Monte Carlo-based analysis of the photon beam fluence with air gap thickness between Linac head exit window and patient’s skin in radiotherapy treatments

Linear accelerators (Linac) are used in radiation therapy treatment and its technology improvement ensures high dosimetry quality that should be conserved for high radiotherapy efficiency. However, does the air gap between the exit window of Linac head and patient’s skin alters the physical properties of the photon beam? The objective of this study is to assess the physical properties changes of photon beam fluence according to air gap thickness under the Linac head. The air gap under the Linac head is the last material in the photon beam path; it induces alterations in the beam quality before reaching the patient’s skin. The Varian Clinac 2100 head and the air gap up to the phantom surface are modelled using Monte Carlo BEAMnrc code; the nominal beam energy is 6 MV. The BEAMDP code is used to extract the photon fluence. The photon beam fluence is affected by the air gap under Linac head and decreases by six times due to the photon beam attenuation with air gap thickness; in addition to increasing of beam contamination by scattered photons and electrons. Thus, the air gap induces the beam quality deterioration which is evaluated in terms of photon fluence with air gap thickness. To remove the particles contaminations and conserve integrally the photon beam quality, the number of the photon interactions with air atoms should be as low as possible under Linac head up to patient’s skin and ensure a higher quality of the radiotherapy treatment of deep tumour.

Feasibility Study of a Proton Irradiation Facility for Radiobiological Measurements at an 18 MeV Cyclotron

A feasibility study of an experimental setup for the irradiation of biological samples at the cyclotron facility installed at the National Centre of Accelerators (Seville, Spain) is presented. This cyclotron, which counts on an external beam line for interdisciplinary research purposes, produces an 18 MeV proton beam, which is suitable for the irradiation of mono-layer cultures for the measurement of proton cell damages and Relative Biological Effectiveness (RBE) at energies below the beam nominal value. Measurements of this kind are of interest for proton therapy, since the variation of proton RBE at the distal edge of the Bragg curve may have implications in clinical proton therapy treatments. In the following, the characteristics of the beam line and the solutions implemented for the irradiation of biological samples are described. When dealing with the irradiation of cell cultures, low beam intensities and broad homogeneous irradiation fields are required, in order to assure that all the cells receive the same dose with a suitable dose rate. At the cyclotron, these constraints have been achieved by completely defocusing the beam, intercepting the beam path with tungsten scattering foils and varying the exit-window-to-sample distance. The properties of the proton beam thus obtained have been analysed and compared with Monte Carlo simulations. The results of this comparison, as well as the experimental measurement of the lateral dose profiles expected at the position of samples are presented. Meaningful dose rates of about 2–3 Gy/min have been obtained. Homogeneous lateral dose profiles, with maximum deviations of 5%, have been measured at a distance of approximately 50 cm in air from the exit window, placing a tungsten scattering foil of 200 μm in the beam path.

The residual effect of lambda-cyhalothrin, deltamethrin and dichlorodiphenyltrichloroethane in Zhombe, Kwekwe district, Zimbabwe

Indoor residual house spraying using lambda-cyhalothrin, deltamethrin and dichlorodiphenyltrichloroethane (DDT) was conducted in Zhombe Resettlement area, Zimbabwe. A total of 204/219 (93.1%), 224/260 (86.2%) and 257/325 (79.1%) rooms were sprayed with lambda-cyhalothrin, deltamethrin and DDT wettable powders respectively. Bioassays were conducted on sprayed walls and roofs using 3-5 day old laboratory reared susceptible <em>Anopheles gambiae sensu lato </em>mosquitoes placed in World Health Organization cones. <br />Bioassays conducted on sprayed walls (1 month), showed that efficacy of lambda-cyhalothrin was the same with DDT but different with deltamethrin and this trend continued in the 2^nd month. During the 3rd month, lambda-cyhalothrin killed more mosquitoes than deltamethrin (P=1.931x10^-14), DDT killed more mosquitoes than deltamethrin (P=0.0001) and lambda-cyhalothrin killed more mosquitoes than DDT (walls). Efficacy of lambda-cyhalothrin and DDT was the same 4 months post spray (P=0.487), notable differences were seen in lambdacyhalothrin and deltamethrin (P=2.57x10^-6), DDT and deltamethrin (P=2.17-10^-8). Efficacy of lambda-cyhalothrin and DDT was the same 5 months post spray (P=0.244), major differences were found in lambdacyhalothrin and deltamethrin (P=0.000), DDT and deltamethrin (P=5.18x10^-5) and this trend continued in the 6^th month. One month after spraying roofs, mortality of mosquitoes due to lambdacyhalothrin/ deltamethrin (P=2.56x10^-5), lambda-cyhalothrin/DDT (P=1.2x10^-7) and deltamethrin/DDT (P=0.013) were significantly different and this continued in the 2^nd month. However, 3 months after spraying, mortality due to lambda-cyhalothrin/deltamethrin (P=1.46x10^-6), lambda-cyhalothrin/DDT (P=0.048), and deltamethrin/DDT (P=0.004) were significantly different and this continued in the 4^th month. Five months after spraying roofs, mortality due to lambda-cyhalothrin/ deltamethrin (P=0.000) and deltamethrin/DDT (P=6.6x10^-7) were significantly different. Six months after spraying, lambdacyhalothrin/ deltamethrin (P=0.34), lambda-cyhalothrin/DDT (P=0.982), and deltamethrin/DDT (P=0.64) were not significantly different. When using exit window traps, no mosquitoes were collected from rooms sprayed with each of the insecticides over a 6-month period. However, 17, 6, 14, 7, 2 and 3 fed <em>An. gambiae sl </em>mosquitoes were collected in the 1^st, 2^nd, 3^rd, 4^th, 5^th and 6^th month respectively from unsprayed rooms and none of them died after 24 h.

Some Aspects of Profiling Electron Fields for Irradiation by Scattering on Foils

) for 1 mA of total beam current as functions of the distance from the beam exit window and of the thickness of the Al scattering foils.