Lec 22 - Radiation and Oncology Flashcards
4 basic patterns of spread
1) local growth-tumor itsle fenlarges over time (size or depth)
2) local extension - tumor invades adjacent organs
3) lymph node metastases
4) hematogenous metasteses - ex prostate to bone and small cell lung to brain
3 main treatments
1) surgery
2) medical therapy -chemo, hormone, biologic, vaccine
3) radiation therapy
adjuvant meaning
usually done after main treatment (aka surgery in most)
neoadjuvant meaning:
before the mos important treatment
RT used as adjunct cancer examples:
Breast cancer
skin cancer
prostate cancer
uterineendometrium
RT used as neoadjuvant cancer examples:
esophgeal
rectal CA
pancreaticCA
extremity sarcoma
a radiosensitive tumor does what with radiation?
melts!
radioresponsive tumor does what with RT?
melts quickly!
4 Rs of radiation therapy
1) repair- splitting radiation into small parts, normal tissue cells are allowed to repair sublethal damage but tumor cells cant do this as well
2) redistribution: allow tumor cells to move into the most sensitive phases of cell cycle over time
3) reoxygenation- allow “inner” hypoxic tumor cells to get a greater exposure to oxygen over the course of treatment
4) repopulation: delivering continuous, daily blows to tumor cells prevents them from repopulating and thriving
How RT works…
- DNA of well-oxygenated tumor cells appears to be the main target for biological effect of radiation
- most important lesion induced is adouble strand DNA break
radiosensitive phase of cell cycle=
M/G2
radioresistant phase of cell cycle =
S
therapeutic ratio
TCP is greater than NTCP = thats why radiation is useful
what type of cells are more radioresistant?
hypoxic cells - O2 for some reason seems to enhance ability to cause double strand DNA breaks
reoxygenation allows for?
progressvie killing of tumor cells
kill the outer oxygenated cell–> reoxygenate outer cells of what didnt die –> kill that new outer oxygenated area… on and on
standard fractionation dosing
180-200cGy 1x/day
palliative standard dosing?
300 cGy daily
hyperfractionation dose and good for?
120-150cGy 2x/day
good for rapidly dividing cancers
hypofractionation dosing
800-2200cGy for 1-3 fractions
give a tumor one really good whack
curative intent treatement style
larger # treatments and lower dose per treatment
palliative intent treatment:
smaller # treatments and higher dose per treatment
5 levels of treatment complexity
nonplanned 2D plan 3DCRT plan IMRT Plan SRS/SBRT plan
2D plan
do a scan and dont measure but just do it? make up the dose bro
3DCRT plan
uses computer based treatment planning
- treat and avoid normal structures as much as possible
- downfall is that it leaks into other tissues
- not such a good option anymore - cant conform to specific organ shapes
Dose volume histogram shows?
with 3DCRT shows how much of the target and normal structures are receiving certain doses
IMRT plan
like 3DCRT but it conforms to whatever shape your target is
SRS/SBRT plan
pretty mcuh as good as you can get to not damage other tissues
photons
due to gradual fall off treats deep lesions - build up strength
skin sparing
can combine fields for better dose distribution
electrons
reats shallow lesions
definite range
usually single field
stereoscopic IGRT is for
wat is it?
bony lesions or non soft tissue
basically youre constantly readjusting for movement
cone beam IGRT is for?
what is ti?
for soft tissue
bassically youre constantly readjusting for movemnt
