Boost converter drawing too much current
My advice: throw away your PCB, and make a new one, per manufacturer's suggestion found in the LM3478 datasheet 



Your design has unfixable skinny traces in ALL critical high-current loops. Do you see the difference? It is likely that most of the loops ring like hell and make horrible switching losses. For clarifications pay attention to Fig.37 of the datasheet, and application guide AN-1229 "Simple Switcher PCB Layout Guidelines".

OBSERVATION #2: The LM3478 operates at 400 kHz. To get 20 -> 170 V upconversion, a MOSFET with 270V Vds 7 A is recommended by Texas Instruments WEBBENCH. Unfortunately, for 400 kHz (2.5 us cycle) the transistor has to switch under a fraction of us, which doesn't seem to be achievable for the 170V switch voltage, and the design tool cannot find a transistor that meets this requirement. As a matter of fact, the WEBBENCH can't offer any design where it can find a proper transistor for the job with boost topology. I believe you might need to change the converter topology to "flyback".