Objective automated assessment of time trends in prostate edema after (125)I implantation.

PURPOSE: To present an objective automated method to determine time trends in prostatic edema resulting from iodine-125 brachytherapy. METHODS AND MATERIALS: We followed 20 patients, implanted with stranded seeds, with seven consecutive CT scans to establish a time trend in prostate edema. Seed positions were obtained automatically from the CT series. The change in seed positions was used as surrogate for edema. Two approaches were applied to model changes in volume. (1) A cylindrical model: seeds from the compared distribution were linked to the reference distribution of Day 28. After alignment, the compared distribution was scaled in cylindrical coordinates, leading to the changes in radial and craniocaudal directions. The volume changes were calculated using these scaling factors. (2) A spherical model: distances of seeds to the center of gravity of all seeds were used as a measure to model volume changes. RESULTS: With Day 28 as reference, the observed volume changes were smaller than 18% ± 6% (1 standard deviation) for the cylindrical model and 12% ± 7% for the spherical model. One day after implantation, the implanted prostate was less than 10% larger than in the reference scan for both models. Apart from Day 0, both models showed similar volume changes. CONCLUSIONS: We present an objective automated method to determine changes in the implanted prostate volume, eliminating the influence of an observer in the assessment of the prostate size. The implanted volume change was less than 18% ± 7% for the studied group of 20 patients. Edema was 9% ± 5% from 1 day after implantation onward.

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 (125)I 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 D(90) 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.