The attached abstract is very interesting (the full paper is too many kB in size for this list).
This is in agreement with many other papers on this subject. We should be getting repeated low doses of X rays to prevent cancer.
Animal data have demonstrated that adding a very small (1–2 mGy), gamma-ray dose to alpha radiation doses up to several hundred mGy during protracted irradiation completely prevented alpha radiation-induced and spontaneous lung cancers. Protracted, total-body exposure to low to moderate gamma-ray doses over many years was found to greatly suppress alpha-radiation-induced lung cancer in humans for alpha radiation doses up to several thousand milligray. Repeated exposures to diagnostic X-ray doses, totaling several hundred milligray, was found to modestly suppress spontaneous lung cancers in humans with tuberculosis, a known risk factor for lung cancer. The indicated low-linear-energy transfer (LET) X- and gamma-ray protective effects relate to activated natural protection (ANP), an adaptive response. Biological processes that contributed to radiation ANP are now better understood and include: increased availability of efficient DNA double-strand break repair (p53-related and in competition with normal apoptosis), stimulated auxiliary apoptosis of aberrant cells (presumed p53-independent), and stimulated immunity against cancer cells.
A radiation-adaptive-response-based cancer relative risk model will be presented in which low doses of low-LET radiation above an individual- and tissue-specific threshold activate the indicated system of natural protection against cancer. With the model, high radiation doses (from low- or high-LET radiation) above a second individual- and tissue-specific threshold inhibit components of the protective system, including immunity against cancer, leading to a substantial increase in risk of cancer. Some key results of applying the indicated model follow: (1) Low doses of X-rays from a single application of diagnostic medical procedures (e.g., computed tomography [CT] scan or chest X-ray) likely reduce rather than increase cancer risk for adults. (2) The level of radiation ANP appears to increase as age increases, based on animal data for lung cancer and human data for breast cancer. (3) Persons at high risk for lung cancer occurrence (e.g., long-time heavy smokers) could have their lung cancer risk reduced by repeated diagnostic chest X-rays or CT scans delivered over an extended period. However, new research is needed to determine optimal schedules for such protective radiation exposures.
Radiation ANP also has important implications for low-dose risk assessment and for cancer therapy. Currently, radiation risk after low radiation doses is based on the linear, no threshold (LNT) model for which any radiation dose, no matter how small, supposedly causes some cancers among a very large irradiated population. Doubling the dose supposedly doubles the number of cancer cases. However, the LNT model does not account for radiation ANP, and therefore ignores natural protection against harm. The continued use of the LNT model for low-dose radiation risk assessment is no longer justifiable for radiation scenarios that involve low-LET radiation (alone or in combination with high-LET radiation). Thus, a new low-dose risk assessment paradigm is needed that addresses radiation adaptive response. Because low doses of low-LET radiation can stimulate immunity against cancer cells while high doses inhibit this immunity, it is reasonable to consider using low doses of low-LET radiation for cancer therapy. Multiple small doses would be expected to be most effective and could be administered in combination with other cancer treatment modalities (e.g., gene therapy, cytokine therapy, application of an antiagiogenic agent). The indicated topics will be the focus of this presentation.
This research was supported by Lovelace Respiratory Research Institute.
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From: Scott, Bobby
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Sent: Friday, February 08, 2008 1:22 PM
Subject: 2008 NIRS Symposium Abstract and Paper
Attached is the abstract for my
invited presentation at the National Institute of Radiological Sciences (NIRS)
Symposium next week in
Bobby R. Scott, Ph.D.
Lovelace Respiratory Research Institute
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