PWM or Phase Control Dimming?
Phase control for AC Mains dimming is old but proven technology.  This is, of course, PWM control that just happens to be synchronized with the incoming AC Mains waveform.  

That said, you can try using a non-synchronized PWM but you need to be aware that you may run into frequency beating problems. That is: if your PWM frequency is not harmonically related to the Ac Mains frequency, you may see the difference in frequency as a low-frequency beat.  This will cause the lamp brightness to vary at a periodic rate.

I honestly don't know how well non-synchronized PWM will work. I hope that you try it and let us know how well it works.