Planar and Volume Implants Flashcards
What are the three major systems for planar and volume implants?
Paterson-Parker or Manchester
Quimby
Paris
Describe the Paterson-Parker System / Manchester:
A non-uniform source distribution is used to obtain an uniform dose distribution. This system was designed to deliver a dose that is uniform to within +/- 10% to a plane or volume. Planar implants are designed so that the dose is uniform to withing +/- 10% over a plane within +/- 0.5 cm of the plane of the implant. The treated volume is a slab of tissue 1.0 cm thick.
T(r) = 1
Describe the Quimby System
The source distribution is uniform which leads to a non-uniform dose distribution.
T(r) = 1
What are the energies of low energy sources?
< 200 keV
What sources can be used with the Paterson-Parker system?
Cs-137 & Ir-192
The classical system of dosimetry for intracavitary cervix treatment is the
Manchester system.
Define Point A:
2 cm superior to the top of the flange and 2 cm lateral to the tandem.
Define Point B:
2 cm superior to the flange along the axis of the patient ( or in some definitions of B, along the tandem) and 5 cm lateral to the axis.
In cervical cancer treatment where is the dose prescribed to?
The dose is prescribed to point A.
What is point B approximate anatomical position?
Point B is around the obturator lymph nodes.
Define distance along:
Distance from the center of the along the length of the tube
Define distance away:
The distance away from the tube in a direction perpedicular to the long axis of the tube.
What the typical dose rate prescribed to point A?
55 cGy/h
What source is to treat cervical cancer with a LDR?
Cs-137
The dose rate at point B is what fraction of the dose rate at point A?
1/3
