A comparison of treatment planning techniques for low-dose-rate (LDR) prostate brachytherapy

Purpose: The purpose of this study was to compare low-dose-rate prostate brachytherapy treatment plans created using three retrospectively applied planning techniques with plans delivered to patients. Methods and Materials: Treatment plans were created retrospectively on transrectal ultrasound (TRUS) scans for 26 patients. The technique dubbed 4D Brachytherapy was applied, using TRUS and MRI to obtain prostatic measurements required for the associated webBXT online nomogram. Using a patient's MRI scan to create a treatment plan involving loose seeds was also explored. Plans delivered to patients were made using an intraoperative loose seed TRUS-based planning technique. Prostate V₁₀₀ (%), prostate V₁₅₀ (%), prostate D₉₀ (Gy), rectum D_0.1cc (Gy), rectum D_2cc (Gy), urethra D₁₀ (%), urethra D₃₀ (%), and prostate volumes were measured for each patient. Statistical analysis was used to assess and compare plans. Results: Prostate volumes measured by TRUS and MRI were significantly different. Prostate volumes calculated by the webBXT online nomogram using TRUS- and MRI-based measurements were not significantly different. Compared with delivered plans, TRUS-based 4D Brachytherapy plans showed significantly lower rectum D_0.1cc (Gy) values, MRI-based 4D Brachytherapy plans showed significantly higher prostate V₁₀₀ (%) values and significantly lower rectum D_0.1cc (Gy), urethra D₁₀ (%), and urethra D₃₀ (%) values, and loose seed MRI-based plans showed significantly lower prostate V₁₀₀ (%), prostate D₉₀ (Gy), rectum D_0.1cc (Gy), rectum D_2cc (Gy), urethra D₁₀ (%), and urethra D₃₀ (%) values. Conclusions: TRUS-based 4D Brachytherapy plans showed similar dosimetry to delivered plans; rectal dosimetry was superior. MRI can be integrated into the 4D Brachytherapy workflow. The webBXT online nomogram overestimates the required number of seeds.