Highest Biological Efficiency Research Articles

Radiotherapy with heavy ions: radiobiology, clinical indications and experience at GSI, Darmstadt.

In the history of external beam radiotherapy, the trend for a better conformation as well as for a higher biological efficiency has been the driving force for the improvement of clinical results. However, these two goals had to be followed with separate types of radiation, i.e. photons and neutrons, and could not be combined. For the first time being, beams of heavy ions like carbon offer the possibility to combine both advantageous properties: better targeting and higher biological efficiency. Particle beams have an inverse depth dose profile, with a maximum dose in the deep seated tumor, a finite range, small lateral scattering, and a drastically increased biological efficiency in the tumor. These properties maximize the deletion effects on tumor cells. In addition, particle beams can be directed precisely in the limit of one or two millimeters, and can be monitored using positron emission tomography (PET) with the same precision. In the following paper the conditions are given that are necessary to translate these properties into clinical routine.

23] Applications of caged compounds of hydrolysis-resistant analogs of cAMP and cGMP

Publisher Summary Cyclic nucleotides—that is, cAMP and cGMP—control a variety of important cellular processes. The study of cAMP- and cGMP-signaling pathways has been greatly facilitated by the design of chemical derivatives, dubbed “caged”compounds. Caged cAMP and caged cGMP have also been used to study the activation kinetics of the cGMP-gated channel from rod photoreceptor cells, the signaling pathways in olfactory sensory neurons (OSNs), 15'16 the enhancement of CI – currents in ventricular cells, and the motile response of fish melanophores. This chapter discusses the properties of these compounds and their usefulness for electrophysiological studies of cyclic nucleotide-gated (CNG) channels in situ using heterologously expressed α subunits of CNG channels from bovine OSNs and cone photoreceptor cells. For many physiological studies, it would be desirable to use caged compounds that liberate cAMP or cGMP derivatives that are hydrolysis resistant or have higher biological efficiency. Derivatives that meet both these criteria are 8-Br-cAMP and 8-Br-cGMP. They are poorly hydrolyzable by phosphodiesterases, and 8-Br-cGMP activates cGK and CNG channels more effectively than cGMP.

The effect of α particles on bacteriophage T4Br +

It is generally accepted that heavy charged particles play an important part in generating the secondary flux of nuclear particles formed by the interaction of space hadrons with nuclei. It is assumed that these particles are responsible for the high biological efficiency of space hadrons in causing cellular damage by their strong interactions. To examine this assumption we investigated the effects of 5.3 MeV α particles on bacteriophage T4. This energy provides a LET value of 88.6 KeV/μm lying in the range of the highest biological efficiency.

The capture of -mesons in oxygen and in other nuclei

An attempt has been made to study the detailed characteristics of the capture of π- mesons in light elements, in particular oxygen. This study was made as an initial investigation into the feasibility of the use of π- mesons in radiation therapy for the treatment of carcinomas. There is a yield of 1.77 ± 0.08 multiply charged particles per π- capture in oxygen with a mean kinetic energy of 6.9 MeV. These particles have a high relative biological efficiency and low oxygen enhancement ratio so that the biological effect of an irradiation with stopping π- mesons would be characterized by these heavy particles. The frequency distribution of the various modes of interaction are given together with energy spectra for protons, alpha and heavier particles.

A HIGH RELATIVE BIOLOGICAL EFFICIENCY OF 650-KEV NEUTRONS AND 250-KVP X-RAYS IN SOMATIC MUTATION INDUCTION.

THE mean linear energy transfers of 650-keV neutrons and of 250-kVp X-rays are so markedly different that it is not usually possible to establish a unique value for their relative biological efficiency. For example, it is well known that the densely ionizing neutrons induce linear dose-response relationships for chromosome aberrations, whereas the dose-response curves for X-rays are often non-linear. Moreover, the former radiation but not the latter is almost independent of environmental factors such as oxygen tension during irradiation. Under certain conditions, and with certain biological test systems, however, some of these difficulties are minimized. For example, Neary et al.1 compared the relative biological efficiency, in terms of chromosome aberration induction, of 0.7- and 3.0-MeV neutrons with cobalt-60 γ-rays administered at low dose rates. There the dose-response relationships were almost linear, and relative biological efficiency values of 35 were obtained; they also derived ultimate maximum relative biological efficiency values from a comparison of the one-hit components of the neutron and γ-dose-response curves and found that these could be as high as 100. Similarly, Smith et al.2, using a test system (somatic mutation induction in dry seed) in which the dose-response relationship for X-rays was linear, obtained an average relative biological efficiency value of about 75 for mono-energetic neutrons of 0.43–1.80 MeV.