Purpose The global incidence of cancer is rising, particularly in low- and middle-income countries. Radiotherapy is an important cancer treatment in the curative and palliative setting. We aimed to estimate the global demand for and supply of radiotherapy megavoltage machines (MVMs) and assess the changes in supply and demand during the past decade. Materials and Methods Cancer incidences for 27 cancer types in 184 countries were extracted from the International Agency for Research on Cancer GLOBOCAN database. The Collaboration for Cancer Outcomes Research and Evaluation radiotherapy utilization rate (RTU) model was used to estimate the number of patients in each country with an indication for radiotherapy for each cancer type and estimate the demand for MVMs. The radiotherapy supply data were accessed from Directory of Radiotherapy Centres database maintained by the International Atomic Energy Agency. Results RTU varied by country, from 32% in Mongolia to 59% in Comoros. The average optimal world RTU was 50%, equating to 7 million people in 2012 who would benefit from radiotherapy. There remains a deficit of more than 7,000 machines worldwide. During the past decade, the gap between radiotherapy demand and supply has widened in low-income countries. Conclusion RTU varies significantly between countries. Approximately half of all patients with cancer worldwide should receive radiotherapy; however, more than 2 million people are unable to access it because of a lack of MVMs. Low- and middle-income countries are particularly disadvantaged by this deficit.