Chemotherapy was a type of cancer treatment that was used on Earth in the 20th century. It was often evaluated against other medical procedures, among which including image therapy.
Doctor Leonard McCoy, while present in the year 1986 after time traveling, was once asked in an elevator what his views were regarding chemotherapy after he remarked that it was "unbelievable" patients had to endure such treatment. McCoy's response was: "Sounds like the goddamn Spanish Inquisition if you ask me!"
Later, in the operating room, he referred to chemotherapy and fundoscopic examinations as "medievalism". (Star Trek IV: The Voyage Home)