, 65 MeV and 70 MeV, respectively. Conclusions The neutron production takes place mainly along the central axis of the beam. The maximum neutron dose appears at about a half of the depth of the maximum proton dose (Bragg peak), i.e. in the volume of a healthy tissue. The doses of neutrons produced in the irradiated medium (water) are about two orders of magnitude less than the proton doses for the considered range of energy of protons.

Mossbauer spectroscopy of green (prasiolite) and violet (amethyst) quartz crystals from the Sudety Mountains (Poland) has shown that neither Fe2+ nor Fe4+ ions are present in them. Only Fe3+ ions have been identified and only in interstitial positions in channels parallel or perpendicular to the c-axis. The valence of Fe3+ ions did not change as a result of irradiation or annealing. Instead, we believe that the Fe3+ ions move within channels or between them.

In this paper, the thermal and epithermal neutron fluence distributions in the vicinity of the Primus Siemens accelerator are presented. The measurements were carried out by the use of the neutron activation method for 15 MV X-rays and electron beams of 18 MeV and 21 MeV. From the radiation safety point of view for the hospital personnel, it is important to know the thermal and epithermal neutron fluence distribution in the vicinity of the accelerator because the neutrons interacting with atoms of a medium by various processes induce the activity of objects (accelerator, other apparatus etc.) and walls in the treatment room. The thermal and epithermal neutron capture, particularly, in high atomic number materials of the accelerator head can be a significant source of gamma radiation and it has to be taken into account for estimation of the work safety of the personnel. Values of the neutron fluence were normalized to the maximum photon (or electron) dose Dmax,γ (e) measured at the central axis of therapeutic X-ray (or electron) beam in a water phantom. The thermal neutron fluences measured during the 15 MV X-ray emission varied between 1.1 × 105 n · cm−2· Gy−1 and 4.4 × 105 n · cm−2· Gy−1 whereas the epithermal neutron fluences ranged from 0.2 × 105 n · cm−2· Gy−1 to 1.8 × 105 n · cm−2· Gy−1. In the case of electron beams, the neutron fluence measurements were performed only at the isocentre. The obtained thermal and epithermal neutron fluences were 1.2 × 104 n · cm−2· Gy−1 and 0.6 × 104 n · cm−2· Gy−1, respectively, for the 18 MeV electrons. In the the case of the 21 MeV electron beams the thermal neutron fluence was 2.0 × 104 n · cm−2· Gy−1 whereas the epithermal neutron fluence was 0.8 × 104 n · cm−2· Gy−1.

The influence of the energy spectrum and the spatial spread of a therapeutic proton beam impinging on an irradiated medium (called the entrance beam) on the depth-dose characteristics in water, in the proton energy range of 50÷70 MeV was studied. It turns out that full width at half maximum (FWHM) of the Bragg peak increases almost linearly with increasing proton energy. It ranges from 1.53 mm for 50 MeV to 2.59 mm for 70 MeV, for monoenergetic protons. Moreover, the significant influence of the energy spread of the entrance proton beam on the intensity and FWHM of the Bragg peak is visible. FWHM of the Bragg peak of 60 MeV protons is equal to 2.03, 3.37 and 5.86 mm for a monoenergetic beam and beams with an energy spread of 0.5 and 1 MeV SD (standard deviation), respectively. The intensity of the Bragg peak of a 60 MeV proton beam with an energy spread of 1 MeV SD is approximately 25% less than that for a monoenergetic beam. Moreover, the Bragg peak shifts to smaller depths as the energy spread of the entrance beam increases. The shift of the peak is about 0.2÷0.3 mm for a beam with an energy spread of 0.5 MeV SD and between 0.4÷0.5 mm for an energy spread of 1 MeV SD, compared with a monoenergetic beam in the energy range from 50 to 60 MeV. However, the spatial spread of the entrance proton beam does not affect significantly the depth-dose characteristic.