clearing cache_menu

I have installed Drupal 6.0 and I know that my cache_menu is broken. I want to free it because of its size:

cache | 59 MB
cache_form | 205 MB
cache_page | 24 kB
cache_menu | 6357 MB
files | 2192 kB
menu_router | 10152 kB
menu_links | 16 MB

I cant update to another version of Drupal. I executed the following command:

cgcom=# delete from cache_menu;
DELETE 890849

but the size of the table is growing up!!!

cache | 59 MB
cache_form | 205 MB
cache_page | 24 kB
cache_menu | 6358 MB

How can I free disk space of that table? Maybe must I execute a vacuum?

vacuumdb -f -z -d database -U user

I have a postgres SQL database 8.1

Any suggestions?

Thanks!!!!!