Access to query param with dashes in the name (no replies)

Hi,
for the http header Nginx Nginx convert the dashes in the header name to underscores.
I have a query string with a param with a dash in the name, but i can't see it with $arg_PARAMETER variable.
There is a way to have the value of this parameter in a variable?
For example my query string is:
response-content-disposition=attachment
I know i can parse manually the query string, but I think if there is an Nginx embeded function, this function could by faster than a manual parsing.
Regards,

Luca