Scientific Article Titled: Secrets of Medical Physics in Cancer Treatment This article is connected to several Sustainable Development Goals, especially SDG 3: Good Health and Well-being, SDG 4: Quality Education, and SDG 9: Industry, Innovation and Infrastructure, because medical physics represents an important scientific link between physics, modern medical technology, and cancer patient care. Medical physics is one of the most important scientific fields that has contributed to the development of cancer diagnosis and treatment. It is not only the application of physics inside hospitals, but also a precise science that helps doctors use radiation and advanced technologies safely and effectively. Its importance appears clearly in radiation therapy, where high-energy beams or particles, such as X-rays, gamma rays, electrons, or protons, are used to destroy or damage cancer cells while trying to protect nearby healthy tissues as much as possible. One of the main secrets of medical physics is its ability to turn cancer treatment into a highly personalized plan for each patient. Before radiation therapy begins, medical images such as CT scans are used to locate the tumor accurately. Then, the treatment team designs a plan that determines the radiation dose, beam directions, number of sessions, and organs that must be protected. This precision makes the treatment safer and more effective, because the goal is not only to deliver radiation, but to deliver it to the right place and in the right amount. Another important secret is radiation dose calculation. In radiation therapy, the dose is not selected randomly. It is carefully calculated according to the type, size, and location of the tumor, as well as the patient’s health condition. Here, the medical physicist plays a major role in ensuring that the treatment machine delivers the planned dose accurately and that the treatment plan balances tumor control with the protection of healthy organs. The International Atomic Energy Agency explains that medical physicists are mainly involved in the safety and performance of medical equipment and computer systems used in radiotherapy, diagnostic imaging, and nuclear medicine. Medical physics also depends on advanced machines such as the linear accelerator, which is used in external beam radiation therapy to direct radiation toward a specific area of the body. External beam radiation therapy is considered a local treatment, meaning that it treats a specific part of the body rather than the whole body. For example, if a tumor is located in a certain organ, radiation is directed to that area according to a carefully prepared treatment plan. Medical physics is not limited to external radiation therapy. It also includes other techniques such as brachytherapy, also known as internal radiation therapy, in which radioactive material is placed inside the body or near the cancer. This method is used for certain cancers, including cancers of the head and neck, breast, cervix, prostate, and eye. Another hidden but essential part of medical physics is quality assurance. Before a patient receives treatment, the equipment is tested carefully to make sure it is working correctly. The treatment plan is also checked, measurements are reviewed, and the radiation delivery is verified. This makes the medical physicist an essential member of the cancer treatment team, working behind the scenes to ensure accuracy, safety, and reliability. The importance of medical physics continues to grow with modern technology. Advanced imaging, computer-based treatment planning, artificial intelligence, and image-guided radiation therapy are helping improve treatment accuracy and reduce errors. Therefore, medical physics is not only a supporting science; it is a central part of the future of cancer treatment. In conclusion, medical physics shows that cancer treatment does not depend only on medicine and surgery. It also depends on accurate science, physical calculations, and advanced technology. Through treatment planning, dose measurement, quality assurance, and patient protection, medical physics has become one of the most important secrets behind successful cancer treatment and modern healthcare. AL_mustaqbal University is the first university in Iraq.