Dependence between the size of the treatment room and the fluence of neutrons undesirable in radiotherapy for the high-energy therapeutic X-Rays generated by the linear medical accelerator

The medical linear accelerator is a very commonly used therapeutic equipment in modern radiotherapy. The high-energy X-ray beams generated by such accelerators induce neutrons undesirable in the radiotherapy treatment. The neutron radiation is produced mainly in (,n) and (,2n) reactions. The problem of induced neutron radiation during emission of high-energy X-ray beams is known but it is still unsolved. The undesirable neutrons induce radioactivity inside the treatment room as well as they are the factor of the additional total body dose to patients. The induced radioactivity gives its contribution to the dose to staff operating an accelerator. The influence of sizes of the treatment room on the neutron fluence in the vicinity of the accelerator was investigated in the presented studies. Two methods were applied. The main one was the Monte Carlo computer simulations based on the Geant4 code. These Monte Carlo calculations were verified by means of the neutron activation method with the use of the indium foil and cadmium in the range of thermal and resonance energies. The performed studies are indicative that there is a sensitive dependence between the treatment room size and the neutron level. The greater neutron fluence was observed for a less treatment room

Determination of energy spectra in water for 6 MV X rays from a medical linac

There is a lack of extensive data comprising energy spectra in water for beams generated by medical accelerators applied in radiotherapy. The purpose of this work was the determination of energy spectra in water for the 6 MV X-ray therapeutic beam from the medical linac — Clinac 2300 by Varian. The spectra were derived with the use of Monte Carlo computer simulations basing on MCNPX code in version of 2.7.0. The performed investigations indicate that shapes of the spectra as well as the mean Energy of the considered beams depend on a depth in water, a distance from the central-axis of the beam and a radiation field size. The obtained results are valuable for constructors of medical linacs and, additionally, they can be applied in advanced treatment planning systems. Therefore, all obtained spectra in a numerical form are available for common use. They will be sent to users after forwarding e-mail message to the authors of this paper

Calculation of perturbation factors for the PTW 23343 Markus ionization chamber in proton beams

In this work, perturbation factors for the PTW 23343 Markus ionization chamber in proton beams were determined using Monte Carlo simulations based on the MCNPX code in version of 2.7.0. The calculations were performed for chosen proton energies from 15 MeV to 80 MeV and for various energy spread. The main conclusion is that the perturbation factors for the considered ionization chamber cannot be neglected in the region with the disturbed proton equilibrium in the above-mentioned energy range

Udział fizyki jądrowej w rozwiązywaniu problemów współczesnej radioterapii

The progress that has been made in radiotherapy lately besides unquestionable advantages, originated many new problems which can be known and even partially or completely solved by means of experimental and computational methods used in nuclear physics. The purpose of this book is a presentation of the contribution of nuclear physics in solving the problems of the contemporary radiotherapy. Reduction of the irradiated field in teleradiotherapy saves healthy tissues located close to tumours. However, it needs a precise localization and immobilization of a patient and a control of its position during an irradiation séance. Therefore the experimental methods of nuclear physics were inculcated to the clinical practice. These methods are based on the use of the various type detectors of ionizing radiation, making it possible to control correctness and repeatability of a course of a irradiation process of a patient. One of the base methods to control a dose delivered to patients is in vivo dosimetry described in the first chapter of this book. The contemporary planning systems take very accurate 3-D images of a patient’s anatomy and a localization of a tumour into account. However, they need many parameters and characteristics. The knowledge of the therapeutic beam spectra is particularly significant. The accurate determination of such spectrum is not easy because of high radiation intensity in the therapeutic beam and a broad energy range of radiation. There are experimental methods to derive the spectra of therapeutic beams. However, the computer calculations based on the Monte Carlo method are a current standard. The methods of a obtention of the therapeutic beam energy spectra are described in the second chapter of this book. Undesirable consequence of an increase of radiation energy in radiotherapy is a neutron contamination of the therapeutic X-ray and electron beams. This contamination causes an additional total body neutron dose to patients. Moreover, nuclear reactions induced by the neutrons are the main factor of radioactivity inside a radiotherapy facility. The methods of a determination of neutron fluence and an identification of induced radioisotope and occurred nuclear reactions are discussed in the third and fourth chapter. The photon needle is a relatively new technology applied in a clinical practice since 1992. First versions of this device were characterized by a significant decrease of their efficiency appearing even during a radiotherapy treatment. This defect was eliminated. However, it is still a big problem to get an uniform dose distribution in an irradiated area. In connection with this fact it is important to perform measurement verifying the uniformity of a dose distribution for each photon needle used in a clinical practice. Results of the measurements testing the Intrabeam system — the photon needle by Photoelectron Corporation & Carl Zeiss Surgical were presented in the fifths chapter. The proton radiotherapy of eye tumours is widely used among the hadrontherapy methods because of a high level of curability. Such therapy requires a high precision of a tumour irradiation and also an accurate determination of influence of the beam parameters as mean energy, an energy and spatial spread of the proton beam on the dose distribution. The determination of dependence between the proton beam parameters can be carried out with the use of computer simulations based on the Monte Carlo method ensuring a good quality of the obtained results. Investigations of the dependence between the parameters of a proton beam and the dose distribution, performed by computer simulations basing on the GEANT4 code are presented in the sixth chapter of the book

Influence of the energy spectrum and spatial spread of proton beams used in eye tumor treatment on the depth-dose characteristics

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

Proton kinetics through the cuticle layer in maize

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

Determination of slow-neutron fluence rate using gamma-ray spectroscopy

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

Measurements of thermal and resonance neutron fluence and induced radioactivity inside bunkers of medical linear accelerators in the center of oncology in Opole, Poland

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 cm2 MU1) as well as the resonance one (0:7 104 cm2 MU1) 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

117mSn - the promising radioisotope for use in nuclear medicine

This review paper is dedicated to ways of production and medical applications of the tin isomer 117mSn in the context of its wider use in nuclear medicine, particularly, in diagnostics. Until now, 117mSn has been used as an effective agent for the palliation of pain from bone metastases. However, the energy of gamma-rays emitted by 117mSn is optimal for scintigraphy and, moreover, this tin isomer can also be connected to many different ligands. Tin-117m can be effectively produced in many nuclear reactions without the use of research reactors, which is a very big advantage particularly in the light of the perceptible crisis in the production of technetium-99m