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Health news:
 
June 2010 - Dec 2013

Minimizing breast cancer risk

May 2010

Time to move beyond salt ?

Salt hypothesis vs. reality

Is sodium bad?

April 2010

Salt studies: the latest score

From Dahl to INTERSALT

Salt hypothesis' story

March 2010

Salt war

Do bone drugs work?

Diabetes vs. drugs, 3:0?

February 2010

The MMR vaccine war: Wakefield vs. ?

Wakefield proceedings: an exception?

Who's afraid of a littl' 1998 study?
 

January 2010

Antibiotic children

Physical activity benefits late-life health

Healthier life for New Year's resolution

 

December 2009

Autism epidemic worsening: CDC report

Rosuvastatin indication broadened

High-protein diet effects

 

November 2009

Folic acid cancer risk

Folic acid studies: message in a bottle?

Sweet, short life on a sugary diet

 

October 2009

Smoking health hazards: no dose-response

C. difficile warning

Asthma risk and waist size in women

 

September 2009

Antioxidants' melanoma risk: 4-fold or none?

Murky waters of vitamin D status

Is vitamin D deficiency hurting you?

 

August 2009

Pill-crushing children

New gut test for children and adults

Unhealthy habits - whistling past the graveyard?

 

July 2009

Asthma solution - between two opposites that don't attract

Light wave therapy - how does it actually work?

Hodgkin's lymphoma in children: better alternatives

 

June 2009

Hodgkin's, kids, and the abuse of power

Efficacy and safety of the conventional treatment for Hodgkin's:
behind the hype

Long-term mortality and morbidity after conventional treatments for pediatric Hodgkin's

 

May 2009

Late health effects of the toxicity of the conventional treatment for Hodgkin's

Daniel's true 5-year chances with the conventional treatment for Hodgkin's

Daniel Hauser Hodgkin's case: child protection or medical oppression?

April 2009

Protection from EMF: you're on your own

EMF pollution battle: same old...

EMF health threat and the politics of status quo
 

March 2009

Electromagnetic danger? No such thing, in our view...

EMF safety standards: are they safe?

Power-frequency field exposure
 

February 2009

Electricity and health

Electromagnetic spectrum: health connection

Is power pollution making you sick?

January 2009

Pneumococcal vaccine for adults useless?

DHA in brain development study - why not boys?

HRT shrinks brains

NEWS ARCHIVE
2009
2008
2007

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June 2010 - December 2013

II - Mammography

17. Mammography radiation exposure

2 good choices to prevent breast cancer

I - BREAST CANCER
 RISK FACTORS
  

II - SCREENING X-RAY MAMMOGRAPHY

III - ALTERNATIVE TESTS

The biggest risk factor
Risk factors overview
Times change

END OF A MYTH
The whistle
Contra-argument
Last decade
Current picture

 OTHER  X-RAY TESTS
Digital standard
Tomosynthesis
Breast CT

Predisposing factors
Diet       Other

BENEFIT
Earlier diagnosis
Fewer breast cancer deaths

Gamma-ray tests
BSGI/MBI 
PEM

INITIATING  FACTORS
Radiation
Chemicals
Viruses

RISK  &  HARM

OTHER  TESTS
Breast MRI
Ultrasound
Thermography
AMAS test

INACCURACY RISKS False negative
False positive

Overdiagnosis
PROMOTING  FACTORS
Hormonal

Non-hormonal

RADIATION

Radiation primer
Screen exposure

Radiation risk
PHYSICAL EXAM
Clinical
Self-exam

Higher all-cause mortality?

• Minimizing breast cancer risk

Ever since the beginning of X-ray mammography screening, decades ago, it was assumed and publicly asserted by both, official medicine and the government, that the health risk from screening radiation is negligibly low. Very few voices back then warned that there is no sufficient evidence to support such assumption. They were effectively sidelined and neglected. Do we have enough evidence today to resolve this question? Probably not to some high level of accuracy, but sufficiently for a meaningful answer.

Unlike the average figures thrown around, actual exposures to radiation in the standard X-ray mammography screening can vary significantly, depending on the intensity of radiation output (so called skin entrance exposure, varying with breast thickness, usually between 0.5 and 5 roentgen), thickness of the aluminum filter, and glandular fraction, representing the weight fraction of glandular (sensitive to radiation) vs. adipose (fatty)  tissue.

