The Holy Grail

Why did the phrase 'holy grail' start to get mentioned in biomedical papers around 1986 (with a similar trend in book popularity)?

The Monty Python film was in 1975, so it can't have been that. Was it the Mastertronic game in 1985? Or the Doctor Who episode in 1986, perhaps? I think it might well have been this 1988 book: The Grail Legend by Emma Jung (Carl Jung's wife), that really kicked things off.