Straight Talk on the "New" Scanner "Study"
Apr 7, 2011, 5:27 am
#1
Original Poster
Join Date: Dec 2010
Posts: 855
Straight Talk on the "New" Scanner "Study"
http://wewontfly.com/that-new-study-...-scanners-fake
What scientists & MDs said about the spurious "study":
http://archinte.ama-assn.org/cgi/ele...2011.105v1#119
(Pretty much what the rest of us have said. The "study" was utter claptrap.)
What scientists & MDs said about the spurious "study":
http://archinte.ama-assn.org/cgi/ele...2011.105v1#119
(Pretty much what the rest of us have said. The "study" was utter claptrap.)
Apr 7, 2011, 7:37 pm
#6
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Apr 7, 2011, 8:24 pm
#7
Join Date: May 2003
Location: Arizona
Posts: 69
Yeah, as as scientist (biology PhD student) myself, the first thing I'd point out is that the study doesn't really contain any original research. It's basically a review article of numbers supplied by other groups with a little math thrown in, and one of the first things every science student learns is that you never take a review article at its word. You always check the original source, because every discipline has its set of "facts" that half the newbies believe because they're in review after review, each review citing the previous one, except only ever vaguely suggested in the original paper.
What is sad is that few people even question the reports/studies as actually reporting/gathering real facts.
Apr 7, 2011, 9:21 pm
#9
Join Date: Mar 2008
Posts: 3,004
This pretty much describes how journalism is "practiced" now....rare to find anyone who actually does the original leg work, research, confirmation of sources and following leads. Most of the news (print/network/cable/internet) pretty much has been guilty of such methodolgy.
What is sad is that few people even question the reports/studies as actually reporting/gathering real facts.
What is sad is that few people even question the reports/studies as actually reporting/gathering real facts.
Apr 8, 2011, 2:05 am
#10
Join Date: Jan 2011
Posts: 120
I didn't see anything that was a "new" study.
The only hard-data we have is material misrepresentations of scanner dosage amounts, failure to comply with FOIAs, and redacted materials.
The things aren't safe people. They really aren't. Don't go in them, and for gods sake don't put your children in them.
I have a particle physics background and scanning your ENTIRE body with soft-tissue wavelength x-rays is I N S A N E if its not for a severe and real medical issue and the risk factors are justified.
The only hard-data we have is material misrepresentations of scanner dosage amounts, failure to comply with FOIAs, and redacted materials.
The things aren't safe people. They really aren't. Don't go in them, and for gods sake don't put your children in them.
I have a particle physics background and scanning your ENTIRE body with soft-tissue wavelength x-rays is I N S A N E if its not for a severe and real medical issue and the risk factors are justified.
Apr 10, 2011, 6:44 am
#11
Join Date: Apr 2011
Posts: 1
Tell a lie long enough.....
I didn't see anything that was a "new" study.
The only hard-data we have is material misrepresentations of scanner dosage amounts, failure to comply with FOIAs, and redacted materials.
The things aren't safe people. They really aren't. Don't go in them, and for gods sake don't put your children in them.
I have a particle physics background and scanning your ENTIRE body with soft-tissue wavelength x-rays is I N S A N E if its not for a severe and real medical issue and the risk factors are justified.
The only hard-data we have is material misrepresentations of scanner dosage amounts, failure to comply with FOIAs, and redacted materials.
The things aren't safe people. They really aren't. Don't go in them, and for gods sake don't put your children in them.
I have a particle physics background and scanning your ENTIRE body with soft-tissue wavelength x-rays is I N S A N E if its not for a severe and real medical issue and the risk factors are justified.
What more can be said!?!
Apr 10, 2011, 11:52 am
#12
Join Date: Jun 2009
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Posts: 867
Welcome to House of Atrades. Well said.
As others have noted, the article published in the Arch.Int.Med., a publication owned by the AMA (which has fallen into serious disrepute among physicians as an organ of the government), is only useful in that reference number 8 described the methodology used to certify the dosimetry of the machine. This was done, apparently on a prototype machine and was performed in 2006. Complete with pictures of their dosimetry setup.
Reference 8 used a monte carlo model which can be accurate, although I am not familiar with PCXMC (my dissertation was done using MCNP, which long predates the PC), I assume it is a reasonable choice. Their dosimetry and models look good too.
From this study we learn that the device does produce 50 kVp x-ray radiation with an Aluminum half value layer of 1.6 mm, which is ionizing and does penetrate the skin to a depth of about 5 cm at the 50% attenuation level. As others have pointed out, the bulk of the absorbed radiation is absorbed in the skin and immediate subcutaneous tissues, including the thyroid gland.
Looking at the PCXMC model, in appendix B we see the model developed. While the figure is too small to really see the model, I will give the author the benefit of the doubt and assume it is reasonably accurate. Target and source modeling accuracy is critical in these types of radiation transport calculations.
There is one key problem with the scientific method which probably was addressed by the author and that is a correction for inverse square factors. Radiation decreases as a function of the square of the distance from the source. When the source is in close proximity to the target, as in the case of the Scan-1000 device a difference in source-detector difference can be significant. It is not clear how or whether this was corrected. Left uncorrected, the skin entrance exposure could be substantially higher than the model depicts. The photograph of the measurement setup shows an ion chamber at the midline of the scanner, and not at a point where a human would be exposed. I'll assume the author did correct for ISF since most of the rest of the paper seems pretty reasonable.
We see that the skin, thyroid and breast doses are on the close order of 0.005 mGy per exposure and that 25% of the tube output is absorbed, and not backscattered.
Again, I'm not sure that the absorbed dose is significant on a one time basis for an individual, or even a small population, but we are exposing a large population, many times a year to repeated x-ray exposures.
