Radiation Therapy Flashcards
What is an alpha particle?
Positively (+) charges electron
Two protons and two neutrons
What is a beta particle?
Negatively (-) charged electron
What is the penetrance of a negatively charged electron/beta particle?
None, it is stopped by a few sheets of aluminum or a few mm of tissue
Which penetrates further, alpha or beta particles?
Beta
What is a gamma particle?
Originates within the nucleus
Where do x-rays originate?
Outside the nucleus
What is an x-ray?
Electron-beams used most commonly to produce photon beams by bombarding material (tungsten) with high-energy accelerated electrons
What is a proton?
Large positively (+) charged, created by acceleration at 300 mEV energies
What is a neutron?
A large neutrally charged particle, MADE by accelerating a charged particle against a suitable substance or by fission
What is a pi meson?
Negative pi mesons appear particularly suited for radiation therapy as their penetration and depth-dose profile lend themselves to shaping the high dose area to the tumor size and location
I.E. nuclear glue to hold up neutrons and protons in the nucleus
What is the clinical application of the photoelectric effect?
Diagnostic radiology
Is the photoelectric effect dependent on atomic number?
Yes, Z^3
What is pair production?
A radiologic phenomenon that starts to occur at 1.02 mEV and continues to 30 mEV
Is pair production dependent on atomic number?
Yes
What is the clinical application of the Compton effect?
Radiotherapy
What particle in the Compton effect interacts with DNA directly and H2O to form hydroxyl free radicals?
Displaced electrons
What is the energy associated with the Compton effect?
2, but usually 6-20 MeV
In the Compton effect, what does the incident photon interact with?
Loosely bound outer orbital electron
In the Compton effect, what is the direct action?
Indirect action?
Direct: DNA Interaction
Indirect: formation of free hydroxyl radicals
In the Compton effect, is absorption dependent on tissue density or number?
No
What are the most common sources of brachytherapy in Gyn cancers?
Cesium 137 (30 yrs)
Iridium 192 (74 days)
What type of energy is produced by bombarding material with highly accelerated electrons?
X-rays
What is the origin of gamma rays?
Originates within the nucleus and are emitted from radioisotope decay
What is linear energy transfer?
Rate of energy deposition along the path of the beam
What has high LET?
Densely ionizing radiation like neutrons, alpha particles, pi-mesons
What has low LET?
Sparsely ionizing radiation like gamma rays and high energy electrons (x-rays)
What are the benefits of high LET energy?
More effective for NECROTIC tumors (hypoxic)
What has the highest LET?
Neutrons
What has the lowest LET?
250 kv x-ray
