Radiation Protection Strategies Research Articles

Shielding of relativistic protons

Protons are the most abundant element in the galactic cosmic radiation, and the energy spectrum peaks around 1 GeV. Shielding of relativistic protons is therefore a key problem in the radiation protection strategy of crewmembers involved in long-term missions in deep space. Hydrogen ions were accelerated up to 1 GeV at the NASA Space Radiation Laboratory, Brookhaven National Laboratory, New York. The proton beam was also shielded with thick (about 20 g/cm2) blocks of lucite (PMMA) or aluminium (Al). We found that the dose rate was increased 40-60% by the shielding and decreased as a function of the distance along the axis. Simulations using the General-Purpose Particle and Heavy-Ion Transport code System (PHITS) show that the dose increase is mostly caused by secondary protons emitted by the target. The modified radiation field after the shield has been characterized for its biological effectiveness by measuring chromosomal aberrations in human peripheral blood lymphocytes exposed just behind the shield block, or to the direct beam, in the dose range 0.5-3 Gy. Notwithstanding the increased dose per incident proton, the fraction of aberrant cells at the same dose in the sample position was not significantly modified by the shield. The PHITS code simulations show that, albeit secondary protons are slower than incident nuclei, the LET spectrum is still contained in the low-LET range (<10 keV/microm), which explains the approximately unitary value measured for the relative biological effectiveness.

Central dose data management and analysis in IT-driven radiation protection strategies

The applications of information technology in health care are now widespread and continue to grow. Medical imaging is at the forefront of this revolution and the introduction of digital detection methods to replace film is now addressing the diagnostic X-ray market, the most routinely employed imaging modality. The introduction of picture archiving and communication systems, hospital and radiology information systems is well underway, and the integration of radiation protection initiatives into these developments is desirable. In north-west UK, a project aimed at developing and implementing IT-driven radiation protection strategies has been underway for the past 10 y. Such strategies are geared towards the support of European Commission patient dose directive 97/43 EURATOM, in particular the need to implement clinical audit, patient dose audit and to establish dose reference levels. This paper demonstrates the national and local requirements for establishing a central dose data management system for use in radiation protection strategies. In particular, such a system can help develop and support the role of a medical physics expert in optimisation. The scientific requirements for such an approach are presented in this paper, and a prototype system is described. Preliminary results obtained with the central data management facility are also presented and the implication for analysing multiple site dose data in optimisation strategies for digital radiographic technology is highlighted.

Ultraviolet radiation, evolution and the π-electron system

Ultraviolet radiation is an important natural mutagen. Because of the energetic characteristics, the carbon compounds most susceptible to UV absorbance are those that contain π-electron systems. The π-electron configuration is most commonly represented in organic chemistry within aromatic ring structures. An analysis of a wide range of biochemically important processes shows that the susceptibility of this system lies at the heart of almost all UV radiation effects on life. Its disruption accounts for UV radiation-induced damage in nucleic acids, proteins and lipids. However, throughout the evolution of the biosphere, life has also used the UV absorbance of π-electron containing compounds to screen out UV radiation, turning their UV absorbance into a protection mechanism. Although UV radiation effects can be analyzed in terms of organism physiology, a more reductionist analysis shows the π-electron system to be the common chemical determinant in the evolution of UV radiation damage effects and protection strategies in organisms. It reveals an interesting evolutionary story.

Ultraviolet radiation, evolution and the π-electron system

Ultraviolet radiation is an important natural mutagen. Because of the energetic characteristics, the carbon compounds most susceptible to UV absorbance are those that contain π-electron systems. The π-electron configuration is most commonly represented in organic chemistry within aromatic ring structures. An analysis of a wide range of biochemically important processes shows that the susceptibility of this system lies at the heart of almost all UV radiation effects on life. Its disruption accounts for UV radiation-induced damage in nucleic acids, proteins and lipids. However, throughout the evolution of the biosphere, life has also used the UV absorbance of π-electron containing compounds to screen out UV radiation, turning their UV absorbance into a protection mechanism. Although UV radiation effects can be analyzed in terms of organism physiology, a more reductionist analysis shows the π-electron system to be the common chemical determinant in the evolution of UV radiation damage effects and protection strategies in organisms. It reveals an interesting evolutionary story.