How much RF power can a microstrip line handle?
A simple method might be: -


Convert power to watts: 45 dBm is 32 watts
Divide by Z0 to get current squared
Take the square root to get current (0.8 amps RMS)


Then use an on-line calculator to reveal the minimum thickness required for a given temperature rise of the copper. This on-line calculator suggests that the minimum trace width (1 oz copper = 35 micron) for a 40 degC rise is 0.35 mm.

I personally think no more than 20 degC is something I'd be comfortable with (generalism alert) so, the trace width has to be at least 0.53 mm.

Conversely, for a 0.37 mm trace width, the current should be no more than 0.77 amps RMS.