This set of Clinical Science Multiple Choice Questions & Answers focuses on “Radiation Therapy – Basic Physics, Oxygen Effect”.
1. The process of destroying cancer cells with the help of radiation is ________
Explanation: Radiotherapy is the process by which the cancerous cells of the body are killed. They use radiations mostly X – Rays and sorts. Sometimes, chemotherapy and radiotherapy are combined together. Chemotherapy uses drugs to reduce the activity of the cancerous cells while the radiotherapy destroys them.
2. Which of the following pair of scattering is important for therapeutic purposes?
a) Coherent and Pair Production
b) Photoelectric and Disintegration
c) Compton and Photoelectric
d) Pair Production and Disintegration
Explanation: In pair production, an incoming photon of 1.02 MeV reacts with the nucleus and disintegrates into a positron and negatron. Positron due to high energy and low mass gets repelled from the nucleus and on meeting an electron, annihilation takes place. In disintegration, a high energy photon is absorbed by the nucleus which makes it excited and radioactive. To become stable again, it emits various radiations. Since both these techniques emit a large variety of radiations, they are used to destroy the cancerous cells and thus used for therapeutic purposes.
3. Which of the following pair of scattering is important for diagnostic purposes?
a) Coherent and Compton
b) Photoelectric and Pair Production
c) Compton and Photoelectric
d) Pair Production and Disintegration
Explanation: In Compton effect, an incoming photon transfers a part of the energy to the outermost electron and then scatters off. The electron may get ejected from its shell and come out and is called the Compton electron. In the photoelectric effect, the incoming photon comes and removes the electron and ceases to exist. This photoelectron interacts with the various atoms and atomic particles by ionizing, energizing etc. The energies given off in these processes is recorded and used for diagnostic purposes.
4. Which of the following cells have a low resistance to radiations?
a) Lymphocytes, Spermatogonia, Erythroblasts, Intestinal crypt cells
b) Megakaryocytes, embryo, pancreatic cells, Intestinal crypt cells
c) Lymphocytes, Spermatogonia, hepatic cells, nephrons
d) Megakaryocytes, neurons, cardiac cells, Intestinal crypt cells
Explanation: According to the researches done, the more mature a cell, higher is its resistance to the radiations. Thus, Lymphocytes, Spermatogonia, Erythroblasts, Intestinal crypt cells, which are all fast dividing cells with a smaller life time, they are highly sensitive to radiation, i.e. they have low resistance to radiation.
5. Between the oesophagus and lungs, lungs are more sensitive to radiations.
Explanation: Oesophagus has more rapidly dividing cells as compared to the lungs so the oesophagus is more susceptible to radiations. However, even the lungs are susceptible to the radiations but since their cells divide more slowly, they rank below oesophagus in sensitivity.
6. In the cardiovascular system, which is more affected by the radiations?
d) Cardiac Muscles
Explanation: Same as other tissues, the capillaries which have fast dividing cells are more susceptible to radiations. The cardiac muscles, arteries, and veins are more stable as they are mature cells and so are not so easily damaged.
7. Why are the fast dividing cells more easily targeted?
a) Due to the high protein and carbohydrate content of the cells
b) Due to the higher energy of the cells
c) Due to the low energy of the cells
d) Due to the high oxygen content of the cells
Explanation: If a cell is fast dividing, then it produces and consumes higher energy. Radiations are also a form of energy, they are electromagnetic waves and have the ability to ionize and penetrate. Thus, a high energy cell my end up absorbing the radiations and then end up suffering damage.
8. The machine used for radiotherapy is called as _________
a) Therapeutic X-Ray machine
b) Linear Accelerator
c) Diathermy Machine
d) Radioactive Ultrasound Machine
Explanation: Linear accelerator, also called as linac is used to destroy the cancer cells with the help of radiations. Higher and more sophisticated versions can destroy at the surface level itself and use electrons rather than photons. The linac used the photons and the electrons to damage the DNA of the cancerous cells. Non cancerous cells are able to repair their DNA but the cancerous cells fail to do so.
