LNT stands for “Linear No Threshold,” a hypothesis that populates exposure to ionizing radiation is directly proportional to cumulative lifetime cancer risk. The LNT’s theoretical foundation is based on cancers induced in the Japanese atomic bomb survivors.
People who survived the nuclear explosion were exposed to tens of thousands of Roentgen equivalent man (rems) of radiation. The LNT model theorizes that even a small radiation dose can cause cancer risk. There is a continued debate among scientists, physicists, and health professionals about the efficacy of the LNT model at low doses of radiation.
According to the U.S Environmental Protection Agency (EPA), the average natural background radiation in the United States is 300 millirem per year from soil and rock, cosmic rays, indoor radon, and food people consume daily. The average exposure from medical procedures in the U.S is an additional 300 millirem per year.
Besides, exposure to cosmic rays increases with height or elevation. For example, the round airline trip from Los Angeles to New York City exposes passengers to five millirem – one millirem for every one-thousand mile. Now that you understand the postulation of the LNT model, let us discuss whether it is effective. Read on!
Is LNT Model Effective?
The LNT is the most widely used model to measure ionizing radiation and estimate its biological risks. The model focuses on biological responses at higher radiation doses and dose rates.
Remember, the higher the dose, the higher the biological response. On the other hand, the lower the dose, the lower the response rate. The LNT model assumes a more straightforward relationship between radiation and biological risks – a straight line. That’s why researchers call it the linear no-threshold model.
A study published by the American Journal of Roentgenology highlights that the linear relationships that exist between dosage and cancer risk have different assumptions, including:
A linear relationship exists between the breakage of double-stranded DNA and the likelihood of cancer development
The risk of cancer is linearly proportional to the radiation dose
Doses outweigh biological variables
Doses are more critical than dose rates
There is no threshold because the risk is additive
The linear no-threshold model has numerous odd paradoxes. Unfortunately, many medical practitioners, health professionals, scientists, and proponents of the LNT model ignore these inconsistencies. Let us now discuss these uncertainties.
A Cumulative Risk Model
The linear no-threshold model is a cumulative risk model. It means lifetime background exposure to radiation is 300 x 85/ 1000 = 26 rem. So, the lifetime risk of cancer from the background radiations 2.6%. In Math, it is 0.001 x 26 = 0.026 = 2.6%.
A Population Risk Model
Because the linear no-threshold is a population risk model, if one-thousand individuals receive 1-rem of radiation exposure, the model says only one person will develop cancer. In addition, if forty people receive 26rem of background radiation in their entire lives, one person will develop radiation-induced cancer.
Of the 329.5 million people living in the United States, about 8.2 million individuals have the risk of developing cancer from background radiation during their lives. Remember, this estimation is valid when you believe in the efficacy of the LNT model.
However, the LNT model’s hypothesis is not valid because if this epidemic were true, health professionals and the public would demand the government supply them with vests to protect them from the deadly radiation.
Radiation Risk is Stochastic
A research study published on PubMed (NCBI) states that the radiation risk is stochastic. It means the risk is statistical and deals with chronic exposures and effects. For example, the LNT model focuses on long-term cancer effects.
On the other hand, the model does not apply to deterministic or non-stochastic short-term effects because high-level radiation exposures result in instantaneous effects. The concept is also known as radiation poisoning.
So, we can’t say the same for the alcohol risk analogy because it is not a population model and stochastic/statistical process. The reason is that it is more analogous to deterministic short-term radiation poisoning.
Moreover, exposing 2,000 people to 1-rem of radiation will cause cancer in two individuals. According to the LNT’s population aspect of the model, this will theoretically leave 1,998 of 2,000 people with no cancer.
The LNT’s radiation risk model that focuses on the population aspects can lead to invalid conclusions. According to the American Nuclear Society (ANS) and Health Physics Society (HPS), there is no research evidence of harmful effects below a lifetime dose of 10-rem.
Therefore, these organizations warn scientists and health physicists to apply the LNT’s population model because it generates an unrealistically higher number of cancers and a higher number of deaths subsequently.
Is the LNT model accurate?
Some scientists believe that it is, while others believe it is not. The LNT model is based on the assumption that all ionizing radiation is harmful and that there is no safe level of exposure. This model is used to estimate cancer risk from exposure to ionizing radiation.
However, some scientists believe that this model is inaccurate because it does not consider the different types of ionizing radiation and how the body responds.
What are the methods of radiation protection?
Radiation protection is the scientific discipline concerned with the safe handling and disposal of radioactive materials.
There are several methods of radiation protection, including the use of lead shielding, distance, and time.