ABSTRACT
Accidents are serious issues in radiation therapy. Overexposure causes clinical complications leading to death and underexposure causes recurrence of cancer making it difficult to treat the patient again. One can refer to incidents as those of relatively minor consequences and accidents as those of severe clinical complications. This chapter lists both types of events that have occurred in radiation oncology. Power failure interrupted an electron mode treatment and the treatment was resumed when the power retuned but without checking the beam characteristics. A high-dose rate (HDR) 192Ir source became detached from the drive cable and remained in the patient, and only the cable was retracted despite the console display indicating source retraction. A comprehensive QA program is a must to prevent many accidents. Safe keeping of radioactive sources is a serious issue that is being widely discussed these days. In countries where the regulatory mechanisms are not strong, or in countries troubled by violence, security of sources becomes particularly important.
