Shutter timer error

Shutter timer error for Co-60 arises due to finite travel time of the source to reach the treatment position.

It can be either positive or negative.

The length of a shutter timer error of a Co-60 unti is approximately 0.1 to 0.2 min.

It can be determined using an ionization chamber.

If the shutter timer error is positive to set the treatment time on the unit, it must be added to the computed "beam on " time. If negative obviously subtract it from the beam on time.