[Report of the 121st Scientific Meeting of the Japan Society of Medical Physics].

The Japan Society of Medical Physics (JSMP) held its 121st semiannual scientific meeting from April 15 to April 18, 2021 in Yokohama, jointly with two other radiological academic societies and radiological industry to constitute Japan Radiology Congress. The congress also included a web-based virtual venue from April 28 to June 3 to provide on-demand services of the same contents. Individual participants, once registered online, were given daily options to participate in either venue. The main theme of the congress was "Milestones and Beyond", which was accidentally ideal for JSMP to commemorate 60th anniversary since its establishment in 1961. Of 121 research presentations collected, 8 were proffered by 7 guest speakers from allied medical physics organizations of India, Bangladesh, Hong Kong, Nepal, and Philippines. The meeting also featured many symposia and lectures on medical physics and interdisciplinary topics. Among them were a special lecture on the history of JSMP with current and past JSMP presidents and an international symposium with distinguished panelists invited from Bangladesh, China, Thailand, Vietnam, and Japan. Of total 919 registrants, 297 participated in the real meeting in Yokohama under the COVID-19 pandemic. Nevertheless, the meeting was perfectly implemented as planned because unvisited speakers had submitted their self-recorded video presentations in advance for onsite viewing in their sessions and many of them remotely participated in real-time discussion over the network. The individual presentations from the speakers, the recorded onsite sessions, and their associated bulletin boards for discussion constituted main contents of the virtual meeting. I would like to express my sincere appreciation to all participants and organizers of this successful meeting. This report supplements the official meeting record including extended abstracts of all presentations, which has been published as the Proceedings of the 121st Scientific Meeting of JSMP (Japanese Journal of Medical Physics Volume 41 Supplement 1, JSMP, Tokyo, April 1, 2021).