**7. Radiobiological dose enhancement effects from molecular and atomic high-Z elements**

It is curious that historically photoelectron emission by internal high-Z elements in living systems has received very little attention. The issue of enhanced doses near bones, due to the higher concentration of calcium in the bone, was addressed as long ago as 1949 by Spiers [35], and more recent work has also looked at photoelectron emission near the bone [36]. In 1988 Castillo reported burns and necrosis around reconstructive wires in mandibular cancer patients [37], and Regulla et al. employed a very sophisticated measuring apparatus to show a physical dose enhancement of about 100-fold and a biological enhancement into tissue of 50-fold within a range of 10μ from gold foil [38]. Despite work on enhancing radiotherapy which has been carried out, no authors appear to have related the question of photoelectron enhancement to health effects. One obvious question must be about the enhanced photoelectron doses near metal prosthetic structures containing zirconium (Z = 40). The element has a photoelectron cross section of 3.5E+3 at 150 keV compared with iron (Z = 26) at 5.4 and so would produce some 650 more photoelectrons.

**189**

*The Secondary Photoelectron Effect: Gamma Ray Ionisation Enhancement in Tissues from High…*

The main question that has to be focused on is the enhancement of dose to the DNA from high-Z atoms or molecules which are attached to the DNA by chemical affinity. If a high-Z atom, ion or molecule were attached to the DNA, then it is easily predicted that this would cause enhanced genetic damage, measurable as downstream effects like cancer and congenital disease but also chromosome breakages and chromosome aberrations. The obvious candidate is uranium, which as the uranyl ion has been known to bind strongly to DNA since the 1960s when it began to be employed as a chromosome stain. The genotoxic effects of uranium exposure are by now well established both in human populations and in in vitro studies [12–20]. They cannot be explained by the intrinsic alpha activity, and indeed one experiment has revealed genetic effects in the absence of alpha decays [20]. The affinity of uranyl ion for DNA has been measured, and it is significant. So uranium (Z = 92) effects are one clear piece of evidence for the effects of secondary photoelectrons.

There is further evidence from the anticancer agent cisplatin, cis-diaminedichloro-platinum (II). Cisplatin has been a chemotherapeutic agent of choice since 1978 and is given to more than half of all cancer patients. Its mode of action has been variously described as "damaging nuclear DNA and arresting cell division". A recent review states: "Almost 30 years after its clinical benefits were first recognised, studies still continue in an effort to understand exactly how cisplatin

Cisplatin also augments radiotherapy, that is to say, the combination of cisplatin and radiotherapy results in much higher cancer therapeutic effects than either agent on its own. This is, of course, a pointer to the mechanism [33, 39]. It is suggested here, based on what has been written above, that cisplatin, a simple diaminedichloro-square planar complex of platinum (II), merely fixes the platinum atom (Z = 78) at the centre of the nuclear DNA where the secondary photoelectron doses are sufficient to fatally damage the DNA either from natural background radiation or in the case of the radiotherapy, from the induced photoelectrons. If this is the mechanism, then two suggestions are obvious: first, uranium as uranyl acetate, for example, also will act as a chemotherapeutic agent for cancer and will augment radiotherapy in the same way. Since it is suggested that it is the high-Z aspect of cisplatin that is the reason for its action, other high-Z molecular agents could be searched for or synthesised to act as DNA-seeking chemotherapeutic agents.

The question of the spectrum of elements utilised by evolution of life on earth has been generally approached from the point of view of physical chemistry and more specifically redox equilibria [40]. There may be a separate or additional explanation for the reason why elements of high atomic number (e.g. mercury, bismuth, lead, uranium) although often commonly available on earth are not used by living creatures. As has been shown, chemical elements absorb gamma and X-rays of energy below about 250 keV approximately in proportion to the fourth power of their atomic number Z, and the energy is converted mainly to photoelectrons and local Auger recoil electrons resulting from internal rearrangements in the case of high-Z elements. For elements immobilised inside living tissue, this results in higher doses to components near high-Z atoms or nanoparticles than would be experienced

*DOI: http://dx.doi.org/10.5772/intechopen.86779*

But there is another one.

**8. Cisplatin**

works" [39].

**9. Evolution**

*The Secondary Photoelectron Effect: Gamma Ray Ionisation Enhancement in Tissues from High… DOI: http://dx.doi.org/10.5772/intechopen.86779*

The main question that has to be focused on is the enhancement of dose to the DNA from high-Z atoms or molecules which are attached to the DNA by chemical affinity. If a high-Z atom, ion or molecule were attached to the DNA, then it is easily predicted that this would cause enhanced genetic damage, measurable as downstream effects like cancer and congenital disease but also chromosome breakages and chromosome aberrations. The obvious candidate is uranium, which as the uranyl ion has been known to bind strongly to DNA since the 1960s when it began to be employed as a chromosome stain. The genotoxic effects of uranium exposure are by now well established both in human populations and in in vitro studies [12–20]. They cannot be explained by the intrinsic alpha activity, and indeed one experiment has revealed genetic effects in the absence of alpha decays [20]. The affinity of uranyl ion for DNA has been measured, and it is significant. So uranium (Z = 92) effects are one clear piece of evidence for the effects of secondary photoelectrons. But there is another one.
