Comparison the treatment time of cobalt and iridium sources in HDR brachytherapy

Introduction: The use of long-half-life Cobalt source instead of iridium source will be very helpful in HDR brachytherapy for treatment of cervical cancer. The aim of this study was compared the treatment time with cobalt and iridium source in brachytherapy for treatment of cervical cancer using Tandem-ovoid applicator. Materials and Methods: In this study, 192Ir source model mHDR-v2r, and BEBIG 60Co source model Co0.A86 was used. The TG-43 formalism was used to calculate the treatment time required for both radionuclides. The reference absorbed doses to points A and B were determined from treatment data of an adult patient treated in a cancer center using Tandem- ovoid applicator, and 192Ir source. The treatment data provide us with the exact dwell positions, and times of the source, and positions of the dosimetry points. The absorbed dose to points A and B were calculated with TG-43 formalism using treatment data for iridium source, then the calculated absorbed doses were compared with absorbed doses in treatment data to determine the accuracy of using TG-43 formalism. The treatment time for iridium source is calculated by using absorbed dose in treatment data and the TG43 formalism. Then, the calculations were performed for 60Co. Considering the absorbed dose in reference points, and using the TG-43 formalism, the treatment time for cobalt source is calculated. Finally, the treatment time obtained for the two sources are compared with each other. Results: The results of this study indicate that the treatment time for cobalt source with a specific activity of 2.131 Ci is almost the same as the treatment time for iridium source with the specific activity of 5.690 Ci. For a treatment duration of 16 minutes, the effective time window for 192Ir is about 1 to 160 days, while for 60Co this time window becomes 2000 days. Conclusion: According to the results obtained in this study, using16 minutes treatment time60Co instead of 192Ir will be beneficial in treatment of cervical cancer patients.