Brachytherapy

Question 1

in the past what was the first tx with radium and what was the dose

Answer 1

gyne

erythema dose

Question 2

1Ci = X Bq = 1gram of Y

Answer 2

X =3.7x10^10

Y = Radium 226

Question 3

when is brachy used

Answer 3

in situations where the treatment area is accessible -tx vol or depth is small
-low risk of met spread

Question 4

what is an advantage of brachy

Answer 4

high dose of rad can be delivered in a short time period with low doses to surrounding tissue

Question 5

disadvantage

Answer 5

• highly specialized

- can be dangerous if proper safety measures are not in place

Question 6

interstitial

Answer 6

within tissue

-usually suited for deep seated lesions in the pelvis, abdo, and lung

Question 7

intracavitary

Answer 7

within a cavity

ei. cervical

Question 8

intraluminal

Answer 8

within a lumen

Question 9

intravascular

Answer 9

within vessels

-done with catheter, most likely after ballon angioplasty

Question 10

topical

Answer 10

on surface

-mold of body can be made so that the sources are placed in a definite arrangement

Question 11

x5 points on LDR

Answer 11

• 0.4Gy/hr
• in patient
• over several days
• manual loading
• I-125 and Pd 103

Question 12

x5 points on HDR

Answer 12

• > 12Gy/hr
• outpatient
• within mins
• remote after-loading
• Ir-192

Question 13

what are the advantages to HDR

Answer 13

• improved optimization
• stable positions
• add distance to normal tissues
• outpatient
• smaller applicators
• can be done intraoperatively, perioperatively
• reduced rad to providers

Question 14

Disadvantages of HDR

Answer 14

• tx unit complexity
• compressed time frame
• rad bio inferior to LDR
• mechanical failure disastrous

Question 15

brief definition of unsealed sources

Answer 15

• “naked sources” instead of being implanted in the body by a capsule of some sort it is injected intravenously usually to treat bone mets
• usually with strontium-89 which is a pure beta emitter with E=1.5MeV

Question 16

brief definition of sealed sources

Answer 16

encapsulated to:

• prevent leakage of materials
• filter undesirable alpha and beta particles
• commonly gold, platinum, stainless steal, titanium

Question 17

why are alpha and beta particles not useful

Answer 17

alpha - lack penetrating power

beta - a little more penetrating than alpha, but not too much

Question 18

what are the parameters used to characterize the distribution of radioactivity within sources

Answer 18

active length
physical length
linear activity

Question 19

active length

Answer 19

distance between the extreme ends of tha radioactive material

Question 20

physical length

Answer 20

the distance between the physical ends of the encapsulated source

Question 21

linear activity

Answer 21

activity per unit length of the source

Question 22

why is radioactive decay a stochastic process

Answer 22

cant predict the decay of a single isotope only a large amount of atoms and how they will decay over time

Question 23

Radioiostope properties

Answer 23

• half life: determine if short or long term
• photon energy: want gamma and characteristic not alpha and betas
• specific activity: activity per unit mass of a material; high is advantageous
• mean life avg lifetime for decay of radioactive atoms; mean life = T1/2 x 1.44

Question 24

Source Specifications

Answer 24

• activity: description of rate of decay (Ci or Bq)
• exposure rate: in air at a specified distance
• exposure rate constant: compares output with that of radium

Question 25

how is the exposure rate constant calculated

Answer 25

divide the exposure rate of a material at 1m by the exposure rate of radium at 1m

Question 26

why as brachy used in the past? what was a disadvantage?

Answer 26

had a high specific activity | radon gas was produced

Question 27

define isotope

Answer 27

equal number of electrons and protons but diff amount of neutrons