Dosimetry Board Review questions with verified
answers
10 MV (Dmax) Ans✓✓✓ Dmax: 2.0 cm
Surface Dose: 18-27%
PDD d10: 72
15 MV (Dmax) Ans✓✓✓ Dmax: 2.9 cm
Surface Dose: 15-22%
PDD d10: 77
18 MV (Dmax) Ans✓✓✓ Dmax: 3.5 cm
Surface Dose: 13-20%
PDD d10: 80
4 MV (Dmax) Ans✓✓✓ Dmax: 1.0 cm
PDD d10: 60
4 R's of Radiotherapy Ans✓✓✓ 1. Repair
2. Repopulation
3. Reoxygenation
4. Redistribution
,6 MV (Dmax) Ans✓✓✓ Dmax: 1.5 cm
Surface Dose: 20-30%
PDD d10: 67
Absolute Dosimetry Ans✓✓✓ Ion chamber
Preferred Agreement: 3%
Max Deviation at Rx: 5%
Absorbed Dose (units) Ans✓✓✓ Rad and Gray
1 rad = 100 erg/g
1 Gy = 100 rad
1 Gy = 1 J/kg
Accelerating Potential (kVp) Ans✓✓✓ Quality increases with kVp
Achromatic vs. Chromatic Ans✓✓✓ Achromatic: Electron beam angled
270 degrees to evenly spread electron energies
Chromatic: Electron beam angled 90 degrees results in an oblong shape
due to faster/slower electrons
Activity (units) Ans✓✓✓ Becquerels (Bq) - Atoms per second
1 Bq = 1 atom/second
Curies (Ci) - Disintegrations per minute
,1 Ci = 3.700 x 10¹⁰ atoms/second (Bq)
ALARA (Distance) Ans✓✓✓ - If you increase your distance by 2, you
decrease your exposure by 4
ALARA (Shielding) Ans✓✓✓ - If you increase your shielding by 1 HVL,
you decrease your exposure by 2
ALARA (Time) Ans✓✓✓ - If you decrease your time by 1/2, you
decrease your exposure by 2
Alpha Decay Ans✓✓✓ 4/2 He
Z > 82
Carries +2 charge
Range: 4 cm in air
Alpha Probe Ans✓✓✓ Used for contamination surveys
Measures alphas
Anode (x-ray) Ans✓✓✓ Target
(+) charge
High Z: more Bremsstrahlung
Tungsten used, high Z and high melting point
, Arc Therapy (Not use if...) Ans✓✓✓ Large Volume
Not a cylinder
Off center
Arc Therapy Ans✓✓✓ Can be used for small deep seated tumors
Skin dose is lower
The smaller the fields the greater the dose fall off
Artifacts (Created from...) Ans✓✓✓ - Contrast Agents
- Prosthesis
- Respiratory Motion
- Anatomy: Inadequate technique used
Atomic Mass Unit Ans✓✓✓ 1/12 the mass of a carbon-12 atom; 1.66 x
10^-27 kg
Atomic Symbol Notation Ans✓✓✓ X = element symbol
A = Mass Number; # protons + neutrons
Z = Atomic Number; # protons
Average Lifetime (Equation) Ans✓✓✓ 1.44 x T (1/2)
answers
10 MV (Dmax) Ans✓✓✓ Dmax: 2.0 cm
Surface Dose: 18-27%
PDD d10: 72
15 MV (Dmax) Ans✓✓✓ Dmax: 2.9 cm
Surface Dose: 15-22%
PDD d10: 77
18 MV (Dmax) Ans✓✓✓ Dmax: 3.5 cm
Surface Dose: 13-20%
PDD d10: 80
4 MV (Dmax) Ans✓✓✓ Dmax: 1.0 cm
PDD d10: 60
4 R's of Radiotherapy Ans✓✓✓ 1. Repair
2. Repopulation
3. Reoxygenation
4. Redistribution
,6 MV (Dmax) Ans✓✓✓ Dmax: 1.5 cm
Surface Dose: 20-30%
PDD d10: 67
Absolute Dosimetry Ans✓✓✓ Ion chamber
Preferred Agreement: 3%
Max Deviation at Rx: 5%
Absorbed Dose (units) Ans✓✓✓ Rad and Gray
1 rad = 100 erg/g
1 Gy = 100 rad
1 Gy = 1 J/kg
Accelerating Potential (kVp) Ans✓✓✓ Quality increases with kVp
Achromatic vs. Chromatic Ans✓✓✓ Achromatic: Electron beam angled
270 degrees to evenly spread electron energies
Chromatic: Electron beam angled 90 degrees results in an oblong shape
due to faster/slower electrons
Activity (units) Ans✓✓✓ Becquerels (Bq) - Atoms per second
1 Bq = 1 atom/second
Curies (Ci) - Disintegrations per minute
,1 Ci = 3.700 x 10¹⁰ atoms/second (Bq)
ALARA (Distance) Ans✓✓✓ - If you increase your distance by 2, you
decrease your exposure by 4
ALARA (Shielding) Ans✓✓✓ - If you increase your shielding by 1 HVL,
you decrease your exposure by 2
ALARA (Time) Ans✓✓✓ - If you decrease your time by 1/2, you
decrease your exposure by 2
Alpha Decay Ans✓✓✓ 4/2 He
Z > 82
Carries +2 charge
Range: 4 cm in air
Alpha Probe Ans✓✓✓ Used for contamination surveys
Measures alphas
Anode (x-ray) Ans✓✓✓ Target
(+) charge
High Z: more Bremsstrahlung
Tungsten used, high Z and high melting point
, Arc Therapy (Not use if...) Ans✓✓✓ Large Volume
Not a cylinder
Off center
Arc Therapy Ans✓✓✓ Can be used for small deep seated tumors
Skin dose is lower
The smaller the fields the greater the dose fall off
Artifacts (Created from...) Ans✓✓✓ - Contrast Agents
- Prosthesis
- Respiratory Motion
- Anatomy: Inadequate technique used
Atomic Mass Unit Ans✓✓✓ 1/12 the mass of a carbon-12 atom; 1.66 x
10^-27 kg
Atomic Symbol Notation Ans✓✓✓ X = element symbol
A = Mass Number; # protons + neutrons
Z = Atomic Number; # protons
Average Lifetime (Equation) Ans✓✓✓ 1.44 x T (1/2)
