How much radiation does Scrutiny of the increasing use of CT scans - - PDF document

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How much radiation does Scrutiny of the increasing use of CT scans - - PDF document

Jan 17, 2023 31 likes •91 views

10/6/2017 Recent history of radiation safety Risks of Radiation In 2012, American Board of Internal Medicine Foundation launched the Choosing Wisely Exposure: Myths vs Reality initiative - to avoid wasteful or unnecessary medical tests,

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Risks of Radiation Exposure: Myths vs Reality

Sue S. Yom, MD, PhD, MAS Associate Professor, UCSF Radiation Oncology

Recent history of radiation safety

  • In 2012, American Board of Internal Medicine

Foundation launched the Choosing Wisely initiative - to avoid wasteful or unnecessary medical tests, treatments, and procedures

  • American College of Radiology launched the

Image Wisely campaign - to eliminate unnecessary imaging and use the minimum amount of radiation needed for an indicated test

Scrutiny of the increasing use of CT scans

  • Doctors rely more on scans as the technical quality

and speed of imaging have improved

  • Annual growth of around 8% in the use of CT scans

in the past decade

  • Physicians mostly decide when to order tests with

little standardized guidance

  • Voluntary guidelines are a weak lever to change

physician practice behavior

  • Institutions have little incentive to reduce scanning

How much radiation does a person really receive

rem = roentgen equivalent man

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How much radiation does a person really receive

  • Radiation is everywhere – in space, in the ground, in our food,

water, air, homes and in our own bodies

  • Average U.S. resident receives annual exposure of 620 mrem
  • Natural and internal sources = 310 millirem
  • 2/3rd = radon and thoron gases from Earth’s crust and in the air
  • 1/3rd = cosmic, terrestrial, and internal radiation (food and water)
  • Manmade sources = 310 mrem
  • 150 mrem from CT scan
  • 150 mrem from other medical procedures
  • 10 mrem from tobacco, fertilizer, welding rods, exit signs,

luminous watch dials and smoke detectors

Examples of “natural” radiation

  • Foods such as bananas and Brazil nuts contain

higher levels of radiation

  • Brick and stone homes have higher radiation levels

than wood homes

  • The U.S. Capitol is largely built of granite and

contains radiation

  • Colorado has more cosmic radiation because of its

altitude and it has more terrestrial radiation from soils rich in uranium

Examples of “internal” radiation

  • All organic plant and animal

matters contains radioactive potassium-40 (40K), radium-226 (226Ra), and other isotopes

  • All water on Earth contains

small amounts of dissolved uranium and thorium

  • Average person receives an

average internal dose of about 30 mrem from food and water

NRC standards

  • Annual average dose per person is 620 mrems
  • U.S. Nuclear Regulatory Commission (NRC)

standards recommend additional exposures of:

  • 5,000 mrem per year for persons working with

and around radioactive material

  • 100 mrem extra per year for members of the

general public

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Personal annual dose calculator

https://www.nrc.gov/about-nrc/radiation/around-us/calculator.html

Personal annual dose calculator

Radiation and cancer

  • Information comes from survivors of the atomic bombs in

Japan or studies of people who have received very large amounts of radiation for medical tests or treatment

  • Exposure >50,000 mrem (500 x the NRC limit for general

public) is associated with leukemia, breast, bladder, colon, liver, lung, esophagus, ovarian, multiple myeloma and stomach cancers

  • Chemical and physical hazards and lifestyle factors

(smoking, alcohol consumption and diet) are related to these same diseases

  • No data showing a link between cancer and doses below

10,000 mrem (100 times the NRC limit)

Therapeutic radiation

  • Gray – total absorbed energy of the radiation
  • Sievert – accounts for type of particles and tissues involved
  • For X-rays and gamma rays 1 mGy = 1 mSv, 1mSv = 100 mrem
  • Dose for radiation therapy ~30,000-60,000 mGy (mSv) =3,000,000-

6,000,000 rem or 3000-6000x the annual NRC max dose

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Cost/benefit of therapeutic radiation

  • Called “radiation oncology” or “radiation therapy”
  • Therapeutic radiation after surgery is usually justified

based on a 20-25% reduction in cancer recurrence

  • Therapeutic radiation (without preceding surgery) is

usually justified for at least 50% chance of cure

  • This is balanced against the known risks of acute

toxicity (usually severe for some weeks) as well as the <1% increased risk of “radiation induced malignancy” over the general risk

Radiation induced malignancy

  • Radiation-induced leukemias (blood cancers)

typically require 2–10 years to appear – much higher risk from chemotherapy rather than radiation

  • Radiation-induced solid tumors usually take 10–15

years to clinically manifest

  • French breast cancer radiation patients:

increased risk of sarcoma of 0.28% to 0.48%

  • United States and Sweden breast cancer

radiation patients: 0.5% increased lung cancer risk but only seen in smokers

Risk is very dependent on individual characteristics

  • Whole body radiation is highest risk; then site specific e.g. highest

risk to testes, cervix, non-limb soft tissue, salivary gland, with low risk to orbit, oral/pharynx/larynx, female breast

  • Recent SEER database study: of 647,672 patients, 60,271 (8%) had

a second cancer but only 3,266 (0.5%) were related to radiation

  • 5 excess cancers per 1000 radiotherapy patients at 15 years after

diagnosis

  • Much greater risks of cancer from lifestyle (e.g. smoking),

carcinogenic exposures, and genetics

  • Persons with complex genetic syndromes e.g. retinoblastoma, are

more susceptible

  • Children and adolescents are twice as likely to develop radiation-

induced leukemia as adults, and live longer to develop solid cancers

de Gonzalez et al, Lancet Oncology April 2011

Radiation safety is based

  • n the ALARA principle
  • ALARA = “As Low As Reasonably Achievable”
  • Radiation protection guidelines are based on the

“linear no-threshold” model of risk

  • Assumes that no dose of radiation is safe – this

model is very conservative and overestimates risk

  • One millisievert (100 mrem)  0.0055% chance of

eventually developing cancer

  • 6.2 mSv (average annual exposure)  0.0341%

baseline risk

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6.2 mSv (average annual exposure)  0.0341% 6.2 mSv (average annual exposure)  0.0341% https://www.acr.org/~/media/ACR/Documents/PDF/QualitySafety/Radia tion-Safety/Dose-Reference-Card.pdf?la=en 6.2 mSv (average annual exposure)  0.0341%

What is being done about CT scans

  • Establish standardized metrics – across health systems or

by national organizations – to assist physicians in ordering

  • nly for high likelihood of benefit
  • University of California CT dose standardization
  • DecisionSelect by the American College of Radiology
  • Penalties – physicians who order more scans than their

peers will be at financial risk

  • Evaluation via Medicare Incentive Payment System

(MIPS) or join an Accountable Care Organization (ACO)

  • MIPS reimbursement penalties will start at 4% at risk in

2019 and increase to 9% by 2022

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Conclusions

  • Awareness of exogenous (non-natural, non-

internal) radiation exposure is increasing

  • Overall the risk to a given individual is very low,

but it is a public health concern on the population level

  • Medical procedures should always be done for

appropriate reasons with consideration of all short and long term effects