Caesar decided to invade Parthia at least partly because of the prophecy that a Roman King would conquer it.
Not really. He had plans to invade Parthia already to regain the standards-really every ambitious Roman with any military experience would jump at the opportunity to use a proconsulship of Syria as a chance to get revenge for Crassus' defeat. The prophesy was likely just a convenient way for him to float the idea around that only under his leadership could Rome conquer Parthia.