Nginx Cache even if it's a 404 response

Hello everybody,

I use 404 rewriting url:

error_page 404 = /url_rewriting.php;

I cache images generated with a php render script which is in a folder /render/framed/:

set $no_cache 0;

location ~ /render/ {
include snippets/fastcgi-php.conf;
#fastcgi_pass unix:/run/php/php7.0-fpm.sock;
fastcgi_pass 127.0.0.1:9000;

fastcgi_buffers 8 16k; # increase the buffer size for PHP-FTP
fastcgi_buffer_size 32k; # increase the buffer size for PHP-FTP
fastcgi_cache_key $scheme$host$request_uri$request_method;
fastcgi_cache PROD;
fastcgi_cache_valid any 20d;
fastcgi_cache_valid 404 1d;
fastcgi_cache_use_stale updating error timeout invalid_header http_500 http_503;
fastcgi_ignore_headers Cache-Control Expires Set-Cookie;
fastcgi_hide_header "Set-Cookie";
fastcgi_cache_bypass $no_cache;
fastcgi_no_cache $no_cache;
expires 10M;
access_log off;
add_header Cache-Control "public";
add_header X-Cache-Status $upstream_cache_status;
}

The cache works with an url like this:

https://mywebsite.com/include/php/render/framed/img.php?VR=1&size=300&image=U3pmwKi

But the cache does not work with an url like this:

https://mywebsite.io/include/php/render/framed/file/VR/1/size/300/image/U3dpwK
This second URL go through error_page 404 = /url_rewriting.php; because the directory 'file' does not exists but the script display the image thanks to url_rewriting.php script which do the trick

What do I have to update to my Nginx config to be able to cache 404 responses?

Thanks,
Vincent.