Which of the following correctly describes the term 'radiation therapy'?

Radiation therapy is accurately described as a treatment modality using ionizing radiation. This form of therapy is primarily utilized to destroy malignant cells in cancerous tissues. It works by targeting specific areas of the body where tumors are located, delivering high-energy particles or waves, such as X-rays or gamma rays, to damage the DNA of cancer cells. This damage inhibits their ability to proliferate and causes cell death.

In contrast, other choices reflect different medical practices. The first choice pertains to diagnostic techniques, which involve methods such as imaging to identify illnesses rather than treating them. The second choice refers to pain management strategies, which may include various pharmacological or non-pharmacological approaches, but these do not involve the direct application of radiation for treatment. The last choice discusses enhancing the immune system, which typically pertains to immunotherapy or other biological interventions unrelated to the application of ionizing radiation. Thus, option C distinctly encompasses the essence and purpose of radiation therapy in medical treatment.