Dr. Efstathiou holds a B.S. from Yale University, M.D. from Harvard Medical School (HMS), Ph.D. from University of Oxford, and completed his residency training in the Harvard Radiation Oncology Program. He serves as Associate Professor of Radiation Oncology at HMS and the Massachusetts General Hospital (MGH). His clinical practice focuses on treatment of patients with prostate, bladder, testicular and other urologic cancers, as well as proton beam and brachytherapy, and he serves as Director of the Genitourinary Division in Radiation Oncology and Clinical Co-Director of The Claire and John Bertucci Center for Genitourinary Cancers Multidisciplinary Clinic. His commitment to service/patient care has been recognized as honoree for the MGH Cancer Center's "The One Hundred" and as nominee for the Brian A. McGovern Award for Clinical Excellence. His research has informed clinical practice guidelines and focuses on the effectiveness of advanced/emerging therapies for prostate cancer including proton beam, as well as the adverse effects of hormonal therapy, improving radiation therapy for testicular cancer, and long-term outcomes of bladder-sparing chemoradiation for bladder cancer. He is the recipient of significant grant funding and serves as Principal Investigator of multiple studies including a multi-center randomized phase III trial of IMRT versus proton beam for localized prostate cancer using patient-reported outcomes. He lectures nationally and internationally and holds leadership positions in Radiation Oncology including within the cooperative groups (NRG), professional societies (ASTRO), and National Cancer Institute (NCI). Other projects of his include the development of web-based patient decision aids/support tools, evaluating the multidisciplinary approach to cancer care, and global oncology outreach efforts with Botswana.