9. When radiation therapy is done to reduce the effect of cancer, it is called as ______
a) Mutative Treatment
b) Reduction Treatment
c) Palliative Treatment
d) Genesis Treatment
Explanation: This kind of treatment is done to reduce the effect and symptoms of cancer in the body. For eg, treating the cancerous cells in the oesophagus to allow the person to swallow better and eat properly. It is done in the spinal region to stop the impingement of the nerves and reduce pain.
10. What radiations occur when the electrons are used in radio therapy?
a) Ionizing Radiations
b) Gamma Rays
c) Bremsstrahlung Radiation
d) Infrared Rays
Explanation: When an electron moves towards the body, it has charge and energy. On collision with the body, it releases some of its energy and changes its directions. This released energy is given out as radiation. This is Bremsstrahlung Radiation.
11. What is the oxygen effect?
a) Detrimental effect of oxygen in presence of therapeutic radiations
b) A positive effect of oxygen in absence of therapeutic radiations
c) Enhancement effect of oxygen in presence of therapeutic radiation
d) Presence of oxygen during radiation treatment
Explanation: When the radiations are used to destroy the cancerous cells, they inflict a certain amount of damage on the cells at a certain dosage. The same amount of damage is inflicted upon them at a lower dosage in the presence of oxygen. This is called Oxygen effect. It is calculated as a ratio between the damage done in hypoxic conditions to the damage in oxygen conditions.
12. There are two cells, one with OER as 2.5 and other as 7. Which cell is more sensitive to radiation?
a) The cell with OER 2.5
b) The Cell with OER 7
c) Both the cells
d) Insufficient data
Explanation: The cells that have a lower OER are more sensitive to radiation. This is because a higher amount of dosage is required to destroy the cell in hypoxic condition as compared to the amount of dosage required to do the same damage in oxygenated condition.
13. What role does oxygen play?
a) It causes a damage to the DNA
b) It oxygenates the cells that have undergone necrosis
c) It regulates the work of free radicals
d) It reduces the tumour size
Explanation: When radiation strikes the cells, it ionizes the water molecules and they break into H and OH ions. These ions are charged with energy due to the radiations and they attack the DNA of the cancerous cells and damages them. In the presence of oxygen, this process is accelerated and also the damage inflicted on the DNA is brought under control. The oxygen reacts with the free hydrocarbon particles and fills up the gaps in DNA allowing it to recover properly.
14. Since there is a tumour, we can ensure that there will be oxygen present.
Explanation: For a tumour to keep growing, it needs oxygen and food. Otherwise, the tumour will die out. Initially, the tumour takes in oxygen and nutrients from the surrounding or the same cells which causes necrosis. As it spreads out, it finally comes in contact with blood vessels which ensures that the tumour receives blood which provides it with oxygen and nutrients. Thus, the oxygen levels in the tumour regions are higher than normal.
15. Batch of cells labeled as A: In the hypoxic condition, the amount of dosage required is 3 Gy but in oxygenic condition, the amount of dosage needed is 2.
Batch of cells labeled as B: In hypoxic condition, the amount of dosage required is 30 Gy but in oxygenic conditions, the amount of dosage needed is 10.
From the above information, what conclusions can be drawn?
a) Batch A is not cancerous
b) Batch B has a higher OER
c) Batch A has a higher OER
d) Batch B is cancerous
Explanation: OER for A = 3/2 = 1.5
OER for B = 30/10 = 3
We know that higher the OER, the cells are more resistant to radiation i.e. they are non cancerous but lower the OER, the cells are cancerous. In the same way, if we look at the amount of radiation given to destroy the cells, the amount needed for Batch B is much higher. We know that non cancerous cells are resistant to radiations so even with this we can say that Batch B is non cancerous. Thus, we can conclude that batch A is cancerous but batch B is not.
Sanfoundry Global Education & Learning Series – Clinical Science.
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