Radiation Therapy Quiz

Explanation
The necessary field width at the skin surface can be calculated by adding the tumor width (3.5 cm) and twice the additional coverage (1 cm on each side). So, the total field width would be 3.5 cm + 2 cm = 5.5 cm. However, the question specifies that a linear accelerator with the isocentric setup is being used. In this setup, the field width is reduced by 5% to account for beam penumbra. Therefore, 5% of 5.5 cm is 0.275 cm, which when subtracted from 5.5 cm gives us 5.225 cm. Rounding this value to the nearest hundredth, we get 5.23 cm, which is closest to the given answer of 5.28 cm.

Explanation
The field size on a film can be calculated by multiplying the collimator setting by the magnification factor. In this case, 7 cm (collimator setting) multiplied by 1.33 (magnification factor) equals 9.31 cm. Since the answer choices are given in whole numbers, the closest answer is 9x25 cm.

Explanation
The dose rate on a linac machine decreases as the distance from the source increases. In this case, the dose rate at 100 cm is given as 102.4 cGy/Min. Since the distance at 85.5 cm is smaller, the dose rate would be higher than 102.4 cGy/Min. Among the given options, the closest value to a higher dose rate is 140 cGy/Min, which is the correct answer.

Explanation
The magnification factor is the ratio of the actual size of an object to its size on the film. In this case, since the film is taken at 133 cm, the magnification factor is 1.33 cm. This means that the size of the object on the film is 1.33 times larger than its actual size.

Explanation
The dose per fraction can be calculated by dividing the total dose (6300 cGy) by the number of fractions (42). In this case, 6300 cGy divided by 42 equals 150 cGy/fraction.

Explanation
The total dose is 5760 cGy and the daily dose per port is 90 cGy. To find the number of daily treatments, we divide the total dose by the daily dose per port. 5760 cGy ÷ 90 cGy = 64. Therefore, the patient will receive 64 daily treatments. However, since the fields are equally weighted, the patient will receive half of the treatments from each field. Therefore, the patient will receive 32 daily treatments from each field.

Explanation
The total dose at d/max can be calculated by multiplying the dose at the isocenter (75 cGy) by the dose at a depth of maximum build-up (83.4 cGy each time the isocenter gets 75 cGy). Since the patient is to receive 2625 cGy from this field, the total dose at d/max would be 2625 cGy multiplied by the ratio of the dose at a depth of maximum build-up to the dose at the isocenter (83.4 cGy / 75 cGy). This calculation results in a total dose at d/max of 2919 cGy.

Explanation
MRI stands for Magnetic Resonance Imaging. It is a process that uses a combination of magnetic fields and radiofrequency waves to generate detailed sectional images of the body. This technique allows healthcare professionals to visualize internal organs, tissues, and structures without the need for invasive procedures or ionizing radiation. MRI is widely used in medical diagnosis and research to detect and monitor various conditions, including tumors, injuries, and abnormalities.

Explanation
Analysis is the correct answer because it refers to the process of examining and evaluating a situation or work in order to understand its cause and effect. It involves breaking down the components, studying the relationships, and drawing conclusions based on evidence and data. This term accurately describes the determination of cause and effect, making it the most suitable answer among the given options.

Explanation
Evaluation is the correct answer because it refers to the process of assessing or judging the quality or value of something, such as work or creation. It involves analyzing and forming an opinion about the strengths, weaknesses, and overall effectiveness of the subject being evaluated. In this context, evaluation would be the most appropriate term to describe the judgment or determination of the quality of work or creation.