Final answer:
The synonym for diathermy is thermotherapy, which is a treatment that uses heat. Unlike radiation therapy or chemotherapy, which are used to treat cancer by damaging DNA or using chemical substances, thermotherapy involves applying heat to relieve pain and improve muscle flexibility.
Step-by-step explanation:
The synonym for diathermy is thermotherapy. Diathermy, often utilizing ultrasound, refers to a medical treatment in which heat is generated in body tissues by high-frequency electric currents or ultrasound to relieve pain and improve flexibility in muscles. Therapeutic applications include both athletics and physical therapy.
In contrast, radiation therapy is quite different, as it involves the use of high-energy radiation to damage the DNA of cancer cells, either via external beams or internally-placed radioactive substances. Similarly, chemotherapy refers to treating cancer with chemical substances, not to be confused with diathermy or its synonym, thermotherapy.