Date format in reports

In reports Parameter use the below format

TRUNC(prh.creation_date)>=nvl(FND_DATE.CANONICAL_TO_DATE(:p_from_date),TRUNC(prh.creation_date))
AND TRUNC(prh.creation_date)<=nvl(FND_DATE.CANONICAL_TO_DATE(:p_to_date),TRUNC(prh.creation_date))

For the above format use the FND_DATE4_REQUIRED_STANDARD valueset.