Deck 27: Radiation Therapy

Question 1

Which of these statements describes the response of normal and malignant cells to radiation exposure?

A)Normal cells are more sensitive to radiation and slower recovering than malignant cells.
B)Malignant cells are more sensitive to radiation and slower recovering than normal cells.
C)Normal cells and malignant cells both have the same recovery from radiation.
D)Normal cells and malignant cells both have the same death rate from radiation.

Answer 1

Malignant cells are more sensitive to radiation and slower recovering than normal cells.

Question 2

Human skin is very sensitive to radiation. Which of these precautions is taken to prevent the skin from being severely affected while being administered a radiation beam from a source to a tumour?

A)In order to avoid skin damage, the radiation source is injected under the skin.
B)Even though the radiation source is at a distance from the skin, the radiation reaches maximum dose under the skin because of an initial build-up region, which causes lower doses on the skin.
C)The beam is focused so finely with collimators that the skin is damaged, but only in a very narrow area.
D)The source of radiation is placed on the surface of the skin and, because of the initial build-up region, the dose on the skin is lowest.

Answer 2

Even though the radiation source is at a distance from the skin, the radiation reaches maximum dose under the skin because of an initial build-up region, which causes lower doses on the skin.

Question 3

Which of the following particles are NOT used in radiation therapy, a treatment of malignant cells?

A)X-ray photons
B)electrons
C)gamma-ray photons
D)neutrons

Answer 3

electrons

Question 4

What kind of radiation with a linear accelerator (a linac) is employed in the treatment of tumours?

A)gamma rays
B)positrons
C)bremsstrahlung X-rays
D)electrons

Question 5

What fraction of prostate cancer cells will be killed by a single radiation dose of 2 Gy? For prostate cancer, constants á = 0.15 Gy^-1 and â = 0.025 Gy^-2.

A)70%
B)67%
C)33%
D)30%

Question 6

Brachytherapy is a procedure that involves which of the following procedures?

A)physical removal of tumour
B)irradiation of the tumour with high energy electromagnetic waves
C)insertion of radioisotopes directly into the tumour
D)chemotherapy

Question 7

Explain the process of shrinking of the tumour, in time, due to exposure to radiation therapy. How does the average human tumour react to radiation therapy? What model is used to predict the surviving fraction of cells?

Question 8

What is the order of magnitude of energy electron gains in a medical linear accelerator that is accelerated to 99% of the speed of light?

A)eV
B)keV
C)MeV
D)GeV

Question 9

Which one of the following factors is NOT relevant to the percent depth dose function?

A)beam size
B)beam energy
C)phantom depth
D)tissue to air ratio

Question 10

The isocentre in a Co-60 anti-cancer treatment unit is the place where the tumour is placed and the treatment head rotates around it, delivering beams from various angles.

Question 11

Percent depth dose tells us about the radiation deposited along both the central beam axis and the off axis.

Question 12

Standard geometry of beams in radiotherapy consists of opposing beams that are parallel.

Question 13

A tumour at a depth of 10 cm is treated with a radiation beam delivering 1.86 Gy. What is the percent depth dose function for the tumour if the maximal dose the patient received was 2.3 Gy?

A)0.8%
B)4%
C)12%
D)81%

Question 14

The ratio of radiation dose in tissue (or phantom) and air under the same geometrical conditions, called tissue air ratio function (TAR), does NOT depend on one of the following factors. Which factor does TAR NOT depend on?

A)distance from the source to the surface of the tissue
B)tumour depth in the tissue
C)field size
D)radiation beam energy

Question 15

In a medical linear accelerator, electrons are accelerated using the electric field component of electromagnetic waves from the microwave region.

Question 16

Malignant cells are more resistant to radiation than normal cells.

Question 17

What of these is the setup in the current design of a Co-60 unit, which is used to administer radiation in radiation therapy?

A)The radiation source is placed in a spot called the isocentre, from which the radiation beam is aimed at the patient.
B)The part of the patient's body where the tumour is located is placed in the isocentre, around which numerous sources of radiation are arrayed in a circle, administering radiation from various angles.
C)The part of the patient's body where the tumour is located is placed in the isocentre.The treatment head with a single source of radiation rotates around the isocentre, administering radiation from various angles.
D)The radiation source is placed in a spot called the isocentre, from which the treatment head goes back and forth toward the patient, administering radiation from various angles.

Question 18

To test radiation transport through human tissue, a container of water is used as a simulation of actual human tissue.

Question 19

A tumour is treated with a Co-60 unit. TAR for the position and the field is determined to be 0.80. What is the administered dose of radiation if the treatment lasts 92 seconds? The machine's in-air dose rate at the isocentre is 1.50 Gy/min.

A)1.8 Gy
B)2.9 Gy
C)49 Gy
D)1.1 × 10² Gy

Question 20

Only X-rays and gamma rays are used in radiation therapy.

Question 21

Briefly explain the advantage of using the tissue air ratio (TAR) function rather than the percent depth dose (PDD) function as a parameter of a radiation beam administered in radiation therapy of a tumour.

Question 22

Describe the role of radiotherapy in treating a brain tumour.

Question 23

How many cancer cells will survive this dose of radiation? Radiation is administered in a dose of 2 Gy. For palpable human cancer, take the initial number of cells to be 10⁹, and constants á = 0.15 Gy^-1 and â = 0.025 Gy^-2.

Question 24

What is the penumbra effect of a Co-60 medical device, what is it good for, and what are its disadvantages?

Question 25

Briefly explain the procedure and benefits of brachytherapy.

Question 26

Briefly describe the linear-quadratic model.