Fractionation, LET, RBE (Dr. Chang's Lecture)

Question 1

what type of damage is related to the shoulder region of cell survival curve?

Answer 1

sublethal

Question 2

Is there a sublethal dose repair after high LET radiation?

Answer 2

No

Question 3

In what rate does the dose-rate effect caused by SLDR (sublethal damage repair) is most dramatic?

Answer 3

0.01 - 1 Gy/min

Question 4

Does decreasing dose rate increase the efficiency of cell killing?

Answer 4

Yes (This is called the inverse dose-rate effect), bc at higher dose rate the cells are dormant

Question 5

What is the unit of LET?

Answer 5

kiloelectron volt/micrometer

Question 6

What is the LET for Cobalt 60 vs 250 kV x-ray?

Answer 6

0.2 vs. 2

Question 7

Higher the energy of the ionization RT how does this impact its LET?

Answer 7

higher energy –> lower LET

Question 8

LET of 10 MeV protons vs. 150 MeV protons?

Answer 8

4.7 vs. 0.5

Question 9

What is the definition of RBE (relative biological effectiveness)?

Answer 9

Dose X-rays / Dose test RT producing equal biologic effect

Question 10

What is the relationship between and LET and RBE

Answer 10

In general LET goes up RBE goes up.

Question 11

High OER means RBE will be low or high?

Answer 11

Low