Low Dose Rate Brachytherapy (LDR)

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

  1. 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
  2. Needle spacing <1cm
  3. 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.
  4. In the case of multiple planes obeying rules 1-3 and planes should be parallel.

Paterson Parker Volume Implant Rules

  1. Total activity is divided into 8 parts
    • The periphery uses 6 parts
    • The core uses 2 parts
  2. Needle spacing <1cm
  3. 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.

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.

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