.htaccess for phpbb deleted forum

[normcdn]

Hi everybody,
Sorry to ask this question, but I am stock and it is quite frustrating for a so simple problem.
I always monitor carefully my error 404 in Google WMT.
I have a phpbb forum with many sub-forums. Some have been deleted, and it generates error 404 like in the following example:

viewtopic.php?f=53&t=8091&p=185507

the forum f=53 no longer exist. Is there a simply way, in the .htaccess, to redirect url containing f=53 to the main page and stop generating error 404.
I tried the (.*) in many scenarios and it did not work.
Thanks for your time.
Normand

[incrediBILL]

Try doing a condition based on the QUERY_STRING containing "f=53" would be a start.

[g1smd]

If the page doesn't exist you should return "410 Gone" status, not a redirect.

It's bad form to mass redirect broken URLs to the home page. Your site may well be flagged for having "soft 404" errors if you do.

[normcdn]

Thanks for the info. I am still trying to figure out a way of this problem.
I was aware about the « soft 404 ». Thanks