AlignRT does not record breathingcurves but switches beam off and on according to a surface matching the reference value. A typical situation would be DIBH ... there is no respiratory rate that is feasible. If you want to treat in DIBH stop the patient from breathing for about 10 or more seconds. If you want to treat in freebreathing the surface is moving and you have to adjust tolerancelevels (e.g. according to your 4D-CT scan) to allow treatment. We would not recommend AlignRT for "real gating" because the a matching surface might be found in the wrong phase of the beathingcycle if you are not aware of the breathingcurve itself.
If you are asking for a respiratory rate for Gate-RT, than we in our department made the best experiences with less than 9 cycles/minute ... there is enough time left for the beam to come on during a typical 30%-70% Phase of the breathingcycle - especially with FFF. (we use Elektalinacs with a slow ramp-up-time. Faster rates may be possible for Varian)