Humans are constantly exposed to radioactivity at an average of 2.7mSv (millisieverts) yearly and further dosage of a few mSv is not worrying. This is because radio waves travel through most things including our bodies without posing any harm. Light waves are an example of a form of radiation and are essential to life. Moreover, the air that we breathe is radioactive due to the cosmic rays entering the atmosphere creating a cabon-14 carbon dioxide but it is slowly turned into normal carbon. However a single dosage of 1000 mSv is possible in causing temporary radiation sickness such as nausea and vomiting.
Ionising radiation is the most energetic radiation and is very dangerous as it can ionise material in the body. Although most of the ionisations are harmless, there are chances that the ionisation of DNA can cause cancer. The main components from the spectrum are atoms emitted from radioactive material such as Alpha particles, Beta particles (electron), neutrons, gamma rays and x-rays. Ultra-violet radiations are less dangerous but it is known to cause skin cancer.
Injury to living tissue resulting from exposure to radiation may include the production of free radicals, breaking of chemical bonds, production of new chemical bonds such as cross-linkage between macromolecules and damage to vital cells such as DNA and RNA. Cells can repair the damage to a certain extent at low dosages such as daily background radiation but higher exposure results in the death of the cell and extremely high exposure kills of cells and it cannot be replaced quickly enough leading to the failure of the tissue function.
Ionizing radiation affects the DNA by ionizing the water molecule in the body producing free radicals. The free radical produced reacts strongly with other molecules as it seeks to restore into the stable configuration of electron. A free radical drift about up to 1x1010 (about 1x10-5 of a second) times longer than the time needed for the initial ionization thus increasing the chance of disruption the DNA molecule.
Long-term exposure to radiation may alter the DNA code causing mutation due to the error in the DNA blueprint. The effect of mutation is very much dependent on the nature of the error and the way it is read. Since it is of a random process, such effects are called stochastic. Two important stochastic effects of radiation are cancer which is a result from the mutation of the nongerm cells (somatic cells) and heritable changes which is the mutations in germ cells. The error produced in the DNA blueprint contributes to eventual loss of control of cell division causing the cells to divide uncontrollably.
There is about 0.005% per millisieverts chance of getting cancer from radiation over a lifetime. An average person receives about 200mSv over a lifetime and the chances of this cancer causing radiation are therefore 0.005% of 200mSv which is 1%. This means that 1% of the people will die from cancer caused by natural radioactivity.
Skin cancer is a type of cancer caused by ultraviolet (UV) radiation. Basically, UV rays have higher energy than visible light, but lower than x-rays. The energy contained in UV rays is enough to damage the DNA in human cell which will lead to cancer. However, it will not have adequate energy to penetrate deep into the human’s body (American Cancer Society, 2010), and thus skin will be the most affected part.
Ultraviolet rays can be divided into 3 categories which are:
1. UVA rays
- UVA are the weakest UV rays which do not absorb by the ozone layer. It will reach the ground and attack the deeper layer of the skin which is the dermis layer (Brannon H., 2008), which causes aging in the skin cells and indirectly, it causes damage to the DNA cells. This may lead to skin cancer in a person.
2. UVB rays
- UVB rays are slightly stronger than UVA rays. This type of UV rays can also cause some skin cancers by damaging the cell’s DNA directly. Epidermis layer will be affected and causes sunburn in a person (Brannon H., 2008).
3. UVC rays
- UVC rays are the strongest UV rays which do not contribute to skin cancer due to its absence in the sunlight (American Cancer Society). This is because it has reacts with the ozone and almost completely absorbed by the ozone layer, and thus it does not reaches the ground.
DNA is a chemical which is found in all the cells that makes up the gene. Some of these genes are used to control the growth, division, and even the death of the cells. UV rays from sunlight or man-made sources can cause damage to the DNA and affect the genes in the cells. The affected gene which controls the life cycle of the cells may cause the formation of abnormal DNA (American Cancer Society, 2011), which may lead to cancer. If the radiation is at low amount, no abnormal DNA is formed due to the repair of damaged cells by the gene. Nowadays, there are many researches done on DNA in human body. However, not all the changes in all type of DNAs can lead to skin cancer. From the scientists’ researches, changes in the tumour suppressor genes have been found in many types of skin cancers (American Cancer Society, 2011). The typical function of the tumour suppressor genes is to keep the normal growth in cells (American Cancer Society, 2011).
