Radiation Therapy Flashcards
what makes up ionizing radiation?
accelerated high energy particles (photons, electrons, protons, neutrons)
(left end of electromagnetic spectrum)
whats it mean to be accelerated?
propelled by electromagnetic fields
what is the cellular target of radiation?
DNA
how does radiation treatment work?
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)
direct ionization
damages directly within the DNA strand
indirect ionization
damages DNA through reactive intermediates (most commonly water)
waters role in indirect ionization?
photon knocks electron out of H2Os orbit, resulting in a hydroxyl radical
two main methods of radiation delivery
external beam radiation therapy (EBRT) & internal radiation therapy (brachytherapy)
EBRT
aiming stuff at the inside from the outside. 3-D conformal
brachytherapy
putting radiation close to what you want to hit. Seeds, cylinders, catheters, sutures, etc
three main types of EBRT
photons (X-rays), light charged particles (electrons), heavy charged particles (protons)
how did the linear accelerator advance radiation therapy?
by allowing high energy beams to be used, we can now treat something deep without the majority of the absorbance occurring at the skin
how does proton therapy work?
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
radiosensitivity
lab term referring to in vitro sensitivity, described by favorable cell survival curves
radioresponsiveness
clinical term referring to a measurable change in tumor size during or after treatment. generally correlated with radio sensitivity, but not always!
therapeutic index
measure of the relative effect of treatment on the tumor compared to normal tissues (aim for 10/15)
unit of radiation
Grey (Gy)
acute toxicity
acute side effects to RT. damage to quickly dividing tissues
late toxicity
late side effects of RT that damage slow/non-dividing cells
fractionation
stretching RT treatments out over a longer period of time. Can get away with higher dose treatments
four Rs of radiobiology
Reassortment, Reoxygenation, Repair, Repopulation
Reassortment/Redistribution
using fractionation to hit cells at different times in their cell cycles
Reoxygenation
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
Repair
Fractionation allows normal tissues time to repair sublethal damage caused by the previous round of therapy
Repopulation
Negative against fractionation. Tumor cells have a chance to grow back when treatment isn’t continuous
hypofractionation
palliative treatment. goal is to help patient manage symptoms.
standard fractionation
curative treatment daily
hyperfractionation
curative treatment twice daily
definitive radiation therapy
using radiation therapy as a cure without surgery. for solid and lymphoid malignancies
neoadjuvant RT
pre-operative radiation.
Advantages: smaller treatment volume, more radiosensitive, improve surgeons success
adjuvant RT
post-operative radiation
Advantages: tailor RT fields to surgical findings, avoid unnecessary RT
chemotherapy’s role with RT?
works as a radio sensitizer. low dose, concurrent chemo is synergistic with RT
how can chemo possibly help RT?
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
