Chapter 14 WS

Question 1

define bracytherapy

Answer 1

Therapy in which sources of radiation are placed at close proximity to or directly in the target volume.

Question 2

what is a sealed source

Answer 2

The radioactive isotope is encased and sealed within a small metal structure, usually titanium or stainless steel tubes that are welded shut at the ends. Recently they are being embedded in plastic or similar material.

Question 3

define activity as it related to brachytherapy

Answer 3

The quantity used to describe the strength of the source.

The number of disintegrations per unit time for a particular source. The activity of any radioactive source changes with time as source decays.

Question 4

what is the historic unit of measurement

Answer 4

Curie

1 gram of radium equals 3.7 x 1010 disintegrations per second.

Question 5

what is the name of the SI unit used

Answer 5

Becquerel

1 Becquerel is one disintegration per second. 3.7 x 1010Bq = 1 Ci

Question 6

what is remote afterloading

Answer 6

The highly radioactive source is housed in a treatment unit that is programmed to send the source into the applicator or catheters according to a predetermined treatment plan

Question 7

what is the dose rate for low-dose rate

Answer 7

up to 2Gy/h

Question 8

what is the dose rate for medium-dose rate

Answer 8

2Gy/h to 12 Gy/h

Question 9

what is the dose rate for high dose rate

Answer 9

> 12 Gy/h

Question 10

define specific activity

Answer 10

Activity per unit mass of a radioactive material.

The specific activity dictates the maximum activity that a source of a given mass can have.

Question 11

interstitial

Answer 11

placement of radioactive source directly into a tumor or tumor bed

Question 12

intracavitary

Answer 12

placement of a radioactive source within a body cavity

ex. cervical cancer

Question 13

intraluminal

Answer 13

placement of a radioactive source within a body tube

ex. esophageal cncer, trachea

Question 14

intravascular

Answer 14

placement of a radioactive source within a blood vessel.

Used in the past

Question 15

surface

Answer 15

placement of a radioactive source on top of the area to be treated.

Ex. non-melanoma skin cancers, melanoma of the eye.

Question 16

What are the most commonly used radioisotopes for treating prostate cancer.

Answer 16

I125 (Iodine 125) and Pd103 (palladium 103)

Question 17

When treating cervical cancer with both external beam radiation and brachytherapy, what are the two purposes of external beam portion of the treatment.

Answer 17

1) to treat parametrial disease and pelvic lymph nodes that cannot be treated with brachytherapy
2) to reduce the tumor volume, thereby reducing the treatment volume and the toxicity associated with the brachytherapy treatment that follows.

Question 18

Describe point A.

Answer 18

Is where the prescription dose is specified. It is located 2cm superior to the top of the ovoids along the tandem and 2cm lateral to the tandem in the plan of the applicator. It approximates the location where the uterine arteries and ureters intersect, and is chosen to ensure that the cervix located between point A and applicator receives at least the prescription dose.

Question 19

describe point B.

Answer 19

Is located 2cm superior to the top of the ovoids and 5 cm lateral to the patient’s midline, represents the parametrial nodes.

Question 20

what are the critical structures for partial breast brachytherapy

Answer 20

skin and chest wall

Question 21

In the treatment of cervical cancer. What is a tandem.

Answer 21

A long narrow tube inserted through the cervix into the uterus

Question 22

In the treatment of cervical cancer. What are ovoids.

Answer 22

Cylindrical or semispherical shaped devices inserted into the lateral vaginal fornices.