Capacitor selection for low output ripple and relativly high voltage

[Chrische]

I got a question regarding the ripple reduction of switch mode power supplies. The problem is the following:
I got at boost converter, that boosts a voltage up to 18V.
The operation frequency of the boost converter is fixed at 1.2Mhz.
The real problem is the voltage ripple of the output. What options do i really have in reducing the voltage ripple. Ceramic capacitors seem to work well at that frequency, but certainly not at that dc bias voltage.
Aluminum and Tantalum seems to have their resonant frequency below the operation frequency if I'm not mistaken (hard to figure out from the datasheets).
Is the only way to change the design and use a boost converter that operates at a lower frequency or am I missing something here?
the maximum output current of the converter is around 300mA.

[rob77]

i would just suggest to use a ceramic caps with higher capacity or even 2-3 of them in parallel.

[SeanB]

How about a LC filter ( using a very lossy inductor or you can make it worse) to reduce the ripple and noise. Then you can use ceramic capacitors, and get a very good attenuation.