this should work, but you'll need to join on a good key, I just used title_rw to show.
FROM(SEL 'Y',title_rw FROM db.source ,db.person_title p
WHERE p.person_id= db.source.person_id) D( Y,titlerw)
CASE WHEN title_rw LIKE '%East%' AND Y = 'Y' THEN 'East'
WHEN title_rw LIKE '%Central%' AND Y = 'Y' THEN 'Central'
WHEN title_rw LIKE '%West%' AND Y = 'Y' THEN 'West'
ELSE 'Region N/A' END
WHERE db.source.title_rw = d.titlerw