fastcgi_cache_key cache only the part afther "?"

Hallo community
I have a question abot the fastcgi_cache_key parameter. I have the uri:

http://domain.com/tex_that_can_change/?640x2048/3/90/custom/323/2600323/0.jpg

Can nginx cache only the part after “?”, because the part before the ? can change and i wont to prevent that the same Image is cached twice?

My Configuration:

fastcgi_cache_path /ramdisk levels=1:2
keys_zone=CDN:2048m
inactive=2d
max_size=100G;

fastcgi_cache_key "$scheme$request_method$host$request_uri";