Future of radiation protection regulations

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Mohan Doss, PhD, MCCPM Medical Physicist, Diagnostic Imaging

Fox Chase Cancer Center,

Philadelphia, PA

E-mail: mohan.doss@fccc.edu

2015 Health Physics Society Annual Meeting, Special Session:

Health Risks from Low Doses and Low Dose-Rates of Ionizing Radiation

July 14, 2015

Copyright © 2015 by Mohan Doss

Version 1.01, Release date: July 15, 2015

This presentation in its entirety may be copied, shared, and distributed freely without any restriction.

If using individual slides or figures, please acknowledge this presentation as the source.

Disclaimer: Opinions expressed in this presentation are my own professional opinion, and do not necessarily represent those of my employer.

How do we decide on radiation protection regulations for low-dose radiation (LDR)?

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How do we decide on radiation protection regulations for low-dose radiation (LDR)?

It is elementary.

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How do we decide on radiation protection regulations for low-dose radiation (LDR)?

1. If LDR increases cancer risk

Regulation: Avoid/Reduce LDR exposures

2. If LDR decreases cancer risk

Regulation: None or minimal, so that

LDR can be used to reduce cancers.

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After we set up regulations, • Be on the lookout for evidence contradicting the

hypothesis used. • If new evidence contradicts the assumed hypothesis,

revise the regulations in accordance with new knowledge.

• Do this promptly, to minimize danger to public from the use of the wrong hypothesis.

What should we do if there is insufficient knowledge of LDR cancer risks?

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Cancer risk in populations exposed to low-dose radiation

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All the data show reduction of cancers following low-dose radiation exposures

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LNT Model: Using radiation cancer risk coefficients averaged for males and females from BEIR VII Report

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Additional Data on Cancer risk in Populations Exposed to Low-dose Radiation

All the data show no increase in cancers or reduction of cancer for low doses.

Cancer Patient Survival after 10-15 cGy total body or half-body irradiation repeated during 5 weeks (Total dose = 1.5 Gy)

Survival following repeated low-dose total body irradiation was as well as or better than

chemotherapy

Addition of Low-dose total body or half body irradiation resulted in better survival than

radiation therapy alone

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Green ovals enclose high radon level areas; Red ovals enclose areas having high lung cancer rates. There is little overlap between red ovals and green ovals.

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Radon Levels and Lung Cancer in UK

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Radon Levels and Lung Cancer in USA

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Note: Iowa is the state that has the highest average radon levels in the USA.

The areas marked as “Exceptions” have high radon levels and high lung cancer rates.

Radon Levels and Lung Cancers in TEXAS

Note: Texas is a state with some of the lowest radon levels in the USA

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Note: California has the second lowest smoking rate in the USA

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Note: Kentucky has the highest smoking rate in the USA

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Kentucky

Note: West Virginia has the second highest smoking rate in the USA

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Ozasa et al. (2012) state: The curvature has become significant with longer observation. Curvature apparently due to lower than expected risks in the 0.3-0.7 Gy range. Doss (2012): A-bomb survivor data more consistent with radiation hormesis than LNT model Dr. Mark Little (NCI) in Debate (Doss, 2014): did not use A-bomb data to claim support for the LNT model. Actions speak louder than words.

Major change in nature of dose-response shape in A-bomb survivor cancer mortality data with recent update.

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Nov 2014 - Scoping Meeting for BEIR VIII report at NAS: No discussion of impact of Ozasa data on LNT model June 2015 - Open Meeting of NRSB at NAS. Dr. Puskin (EPA) said: Not much has changed in the A-bomb survivor data, regarding LDR cancer risk. ICRP, NCRP, UNSCEAR, IAEA, WHO, NRC, CNSC: No recognition of impact of the update on the LNT model. Nobody is on the lookout for evidence contradicting the

hypothesis used, to minimize danger to public from current recommended regulations.

How did advisory and regulatory bodies respond to this major change in A-bomb survivor data?

How about publications claiming LDR increases cancer risk?

•The record of publications that have claimed increased cancer risk from LDR has been pathetic, with their conclusion negated on a later date due to faults identified, corrections to the data/analysis/interpretation, or updates to the data.

•There is not even a single publication with conclusive evidence that LDR increases cancer risk, that has withstood the test of time.

