Dosimetry I Midterm questions with verified
answers
_______________ contours are the most accurate of all transverse
contouring methods.
A. Solder wire
B. A thermoplastic tube
C. A plaster strip
D. CT-generated Ans✓✓✓ D. CT-generated
A 10 x 10 cm field is abutted to a 20 x 20 cm field, both at 100 cm SSD.
What is the skin gap necessary if the fields are matched at a depth of 5
cm?
A. 0.75 cm
B. 0.89 cm
C. 1.00 cm
D. 1.21 cm
E. 1.50 cm Ans✓✓✓ A. 0.75 cm
A dose of 5000 cGy is to be delivered at a depth of 8 cm where the
percentage depth dose is 60.3%. What is the dose to an underlying
,sensitive organ at a depth of 10 cm where the percentage depth dose is
55.5%.
A. 2775 cGy
B. 3015 cGy
C. 4602 cGy
D. 5432 cGy Ans✓✓✓ C. 4602 cGy
A field size of 40 cm x 40 cm is required and a maximum field size of 28
cm x 28 cm is obtained at an 80 cm SSD, what SSD is required to treat
this patient?
A. 83 cm
B. 89 cm
C. 94 cm
D. 114 cm Ans✓✓✓ D. 114 cm
A film taken on the simulator has a source to film distance of 160 cm.
The technologist forgets to note the field size at the treatment distance
of 80 cm. The field measures 10 cm x 20 cm on the film. The field size at
80 cm is:
A. 8 cm x 16 cm
B. 12.5 cm x 25 cm
,C. 10 cm x 20 cm
D. 5 cm x 10 cm
E. 20 cm x 40 cm Ans✓✓✓ D. 5 cm x 10 cm
A lateral radiograph shows the spinal cord to be at a measured depth of
9 cm. If the film magnification is 1.5, the actual depth of the cord in the
patient is:
A. 4 cm
B. 6 cm
C. 9 cm
D. none of the above Ans✓✓✓ B. 6 cm
A patient is being treated with POP fields (A/P and P/A) through an SSD
technique. The midline dose to be delivered is 200 cGy. The patient
separation along the central axis is 20 cm. The treatment beam PDD
(10cm) is 68% and PDD (18.5 cm at exit point) is 42%. Calculate the
total dose at the dose maximum point on the anterior side, for this
treatment.
A. [200/68] x 100
B. [100/68] x 100
C. [200/42] x 100
, D. {[100/68] x 100} + {[100/68 x 42]} Ans✓✓✓ D. {[100/68] x 100} +
{[100/68 x 42]}
A patient is being treated with POP fields (A/P and P/A). The total dose
at the dose maximum point onthe anterior side, for this treatment, is
given by:
A. entrance dose (due to A/P field)
B. exit dose (due to P/A field)
C. entrance dose (A/P field) + exit dose (P/A field)
D. none of the above Ans✓✓✓ C. entrance dose (A/P field) + exit dose
(P/A field)
A patient is planned for equally weighted, parallel-opposed 6 MV
photon fields treating the mediastinum, AP thickness 22 cm. If the
beam energy is changed to 18 MV photons, all of the following would
decrease except:
A. MU
B. Skin dose
C. Depth of maximum tissue dose
D. Percent variation in dose across the treated volume Ans✓✓✓ C.
Depth of maximum tissue dose
answers
_______________ contours are the most accurate of all transverse
contouring methods.
A. Solder wire
B. A thermoplastic tube
C. A plaster strip
D. CT-generated Ans✓✓✓ D. CT-generated
A 10 x 10 cm field is abutted to a 20 x 20 cm field, both at 100 cm SSD.
What is the skin gap necessary if the fields are matched at a depth of 5
cm?
A. 0.75 cm
B. 0.89 cm
C. 1.00 cm
D. 1.21 cm
E. 1.50 cm Ans✓✓✓ A. 0.75 cm
A dose of 5000 cGy is to be delivered at a depth of 8 cm where the
percentage depth dose is 60.3%. What is the dose to an underlying
,sensitive organ at a depth of 10 cm where the percentage depth dose is
55.5%.
A. 2775 cGy
B. 3015 cGy
C. 4602 cGy
D. 5432 cGy Ans✓✓✓ C. 4602 cGy
A field size of 40 cm x 40 cm is required and a maximum field size of 28
cm x 28 cm is obtained at an 80 cm SSD, what SSD is required to treat
this patient?
A. 83 cm
B. 89 cm
C. 94 cm
D. 114 cm Ans✓✓✓ D. 114 cm
A film taken on the simulator has a source to film distance of 160 cm.
The technologist forgets to note the field size at the treatment distance
of 80 cm. The field measures 10 cm x 20 cm on the film. The field size at
80 cm is:
A. 8 cm x 16 cm
B. 12.5 cm x 25 cm
,C. 10 cm x 20 cm
D. 5 cm x 10 cm
E. 20 cm x 40 cm Ans✓✓✓ D. 5 cm x 10 cm
A lateral radiograph shows the spinal cord to be at a measured depth of
9 cm. If the film magnification is 1.5, the actual depth of the cord in the
patient is:
A. 4 cm
B. 6 cm
C. 9 cm
D. none of the above Ans✓✓✓ B. 6 cm
A patient is being treated with POP fields (A/P and P/A) through an SSD
technique. The midline dose to be delivered is 200 cGy. The patient
separation along the central axis is 20 cm. The treatment beam PDD
(10cm) is 68% and PDD (18.5 cm at exit point) is 42%. Calculate the
total dose at the dose maximum point on the anterior side, for this
treatment.
A. [200/68] x 100
B. [100/68] x 100
C. [200/42] x 100
, D. {[100/68] x 100} + {[100/68 x 42]} Ans✓✓✓ D. {[100/68] x 100} +
{[100/68 x 42]}
A patient is being treated with POP fields (A/P and P/A). The total dose
at the dose maximum point onthe anterior side, for this treatment, is
given by:
A. entrance dose (due to A/P field)
B. exit dose (due to P/A field)
C. entrance dose (A/P field) + exit dose (P/A field)
D. none of the above Ans✓✓✓ C. entrance dose (A/P field) + exit dose
(P/A field)
A patient is planned for equally weighted, parallel-opposed 6 MV
photon fields treating the mediastinum, AP thickness 22 cm. If the
beam energy is changed to 18 MV photons, all of the following would
decrease except:
A. MU
B. Skin dose
C. Depth of maximum tissue dose
D. Percent variation in dose across the treated volume Ans✓✓✓ C.
Depth of maximum tissue dose
