how to delete the *.ismv files in the smooth streaming

I create a directory which contains the *.ism , *.ismc,*ismv files in the inetpub/wwwroot/ . then the client requests the smooth streaming .

after that , when I want to delete the directory, I only can delete the *.ism,*ismc files . The *.ismv files can't be deleted unless i restart the IIS(seems the files is in use).  How can i delete these files without restart the IIS? thanks a lot!