Radiation Physics Quiz: Percentage Depth Dose

<p>Exponential attenuation (A)</p> Signup and view all the answers

<p>A higher µ results in a lower percentage depth dose (C)</p> Signup and view all the answers

<p>Dose build-up region (B)</p> Signup and view all the answers

<p>Skin-sparing effect (B)</p> Signup and view all the answers

<p>Percentage depth dose decreases with depth (A)</p> Signup and view all the answers

<p>They have a lower surface dose, minimizing skin damage while delivering high doses to the tumor. (A), They have a higher penetration depth, reaching the tumor more effectively than lower energy beams. (B)</p> Signup and view all the answers

<p>Kerma is maximum at the surface and decreases with depth, while absorbed dose initially increases with depth and then decreases. (B)</p> Signup and view all the answers

<p>The deposition of energy by electrons ejected from the tissue by photons. (C)</p> Signup and view all the answers

<p>The depth of maximum dose is approximately equal to the range of electrons in the medium. (C)</p> Signup and view all the answers

<p>The energy transferred from photons to charged particles in the tissue. (D)</p> Signup and view all the answers

<p>The energy of the photons decreases as they penetrate deeper into the tissue. (A)</p> Signup and view all the answers

<p>The size of the collimator opening as seen from the radiation source. (D)</p> Signup and view all the answers

<p>The absorbed dose is directly proportional to the electron fluence. (C)</p> Signup and view all the answers

<p>The field size is very small. (A)</p> Signup and view all the answers

<p>The distance from the source to the isocenter, which is the axis of gantry rotation. (D)</p> Signup and view all the answers

<p>Lower energy beams have a more pronounced field size dependence. (B)</p> Signup and view all the answers

<p>It simplifies the calculation of depth dose for non-square fields. (C)</p> Signup and view all the answers

<p>Equivalent square has the same A/P. (B)</p> Signup and view all the answers

<p>Scattered radiation (B)</p> Signup and view all the answers

<p>It represents the point where the dose is half of the maximum dose. (C)</p> Signup and view all the answers

<p>It increases. (A)</p> Signup and view all the answers

<p>Photon fluence is inversely proportional to the square of the distance from the source. (A)</p> Signup and view all the answers

<p>TAR is independent of source-to-surface distance (SSD), while PDD is not. (A)</p> Signup and view all the answers

<p>The effective attenuation coefficient (µ_eff) (A)</p> Signup and view all the answers

<p>Source-to-surface distance (SSD) (A)</p> Signup and view all the answers

<p>BSF is the TAR at the depth of maximum dose (d_m). (A)</p> Signup and view all the answers

<p>It becomes less exponential and more complex. (C)</p> Signup and view all the answers

<p>TAR is independent of the source-to-surface distance (SSD). (C)</p> Signup and view all the answers

<p>SSD (Source-to-surface distance) (C)</p> Signup and view all the answers

<p>The amount of scatter radiation reaching the depth of maximum dose. (C)</p> Signup and view all the answers

<p>Orthovoltage beams have a lower energy, resulting in greater scattering in the medium. (C)</p> Signup and view all the answers

<p>BSF is a measure of the increase in dose at the surface due to scattered radiation. (D)</p> Signup and view all the answers

<p>3.6% (B)</p> Signup and view all the answers

<p>To adjust for changes in the field size at the depth of interest. (D)</p> Signup and view all the answers

<p>To calculate the amount of scattered dose at a given point in the medium. (B)</p> Signup and view all the answers

<p>Distance from the source (A)</p> Signup and view all the answers

<p>TAR and PDD are related, and TAR can be used to convert PDD from one SSD to another. (B)</p> Signup and view all the answers

<p>By multiplying the TAR by the ratio of field sizes at depth. (B)</p> Signup and view all the answers

High energy radiation beams like cobalt-60 that deliver doses deep in the body without affecting the skin.

Quotient of absorbed dose at depth d to absorbed dose at reference depth do, expressed as a percentage.

The dose of radiation delivered at the surface of the skin.

The ratio of dose delivered at a certain depth to the dose delivered at surface level.

Depth at which absorbed dose is measured for percentage depth dose; varies by energy level.

Kinetic energy released in material, defined as the initial kinetic energies of charged particles from neutral particles.

The peak absorbed dose at the central axis, usually called maximum dose.

The increase in absorbed dose as radiation penetrates tissue, especially evident in higher energies.

The number of electrons passing through a unit area; impacts dose delivery in tissues.

Higher-energy beams deposit maximum dose deeper in tissue, minimizing dose at the surface.

The phenomenon where dose increases with depth due to electrons traveling downstream until maximum is reached.

The amount of radiation energy absorbed per unit mass of tissue, varies with photon energy fluence.

Refers to the energy or penetrating power of a radiation beam; affects depth dose distribution.

A measure of how easily the beam is absorbed; lower values indicate more penetration.

The physical dimensions of the treatment area defined geometrically or dosimetrically.

Area between the surface and the maximum dose point where dose initially increases.

The distance intercepted by a given isodose curve on a plane perpendicular to the beam at a specified distance.

A predefined distance from the radiation source to the patient's skin surface for assessing dosimetric field size.

The distance from the radiation source to the axis of gantry rotation, known as the isocenter.

Radiation that has interacted with matter and changed direction before reaching the target area.

As field size increases, the contribution from scattered radiation to the absorbed dose also increases.

A rectangular field can be equated to a square field based on area/perimeter equivalence.

A rule to equate rectangular and square fields by comparing their area to perimeter ratios.

A square field has equal width and length, here 13.3 cm each.

Intensity of radiation decreases with the square of the distance from the source.

The number of photons passing through a unit area, varies with distance from the source.

The process of narrowing a beam of particles or waves, influencing dose distribution.

The amount of radiation dose delivered per unit time, decreases with distance per the inverse square law.

Minimum recommended SSD is 80 cm for effectively treating deep-seated lesions.

Ratio of dose at a certain point to the dose in free space, influenced by beam quality and field size.

Ratio comparing absorbed dose in tissue to that in air at a specific depth.

Larger field sizes can lead to higher BSF values, increasing surface doses.

Comparison of dose at various depths to a reference depth dose; crucial for dosimetry.

Correction factor used to adjust PDD between different source-surface distances (SSDs).

Ratio of scattered dose at a point in the medium to the dose in free space at the same point.

Dmax is the point where maximum dose is achieved; BSF can increase the effective dose at Dmax.

TAR and PDD are interrelated; understanding one aids in comprehending the other.

Adjustment to PDD based on the source-to-surface distance.

TAR (d, rd) = Dd/Dfs, where Dd is dose in phantom and Dfs is dose in free space.

TAR is approximately independent of the distance from the source in clinical ranges.

Larger field sizes increase scatter, making TAR variation with depth more complex.

For megavoltage beams, TAR varies approximately exponentially with depth beyond maximum dose.