In squamous cell cancer, p53 is the gene that mostly found to be altered in the cells. The p53 tumour suppressor gene is responsible either in the repairing system of damaged DNA or the removal of broken cells (Brannon H., 2008) can be mutated due to the damaged skin cells. As this gene is altered, the abnormal cells can live longer and undergo continuous division (Brannon H., 2008) where more highly damaged cells like cancerous cells are produced. While in basal cell cancer, “patched” (PTCH) gene is always found to be altered (American Cancer Society, 2011). This gene is normally involved in the cell growth in cheek. The mutation in this gene will affect the cell which may allow the cell to grow out of control and causes the development of cancerous cells.
Xeroderma pigmentosa is rare a condition which is passed down from one generation to the next in which the skin and tissue covering the eye of a person are very sensitive to UV light (Medline Plus, n.d.). People suffering from xeroderma pigmentosum (XP) are very susceptible to high risk of skin cancer. This is because the DNA in the skin cells will be damage by the UV radiation and repairing of damage cells are impossible. Hence, the skin becomes thinner and patches with different colours appear (Medline Plus, n.d.). Moreover, spidery blood vessels can be found in the skin for those who having this problem. The skin cancer will normally happen before the patient reaches the age of 5.
Besides that, the combination of UVA and UVB radiation can also decrease the number of the Langerhans cells (Brannon H., 2008), which are important in human immune system. Therefore, the body’s defence system may be reduced where the development of skin tumours is hardly limited by the body.Skin Cancer - How Skin Cancer Develops - What Is a Malignant Melanoma Video
examples of skin cancer are as below:
1. Basal cell cancer (Non-melanoma skin cancer)
Basal cell cancer is usually appears as a small, nodule on the sun exposed parts (Stanford Medicine) such as head, neck, and hands.
[Sources adapted from: Laura J. Martin, 2010]
It is the most common cancer in the United States where more than 90% of the skin cancers are basal cell cancer. However, it will not spread to other part of the body and can be easily detected. Some of the cancer patients had been successfully recovered from this disease. This type of cancer is rarely happen in dark-skinned person compared to fair-skinned person due to the evenly distribution of melanin in the skin of dark-skinned person. The cancer cells will start to grow slowly from the epidermis layer. Hence, it takes very long time to for the cancer cells to develop and it is rarely fatal.
2. Squamous cell cancer (Non-melanoma skin cancer)
Squamous cell cancer is another common type of skin cancer which is also rarely fatal. It is often appears as nodules, or scaly patches of skin (Stanford Medicine). It is normally found on face, lips, and mouth (Stanford Medicine).
Figure 2: Squamous Cell Carcinoma
[Sources adapted from: Menstuff, n.d.]
Figure 3: Squamous cell carcinoma found in the mouth.
[Sources adapted from: Entusa, n.d.]
It is always found in fair-skinned person due to the distribution of the melanin in the skin. It can be spread to other part of the body. However, according to the American Academy of Dermatology, the cure rate for this cancer is 95% (Stanford Medicine).
3. Melanoma skin cancer
Melanoma is a form of skin cancer in which the cancer cells are found in the melanocytes (Stanford Medicine). It is the rarest, but most dangerous form of skin cancer compare to others as it can cause death in a person (Environmental Protection Agency). Melanoma is usually found in adults, but sometime it can also be found in children and adolescents. Melanoma is often appears on fair-skinned person. However, it does not mean that dark-skinned person will not have chances in getting the disease. Development of this cancer in dark-skinned person especially on their palms, soles of the feet, under nail, and even in the mouth are also been found (Stanford Medicine). Besides, a person who has several characteristics such as a changing in the size and colour of moles, many freckles, and long term sun exposure, and inability to tan may has high risk in getting melanoma (Stanford Medicine). Moles that are present during birth and atypical moles will also have a chance to develop into malignant. In order to prevent melanoma, ABCD Chart is suggested as a reference table while diagnosing the present of malignant melanoma at its earliest stage. The warning sign are as below:
[Sources adapted from: Stanford Medicine]
Typically, the characteristic of a mole is used to detect the present of skin cancer. A mole which is changing in size, colour, and shape may be the symptom of melanoma. Bleeding from a mole, itchiness, swelling, and tender touch of a mole might be the symptoms of melanoma too (Stanford Medicine). Other than that, melanoma can also appear on the body as a new mole.