Table below shows radiation delivered to breast tissue at near minimum, median and near maximum levels (based on Duke University's online computation display).
 

MAMMOGRAPHY: BREAST GLANDULAR IRRADIATION DOSE

Breast's compressed
thickness (cm)

2

4

6

8

Radiation output
in roentgen (R)

0.5

1

3

5

HVL (cm Al)

0.24

0.33

0.43

0.24

0.33

0.43

0.24

0.33

0.43

0.24

0.33

0.43

Glandular fraction

1.00

0.50

0

1.00

0.50

0

1.00

0.50

0

1.00

0.50

0

Absorbed radiation,
mSv per R of output

2.05

3.06

4.34

1.10

1.78

2.80

0.69

1.17

1.96

0.51

0.87

1.48

Absorbed radiation per view (mSv)

1.02

1.53

2.17

1.10

1.78

2.80

2.08

3.51

5.89

2.57

4.34

7.38

Breast radiation dose, each
(mSv)

2 views

2.05

3.06

4.34

2.2

3.56

5.6

4.14

7

11.8

5.1

8.7

14.8

4 views

4.1

6.1

8.7

4.4

7.1

11.2

8.3

14

23.6

10.2

17.4

29.6

Level

Min

Med

Max

Min

Med

Max

Min

Med

Max

Min

Med

Max

TABLE 1: radiation dose delivered by X-ray mammography (breasts radiation dose equals per view dose multiplied by number of views per breast)

Note that the calculator gives the absorbed dose in millirads (mrad) per roentgen; to convert to milliSieverts (mSv), i.e. equivalent dose, 1mSv=100mrad, so dose in mSv equals the dose in mrad divided by 100. Breasts radiation dose is a product of the absorbed radiation per view and number of views (it does not get multiplied by two for two breasts, because the radiation risk assumes dose delivered to both breasts).

The main variable is the breast thickness, on which is based radiation output, but the level of radiation delivered also varies significantly with the value of glandular fraction (from near zero for "fatty", or "fibrous" breast to near 1 for "dense" breast; the more of glandular tissue, the lower its irradiation for given output level), and the beam "hardness" , expressed as half-value layer of aluminum. Peak voltage is kept constant, at 28 kV (the voltage is also a variable in actual setups, but its effect on irradiation dose is relatively small within the usual 22-35 kVp range).

This technical calculation only approximates the actual irradiation level - which can vary unpredictably and significantly with the specific machine, operator and breast - but does give a usable general estimate.

For the common 2-view screening procedure, it gives the range of possible exposures anywhere from 2 mSv to 15 mSv absorbed/equivalent dose. For 2+2 views, which can be either a single procedure with two extra views, or additional 2-view procedure, the radiation dose is doubled, ranging from 4 mSv to 30 mSv.

Note that the actual maximum could be still higher, since the compressed breast thickness in this consideration is limited to 8 cm.

The magnitude of mammography radiation dose is often illustrated by a comparison with the ordinary chest X-ray dose. But it may not be neither as simple, nor accurate, as one would imagine. Commonly cited effective doses for chest X-ray are 0.02 mSv (posteroanterior, or PA) and 0.1 mSv (posteroanterior and lateral, or PA/LAT). Reported range for the former is 0.007-0.050 mSv, and for the later 0.05-0.24 mSv (Mettler et al. Effective Doses in Radiology and Diagnostic Nuclear Medicine, 2008).

However, according to the U.S. Office of Research Services, the effective dose for the PA/LAT chest X-ray is 0.40 mSv - nearly double the highest reported doses, and four times higher than what is commonly cited (http://drs.ors.od.nih.gov/services/rsc/tables/CXR-PA-LAT.xls ).

Who's got it right? Where does the difference come from? First glance at the agency's list of irradiated organs suggests the answer: among irradiated organs during chest X-rays, it lists as many as 18 organs directly (including a few that receive near-zero radiation) plus 10 more within "reminder" tissues/organs. Lungs actually receive

less than one sixth of the total dose,

and by far the largest dose goes to - guess where - the breasts: 44% of the total effective dose, or over three times more than to the lungs.

The most likely scenario is that those other, commonly cited figures originate from estimates including only a partial list of organs irradiated during the conventional chest X-ray exam. And if the correct figure for the PA/LAT test is four times higher than the commonly cited value, it is to expect the same for the PA chest X-rays as well, which would put their average effective dose closer to 0.1 mSv.

