Final answer:
The Joint Commission (TJC) is the regulatory agency that focuses on improving health care quality and mandates radiation oncology departments to have a QI plan.
Step-by-step explanation:
The regulatory agency dedicated to improving the quality of care in health care settings and requiring a dedicated Quality Improvement (QI) plan for every radiation oncology department is The Joint Commission (TJC). The Joint Commission is an independent, not-for-profit organization that accredits and certifies health care organizations and programs in the United States. Its goal is to ensure that patients receive the safest, highest quality, best-value health care across all settings. Specifically in radiation oncology, a QI plan is critical for maintaining safety and effectiveness in treatments involving radiation.