25 Questions
What is the purpose of using a tissue equivalent phantom in isodose measurement?
To determine the dose distribution in a specific patient volume
What is the characteristic of the material used to make the phantom?
It has the same atomic number, electron density, and density as tissue
What is the advantage of using higher energy X-rays in radiotherapy?
Better defined beam edges
What is the relationship between the photon energy and the depth of the peak dose?
The depth of the peak is roughly a quarter of the photon energy in megavolts
What is the typical range of the surface dose for most teletherapy units?
20–50%
What does the physician do with the plan of the medical physicist?
Verifies and approves the plan for use
Why does the beam enter the skin at an angle other than 90◦?
Because the skin is curved
What is used at higher energies to correct the dose distribution?
Mathematical corrections
What is the purpose of collimators in LINAC planning?
To spare sensitive organs
What is plotted on the anatomy during LINAC planning?
Isodose curves
What is the volume that has to be treated called?
Treated volume
What is the minimum dose difference required between the treated volume and elsewhere?
20%
What is the purpose of using multiple beams in treatment planning?
To conform the radiation to the treatment volume
What is the role of a Medical Physicist in LINAC planning?
All of the above
What is the primary purpose of a CT scan in LINAC planning?
To guide the radiation therapy
What is the primary purpose of a treatment simulator in radiation therapy?
To provide information on the treatment area for planning and verify patient positioning
What is the function of multileaf collimators in IMRT?
To shape the radiation beam and modulate the beam intensity
Why is patient positioning crucial in radiation therapy?
To ensure accurate delivery of radiation beams
What is the purpose of a patient shell in radiation therapy?
To position the patient correctly during treatment
What aspect of quality assurance is involved in ensuring the proper functioning of new equipment?
Commissioning of new equipment
What is the main reason for the dose to fall with depth in a tissue?
Due to the absorption of the beam by the tissue
What is the purpose of plotting the dose distribution in the form of isodose charts?
To determine the dose at a specific patient volume
What is the effect of Compton scattering on the beam at low energies?
It leads to the diffuse edges of the beam
What is the characteristic of the isodose lines?
They are lines of constant dose
What is the most penetrating beam used in external beam radiotherapy?
150 MeV proton beam
This quiz covers the fundamentals of dose measurement and quality assurance in radiotherapy, including safety issues in isodose measurement and the use of tissue-equivalent phantoms.
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