Card Set Information
the inverse square law states that:
intensity is inversely proportional to the square of the distance
if the distance from a point source is tripled, the intensity will be?
to apply the inverse sq. law, one must know...
2 distances and 1 intensity
(you only need 3 pieces to the equation, then solve for the 4th/missing)
an instrument positioned 1m from a source is moved 50 cm closer, what will the radiation intensity do? (increase/decrease, and by what fraction)
increase by 4 times (increases by a square of the change in distance: .5m)
eqation to solve for D2?
decay constant (lamda) formula
lamda (decay constant)
A = A
advantages of brachy (3):
-enables us to give a high tumoricidal dose
-sparing normal tissues surrounging tumor (high dose fall off)
*ideally these 2 advantages enable us to help the therapeutic ratio of Tx
high half life typically means implants will be________?
short half life typically means implants will be __________?
most popular cancer treated with brachytherapy?
prostate (treated interstitially with permanent seeds)
What "R" of radiobiology is important to brachytherapy?
redistribution - high dose getting to the tumor, cells tend to redistribute into G2 (next phase is M = radiosensitive --> good!)
tandems and ovoids are used for what treatment
(give good distribution to the cervix,
GYN most common sources used
side effects of GYN cancers with brachytherapy often have side effects that are... acute or chronic?
chronic effects (due to high dose)
: vaginal stenosis, atrophy, fibrosis