STD18NF25 [SOA] [Power Dissipation Derating]

[CBR600RR]

Hello
I have a question regarding SOA of STD18NF25.
How should we consider derating when Ta=100℃?
What is the calculation method if there is no graph for [Power Dissipation Derating Curve]?
MOSFET is used as a low side switch.
Each voltage and current condition is planned to be Vgs=5V, Vds=30V, Ids=15A (1us or less).