Chondrosarcoma is a malignant tumor with the characteristic formation of cartilage tissue by tumor cells. One of the condosarcoma cancer handlers is with radiotherapy, which is a measurable dose of radiation on the target volume to kill cancer cells as much as possible by minimizing the effects of radiation on healthy tissue around the tumor. The purpose of this study to determine the treatment of irradiation, the basis of replanning and basic selection techniques used in cancer kondrosarkoma at Radiotherapy Installation RS Kensaras This type of research is qualitative with case study approach. The data were collected in October-January 2018 at Radiotherapy Installation of Kensaras Hospital by observation method, interview with Radiation Oncology Specialist, Medical Physicist and Radiotherapy Radiographer. The data obtained from the study were analyzed by an interactive model, making the interview transcripts subsequently reduced in category table and processed in the form of open coding, presented in the form of quotations and then can be drawn conclusions. The results of this study showed that treatment of chondrosarcoma cancer in Radiotherapy Installation of Kensaras Hospital included patient consultation, CT Simulator shooting, contouring, planning of medical physics and verification and radiation treatments. Replanning is done due to changes in tumor mass in the mandible area. Basic selection of irradiation techniques based on tumor location, technique effectiveness and palliative radiotherapy goal.