If you find such sloppiness in assessing and presenting radiation risk of such a common procedure surprising and unacceptable, you are in for more frustration. According to a recent study focused on cardiac diagnostic imaging, wide discrepancies in dose estimates from one study to another, and form manufacturers' vs. those based on ICRP (International Committee on Radiation Protection) standards are rather common.

Part of it is due to the incomplete list of irradiated organs and tissues serving as the basis for estimates; also, some still use outdated methods for radiation dosimetry (for instance, effective radiation dose for commonly used radio-isotopes in gamma-ray imaging, like Technecium99, is routinely based on methodologies dating back to 1975, even 1968, in addition to be limited to only a handful of affected organs/tissues). On top of that, plain errors due to insufficient knowledge about radiation dosimetry are fairly frequent.

This little digression was needed to bring to reader's attention the fact that the present day radiation risk assessment and presentation in medical imaging is, for these and other reasons, often

inconsistent, unreliable and not seldom erroneous.

Back to mammography vs. chest X-ray radiation risk. Taking the 0.4 mSv effective dose figure for PA/LAT chest X-ray, and  0.72 mSv effective dose for the average mammography session (from 3 mSv absorbed dose per view multiplied by 2 for two views, and by 0.12 breast tissue weighting factor), the latter delivers a nearly double the effective dose delivered by PA/LAT chest X-rays.

With nearly half of the effective dose with the chest X-ray procedure going to the breasts, average breast cancer risk of the standard 2-view mammography is about

four times higher than breast cancer risk with PA/LAT chest X-rays.

Assuming the actual effective dose for the common posteroanterior (PA) chest X-ray higher than the routinely cited 0.02 mSv figure by the same ratio of 4 as for PA/LAT, it comes to 0.08 mSv total effective dose, and nearly 0.04 mSv for the breasts alone. Thus the average breast cancer risk with the standard 2-view mammography is about

20 times higher than with the standard PA chest X-ray.

Considering questionable accuracy of the radiation weighting factor, officially set at 1 for the wide range of radiation energy levels from low-energy X-rays to high-energy gamma-rays, the actual risk with mammography is probably somewhat higher. The reason is that the standard chest X-rays are performed at a peak voltage exceeding
100 kVp, more than four times higher than the average 25 kVp peak voltage with the standard mammography.

The lower-energy X-rays have more interactions with tissue molecules, thus causing more damage; assuming, very approximately, that their actual effective dose is 50% higher, puts the average risk of developing breast cancer with standard 2-view mammography at about 9 times higher than that for any cancer in the chest cavity (from 0.72 vs. 0.08 mSv effective dose), and about 40 times higher than for developing breast cancer due to a single regular PA chest X-rays (from 0.72 vs. near 0.04 mSv).

In other words,

a single average mammography procedure a year would pose
as much of a risk of inducing breast cancer as nearly
2 standard chest X-rays a month, for a year.

Obviously, it cannot be assumed neither harmless nor insignificant, particularly for women with above average vulnerability to ionizing radiation, undergoing regular longer-term screening.

Evidently, thicker breasts are exposed to higher levels of glandular irradiation (while the average compressed breast thickness in the U.S. is 4-5cm, those of up to 12cm, or more, are not uncommon). A woman with thick breasts could be irradiated with a dose more than twice higher than 0.72 mSv in a single 2-view mammography session, and double that in a single 4-view session. That is comparable to the risk from

over 3 and nearly 7 standard chest X-rays a month, respectively, for a year,

assuming annual mammography screening.

Damage to the cells exposed to X-ray irradiation is caused by the transfer of radiation energy to the electrons within tissue molecules. These electrons are pushed to higher-energy orbits, or out of atoms altogether, altering molecular structure of the surrounding tissue and/or causing formation of reactive chemical species (free radicals). Being ionizing radiation, X-rays have energy high enough to break atomic bonds, causing direct damage to the cellular structures, including the central control molecule of the cell, the DNA (single and double strand breaks, gene fusions/deletions, translocations, etc.).

By altering molecular structures, X-rays also cause cross-linking between body molecules and twisted molecules formed by radiation; this causes both, structural and functional damage (to gene expression, cellular enzymes and regulatory proteins, hormones, etc.).

How, specifically, the level of breast tissue irradiation by X-ray mammography translates into increased risk of developing cancer? Will try to answer this question next.

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