Radiation Therapy

Front 1

What's excitation?

Back 1

- Energy absorbed that raises an electron in an atom to a higher level without ejection of the electron

Front 2

What's ionization?

Back 2

- Radiation that has enough energy to release 1 or more electrons from an atom

Front 3

Alpha particle

Back 3

- Positively charged particle emitted from nucleus during radioactive decay, BIG, very ionizing, easily stopped

Front 4

Beta particle

Back 4

- Negative charged electron emitted from nucleus during radioactive decay, SMALL, stopped by plastic

Front 5

Gamma radiation

Back 5

- Very high energy photons, very dangerous, need lead to be stopped.

Front 6

Ionization of water forms:

Back 6

- H2O ion radical + e-, that can generate free radicals, ions, and molecular species

Front 7

What are the direct and indirect effects of radiation?

Back 7

- Direct effect: radiation interacts directly with target molecule to eject electron
- Indirect effect: Ionization of water forms free radicals that attack target molecule

Front 8

Steps to get from absorption of radiation to biological effect

Back 8

- Absorption of radiation
- Ionization/excitation
- Chemical lesion
- Enzymatic repair or fixation of damage
- Biological effect

Front 9

Radiation dose to kill cell on cytoplasm and nucleus

Back 9

- Cytoplasm - > 250 Gy
- Nucleus - 2 Gy (mitosis)
DNA DAMAGE INDUCES CELL DEATH BY RADIATION

Front 10

Cell that can divide indefinitely

Back 10

Clonogenic cell

Front 11

How do you construct an in vitro survival curve?

Back 11

- Plate X number of cells, irradiate with increasing amount, then count colonies left, calculate plate efficiency and surviving fraction (mean number of colonis after dose per dish/mean number of cells plated per dish x PE)

Front 12

Densely ionizing particles need ______ dose to kill. Name one of this particles.

Back 12

- Low, alpha particle.

Front 13

If you give dose in fractions then at the end you need ______ dose to kill cells

Back 13

- More

Front 14

A single dose doesn't allow:

Back 14

- Repair

Front 15

Name the three types of radiation damage, describe them.

Back 15

- Lethal (irreversible and irreparable)
- Potentially lethal (can be modified by environment using delay to repair)
- Sublethal (can be repaired within 24 hrs)

Front 16

What does shift of the dose-surviving curve to the right up mean?

Back 16

Repair

Front 17

Sublethal damage meaning

Back 17

Increase in survival when a single does is split into two equal fractions separated by a time interval.

Front 18

S phase

Back 18

- More resistant phase

Front 19

G2 phase

Back 19

- More sensitive phase

Front 20

Dose-rate effect

Back 20

- When dose of radiation rate smaller and more time of exposure, biological effect reduced because of repair

Front 21

Inverse dose-rate effect

Back 21

- Seen when lowering dose rate is associated with increased cell kill, this happens because cells are arrested in the G2 phase (more sensitive-reassortment). At high dose, cells stay in the phase they are; at low dose, cells continue until they arrive to G2 phase.

Front 22

What happen if there is proliferation of cells at low dose rate?

Back 22

The curve moves up where there is little effect on cells.

Front 23

Normal tissue response IMPORTANT, divided in:

Back 23

- Acute responding tissues - express injury after weeks.
- Late responding tissues - express injury after months or years

Front 24

4 R's of biology

Back 24

- Repair
- Repopulation
- Reassortment or Redistribution
- Reoxygenation

Front 25

Why is fractionation of dose good for normal tissues?

Back 25

- Because give time to Repair by sublethal damage repair so Repopulation can occur if treatment long enough.

Front 26

Why is fractionation of dose good to damage tumor tissues?

Back 26

- Because of Reoxygenation (hypoxy tumors are radiation resistant) and Reassortment of cells. However, if too long time, tumor cells can proliferate.

Front 27

At the beginning (for 12 weeks) no triggering of proliferation of normal cells, but after that you need more and more radiation to kill this normal cells, why?

Back 27

- Because stem cells start to proliferate again, after being killed at the beginning.

Front 28

Late normal tissue need _______ time to start proliferating.

Back 28

- More, early responding normal tissue is triggered to proliferate within weeks, but late needs more, so this is why the overall treatment duration is not important for this tissues (you can not give radiation for years! because of repair of cancer cells).

Front 29

Late responding tissues are ______ sensitive to change per dose per fraction than acute responding tissues.

Back 29

- More, so decreasing dose per fraction should spare these tissues; however there can be more SLR, bad! Dose response curve, curvier for late responding tissues, dose-reponse curve bends at lower doses and so alpha/beta is lower.

Front 30

There is _____ repair for late responding tissues when you increase dose fraction.

Back 30

- More, the curve is stipper; but also for acute there is repair.

Front 31

alpha in linear-quadratic mode refers to:

Back 31

- killing proportional to dose

Front 32

beta in linear-quadratic mode refers to:

Back 32

- killing proportional to dose2

Front 33

For late effects, alpha/beta

Back 33

- Small, beta has influence at low doses. 2-3 Gy

Front 34

For early effects, alpha/beta

Back 34

- Large, alpha dominates at low doses. 10 Gy

Front 35

The fractionated response of well-oxygenated tumors is similar to...

Back 35

- Early responding normal tissues.

Front 36

Fraction size is dominant factor in determining ___________, while overall treatment time has little influence because repopulation is not triggered.

Back 36

- Late responding tissues

Front 37

Both fraction size and overall treatment time are important in _______.

Back 37

- Early responding tissues

Front 38

What is accelerated repopulation?

Back 38

Cancer cells treated with radiation can divide faster than before!

Front 39

Advantages of prolongation of overall treatment time.

Back 39

- Spares early normal tissues, more repair
- Allows adequate reoxygenation of tumors

Front 40

Disadvantages of prolongation of overall treatment time.

Back 40

- Little further effect on early responding tissue, no effect on late.
- Allows surviving of tumor cells through proliferation

Front 41

Advantages of fractionation of dose.

Back 41

- Mainly will spare late injury.