Dosimetry questions with verified answers
1 Gy is equal to which of the following? (This question has more than
one correct answer so select all that apply). Ans✓✓✓ 1 J/kg
100 rads
100 cGy
A cobalt-60 machine delivers 400 cGy in 3 minutes. What is the dose
rate of the machine? Ans✓✓✓ 133cGy/min
A patient is being treated isocentrically with a single AP field. What is
the isocenter depth if the SAD is 100 cm and the SSD is 91 cm?
Ans✓✓✓ 9 cm
A patient is being treated using opposed lateral photon beams both at
100 SAD. If the SSD of the right lateral is 88 cm and the depth of left
lateral is 5 cm, what is the patient's total lateral separation? Ans✓✓✓
17 cm
A patient is being treated with a single posterior field. What is the
depth from the PA if the SAD is 100 cm and the SSD is 89 cm Ans✓✓✓
11 cm
A pelvic plan was created with 180 cGy prescribed to the isocenter. The
physician normalozed the plan to 96% isodose line. What is the new
dose to the isocenter? Ans✓✓✓ 187.5 cGy 180/.96
, A physician prescribes an AP/PA treatment to be weighted 3:1 for a
total of 200 cGy. How much dose will be given from the AP field and
how much from the PA? Ans✓✓✓ AP = 150 cGy, PA = 50cGy
A physician would like to use a 15 Mev electron beam for a breast
boost. He asks you what the minimum diameter cutout should be
Ans✓✓✓ 15/2= 7.5cm
Absorbed dose at a given depth divided by the dose in air at the same
point is the definition of which of the following? Ans✓✓✓ TAR
According to QUANTEC guidelines, the lung V20 should be limited
to__if we want no more than 20% risk of symptomatic pneumonitis
Ans✓✓✓ 30%
An electron beam traverses 6cm of tissue in which 1.5 cm of compact
bone is embedded. if the density of the bone is 1.65, what is the
effective depth? Ans✓✓✓ 6cm -1.5cm=4.5cm, 4.5+1.5 (1.65),
4.5+2.475= 6.975cm
An electron beam with a custom insert has a measured output of 0.954
cGy/mu at dmax. If 200cGy is prescribed to 90% depth dose level, the
MU setting is_____ Ans✓✓✓ 233 200/(0.954*.90)
1 Gy is equal to which of the following? (This question has more than
one correct answer so select all that apply). Ans✓✓✓ 1 J/kg
100 rads
100 cGy
A cobalt-60 machine delivers 400 cGy in 3 minutes. What is the dose
rate of the machine? Ans✓✓✓ 133cGy/min
A patient is being treated isocentrically with a single AP field. What is
the isocenter depth if the SAD is 100 cm and the SSD is 91 cm?
Ans✓✓✓ 9 cm
A patient is being treated using opposed lateral photon beams both at
100 SAD. If the SSD of the right lateral is 88 cm and the depth of left
lateral is 5 cm, what is the patient's total lateral separation? Ans✓✓✓
17 cm
A patient is being treated with a single posterior field. What is the
depth from the PA if the SAD is 100 cm and the SSD is 89 cm Ans✓✓✓
11 cm
A pelvic plan was created with 180 cGy prescribed to the isocenter. The
physician normalozed the plan to 96% isodose line. What is the new
dose to the isocenter? Ans✓✓✓ 187.5 cGy 180/.96
, A physician prescribes an AP/PA treatment to be weighted 3:1 for a
total of 200 cGy. How much dose will be given from the AP field and
how much from the PA? Ans✓✓✓ AP = 150 cGy, PA = 50cGy
A physician would like to use a 15 Mev electron beam for a breast
boost. He asks you what the minimum diameter cutout should be
Ans✓✓✓ 15/2= 7.5cm
Absorbed dose at a given depth divided by the dose in air at the same
point is the definition of which of the following? Ans✓✓✓ TAR
According to QUANTEC guidelines, the lung V20 should be limited
to__if we want no more than 20% risk of symptomatic pneumonitis
Ans✓✓✓ 30%
An electron beam traverses 6cm of tissue in which 1.5 cm of compact
bone is embedded. if the density of the bone is 1.65, what is the
effective depth? Ans✓✓✓ 6cm -1.5cm=4.5cm, 4.5+1.5 (1.65),
4.5+2.475= 6.975cm
An electron beam with a custom insert has a measured output of 0.954
cGy/mu at dmax. If 200cGy is prescribed to 90% depth dose level, the
MU setting is_____ Ans✓✓✓ 233 200/(0.954*.90)
