What is radiation?

Radiation can be described as the energy in the form of a particular matter or electromagnetic waves traveling in the air and can be in the form of light, sound, and heat. Radiation can be detected through special instruments like X-rays. The radiation from a cooler object is less intense as compared to the radiation from hot objects.

What are the sources of radiation?

There are following two sources of radiation:

  • Natural radiation
  • Man-made radiation

Natural radiation

Natural radiation consists following three kinds of radiations:

Cosmic radiation

All living things on the Earth are continually attacked by radiation from outer space. When the charged particles (proton, electron, or neutron) from the stars and the Sun interact with the atmosphere of the Earth, a magnetic field is produced, which results in a shower of radiation on the surface of the Earth. The quantity of cosmic radiation differs in various sections of the world due to variations in elevation and the Earth's magnetic field influences.

The sun emits a constant stream of cosmic radiation to Earth.
Cosmic radiation

Terrestrial radiation

Radioactive elements are also obtained in nature in water, plants, and clay. The significant radioactive material comprises thorium, uranium, and isotopes of potassium, and some radioactive elements are ingested with water and food. The quantity of terrestrial radiation is approximately 50 mrad/year.

Solar radiations coming to the Earth surface and reflected back to atmosphere.
Terrestrial radiation

Internal radiation

People are exposed to radiation from radioactive material inside their bodies. Potassium-40, which is the most important naturally occurring internal radioactive material, besides radon. Other radioactive materials that are found in human bodies are carbon, thorium, strontium, and uranium. The quantity of internal radiation is approximately 25 mrad/year that may go up to 70 or 80.

Man-made radiation

Some examples of man-made sources of radiation to members of the public are as follows:

  • Coal power plants
  • Radium watches
  • Tobacco
  • Televisions
  • Phosphate fertilizers
  • Nuclear power plants
  • Medical diagnosis
  • Building materials
  • Lantern mantels

Types of radiation

There are following two kinds of radiations:

  • Ionizing radiation
  • Non-ionizing radiation

Ionizing radiation

Ionizing radiation is a kind of radiation that is capable of obstructing molecules and atoms on which they move , providing a start to free radicals and ions. It has a low wavelength but high penetration power and can damage the living cells by ionizing them. Examples of ionizing radiation are gamma rays, beta particles, alpha particles, cosmic rays from the Sun, and x-rays.

Non-ionizing radiation

Non- ionizing radiation is a kind of radiation that is not as energetic as ionizing radiation and cannot remove electrons from molecules or atoms. It is considered as the electromagnetic waves that are inadequate of creating ions while moving within a matter due to their low energy. Visible light, infrared radiation, televisions and radios, power transmission, microwaves, and ultraviolet lights are some common sources of non-ionizing radiation.

Radiation therapy

Radiation therapy may be described as a treatment modality for cancer. Radiation therapy employs high-energy radiations that cure cancer by destroying the cancerous cells, relieving pain, and alleviating other cancer-related symptoms. When the infected cancer cells are damaged by radiation therapy, the body naturally rejects the cancer cells. Healthy cells can be influenced by radiation therapy, but they are capable of improving themselves. Seldom radiation therapy is considered as the only therapy a patient requires, and other times, radiation therapy is coupled with different treatments, like chemotherapy and surgery.

Overview of radiation therapy

Illustration of external beam radiotherapy.
Radiation therapy

Radiation therapy also termed radiotherapy, x-ray therapy, or irradiation is a broadly utilized cancer medication with a huge success rate. This employs high-speed and high-energy radiation particles, often in the form of x-rays that damage the cancer tissues. A radiation oncologist prescribes radiotherapy either as a primary treatment option or treatment in combination with other therapies. Other cancer therapies like chemotherapy are done by taking drugs via oral or injection route, and the whole body gets exposed to the drug leading to many side effects. However, radiation therapy will focus only on the target area and reduce side effects. 

Principle of radiation therapy

Radiations of x-rays and protons deliver huge quantities of high energy through ionization. The strong ionization forces can remove the electron from its atom and destroy the cancer tissues by attacking the genetic material, thereby preventing them from cell division and growth. Radiation therapy should be done specifically to target the cancer cells without harming neighboring healthy cells.

Uses of radiation therapy

Based on treatment goals, radiation therapy can be applied in the four following ways:

Primary/Palliative therapy

  • To treat or shrink (reduce) the spread or intensity of early-stage cancer.
  • Reduce the tumor size.

Adjuvant/combination therapy

It is used in combination with other treatment options.

Neoadjuvant therapy

It is used as a pre-operative procedure.


It is used as a drug that facilitates radiation.

Treatment process

Medical Decision Making

Choosing a suitable cancer medication depends upon the type of cancer, tumor size and location, areas surrounding the tumor, overall health, age, other illnesses, and treatments.

An appropriate medical decision is taken after:

  • Defining treatment goals
  • Understanding side effects
  • Weighing pros and cons
  • Being aware of chances of remission and improved survival rate with the treatment; quality of life after treatment
  • Considering personal choices

Imaging tests like CT and MRI guide the radiation oncologists to locate and view the shape and boundaries of tumors and define treatment.

