 When a person is diagnosed with cancer, ionizing radiation is often used to destroy the tumor cells. But treating the patient with the correct amount of radiation is essential to help cure the disease. Radiotherapy can be an effective tool to treat cancer, but only if the right dose is applied. If the dose is too high, it may be harmful for the patient. If the dose is too low, cancer cells will not be under control and the patient will not be cured. Dosimetry is used to determine the necessary dose of radiation. This science measures the radiation absorbed by the human tissue. The IAEA helps member states ensure that patients receive the exact amount of radiation they need. It provides calibration and audit services needed for accurate dose measurements in clinics. For radiotherapy centers, we send annually 600 to 700 dose meters for those audits. We provide comparison so that we can check that in each national laboratory they are doing the calibrations in the same way. Accurate dosimetry measurements are crucial to make sure radiation treatment is safe and effective.