Radiation Biology

Question 1

What is the most commonly used permanent implants?

Answer 1

Iodine-125 (I-125)

Question 2

What are the 3 MOAs of hydroxyurea?

Answer 2

1. Inducing synchrony
2. Kills cell in S phase
3. Imposes block at the end of G1 phase

Question 3

What Gy can induce oligospermia & reduced fertility in men?

Answer 3

oligospermia = diminished sperm counts

0.15 Gy

Question 4

What Gy can induce azoospermia & temporary sterility in men?

Answer 4

azoospermia = absence of living spermatozoa

0.5 Gy

Question 5

What Gy can induce permanent sterility with single fraction & fractionated dose in men?

Answer 5

Single fraction: 6 Gy
Fractionated dose: 2.5-3 Gy within 2-4 weeks

Fractionation cases more gonadal damage than a single dose in men*

Question 6

What does HRR involves?

Answer 6

HRR

RAD51, MRN complex, XRCC, BRACA2

Question 7

What does NHEJ involves?

Answer 7

NHEJ

Ku70, Ku80, RAD50, DNA-PKs, XRCC4, LIG4, NHEJ1

Question 8

What are the steps of BER in single nucleotide?

Answer 8

BER

• Single nucleotide*
  1. Glycosylase/DNA lyase remove a putative single-base mutation
  2. APE1 removes sugar residue
  3. DNA polymerase β replaces with correct nucleotide
  4. DNA ligase III-XRCC1-mediated ligation completes the process

Question 9

What are the steps of BER in multiple nucleotides?

Answer 9

BER

• Multiple nucleotides*
  1. RFC/PCNA/DNA polymerase performs the repair synthesis
  2. Overhanging flap structure is removed by FEN1
  3. DNA strands are sealed by ligase I

Question 10

What aberration is overlapping double rings?

Answer 10

Chromosomal aberration

Question 11

What is the LQ model’s equation?

S =

Answer 11

S = e^-αD-βD2

Question 12

Plating efficiency (PE) =
Surviving fraction (SF) =

Answer 12

Plating efficiency (PE) = # of colonies counted / # of cells seeded x 100
Surviving fraction (SF) = # of colonies counted / cells seeded x PE/100

Question 13

If G1 phase is long enough,

resistent period is evident in _____ phase, followed by a sensitive period towards the ______.

Answer 13

Resistant: early G1
Sensitive: late G1

Question 14

Most sensitive phases: ____, _____

Most resistant phases: _____, _____

Answer 14

Most sensitive phases: M, late G2

Most resistant phases: late S, early G1

Question 15

Isotope =
Isotone =
Isobar =
Isomer =

Answer 15

Isotope = same Z 
Isotone = same N
Isobar = same A
Isomer = same Z, N, A, but different nuclear energy state