Radiation Therapy Dosimetry and Quality Assurance

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What is the purpose of using a tissue equivalent phantom in isodose measurement?

To move ionization chambers within the phantom
To measure the dose at a specific depth
To absorb the X-ray beam
To determine the dose distribution in a specific patient volume (correct)

What is the characteristic of the material used to make the phantom?

It has the same density as wood
It has the same atomic number, electron density, and density as tissue (correct)
It has the same atomic number as air
It has the same electron density as metal

What is the advantage of using higher energy X-rays in radiotherapy?

Increased Compton scattering
Increased skin damage
Better defined beam edges (correct)
Increased absorption by the tissue

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 (C) Signup and view all the answers

What is the typical range of the surface dose for most teletherapy units?

20–50% (C) Signup and view all the answers

What does the physician do with the plan of the medical physicist?

Verifies and approves the plan for use (D) Signup and view all the answers

Why does the beam enter the skin at an angle other than 90◦?

Because the skin is curved (D) Signup and view all the answers

What is used at higher energies to correct the dose distribution?

Mathematical corrections (A) Signup and view all the answers

What is the purpose of collimators in LINAC planning?

To spare sensitive organs (A) Signup and view all the answers

What is plotted on the anatomy during LINAC planning?

Isodose curves (C) Signup and view all the answers

What is the volume that has to be treated called?

Treated volume (A) Signup and view all the answers

What is the minimum dose difference required between the treated volume and elsewhere?

20% (C) Signup and view all the answers

What is the purpose of using multiple beams in treatment planning?

To conform the radiation to the treatment volume (C) Signup and view all the answers

What is the role of a Medical Physicist in LINAC planning?

All of the above (D) Signup and view all the answers

What is the primary purpose of a CT scan in LINAC planning?

To guide the radiation therapy (B) Signup and view all the answers

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 (A) Signup and view all the answers

What is the function of multileaf collimators in IMRT?

To shape the radiation beam and modulate the beam intensity (B) Signup and view all the answers

Why is patient positioning crucial in radiation therapy?

To ensure accurate delivery of radiation beams (C) Signup and view all the answers

What is the purpose of a patient shell in radiation therapy?

To position the patient correctly during treatment (C) Signup and view all the answers

What aspect of quality assurance is involved in ensuring the proper functioning of new equipment?

Commissioning of new equipment (A) Signup and view all the answers

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 (B) Signup and view all the answers

What is the purpose of plotting the dose distribution in the form of isodose charts?

To determine the dose at a specific patient volume (D) Signup and view all the answers

What is the effect of Compton scattering on the beam at low energies?

It leads to the diffuse edges of the beam (D) Signup and view all the answers

What is the characteristic of the isodose lines?

They are lines of constant dose (D) Signup and view all the answers

What is the most penetrating beam used in external beam radiotherapy?

150 MeV proton beam (B) Signup and view all the answers