Most of the melanoma tumors are shaded brown or black due to the production of melanin in most of the malignant melanoma cells (Stanford Medicine).
Figure 4: Malignant Melanoma
[Sources adapted from: Stanford Medicine]
This form of cancer can spread very fast throughout the whole body through the lymph and the blood system (Stanford Medicine). Hence, it is best to be detected at the early state so that proper treatment can be applied.
There are several types of treatment used for skin cancers.
1. Surgery - most common method used to treat skin cancer.
2. External radiation
3. Electrochemotherapy
4. Chemotherapy
5. Biological therapy
6. Photodynamic therapy
[Sources adapted from: Stanford Medicine]
Thyroid cancer is a kind of cancer that occurs in the thyroid gland where a lump or nodule forms at the front of the lower neck. There are four major kinds of thyroid cancer which are papillary, follicular, medullary and anaplastic. Causes of thyroid cancer are still yet to be figured out. However, several risk factors have been identified where exposure to high levels of radiation is one of the factors (MedicineNet, n.d.).
Radioactivity is a spontaneous disintegration of atomic nuclei (Thinkquest, 1998) and fallout is the deposition of airborne radioactive contaminants on Earth (Britannica, n.d.). Fallout from a nuclear test involves many kinds of radiation including isotopes of iodine such as I-131, I-133 and I-132. Due to the beta decay of the isotopes, it may cause mutation and even death in cells which it penetrates.
Exposure to the isotopes (mainly I-131) especially during childhood may increase the risk of developing thyroid cancer (National Cancer Institute, n.d.). The risk also increases for people who have had multiple exposures. Research showed that adolescents have higher-than-average risk of developing thyroid cancer years later if they were exposed to radiation (National Cancer Institute, n.d.). A child’s thyroid dose from ingestion can be up to 20 times of an adult due to the same amount of energy is deposited in a smaller tissue mass. A child’s thyroid dose from inhalation can be twice that of an adult and is 15-20 times higher than the overall dose to the rest of the body (ATSDR, n.d.).
Thyroid gland needs iodine to produce hormones that regulate the body’s energy and metabolism (American Thyroid Association, n.d.). Thyroid gland produces several hormones of which triiodothyronine (T3) and thyroxine (T4) are the two main hormones. These hormones help oxygen to diffuse into the cells and make the thyroid gland the master of metabolism (Shomon M., n.d.). In order to carry out its function, thyroid gland will absorb the available iodine from the bloodstream that is obtained through food or supplements and combines it with amino acid tyrosine. Thyroid gland then converts iodine or tyrosine into hormone triiodothyronine (T3) and thyroxine (T4). Once the hormones are released by the thyroid, they travel through the bloodstream and help cells convert oxygen and calories into energy.
When radiation occurs, radioactive iodine is released into the atmosphere which is then inhaled into the body and finally absorbed into the bloodstream. Therefore, thyroid gland will absorb whatever it can as it is not able to distinguish between the stable iodine and radioactive iodine (American Thyroid Association, n.d.). Most of the iodine that enters the body instantly becomes systemic with approximately 30% of it depositing in the thyroid gland (ATSDR, n.d.). When the thyroid cells absorb a very higher amount of radioactive iodine, thyroid cancer eventually developed several years after the exposure where most of the cells are killed to disrupt tissue function (acute health effects) or damaged cells are incompletely repaired but still viable (carcinogenic, tumorigenic) (ATSDR, n.d.).
Research was conducted on the Japanese population after the atomic bombings of Hiroshima and Nagasaki many years back. Reports actually shown that many people at Hiroshima and Nagasaki actually died from the radiation released from the atomic explosion. For example, a fourteen-year-old boy was admitted to a Hiroshima hospital two days after the explosion due to high fever and nausea and he passed away twenty one days later. Survivors of the bombings suffered physically from cancers such as thyroid cancer, and leukemia (Thinkquest, 1998).
Figure 1: Thyroid cancer
[Source adapted from: Pandey A., 2011]
As a conclusion, exposure to radioactivity or radiation may cause cancer towards people but it is dependent on the exposure time as well as the dosage of radiation. It is impossible for us to avoid not being exposed to radiation on our daily basis. As such, precautionary steps should be taken to avoid excessive exposure to sunlight radiation by applying sunblock lotion as well as not exposing the skin to more than 15 minutes of sunlight.
