A discussion of the concept of a “conditioning dose” in cancer treatment

Relevant quote from:

  • The following is taken from “Low-dose ionizing radiation exposure: Understanding the risk for cellular transformation” By L. DE SAINT-GEORGES,*
  • SCK•CEN, Department of Radiobiology, Mol, Belgium. Published in: Journal of Biological Regulators and Homeostatic Agents
    Received:May 15, 2004\, Accepted:June 26, 2004. Full paper download link:http://www.radiationhormesis.com/RadiationHormesis/Low-dose%20ionizing%20radiation%20exposure.pdf

    Adaptive response and hormesis are often mentioned to minimize the risk of radiation or sometimes to deny any adverse outcome below a dose threshold, as detailed below.

    Hormesis is a hypothesis that emphasises the possible beneficial effect of low doses of radiation and claims the necessity of a low-dose exposition to get some benefits while excluding any risk. However, this concept is controversial.

    According to the hormesis model, people should be exposed to low radiation dose unless it is demonstrated with certitude that there is no benefit from such exposure. The possibility of adverse effects is not even considered.

    We may wonder why the proponents of the hormesis model acknowledge a radiation threshold value for harmful effects, but reject it for beneficial effects.

    Considering the essentially random interaction between radiation and target molecules leading to unpredictable molecular damage, it appears surprising that at low doses only beneficial effects would occur while noxious effect would require a dose above a certain threshold. To consider hormesis as an argument against actual dose limits would only be valid if the efficacy of hormesis could be demonstrated for the effects against which one wants to protect at low radiation doses, i.e. cancer and genetic damages.

    Unfortunately this is not yet demonstrated in an unequivocal way. Therefore, the hormesis model is currently not considered in radioprotection.

    The theory of “adaptive response”, (not to be confused with hormesis) shows that a low dose can reduce the effect of a higher dose when administered after a short time delay. This theory is based on substantial evidence.

    To reduce a risk appears beneficial, but it does not mean that the risk is eliminated. According to the “adaptive response” model, a first low dose (conditioning dose) is considered to stimulate the DNA repair mechanisms that contribute to reduce the effect of a subsequent higher dose. But the initial low dose can only stimulate the limited number of cells actually hit, the total of which in function with the dose. This situation never excludes the possibility of a transformation of one of the cells.

    The next higher dose concerns all cells. Some of them having the repair mechanisms stimulated by the first conditioning dose, and may repair the damage more easily. The other cells, that were not previously hit, are not protected. The total damage can be reduced by a factor depending on the number of the cells conditioned but will always be dependent on the total number of the cells exposed to both doses.

    Would the conditioning of all cells solve the question? No, because to reach such a goal we have to increase the conditioning dose and the risk remains proportional to the dose and to the number of cells irradiated.

    Therefore the adaptive response does not appear to be a relevant mechanism for radiation protection because the (low) conditioning dose that defines it, also generates a risk of transformation. On the other hand the challenging dose is not a low dose.

    We suggest that natural background irradiation and metabolic ROS are already stimulating toward some adaptive response by a constant stimulation of the repair mechanisms. Then it would appear that there is no need to add to this radiation burden.

    Evolution, in our natural radioactive environment, is often used as an argument to support such beneficial effects of low-dose radiation. We should remember that if Evolution has led to the current scala of successfully living species, the eliminated species are unavailable to analyse the non-beneficial aspect of evolution.

    end quote.

    Flinders University has been researching the use of a conditioning dose in the treatment of cancer since 2000 AD. So far the results of its reseach into adaptive response induced by conditioning dose has been given less publicity than its opinions regarding the theory of hormesis and the alleged benefits of additional nuclear pollution.

    As the man says, Adaptive Response – a potential tool for the use in medicine – is quite different to the theory of hormesis.

    When an expert seems to me to deliberately confuse the two in the public arena, and when that expert, citing their qualifications in the realm of cancer treatment, defends nuclear pollution in the general environment as a health benefit, I am forced to ponder which hat the expert is wearing. The medical researcher pursuing the theory of adaptive response or a nuclear industry advocate attenmpting to minimise the impact of reactor meltdowns and uranium mine emissions.

    Medicine occurs when there is a medical need, a consenting, informed patient and a qualified doctor.

    Anything else is either politics, advertising, propaganda or human radiation experimentation.

    What patient would be willing to be treated by a doctor with whom they violently disagreed, and of whom they that cause to ponder “Is this medicine, politics, advertising, propaganda, or experimentation?”

    See next post.

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