How do ALARA, and/or ICRP - Radiation Shielding for Medical ...

Radiation Shielding
guidelines – do you really
need ALARA or source
constraints
Robert L. Dixon
Wake Forest University it School of Medicine
i

Natural Background in USA- Exclusive
of Radon (NCRP #45 & #94)
Atlantic & Gulf Coastal Plain- 1.05 mSv/yr
Middle America-
Rocky Mountain Plateau-
1.25 mSv/yr
1.45 mSv/yr
Denver Colorado-
165 1.65 mSv/yr
Population-weighted average-1.09 mSv/yr
Average +0.25 mSv/yr = 1.34 mSv/yr

Despite the variation in natural
background, most locales l in the US
are below 6 mSv per annum.
So where would logic dictate setting
thepublicdoselimit limit, perhaps5mSv
Au contraire – they picked 1 mSv per year
They evidently don’t believe it’s safe
to live in Denver, CO

The 1 mSv per yr public dose limit is “Down in the
noise”
3.5
4.0 mSv Avg +1 mSv
Avg

Public Dose Limit
1 mSv/yr

But the “Lords of Protection”
(ICRP) secretly yearned to set it even
lower, so they turned to a little
trickery to try to accomplish the same
thing
With “constraints”
they could create a
new and even lower
“de facto” dose limiti

Public Dose Limit- simplified
Rule one : 1 mSv/yr
Rule two : Now Divide
Rule one by 3

Source Constraints
– An ICRP fantasy
The Myth of Multiple Sources–
which fails to consider:
• Most sources do not converge to a
single location
(short range, inactive at night)
• A given person cannot be in more than
one place at a given time
This argument is developed in much greater detail in our
paper in published in Radiation Protection
Dosimetry(2005),v.115, No. 1-4, pp. 16-22.

1 mSv
1
1
1
1
1
1

1 mSv
1
1
This
1

ICRP SPEED LIMIT
SOURCE CONSTRAINTS
• SPEED LIMIT- 60 MPH
• BUT WE MUST CONSTRAIN YOU TO 20 MPH
SINCE YOU MAY OWN MORE THAN ONE AUTO,
OR DRIVE ON MORE THAN ONE HIGHWAY
This logic is closely analogous to that used for
“source –constraints” - ignoring simultaneity

The International Council for Radiation
( ) p
Protection(ICRP) in 2003 expanded its charter to
protect animals as well
They choose the duck as their animal model

But we can still
shoot the
ducks, right
No problem, we
just can’t “nuke”
‘em

Cost per (hypothetical) Life-year
saved 1
Radiation Emission Standards for Nuclear
Power Plants: $100 Million/life-yr
Radionuclide Emission Control at NRC-
licensed facilities: $2.6 Billion/life-yr
Widen lanes on Rural Roads by 2 ft:
$120,000/life-yr
_______________________________________________
1. Tengs et al., Risk Analysis 15, , 369-390, 390, 1995

ld15
Thinking Inside the Box
Lower is
always better
in here

Slide 18
rld15
1. only hazard is radiation
2. no coupling between the box and the outside world
3. money is no object
rdixon; 02-10-2003

I can readily prove that most of you
are “inside the box” thinkers
How many of you drove here
ALARA

Driving ALARA*
Keep your Speed ALARA
*As Low As Reasonably Achievable

Driving ALARA would inarguably reduce
the risk of death - not only to you, but to
other members of the public in your path .
•A definite, it proven benefit to you and the public.
•Saves on fuel
•It seems a “no-brainer”

ALARA Sure it’ll cost
more, but don’t forget
we’re dealing with
“deadly radiation”
here.
Hey, It doesn’t apply to
driving – just radiation!
I’m not driving ALARA
(or Miss Daisy)!

Secret ICRP training camp
Behold! multiple sources!

So how did I get involved in this Orwellian world
We presented our final
report to NCRP, and
were called before “the
Pope” (like Gallileo)
BEN ARCHER, JOEL GRAY,
BOB DIXON, DOUG
SIMPKIN

Thou shalt design all thy shielding to ¼ mSv per annum
whether thou believest or not, for it is thus “written” in
NCRP 116 chapter one, verse 122
Zip it!
Our reply pyto NCRP
But..
It is futile to resist

Administrator
It’s going to cost you $250,000 to
“upgrade” your vault to 0.25
mSv/yr for a slight (hypothetical)
increase in protection for the 5 or
so members of the public who
work in its immediate vicinity
Also, those 5 people will be getting more
radiation from natural radioactivity inside their
own bodies than from your accelerator
And by the way, every pizza parlor, ice cream shop,
home or business in the Denver region will have a
higher radiation level than that just outside your
expensive new leaded accelerator walls-

Many developing countries who cannot
afford modern medical x-ray equipment,
waste their precious resources on
shielding to the ICRP suggested “limit” of
1/3 mSv/yr blindly adopted by their
regulators.

Predictions if Designing Shielding to
025 0.25 mSv per year
• An estimated additional 10 9 kg g( (1/2 billion pounds)
of lead would be required for medical x-ray alone
(50% of total annual production).

(hypothetical) annual risk from 3/4 mSv/yr
4x10 -5
(real) annual risk to 2 :
metal miners & smelters 56 x 10 -5
Construction workers 14 x 10 -5
2
Wilson and Crouch, Risk-Benefit
Wilson and Crouch, Risk Benefit
Analysis, Harvard 2001.

Recent NCRP report series for shielding
medical x-ray sources
“ NCRP has concluded that a suitable source
control for shielding individuals in uncontrolled
areas in or near medical radiation facilities is an
effective dose of 1 mSv in any year. “
1 mSv.y-1 to the maximally exposed individual
in an uncontrolled area will provide adequate
protection to the employees and the members
of the public that access the uncontrolled
o areas.

Reconfirms Source Control of
1 mSv per year

IAEA Training Material on Radiation
Protection in Diagnostic and Interventional
Radiology
RADIATION PROTECTION IN
DIAGNOSTIC AND
INTERVENTIONAL RADIOLOGY
L12: Shielding and X Ray room design

Radiation Shielding - Calculation
Based on NCRP 147
Assumptions used are very pessimistic, so
overshielding is common
Various computer programs are available,
giving ii shielding hildi in thickness thik of various
materials
IAEA continued
33
12: Shielding and X Ray room
design

Radiation Shielding Parameters
()
(I)
P - design dose per week
• usually based on 5 mSv per year for
occupationally exposed persons (25% of
dose limit), and 1 mSv for public
• occupational dose must only be used in
controlled areas i.e. only for
radiographers and radiologists
i IAEA continued
34
12: Shielding and X Ray room
design

Implications of 1/3 mSv per
annum “Constraint”
• Attempting to increase public protection
by forcing the doses allowed from
medical X-ray sources to Heroically low
levels (10% of natural background) limit
is likely to represent net harm to the
patient population (the same public) in
terms of both increased healthcare costs
as well as increased health risk to
individual patients, with no proven
benefit whatsoever.

How’re they gonna find
enough duck A-bomb
survivors to figure risks,
Eh
I guess we’ll
have to “nuke”
a bunch of
them
They’re not gonna
like that, t Eh

And the “duck” rebellion is already beginning
The ICRP is
next- bring it
on Lars-Erik
Two can play
this decoy game

The risk coefficient
The End is Here

This is
my lucky
day,
I’m from upstairs, and am
conducting an ”NCRP - type”
investigation-So where do you
live or go after work Is
anybody else irradiating you
besides me