Dosimetry Formulas Exam Actual Questions and Answers 2026.docx

Dosimetry Formulas Exam Actual
Questions and Answers 2026
Calculating beam flatness and beam symmetry -
correct answer ✅Beam Flatness (for uniformity) =
[D(off axis)-D(CAX)]÷[D(off axis)+D(CAX)]
Beam Symmetry (for tilt) =
[D(x1)-D(x2)]÷[D(x1)+D(x2)], where x1 and x2 are points off CAX at
same depth


wedge angle formula
hinge angle formula -
correct answer ✅Wedge Angle θ = 90 - φ/2
Hinge Angle φ = 180 - 2θ
**These do not account for surface irregularity


Geometric penumbra formula -
correct answer ✅P = S(SSD+d-SCD)/SCD, where
S = source size
SSD = source to skin distance
d = depth
SCD = source to collimator/diaphragm distance

,Dosimetry Formulas Exam Actual
Questions and Answers 2026
P↑ if S↑, SCD↓, SSD↑
P is independent of field size


Gap calculation -
correct answer ✅G = S1 + S2
where
S1 = d(L1/2)÷SAD1 and S2 = d(L2/2)÷SAD2
or for like SAD's,
G = (d/SAD)·(L1+L2)/2


Co-60 dmax and PDD at 10 cm ref depth -
correct answer ✅0.5 cm, 56%


4 MV dmax and PDD at 10 cm ref depth -
correct answer ✅1.0 cm, 61%


6 MV dmax and PDD at 10 cm ref depth -
correct answer ✅1.5 cm, 67%


10 MV dmax and PDD at 10 cm ref depth -
correct answer ✅2.5 cm, 73%

, Dosimetry Formulas Exam Actual
Questions and Answers 2026

15 MV dmax and PDD at 10 cm ref depth -
correct answer ✅3.0 cm, 77%


18 MV dmax and PDD at 10 cm ref depth -
correct answer ✅3.5 cm, 80%


25 MV dmax and PDD at 10 cm ref depth -
correct answer ✅4.0 cm, 83%


%/cm attenuation for Co-60 -
correct answer ✅4.0% per cm


%/cm attenuation for 6 MV -
correct answer ✅3.5% per cm


%/cm attenuation for 20 MV -
correct answer ✅2.0% per cm


Air to tissue density ratio -
correct answer ✅air = 0.3 (tissue)