Intraoperative adaptive brachytherapy of iodine-125 prostate implants guided by C-arm cone-beam computed tomography–based dosimetry

Purpose (1) To demonstrate the feasibility of C-arm cone-beam computed tomography (CBCT)-based postplanning and subsequent adaptation of underdosed critical areas by adding remedial seeds during the transrectal ultrasound (TRUS)-guided implantation of 125I seeds and (2) to assess the duration of this procedure. Methods and materials After finishing the implant, three fiducial markers were implanted and a TRUS study was performed to delineate the prostate. A C-arm CBCT unit with isocentric design was used to generate a CT data set to localize the seeds. The TRUS and CBCT data sets were coregistered by the radiation oncologist to assess the dosimetry of the implant. If underdosages existed at critical areas, dosimetry was adapted by adding remedial seeds while the patient was still under anesthesia. Results Of 20 patients studied, 9 demonstrated underdosage in critical areas. On average four additional seeds were implanted, resulting in a mean D90 of 100.7% (increase 4.9%) and 117.5% (increase 17.8%) of the prescribed dose of 145 and 110 Gy, respectively. The average additional time involved in performing the adaptation procedure was less than 30 min. Conclusions C-arm CBCT-guided intraoperative postplanning during TRUS-guided brachytherapy for prostate cancer is both feasible and time efficient. The adaptation resulted in improved dosimetry of the prostate implants