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Conclusion based on current state of knowledge:

LDR reduces cancer risk.

In view of evidence for radiation hormesis, how should we regulate radiation use?

• We should identify types of radiation exposures that can cause harm

• Establish regulations to prevent such radiation exposures

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Acute Radiation Exposures

In view of uncertainties in Data and Dosimetry

Threshold dose could be as low as 35 cGy.

Applying an additional safety factor of 3

Acute dose of 10 cGy can be considered to be well below the threshold dose for increased cancers, and so safe.

Suggested Regulation:

Dose guidance level of 10 cGy for acute exposures.

For acute exposures, the atomic bomb survivor data indicate a threshold dose of ~70 cGy for increased cancer risk (Doss, 2013).

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Radiation Exposures over Extended Periods of Time

• Increased cancers have been observed following radiation exposures over extended periods of time also, but the threshold dose for increased cancers has been higher.

• Cumulative radiation doses, which are clearly carcinogenic in acute exposure situations, have shown a cancer preventive effect.

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Details of Studies and Reference(s) Duration

of

radiation

exposure

Range of

cumulative

doses (Gy)

Threshold

dose (Gy) for

increased

cancers

Cumulative

dose for

reduction

of cancers

Thyroid cancers following diagnostic I-131

administration in children (Hahn et al.,

2001)

A few

weeks

0-7 Gy 1.5 Gy -

Cancer patient survival following periodic

low-dose total-body (or half-body)

irradiation (Chaffey et al., 1976), (Choi et

al., 1979), (Sakamoto, 2004), (Mendenhall

et al., 1989)

5 weeks 1.5 Gy to 3 Gy

whole body or

half-body

2 Gy 1.5 Gy

Second cancers in radiation therapy

patients (Tubiana et al., 2011), (Suit et al.,

2007)

6 weeks 0.05 Gy to 60

Gy to different

parts of body

2 Gy ~0.2 Gy

Breast and lung cancers in TB patients

who underwent repeated fluoroscopic

examinations (Howe and McLaughlin,

1996), (Davis et al., 1989), (Rossi and

Zaider, 1997)

3 years 0-18 Gy Chest 1 Gy for

Breast

Cancer,

2 Gy for

Lung Cancer

~0.8 Gy for

Lung

Cancer

Bone sarcomas in radium dial painters

(Evans, 1974), (Rowland, 1996)

40-50 yrs 0-500 Gy 10 Gy - 30

Lowest threshold dose

- 1 Gy for exposure over 3 years or

~30 cGy for exposure during 1 year

Using a safety factor of 3:

10 cGy per year can be considered to be safe

Suggested Regulation, for exposures over extended periods of time:

Dose guidance Level of 10 cGy per year

Radiation Exposures over Extended Periods of Time

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• Dose Guidance Level is Not a Dose Limit • Guidance means: Caution not to exceed this value

significantly in order to stay in the safe zone • Doses somewhat above guidance level would not be of

concern • If dose guidance level were exceeded by a factor of 2 or

more, could face increased risk of cancer – this should be avoided

• Same dose guidance level for radiation workers and the public. We want everyone to be safe, unlike present regulations that penalize radiation workers with increased cancer risk (according to their own estimations using the LNT model)

Dose Guidance Level of 10 cGy acute Dose or Annual Dose

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New Paradigm of Radiation Protection

• The new paradigm would encourage prospective studies of health effects of LDR

• No more ALARA • But, care in the use of LDR will be mandatory,

to avoid exceeding the dose guidance levels significantly.

• Most current radiation protection regulations and practices would be limited to potential high radiation exposure situations, and would not apply to LDR.

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Big Changes are Ahead … maybe.

• NRC is currently considering three petitions asking it to change the basis of its regulations from the LNT model to the radiation hormesis model, rather than dismissing the petitions.

• This is indeed unexpected, encouraging news and may portend forthcoming changes.

• Comments so far have overwhelmingly supported the move away from the LNT model.

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Questions:

• How can we speed up the change?

• How do we convince advisory bodies and regulatory agencies to recognize the evidences and accept change?

• How do we convince the public that LDR is safe?

• How do we convince governments to act?

Please give your opinion on the presentation by clicking on the link: https://www.surveymonkey.com/r/futrpreg

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