242b intro to radiation oncology

Question 1

ionizing radiation

Answer 1

orbital e ejection from atom

Question 2

x ray/gamma rays

Answer 2

packets of E

shorter wavelength/higher E

Question 3

x-ray vs gamma ray

Answer 3

x ray = artificial from machine

gamma = decay from intranuclear particles

Question 4

direct vs indirect radiation? what causes cell death?

Answer 4

direct = charged particles that cause damage

indirect = interacts with water to create OH radicals

dsDNA breaks –> cell death

Question 5

dosing - cure vs palliation

Answer 5

cure = 5-7 weeks with standard dose ( 2 Gy/day)
palliative = 2-4 weeks with higher dose

Question 6

fractionation

Answer 6

spare normal tissue - sublethal damage repair (tumor cells may not have machinery)

better efficacy of cell kill - re-assortment of tumor cells into radiosensitive phase + reoxygenation of tumor allows better killing (hypoxic = radio-resistnat)

Question 7

time -

Answer 7

+prolonging allows reassortment and reoxygenation of tumor

-allows tumor repopulation

Question 8

why add chemo to surgery and RT?

Answer 8

radiation sensitizer

Question 9

modalities

Answer 9

EBRT - outside of patient, 3D-CRT (palliative) and IMRT (special 3D with more beams - irregular masses near important structures), SBRT even more specialized, $, recurrent disease in a sensitive area (spine, CNS)

brachytherapy - inside patient

IORT - during surgery (breast)

unsealed sources/targeted - I-131 decays in thyroid cancer; radium 223 - PC that decays in bone

Question 10

e vs photons

Answer 10

e - limited penetration (superficial cancers - skin)

xray/photons - deep penetration

Question 11

brachytherapy - low vs high dose

Answer 11

low - temp or permanent, PC and cervical ca

high - temporarily only for a few minutes (endometrial cancer)

Question 12

SE of radiation

Answer 12

acute = predictable, last 2-4 weeks, made worse by surgery, irritants, etc

chronic = >90 days-years, permanent, osteoradionecrosis, secondary malignancy