ABRII Exam
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- TG-21 electron calibration protocol uses Pwall. Pwall = 1, if the wall thickness is less than ?
- Wall thickness < 0.5mm
- What depth is used to calibrate electrons in TG-21?
- Dmax
- What is the equation for the Bragg-Gray relationship?
- Dmed = Jgas * (W/e)gas * (S/P)med/gas
- How many terms are used in the TG-21 equation to calculate absorbed dose to water from Photons? List all?
- 11 terms Mraw, CTP, Pol, Pelec, Ngas, L/p med/air, Pion, Prepl, Pwall, Uab/p water/med, SC
- What is Pwall?
- Pwall accounts for the attenuation and scatter caused by the wall of the chamber in water/phantom material.
- What is Prepl in TG-21 photon calibration protocol?
- Prepl corrects for perturbations caused by the chamber being in the water. Acts as a correction in shifting in the depth dose.
- What is Pion?
- Pion corrects for losses in ionization due to ions recombining. Pion is the inverse of ionization collection efficiency
- What is the SC term in TG-21 protocol?
- SC corrects for the different amount of photon scatter in phantom materials.
- According to TG-21, what is the reccomended depths of calibration for photon E < 15 MV, 16MV < E < 25MV
- 5cm and 7 cm
- According to TG-21 Electron calibrations, what is Prepl?
- Prepl does not include gradient correction. Prepl does include electron fluence correction. Prepl = 1 for plane parallel plate chambers
- According to TG-21, what components make up Mcor?
- Mraw Ppol Pelec CTP
- What is the difference between the Bragg-Gray cavity theory and the Spencer-Attix relationship?
- Spencer Attix uses restricted Mass collisional stopping power which accounts for the loss of secondary electrons which are above 10kev that are carried outside of the cavity
- What is the approximate TVL of concrete for 6MV Photons
- 35 cm
- What is the approximate TVL of concrete for 10MV Photons
- 40 cm
- What is the approximate TVL of concrete for 20MV Photons
- 47 cm
- What are the Max and Mean Radiation Dose limits for Brain
- Max 60 Gy No Mean
- What are the Max and Mean Radiation Dose limits for Brainstem
- Max 54 Gy No Mean
- What are the Max and Mean Radiation Dose limits for Optical Chiasm or Optic Nerves
- Max 54 Gy
- What are the Max and Mean Radiation Dose limits for Retina
- Max 45 Gy
- What are the Max and Mean Radiation Dose limits for Lens
- Max 12 Gy
- What are the Max and Mean Radiation Dose limits for Parotids
- Max 70 Gy Mean 26 Gy
- What are the Max and Mean Radiation Dose limits for Larynx
- Max 70 Gy Mean 25-30 Gy
- What are the Max and Mean Radiation Dose limits for Mandible
- Max 65 Gy Mean 35-45 Gy
- What are the Max and Mean Radiation Dose limits for Spinal Cord
- Max 45 Gy No Mean
- What are the respective PDD values at 5, 10 and 20 cm for 6 MV Photons
- 5 cm ~ 87% 10 cm ~ 68% 20 cm ~ 40%
- What are the respective PDD values at 5, 10 and 20 cm for 10 MV Photons
- 5 cm ~ 93% 10 cm ~ 75% 20 cm ~ 47%
- What are the respective PDD values at the following depths for 20 MV Photons
- 5 cm ~ 95% 10 cm ~ 77% 20 cm ~ 49%
- What is the standard density of Concrete?
- 2.35 g/cm3
- What is the standard density of Lead?
- 11.35 g/cm3
- What is the standard density of Steel?
- 7.8 g/cm3
- What is the standard density of Earth?
- 1.5 g/cm3
- What equation is used to determine the width of the primary barrier?
- Width = 0.56(X) + 0.6 Where X is the distance from the Target to the Inside Wall of Barrier
- What is the standard distance used for determining the location outside a Wall?
- 0.305 Meters
- What is an standard dose Rx for a TBI treatment?
- 120 cGy/Fx for 11 Fx
- Describe the Alpha/Beta ratio.
- The dose at which the Linear and Quadratic terms contribute equally to the Biological Response.
- What happens to the Alpha/Beta ratio when the LET increases?