Reference:
1. ACHRE Report, n.d. How Does Radiation Affect Humans? [Online]. Available from: < http://www.hss.energy.gov/HealthSafety/ohre/roadmap/achre/intro_9_5.html > [Accessed by 1st July 2011]
2. Princeton University. Open Source Radiation Safety Training, Module 3: Biological Effects [Online]. Available from: < http://web.princeton.edu/sites/ehs/osradtraining/biologicaleffects/page.htm > [Accessed by 1st July 2011]
3. Regulation, n.d.. Radiation, Radioactivity and Cancer [Online]. Available from: < http://www.regulation.org.uk/radiation.shtml > [Accessed by 1st July 2011]
4. American Cancer Society, 2010. Radiation Exposure and Cancer [Online]. Available from: < http://www.cancer.org/cancer/cancercauses/othercarcinogens/medicaltreatments/radiation-exposure-and-cancer > [Accessed by 1st July 2011]
5. American Cancer Society, 2011. Skin Cancer: Basal and Squamous Cell [Online]. Available from: < http://www.cancer.org/Cancer/SkinCancer-BasalandSquamousCell/DetailedGuide/skin-cancer-basal-and-squamous-cell-what-causes > [Accessed by 11th July 2011]
6. Environmental Protection Agency. Health effects of overexposure to the sun, SunWise Program [Online]. Available from: < http://www.epa.gov/sunwise/uvandhealth.html#sc > [Accessed by 1st July 2011]
7. Entusa, n.d. Oral (Mouth & Throat) Photographs [Online]. Available from: < http://www.entusa.com/oral_photos.htm > [Accessed by 10th July 2011]
8. Heather Brannon, MD, 2008. UV Radiation [Online]. Available from: < http://dermatology.about.com/od/skincancers/a/UV_radiation.htm > [Accessed by 1st July 2011]
9. Laura J. Martin, MD, 2010. WebMD [Online]. Available from: < http://www.webmd.com/skin-problems-and-treatments/slideshow-summer-skin-hazards > [Accessed by 10th July 2011]
10. Medline Plus, n.d. Xeroderma pigmentosa [Online]. Available from: < http://www.nlm.nih.gov/medlineplus/ency/article/001467.htm > [Accessed by 11th July 2011]
11. Menstuff, n.d. Skin Cancers [Online]. Available from: < http://www.menstuff.org/issues/byissue/skincancers.html#top > [Accessed by 10th July 2011]
12. Stanford Medicine, Cancer Institute. Information about Basal Cell Carcinoma [Online]. Available from: < http://cancer.stanford.edu/skincancer/skin/types/basal.html > [2nd July 2011]
13. Stanford Medicine, Cancer Institute. Squamous Cell Carcinoma [Online]. Available from: < http://cancer.stanford.edu/skincancer/skin/types/squamous.html > [2nd July 2011]
14. Stanford Medicine, Cancer Institute. Information About Melanoma [Online]. Available from: < http://cancer.stanford.edu/skincancer/skin/types/melanoma.html > [Accessed by 2nd July 2011]
15. Stanford Medicine, Cancer Institute. Skin Cancer Treatment [Online]. Available from: < http://cancer.stanford.edu/skincancer/skin/treatment.html > [Accessed by 2nd July 2011]
16. Video of Types of Skin Cancer [Online]. Available from: < http://video.about.com/dermatology/Skin-Cancer.htm > [Accessed by 10th July 2011]
17. American Thyroid Association, n.d.. Nuclear Radiation and the Thyroid [Online]. Available from: <http://www.thyroid.org/patients/patient_brochures/nuclearradiation.html> [Accessed on 10 July 2011]
18. Ankit Pandey, 2011. Symptoms of thyroid cancer [Online]. Available from:
19. ATSDR, n.d.. Radiation Exposure from Iodine 131 [Online]. Available from: <http://www.atsdr.cdc.gov/csem/csem.asp?csem=23&po=6> [Accessed on 10 July 2011]
20. MedicineNet, n.d.. Thyroid cancer [Online]. Available from: <http://www.medicinenet.com/thyroid_cancer/article.htm> [Accessed on 10 July 2011]
21. National Cancer Institute, n.d.. Radioactive I-131 from Fallout [Online]. Available from:
22. Thinkquest, 1998. Radioactivity [Online]. Available from: <http://library.thinkquest.org/17940/texts/radioactivity/radioactivity.html> [Accessed on 11 July 2011]
No comments:
Post a Comment