XRT Rules

Question 1

Where is DMax for KV treatments?

Answer 1

Skin surface

Question 2

Should you used kV or MeV for a skin cancer overlying bone or cartilage?

Answer 2

MeV

Should avoid kV due to the photoelectric effect

Question 3

What depth is D90 for 90kV treatment (5cm diameter)?

Answer 3

0.5cm

Question 4

What depth is D90 for 170kV treatment? (5cm diameter)

Answer 4

0.7cm

Question 5

What is the minimum diameter that a field treated by electrons should be and why?

Answer 5

4cm due to decreased penetration and loss of beam flatness below this size

Question 6

How do you calculate DMax for MV and MeV treatments?

Answer 6

Divide beam energy by 4 (Cm)

or x2 for mm

Question 7

How do you calculate D90 for MeV treatments?

Answer 7

Beam energy x3 (mm)

Question 8

How do you calculate the thickness of lead required for shielding in MeV treatments?

Answer 8

Beam energy divided by 2 (mm)

Question 9

What margin should be applied for a well differentiated BCC treated with kV?

Answer 9

0.5cm

Question 10

What margin should be applied for a SCC treated with kV

Answer 10

1cm

Question 11

What margin should be applied for a well differentiated BCC treated with MeV?

Answer 11

0.5cm plus 0.5-1cm to account for penumbra