Adam Konefał

Correlation between radioactivity induced inside the treatment room and the undesirable thermal/ resonance neutron radiation produced by linac

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.

Nuclear reactions in linear medical accelerators and their exposure consequences.

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.

Spectroscopic study of prompt-gamma emission for range verification in proton therapy

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 130.87MeV 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: 12C4.44→g.s. and 16O6.13→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.

Significant change in the construction of a door to a room with slowed down neutron field by means of commonly used inexpensive protective materials

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.

Verification of the use of GEANT4 and MCNPX Monte Carlo Codes for Calculations of the Depth-Dose Distributions in Water for the Proton Therapy of Eye Tumours

Abstract 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.

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.

Gamma emission in hadron therapy — Towards new tools of quality assurance

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.

Gamma Emission in Hadron Therapy --- Experimental Approach

Experiment Gamma-CCB at the Cyclotron Centre Bronowice focuses on investigation of gamma emission in experimental modelling of hadron therapy, searching for manifestation of the Bragg peak in gamma spectra. Experimental program comprises a series of measurements for different energies of the beam accelerated in the cyclotron Proteus C-235, as well as for several phantom materials. The paper reports on the results of the first measurements performed at 70 MeV proton beam energy and for two target materials: graphite and polymethyl methacrylate PMMA. Two different experimental techniques were tested, resulting in differential gamma spectra or spectra integrated over whole proton penetration path in a phantom. Strong correlation of the intensity of the carbon and oxygen excitation lines with the Bragg peak position has been observed in both types of measurements, confirming potential of the method in the future application in hadron therapy.