There are striking global disparities in the diagnosis and treatment of cancer. Less than 5% of global cancer resources are directed toward low- and middle-income countries (LMIC), and the cancer mortality-to-incidence ratio in LMICs is nearly double compared to high-income countries. Better, more accessible therapies are urgently needed to address this challenge. Radiation therapy is one of the most cost-effective cancer therapies. It is non-invasive, allows for organ preservation, and is indicated for the majority of the common cancer types in LMICs. The Global Task Force on Radiotherapy for Cancer Control suggest that scaling up RT will result in a net economic benefit of US$11 to $280 Billion per country over the next 20 years. At present, however, state-of-art targeted and sufficiently organ-sparing radiation therapy, such as intensity-modulated radiation therapy (IMRT), remains out-of-reach for most cancer patients in LMICs, largely because the technology is too complex and costly. The goal of this proposal is to develop a cost-effective system for delivering radiation therapy that will provide state-of-the-art IMRT with affordable, reliable technology. This will be achieved using a ring physical compensator system that provides highly efficient beam delivery and is adaptable to either a pre-existing Cobalt-60 device or a linear accelerator. We have developed prototypes that have already been constructed by our industrial partner. The design maximizes efficiency and patient throughput while minimizing requirements for maintenance, infrastructure, and staffing to perform quality assurance. This project brings together a team of radiation oncology clinicians, medical physicists, engineers, and other educators with industrial partners. The project will be undertaken in close collaboration with an established partner clinical site in Chennai, India. We have four Specific Aims: UG3 Aim 1: Further test and develop a physical compensator system capable of delivering highly efficient IMRT treatments. UG3 Aim 2: Develop a clinical training and implementation program specifically designed to support use of the physical compensator system in the LMIC environment. UH3 Aim 3: Test the performance and efficiency of the system in clinical operation at the partner site cancer clinic in India. UH3 Aim 4: Perform a clinical validation trial of the system to deliver IMRT in patients with select disease sites at the partner site, and test the hypothesis that toxicity and local tumor control are equivalent to those achieved in cooperative group trials in developed countries.