Low Dose Rate Brachytherapy (LDR)

Overview

Low dose rate brachytherapy refers to permanent or temporary implants with an instantaneous dose rate of less than 20cGy/minute.

Interstitial Seed Placement Systems

Paterson-Parker System

The Parterson-Parker seed placement system was developed to deliver a uniform dose (+/- 10%) to a plane or volume. Tables were produced giving the dose distribution for given activity and geometries used in the Paterson-Parker system.

Paterson-Parker Planar Implant Rules

Determine fraction of activity at the periphery of implant area.
- Area < 25cm²: 2/3 of activity in periphery
- Area 25 – 100cm²: 1/2 of activity in periphery
- Area > 100cm²: 1/3 of activity in periphery
Needle spacing <1cm
If the ends of the distribution are uncrossed (needle rows are not capped with a perpendicular row) then the uniform area is reduced by 10% for each uncapped end.
In the case of multiple planes obeying rules 1-3 and planes should be parallel.

Paterson Parker Volume Implant Rules

Total activity is divided into 8 parts
- The periphery uses 6 parts
- The core uses 2 parts
Needle spacing <1cm
If ends are uncrossed (needle rows are not capped with a perpendicular row) then the uniform volume is reduced by 7.5% for each uncapped end.

Illustration of the Paterson-Parker low dose rate (LDR) brachytherapy seed placement system.

Quimby System

In contrast to the Paterson-Parker system, the Quimby system uses uniform source activity to yield a non-uniform distribution of dose. Like the Paterson-Parker system, the Quimby system relies on dose distribution tables for dose calculation.