Treatment goals

  • Reduce tumor size, intensity, and metastasis of cancer.
  • Treat and prevent recurrence and metastasis of cancer.
  • Reduce symptoms of headache, dizziness, and nausea associated with cancer.

Treatment Team

Radiation oncologist, medical radiation physicist, radiation oncology nurse, dosimetrist, therapists, technologists, dieticians, and social workers.

Treatment steps

  • Verification and explanation of the process to the patient by the RT team
  • Simulation scan
  • Informed consent
  • Patient positioned and protected
  • Contrast administration - IV or oral routes
  • Fixed units of radiation delivered as planned

Treatment dose

In the standard international system, the effective dose and radiation absorbed dose for the determination of radiation practices sievert (Sv) and gray (Gy), sequentially. The treatment dose is based on therapy goals.

Prognosis of radiation therapy

Modern technological devices, 3-D imaging, computerized treatment makes radiation therapy highly effective, with good treatment outcomes like survival rate (more than 95%) and the metastasis-free period.

Side effects of radiation therapy

Side effects arise mainly due to radiation exposure on larger area coverage affecting many organ systems like:

  • Skin: Redness, soreness, itching, sunburn, swelling, blisters, peeling, etc.
  • Head and neck: Dry mouth, difficulty swallowing, headache, dry mouth, hoarseness of throat, sore throat, tooth decay, change in taste.
  • Chest: Cough, shortness of breath, swallowing difficulties.
  • Abdomen: Nausea and vomiting, diarrhea.
  • Pelvis: Frequent urination, irritation of the bladder.
  • Endocrine: Hormonal changes.

Post therapy

The normal life of a person after receiving radiation therapy:

  • It becomes extremely challenging with physical changes (hair loss) and psychological stress (depression); proper counseling and support are necessary; various forms of cancer support groups are available.
  • Coping with cancer and its treatment is an extremely difficult ordeal. Living a new normal life should be adopted.
  • Any official, legal, or financial issues due to prolonged illness and treatment conditions should be managed properly.

General care

  • Call emergency services or seek medical advice immediately if any trouble breathing, excessive sweating, seizures, sudden extreme confusion, fainting, or any worsening of symptoms.
  • A healthy balanced diet along with supplements as advised; small but frequent meals; low-fiber, bland and soft foods.
  • Good hydration.
  • General hair care for any hair loss.
  • Adequate rest to cope with fatigue.
  • Moisten dry mouth or lips.
  • Medications: OTC drugs, herbal remedies, supplements can be taken under medical supervision.

Common Mistakes

Students get confused between ionizing radiation and non-ionizing radiation. Ionizing radiations are huge energy radiation, which can ionize an atom upon colliding with it to emit more radiation. In contrast, non-ionizing radiations are low-energy radiation which does not release particles from other materials.

Students also get confused between chemotherapy and radiotherapy. Chemotherapy is a method of killing cancer cells using certain chemicals, while radiotherapy uses high-energy radiation to treat cancer.

Context and Applications

The topic of radiation is very much significant in the several professional exams and courses for undergraduate, diploma level, graduate, and postgraduate. For example:

  • Bachelor of Science in Biology
  • Bachelor of technology in Mechanical Engineering
  • Master of technology in Mechanical Engineering
  • Conduction
  • Convection
  • Heat transfer
  • Radiation effect
  • Medical applications of radioactivity

Practice Problems

Q1: The alpha particles have relatively:

(a) High kinetic energy

(b) Low kinetic energy

(c) High potential energy

(d) None of these

Correct option: (a)

Explanation: The alpha particles include high kinetic energy because of the mechanism of these particles in the radioactive decay process.

Q2: Among the four options, which one is the strongest ionizing radiation?

(a) X-rays

(b) Beta

(c) Gamma

(d) Alpha

Correct option: (d)

Explanation: The alpha particles are composed of the greatest ionizing radiation compared to beta, gamma, and x-rays because of their 2 positive charges as well as these particles are comparatively slow.

Q3: Radiation emitted by radioactive elements is

(a) Gamma

(b) Beta

(c) Alpha

(d) All of above

Correct option: (d)

Explanation: Radioactive elements eject all 3 types of radiation that is alpha, beta, and gamma.

Q4: Perfectly black body has an emissivity of

(a) 0.5

(b) 1

(c) 0.75

(d) 0

Correct option: (b)

Explanation: The perfect blackbody can be represented as the body that absorbs light entirely without reflecting. Also, the emissivity of perfectly black body is equivalent to 1.

Q5: Heat transfer method that does not need any medium

(a) Convection

(b) Radiation

(c) Conduction

(d) None of these

Correct option: (b)

Explanation: The transferring of radiation is quite similar to the movement of electromagnetic waves, which doesn't require any certain medium. So, radiation doesn't need any medium to transfer.

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