Radiation Therapy

Question 1

what makes up ionizing radiation?

Answer 1

accelerated high energy particles (photons, electrons, protons, neutrons)
(left end of electromagnetic spectrum)

Question 2

whats it mean to be accelerated?

Answer 2

propelled by electromagnetic fields

Question 3

what is the cellular target of radiation?

Answer 3

DNA

Question 4

how does radiation treatment work?

Answer 4

waves and particles result in lethal double stranded DNA damage. When the cell tries to divide before repairing the damage, it is killed or apoptosed. (Cancer cells divide more often and have mutated repair systems)

Question 5

direct ionization

Answer 5

damages directly within the DNA strand

Question 6

indirect ionization

Answer 6

damages DNA through reactive intermediates (most commonly water)

Question 7

waters role in indirect ionization?

Answer 7

photon knocks electron out of H2Os orbit, resulting in a hydroxyl radical

Question 8

two main methods of radiation delivery

Answer 8

external beam radiation therapy (EBRT) & internal radiation therapy (brachytherapy)

Question 9

EBRT

Answer 9

aiming stuff at the inside from the outside. 3-D conformal

Question 10

brachytherapy

Answer 10

putting radiation close to what you want to hit. Seeds, cylinders, catheters, sutures, etc

Question 11

three main types of EBRT

Answer 11

photons (X-rays), light charged particles (electrons), heavy charged particles (protons)

Question 12

how did the linear accelerator advance radiation therapy?

Answer 12

by allowing high energy beams to be used, we can now treat something deep without the majority of the absorbance occurring at the skin

Question 13

how does proton therapy work?

Answer 13

protons deposit energy and then stop. beam peaks where you want to treat and then has no exit dose. deposits all energy at area of interest

Question 14

radiosensitivity

Answer 14

lab term referring to in vitro sensitivity, described by favorable cell survival curves

Question 15

radioresponsiveness

Answer 15

clinical term referring to a measurable change in tumor size during or after treatment. generally correlated with radio sensitivity, but not always!

Question 16

therapeutic index

Answer 16

measure of the relative effect of treatment on the tumor compared to normal tissues (aim for 10/15)

Question 17

unit of radiation

Answer 17

Grey (Gy)

Question 18

acute toxicity

Answer 18

acute side effects to RT. damage to quickly dividing tissues

Question 19

late toxicity

Answer 19

late side effects of RT that damage slow/non-dividing cells

Question 20

fractionation

Answer 20

stretching RT treatments out over a longer period of time. Can get away with higher dose treatments

Question 21

four Rs of radiobiology

Answer 21

Reassortment, Reoxygenation, Repair, Repopulation

Question 22

Reassortment/Redistribution

Answer 22

using fractionation to hit cells at different times in their cell cycles

Question 23

Reoxygenation

Answer 23

when you first use RT, you damage some tumor cells and they then are remodeled, allowing more oxygen radicals to flow in and damage them the second time around

Question 24

Repair

Answer 24

Fractionation allows normal tissues time to repair sublethal damage caused by the previous round of therapy

Question 25

Repopulation

Answer 25

Negative against fractionation. Tumor cells have a chance to grow back when treatment isn’t continuous

Question 26

hypofractionation

Answer 26

palliative treatment. goal is to help patient manage symptoms.

Question 27

standard fractionation

Answer 27

curative treatment daily

Question 28

hyperfractionation

Answer 28

curative treatment twice daily

Question 29

definitive radiation therapy

Answer 29

using radiation therapy as a cure without surgery. for solid and lymphoid malignancies

Question 30

neoadjuvant RT

Answer 30

pre-operative radiation.

Advantages: smaller treatment volume, more radiosensitive, improve surgeons success

Question 31

adjuvant RT

Answer 31

post-operative radiation

Advantages: tailor RT fields to surgical findings, avoid unnecessary RT

Question 32

chemotherapy’s role with RT?

Answer 32

works as a radio sensitizer. low dose, concurrent chemo is synergistic with RT

Question 33

how can chemo possibly help RT?

Answer 33

direct enhancement of radiation damage by incorporating drugs into DNA, inhibits cellular repair, accumulates cells in radiosensitive cycle phase, works against hypoxic (radioresistant cells), inhibits accelerated repopulation