For multisession you'd do something like:
growisofs -dvd-compat -speed=4 -use-the-force-luke=bufsize:32m -M /dev/dvdrw -graft-points -rational-rock -full-iso9660-filenames -iso-level 2 /path/to/files
adjust speed=, /dev/dvdrw, and /path/to/files as necessary.
see 'man growisofs' for the meaning of -M versus -Z
Burn an initial session to the selected device. A special form
of this option is recognized to support burning of pre-mastered
images. See EXAMPLES section for further details.
Merge a new session to an existing one.