242- rad onc

Question 1

difference b/w excitation and ionization? which is used in RT? What are the two types?

Answer 1

excitation: higher E level w/o ejection. Ionization: excitation adequate to eject electron. We use ionizing. Can be electromagnetic (x-rays, gamma rays) or particles (protons, neutrons, e-, etc)

Question 2

how do x rays and gamma rays compare to visible light?

Answer 2

shorter wavelengths, higher frequency, higher photon energy

Question 3

how are x rays vs gamma rays created?

Answer 3

x rays: artificially by machines (LINAC)

Gamma: decay of cobalt

Question 4

directly vs indirectly ionizing radiation:

Answer 4

Directly: charged particle interact directly w/ DNA.
Indirect: EM radiation interacts w/ H2O generating free radicles w/ interact with DNA

Question 5

what type of DNA damage is thought to mediate cell death in RT?

Answer 5

double strand breaks

Question 6

what are the two main reasons we fractionate RT?

Answer 6

Spare normal tissue (normal cells re-populate better than tumor cells)
Better cell kill (re-assortment from radio-resistant phases into sensitive ones) (reoxygenation: hypoxic cell are resistant to RT but may reoxygenate b/w fractions)

Question 7

External Beam RT: when do we use x-rays vs electrons?

Answer 7

x-rays: deep seated tumors

Electrons: superficial tumors like skin cancers

Question 8

when would you use intensity modulated RT? When would you use stereotactic treatment?

Answer 8

more complex scenario than 3d-CRT allows for (brain tumors, H&N cancers, prostate)

small, well-defined lesions in head, lung, liver, spine. Can be used if spine mets are found after EBRT

Question 9

brachytherapy: what is it? advantage? what cancers? low dose vs high dose?

Answer 9

source is placed inside the patient next to the area of interest. Can minimize doses to surrounding tissue (prostate, cervical, endometrial)
Low dose can be temporary or permanent (prostate or cervical). High dose is temporary (endometrial)