- Alpha/Beta Increase with Increasing LET
- What are the Alpha/Beta ratios for Early Responding Tissues and Late Responding Tissues?
- A/B (Early) 10 Gy A/B (Late) 3 Gy
- Do Tumors/Cancer tend to respond as Early or Late responding tissues?
- Tumors - Early Responding Tissues
- Describe a standard manner to evaluate the dose to the Rectum in an IMRT Prostate Plan.
- The rectum should receive less than 70 Gy to 25% of volume and 60 Gy to 40% of volume
- What is a typical Neutron Dose Equivalent produced in a Linac per Photon dose at Isocenter?
- For Photons with Energies above 15, the approximate ratio is 1 mGy (Neutrons)/ 1 Gy (Photons) at 1.4 meters
- How do you calculate the Blocked Equivalent Squared Value?
- Find the percentage or Ratio of Unblocked. Multiply Ratio by Area of Equivalent Square Field Size. Take the Square root of Product
- What are the conditions when a room is posted with a Radiation Area sign according to NRC?
- 5 mrem/hr at 30cm
- What are the requirements in which the room should be posted when using radioactive material?
- Dose Rate < 5 mrem/hr at 30 cm from container surface.
- What constitutes a High Dose Rate Source according to the NRC?
- > 12 Gy/hr at the Rx point.
- What constitutes a Low Dose Rate Source according to the NRC?
- < 2 Gy/hr at the Rx point.
- How frequent should Radioactive sources be tested?
- Prior to first use or every 6 months.
- What is the allowable leakage of radioactivity?
- 0.005 uCi
- At what condition must the licensee provide instructions to patients?
- If the dose to another person is likely to exceed 100 mrem.
- Peak power of Klystron?
- 5 MW
- Peak power of Magnetron?
- 2 MW
- What does the Modulator do in a Linac?
- Simultaneously provided a DC pulse to Power Supply and electron gun.
- What is the approximate attenuation of a Cobalt beam per cm in tissue/water?
- 4~5%/cm
- What is the difference between an elastic and inelastic collision
- No Kinetic Energy is lost in Elastic Collisions. Kinetic Energy is lost in Inelastic collisions.
- Is the Stopping Power greater for high or Low Z materials
- Low Z Materials, because high Z materials have fewer electrons per gram and are more tightly bound inner electrons.
- What is different about Restricted Stopping Power when compared to basic Stopping Power?
- Restricted Stopping Power excludes energy carried away by delta rays which will not deposit their dose near the interaction site. Usually set at 10 Kev
- What happens to the energy of electrons as they increase in depth of tissue or water?
- Energy decreases. This is why Ionization Curves need to be converted to depth doses.
- What is the equation describing most probable incident electron energy (Ep) with the practical range (Rp)
- Ep = (0.72) + 1.9*Rp
- What equation can be used to estimate the Energy of an electron at depth d?
- Ep(d)=Ep*(1-(d/Rp))
- At what photon energy is coherent scattering important?
- less than 10 kev
- What is the maximum energy of a photon after a direct hit with an electron where the photon is scattered back in te opposite direction?
- 256 kev
- What is the maximum energy of a photon after a hitting an electron where the photon is scattered 90 deg?
- 511 kev
- If an electron is forwardly scattered by a photon a distance x, what is the approximate lateral scatter distance?
- 1/3 to 1/2 times x ex: x = 3cm (15 mv) lateral scater approx: 1 to 1.5cm
- Describe the Geometry factor with regard to TG-43.
- The Geometry Factor G(r,Theta) accounts for the variation of relative dose due to spatial distribution of activity within the source. G(r,theta) point = 1/r^2 G(r,theta) line = Beta/(Lrsin(theta))
- Describe the Radial Dose function according to TG-43.
- The radial dose function g(r) accounts for the effects of absorption and scatter in water along the transverse axis of the source.
- Describe the Anisotropy function according to TG-43.
- The Anisotropy function accounts for the assymetrical distribution of dose around the source.
- List the full equation for calculating the dose rate of a radioactive source according to TG-43 protocol.
- Dose Rate = (Air Kerma Strength)*(Dose Rate Constant)*(Geometry Factor)*(Radial Dose Function)*(Anisotropy Function)