Background: Japan has recently begun introducing educational programmes on cancer as part of health and physical education (HPE) classes in schools. In support of this work, the Japanese Society for Radiation Oncology has developed an educational video to enhance children's understanding of cancer and radiotherapy. Objectives: This study examined the perceived effectiveness of this video among teachers and clarified whether their specialisation played a role in their responses. Methods: An online survey was administered to junior and senior high school teachers without a history of cancer. Respondents' demographic characteristics, healthy lifestyle habits, anxiety about cancer treatment and knowledge about cancer and radiotherapy were surveyed pre- and post-video. We compared the data from science teachers, HPE teachers and teachers of other specialties. Subsequently, we performed a multiple logistic regression analysis to estimate significant factors that predicted post-watch correct-answer rates. Results: Science teachers were less anxious about radiotherapy and surgery than the other-specialty teachers. They were also the most knowledgeable about cancer and radiotherapy. Post-viewing correct-answer rates improved, except for questions about the work of medical physicists and damage to normal cells. The multiple regression analysis identified age ([beta] = 0.07), sex ([beta] = 0.08), anxiety about radiotherapy ([beta] = -0.09) and pre-video correct-answer rates ([beta] = 0.46) as significant factors predicting post-watch correct-answer rates. Conclusion: The video was beneficial in enhancing teachers' understanding of cancer and radiotherapy. Compared with HPE and other-specialty teachers, science teachers were superior in terms of cancer and radiotherapy comprehension. There may be value in exploring possibilities for cross-disciplinary instruction involving not only HPE but also science teachers in cancer education, especially radiotherapy education.