Tag: alara

21 Apr 2021

Deterministic vs. Stochastic Effects

Ionizing radiation is useful for diagnosing and treating a range of health conditions–broken bones, heart problems, and cancer, for example.  Medical imaging with x-rays, diagnostic radiopharmaceuticals, and radiation therapy are often life-saving procedures. However, the accidental or misuse of medical radiation can sometimes cause unforeseen and unfortunate consequences.  Radiation protection guidelines and policies help to ensure the safe use of radiation in the medical setting for both patients and staff.

Health effects of ionizing radiation are usually classified into two categories: deterministic and stochastic.

Deterministic Effects


According to the International Atomic Energy Agency (IAEA), a health effect that requires a specific level of exposure to ionizing radiation before it can occur is called a deterministic effect. The severity of a deterministic effect increases as the dose of exposure increases and considers a minimum threshold, below which no detectable clinical effects occur. This type of effect is predictable and reproducible.  For example, localized doses to certain parts of the body at increasing levels will result in the same biological effects.

Deterministic effects are caused by severe cell damage or death. Individuals who experience the physical effects of this cell death do so when it is large enough to cause significant tissue or organ impairment.

Deterministic effects are short-term, adverse tissue reactions resulting from a dose that is significantly high enough to damage living tissues.  The severity of a deterministic effect increases with radiation dose above a threshold, below which the detectable tissue reactions are not observed.  Deterministic effects are usually predictable and reproducible.  For example, localized doses to certain parts of the body at increasing levels will result in well-understood biological effects.

Figure 1 Radiation – Deterministic and Stochastic Effects – Image Wisely, March 2017 “How to Understand and Communicate Radiation Risk”

Some examples of deterministic effects include:

  • Radiation-induced skin burns
  • Acute radiation syndrome
  • Radiation sickness
  • Cataracts
  • Sterility
  • Tumor Necrosis

Stochastic Effects


Stochastic effects are probabilistic effects that occur by chance.  An extremely rare stochastic effect is development of cancer in an irradiated organ or tissue.  The probability of occurrence is typically proportional to the dose received.  Stochastic effects after exposure to radiation occur many years later (the latent period).  The severity is independent of the dose originally received. Since many agents in the environment are also known carcinogens, and since many cancers occur spontaneously, it is not possible in most cases to directly link radiation exposure to an observed cancer.  If a population group receives a dose of ionizing radiation at one time, it is therefore not possible to predict who in that group will develop cancer, if any, or to tell if the people who do develop cancer did so as a result of the dose of ionizing radiation or some other lifestyle factor, such as smoking.   

Examples of stochastic effects include:

  • Cancer
  • Heritable or genetic changes


Dose Limits and Radiation Protection


In our day-to-day lives, we are exposed to both background and manmade sources of radiation.  Everyone receives radiation exposure from natural cosmic and solar rays, and radionuclides in soil.  The benefits of diagnostic and therapeutic medical radiation far exceed the risks.  Fortunately, the health risks associated with natural background levels are small, and by regulations, we are protected from man-made radiation.  The National Council on Radiation Protection and Measurements (NCRP) recommends dose limits for managing exposures to ionizing radiation and protecting humans from adverse effects.  Their purpose is to prevent acute and chronic radiation-induced tissue reactions (deterministic effects) and to reduce the probability of cancer (stochastic effect) while maintaining the benefits to people and society from activities that generate radiation exposures (NCRP Report No. 180, 2018).

Type of limitRadiation workerPublic
Stochastic limits Effective dose, whole body (mSv/year) 501
Deterministic limits Tissue absorbed dose (mGy/year)
Lens of the eye5015
Skin500
Extremities (hands and feet)500

Figure 2.  Values from NCRP Report No. 180, Management of Exposure to Ionizing Radiation:  Radiation Protection Guidance for the United State (2018).

The concept of dose limits also takes into account the ideas that any use of radiation should do more good than harm, and that permissible exposures should be maintained “as low as reasonably achievable” (ALARA).   In line with this philosophy, medical professionals strive to minimize medical radiation exposures to patients without compromising imaging quality and therapy effectiveness. 

Conclusion


Adverse health effects can occur after exposure to ionizing radiation.  For radiation protection, scientific advisory organizations have recommended dose limits to prevent deterministic effects and reduce the probability of stochastic effects in radiation workers, medical professionals, patients, and other members of the general public. 


