It is time to consider the lack of science in "effective dose"

[John Cameron <jrcamero@facstaff.wisc.edu>]

Title: It is time to consider the lack of science in "effecti

Dear Colleagues,  I think we should discuss the weak scientific basis of effective dose from background or otherwise. Let us consider the following debatable statements:

1. The WR value of alpha particles is probably closer to 3 than to 20. (Personal communication from Robley Evans.)  There is (as far as I know) no measured  RBE for alpha particles  close to 20.  The book Radiation Protection Quantities:  A Radical Reappraisal by Simmons and Watt (Med. Phys. Publ) states that no measured RBE of alphas is above 10. The ICRP gave no documentation for their choice of 20.  When using helium nuclei in radiation therapy, the RBE appears close to 1.

2. The equivalent dose to the lungs which presumably only increases the risk of lung cancer cannot scientifically be added to the equivalent dose to the other organs of the body. The tissue weighting factors have never been evaluated by an independent scientific body other than the ICRP which chose the values. NCRP Report No. 104 (1990) RE: determining RBE values at doses below 0.2 Sv for radiation protection purposes, the authors concluded that the Q value (now WR) could not be determined. They suggested you choose an RBE you feel is reasonable! There is no reason to believe that WT can be scientifically determined or that the concept of adding up effective values from various organs can be justified.

3. It is time to reject the unscientific concept of effective dose.  I claim that the effective dose to the lungs from radon progeny is the product of 3 unknowns: the dose to the lung tissue, the WR of alphas and the WT for lungs.

4. I strongly suggest that we  use the physics quantity "imparted energy" to describe the radiation to humans. This information would be supplemented by a description (if available) of the type of radiation, time factors, tissues exposed, etc. It is a rare event where an accidental dose is of medical concern.

5. The IPSM (UK) report 53 on doses from diagnostic radiology shows that the imparted energy correlates well with the effective dose.  The imparted energy varies from 7 mJ (chest radiograph) to about 700 mJ for a lower GI series. CT whole body doses are generally larger.  It should be straight forward for the computer which is part every CT unit be programmed to estimate the imparted energy from the physical parameters for the scan.

6. The evidence from the nuclear shipyard worker study and the 100 years of British radiologist mortality makes it clear that fractionated doses up to about 0.2  Gy are almost certainly beneficial. See my article Is radiation an essential trace energy? http://www.aps.org/units/fps/oct01/a5oct01.html

7. We can not hope to see a scientific evaluation of radiation protection quantities by the ICRP or NCRP. I suggest that HPS appoint an ad hoc committee (perhaps in cooperation with other radiation scientific groups) to study the validity of our present radiation protection policies.

I suspect private $  would be available to help support this study. I would be willing to donate $10K.

Best wishes, John

--
John R. Cameron, Ph.D.
Professor Emeritus,UW-Madison
Departments of Medical Physics, Radiology & Physics
Winter home address:
2678 SW 14th Dr.
Gainesville, FL 32608
(352) 371-9865  FAX 371-9866
e-mail: jrcamero@facstaff.wisc.edu