pstopdf problem

[Niarf]

Hi,
A couple of weeks, I configure a new CUPS printer server to be able to use 200 printers, but, recently, I saw the partition /tmp is full.

A lot of pstopdf.ABCDE, where ABCDE is a random string, which belongs to 'lp', right 600, size between 0 and 2.6MB.

Why doesn't CUPS remove them ?
Can I remove them, cups being off ?

How can I configure cups to remove them ?

Thanks.
And good week.

Niarf