Questions with Complete Solutions

RTTT 214-Dosimetry II Last Semester Questions with Complete Solutions (Latest 2025) A patient is treated at a distance of 70 cm SSD with a SDD of 49.8 cm. The source size is 1.5 cm. What is the geometric penumbra at a depth of 7.5 cm?

• 0.65 cm
• 0.83 cm
• 1.20 cm
• 3.26 cm
• 3.83 cm - Correct Answers ✅0.83 cm

A patient is to be treated with 6 MV photons to a sarcoma of the leg, requiring an extended SSD of 130 cm. Compared with the PDD at 100 cm SSD, the PDD at 8 cm depth at 130 cm SSD will be approximately ______ than that at 100 cm SSD.

• 0.5% greater
• 3% greater
• 10% greater
• 5% less
• 1.5% less - Correct Answers ✅3% greater

Which of the following represents the ratio of the dose at a given point in a phantom to the dose in free space at the same point? 1 / 4

RTTT 214-Dosimetry II Last Semester Questions with Complete Solutions (Latest 2025)

• Scatter-air ratio (SAR)
• Off-axis ratio
• Tissue-phantom ratio (TPR)
• Tissue-air ratio (TAR)
• Tissue-maximum ratio (TMR) - Correct Answers ✅Tissue-

air ratio (TAR)

The side of the equivalent square of a 5 x 25 cm field is:

• Approximately equal to the square root of (5x25)
• Closer to 25 than 5
• The square field, which has the same PDD as the rectangle
• Approximated by the (area/perimeter of the rectangle) -

Correct Answers ✅The square field, which has the same PDD as the rectangle A patient was simulated for treatment on a linear accelerator at 100 cm SAD for a 10 cm x 10 cm field but has been scheduled for treatment on a Cobalt-60 at 80 cm SAD. If blocks need to be cut for the Cobalt-60 unit from the 100 cm film that has a target-to-film (TFD/SFD) distance of 150 cm, what TFD should be used? (Assume that the field size does not need to be adjusted) 2 / 4

RTTT 214-Dosimetry II Last Semester Questions with Complete Solutions (Latest 2025)

• 120 cm
• 130 cm
• 150 cm
• 188 cm
• Cannot use the same simulator field, must re-simulate -

Correct Answers ✅120 cm What determines the wedge angle?

• The angle of the 100% isodose line with a line

perpendicular to the central axis

• The actual measurements of the wedge
• The angle of the 80% isodose line with a line perpendicular

to the central axis

• 2 times the hinge angle - Correct Answers ✅The angle

of the 80% isodose line with a line perpendicular to the central axis

• times the hinge angle

As the SSD increase, the PDD:

• Increases 3 / 4

RTTT 214-Dosimetry II Last Semester Questions with Complete Solutions (Latest 2025)

• Decreases
• Remains the same
• There is no effect - Correct Answers ✅Increases

Which of the following is a plot of target or normal structure volume as a function of dose?

• BEV
• DVH
• DRR
• REV - Correct Answers ✅DVH

As the field size increases, the PDD:

• Increase
• Decrease
• Remains the same
• There is no effect - Correct Answers ✅Increase

Which of the following accounts for target motion and uncertainty in positioning?

• / 4