[ RadSafe ] Cancer

[Doss, Mohan]

Dear Joe,
    The basic concept you are implying, that DNA damage causes cancer, is not consistent with evidence.  Of course DNA damage is needed to have cancer, but it is not sufficient.  In fact almost everyone has covert cancer http://www.nature.com/nrc/journal/v14/n4/full/nrc3703.html , i.e. cells with carcinogenic mutations, but a majority of us are not diagnosed with cancer even in all of our lifetime.  What gives rise to clinical cancer is the depression of the immune system, which allows these covert cancers to grow uncontrollably.  If the immune system is not depressed, the slightly increased number of mutations from any cause, e.g. radiation, would not affect cancer risk.    Low-dose radiation boosts the immune system and so would reduce rather than increase cancers.  The adaptive response due to low-dose radiation would boost defenses like DNA repair enzymes and so would reduce the damage to DNA over the longer term, since the increased protection would reduce the endogenous DNA damage that would have occurred otherwise. I have described this briefly in the recent debate on health effects of low-dose radiation in Medical Physics http://scitation.aip.org/content/aapm/journal/medphys/41/7/10.1118/1.4881095. 
   So, doing MCNP, etc. to calculate the DNA damage, without including the adaptive response of the body, may not help with estimating cancer risk from radiation.
   There is evidence cancers have resolved spontaneously, and this is probably because the immune system got rid of the cancer cells.   
   With best regards,
                                           Mohan

Mohan Doss, Ph.D., MCCPM
Medical Physicist,
Associate Professor, Diagnostic Imaging,
Fox Chase Cancer Center,
333 Cottman Avenue,
Philadelphia, PA 19111-2497.
Phone: 215 214-1707
Website: http://www.fccc.edu/research/pid/doss/
Blogs: http://mohan-doss-home-page.blogspot.com/


-----Original Message-----
From: radsafe-bounces at agni.phys.iit.edu [mailto:radsafe-bounces at agni.phys.iit.edu] On Behalf Of JPreisig at aol.com
Sent: Sunday, August 17, 2014 11:20 PM
To: radsafe at agni.phys.iit.edu
Subject: [ RadSafe ] Cancer

Radsafe,
 
      I guess in cancer production, the carcinogen  is in some volume within the body, and this volume can grow if the carcinogen  continues to be introduced into the body.  The cancer is probably in the  vicinity of this carcinogen volume.  One question I might ask is that once  the cancer grows outside of the carcinogen volume, will the cells (upon cellular  division) continue to be cancerous?  I expect bodily circulation and other  processes could 
also cause the carcinogen volume to diminish in size.   Quite a dynamic 
process....
 
     I guess cancer production via radiation is a whole  different process, mostly a scattering process of the various forms of radiation  by cells, DNA and so on.  Any new science on single strand breaks, double  strand breaks etc. in the literature lately???
 
    Maybe someone (a young person) could start to use MCNP,  MCNPX or some similar computer code, to model computationally (on a  supercomputer these
days) the scattering of radiation from DNA strands, whole  human cells, 
groups of cells, various human tissues and so on.   Computationally setting up 
the first DNA strand or human cell would be pretty  daunting.  The repeated 
structures capability of MCNP might be  helpful.   Doing some studies 
computationally may allow us to avoid  doing all the studies via lab experiments on various animals.  I guess  animal studies would still be required for important intellectual steps...
 
    Has it ever been observed that a cancerous human cell  has reverted to a non-cancerous state????
 
    Have a good week.     Regards,    Joseph R. Preisig
 
 
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