[en] Cancers once considered unmanageable and fatal can now be diagnosed earlier and treated more effectively using nuclear medicine and radiation therapy, giving patients a better quality of life and, for many, a significant possibility of being cured. These developments can be attributed to advances in research and innovations in technology, which are becoming increasingly accessible. But cancer remains a disease that is on the rise globally, having claimed the lives of 9.6 million people in 2018, a number that is expected to increase, with an estimated 16.3 million deaths predicted worldwide in 2040. Cancer occurs when cells in the body grow and divide abnormally and uncontrollably, often forming clusters called tumours. Tumours can be diagnosed using small amounts of radiation and then treated with higher doses. Confirmation of the type of tumour, as well as of its size, location and extent of spread, is essential to selecting the appropriate treatment approach, such as surgery, radiotherapy, chemotherapy or immunotherapy, that is used either alone or in combination. When radiotherapy is appropriate, it is necessary to select the dose required carefully and to deliver it to the tumour with accurately calibrated equipment to maximize the effectiveness of the process while minimizing harm. The science of measuring, calculating and assessing absorbed doses of radiation is called dosimetry.