Sources:

  1. https://hps.org/publicinformation/ate/faqs/regdoselimits.html
  2. https://www.nrc.gov/reading-rm/basic-ref/glossary/non-stochastic-effect.html
  3. https://www.nrc.gov/about-nrc/radiation/around-us/uses-radiation.html
  4. https://www.radioactivity.eu.com/site/pages/Deterministic_Effects.htm
  5. https://www.imagewisely.org/Imaging-Modalities/Computed-Tomography/How-to-Understand-and-Communicate-Radiation-Risk
  6. https://www.radiation-dosimetry.org/what-is-dose-limit-radiation-definition/

08 Apr 2021
X-ray Technician Behind Shielding

ALARA: The Gold Standard of Radiation Protection

The ALARA principle is a relatively simple safety protocol designed to limit ionizing radiation exposure to workers from external sources.

This principle was established by the National Council on Radiation Protection and Measurements (NCRP) in 1954 in response to the atomic bombings of Hiroshima and Nagasaki and the increased interest in nuclear energy and weaponry post-WWII. The philosophy has been refined over the years by different regulatory agencies such as the Atomic Energy Commission (AEC) and Nuclear Regulatory Commission (NRC) as more knowledge about radiation and its effects on living tissue has come to light. In its current form, ALARA stands for “as low as reasonably achievable” and is considered the gold standard for radiation protection.

ALARA is based on the idea that any amount of radiation exposure, big or small, can increase negative health effects, such as cancer, for an individual. It is also based on the principle that the probability of occurrence of negative effects of exposure increases with cumulative lifetime dose. As such, the ALARA principle is considered a regulatory requirement for all radiation programs licensed with the NRC and any activity that involves the use of radiation or radioactive materials.

Check out VersantCast Episode 3: Linear No Threshold with Dr. Alan Fellman

To successfully implement ALARA principles in your radiation safety program, “it is important that every reasonable effort be made to maintain exposures to radiation as far below the dose limits in this part as is practical consistent with the purpose for which the licensed activity is undertaken, taking into account the state of technology, the economics of improvements in relation to state of technology, the economics of improvements in relation to benefits to the public health and safety, and other societal and socioeconomic considerations, and in relation to utilization of nuclear energy and licensed materials in the public interest.” (10 CFR 20.1003)

Time, Distance, and Shielding


There are three factors to the ALARA philosophy which, when executed correctly, can reduce and even prevent unnecessary exposure: time, distance, and shielding.

Time

Limit the amount of time spent near a radiation source. If you must work near a radioactive source, you should work as quickly as possible and then leave the area to avoid spending more time around the source than necessary.

Distance

Increase the distance between yourself and a radiation dose. The farther away you are, the lower the dose you will receive. In many cases, the dose rate decreases as the inverse square of the distance – when the distance is doubled, the dose rate goes down by a factor of four.

Shielding

Put a barrier between you and the radiation source. The type of barrier will depend on what kind of radiation source is being emitted but should be made of a material that absorbs radiation such as lead, concrete, or water. This can also include PPE such as thyroid shields and lead vests.

Conclusion


The ALARA principle has successfully limited exposures to workers—and patients undergoing medical procedures involving radiation—for several decades. Adhering to this principle as well as your state’s radiation safety regulations will result in keeping workers healthy and protected.

Visit our website for more information on how Versant Physics’ board-certified health physicists, medical physicists, and radiation safety officers can help you implement safe practices in your radiation safety program.

Sources

  1. https://nucleus.iaea.org/sites/orpnet/resources/frquentlyaskedquestions/Shared%20Documents/faq-list-en.pdf
  2. https://hps.org/publicinformation/ate/q8375.html
  3. https://www.cdc.gov/nceh/radiation/alara.html#shielding
  4. https://www.nrc.gov/reading-rm/basic-ref/glossary/alara.html
  5. http://large.stanford.edu/courses/2015/ph241/baumer2/

Permits

THE PERMISSION SYSTEM FOR INVENTORY TRACKING, MACHINE MANAGEMENT & EQUIPMENT CATALOG MODULES

Permit Profile

Each permit has a dedicated profile of information that includes authorized personnel, radioactive material, machines, and devices. Permit conditions, completed audits, and forms are also found on this profile.

Authorized Condition Database

Create and view authorized conditions included on permits. Previously created authorized conditions are listed with their code, category, and description.

Permit Enforcement

Information specified on a permit not only serves as a record of that permit, but also controls what can be added to other modules. The location, owner and type of radioactive materials, machines, and equipment can be enforced by permits.

Permit Audits

Perform permit audits, mail the results to relevant personnel, and track responses to non-compliances.