A low-dose-rate (LDR) brachytherapy device having a spatiotemporal radiation profile includes an elongated body having a radioactive material in a spatial pattern to provide a spatial radiation profile with a radiation intensity that varies along a length of the elongated body. The radioactive material includes at least first and second radioisotopes having at least first and second respective decay profiles that together provide a temporal radiation profile that is different from the first and second decay profiles. The spatial radiation profile and the temporal radiation profile form a net spatiotemporal radiation profile configured to provide a radiotherapy plan for a patient.