The article attempts to give de minimis status to the exposures comparing them to chest xrays and CT scans. CT scans give about 15-20 mGy to put things into perspective and this is true. But CT scans and chest xrays are only used when medically indicated due to an underlying pathology. We discontinued CXR screening for lung cancer in high risk people because it didn't work, even though there might have been a few cancers caught earlier.
But, what about the unclear scan, or the back booth TSO had a bad night and is a shade hung over, or a good night and didn't sleep much. Re-scan of course, and rescan to clarify the "questionable threat in the left front pocket."
So, we go from 0.005 mGy to 0.005x3=0.015 mGy on the first leg of the 4 leg trip and ultimately on each leg as the same factors flow with the traveler, so we are looking at the single trip dose of 0.060 mGy.
The review article by Prehta and Smith-Bindeman is handwaving and factually wrong. It is unclear how peer review works at AMA owned journals, but if one of my physics undergrad students attempted to push some of the concepts published in this paper, I would suggest that she/he re-consider their choice of physics as a career.
It is evident that the authors did not read reference 8 and have no clear understanding of the physics of radiation dosimetry and radiation behavior, nor did the peer reviewers, if any, or this article would have been sent back or outright rejected on that note alone. The comment that the radiation exposure increases in flight due because the airplane is closer to the sun than we ground pounders is ludicrous. Radiation decreases by a function of 1/r-squared. The distance to the sun is 93,000,000 miles give or take a few thousand miles. The difference of 4-5 miles in an airliner drops to insignificance at this distance from the sun. Further, if that were true, we'd all get more radiation because the north pole is closer in the summer than the winter and vice versa.
The real explanation is atmospheric scatter and density changes significantly with altitude and thicker air shields much better than thin air.
Likewise, the author's conclusions have not been scientifically justified and I am disappointed as I hold UCSF in high regard.
As others have noted, the article published in the Arch.Int.Med., a publication owned by the AMA (which has fallen into serious disrepute among physicians as an organ of the government), is only useful in that reference number 8 described the methodology used to certify the dosimetry of the machine. This was done, apparently on a prototype machine and was performed in 2006. Complete with pictures of their dosimetry setup.
Reference 8 used a monte carlo model which can be accurate, although I am not familiar with PCXMC (my dissertation was done using MCNP, which long predates the PC), I assume it is a reasonable choice. Their dosimetry and models look good too.
From this study we learn that the device does produce 50 kVp x-ray radiation with an Aluminum half value layer of 1.6 mm, which is ionizing and does penetrate the skin to a depth of about 5 cm at the 50% attenuation level. As others have pointed out, the bulk of the absorbed radiation is absorbed in the skin and immediate subcutaneous tissues, including the thyroid gland.
Looking at the PCXMC model, in appendix B we see the model developed. While the figure is too small to really see the model, I will give the author the benefit of the doubt and assume it is reasonably accurate. Target and source modeling accuracy is critical in these types of radiation transport calculations.
There is one key problem with the scientific method which probably was addressed by the author and that is a correction for inverse square factors. Radiation decreases as a function of the square of the distance from the source. When the source is in close proximity to the target, as in the case of the Scan-1000 device a difference in source-detector difference can be significant. It is not clear how or whether this was corrected. Left uncorrected, the skin entrance exposure could be substantially higher than the model depicts. The photograph of the measurement setup shows an ion chamber at the midline of the scanner, and not at a point where a human would be exposed. I'll assume the author did correct for ISF since most of the rest of the paper seems pretty reasonable.
We see that the skin, thyroid and breast doses are on the close order of 0.005 mGy per exposure and that 25% of the tube output is absorbed, and not backscattered.
Again, I'm not sure that the absorbed dose is significant on a one time basis for an individual, or even a small population, but we are exposing a large population, many times a year to repeated x-ray exposures.
The article attempts to give de minimis status to the exposures comparing them to chest xrays and CT scans. CT scans give about 15-20 mGy to put things into perspective and this is true. But CT scans and chest xrays are only used when medically indicated due to an underlying pathology. We discontinued CXR screening for lung cancer in high risk people because it didn't work, even though there might have been a few cancers caught earlier.
But, what about the unclear scan, or the back booth TSO had a bad night and is a shade hung over, or a good night and didn't sleep much. Re-scan of course, and rescan to clarify the "questionable threat in the left front pocket."
So, we go from 0.005 mGy to 0.005x3=0.015 mGy on the first leg of the 4 leg trip and ultimately on each leg as the same factors flow with the traveler, so we are looking at the single trip dose of 0.060 mGy.
The review article by Prehta and Smith-Bindeman is handwaving and factually wrong. It is unclear how peer review works at AMA owned journals, but if one of my physics undergrad students attempted to push some of the concepts published in this paper, I would suggest that she/he re-consider their choice of physics as a career.
It is evident that the authors did not read reference 8 and have no clear understanding of the physics of radiation dosimetry and radiation behavior, nor did the peer reviewers, if any, or this article would have been sent back or outright rejected on that note alone. The comment that the radiation exposure increases in flight due because the airplane is closer to the sun than we ground pounders is ludicrous. Radiation decreases by a function of 1/r-squared. The distance to the sun is 93,000,000 miles give or take a few thousand miles. The difference of 4-5 miles in an airliner drops to insignificance at this distance from the sun. Further, if that were true, we'd all get more radiation because the north pole is closer in the summer than the winter and vice versa.
The real explanation is atmospheric scatter and density changes significantly with altitude and thicker air shields much better than thin air.
Likewise, the author's conclusions have not been scientifically justified and I am disappointed as I hold UCSF in high regard.