A comparative dosimetric analysis of virtual stereotactic body radiotherapy to high-dose-rate monotherapy for intermediate-risk prostate cancer

PURPOSE: Stereotactic body radiotherapy (SBRT) is being used with increasing frequency as definitive treatment of early stage prostate cancer. Much of the justification for its adoption was derived from earlier clinical results using high-dose-rate (HDR) brachytherapy. We determine whether BDR's dosimetry can be achieved by virtual SBRT. METHODS AND MATERIALS: Patients with intermediate-risk prostate cancer on a prospective trial evaluating the efficacy of HDR monotherapy treated to dose of 9.5 Gy x 4 fractions were used for this study. A total of 5 patients were used in this analysis. Virtual SBRT plans were developed to reproduce the planning target volume (PTV) BDR dose distributions. Both normal tissue and PTV-prioritized plans were generated. RESULTS: From the normal tissue-prioritized plan, 11DR and virtual SBRT achieved similar PTV V-100 (93.8% vs. 93.1%, p = 0.20) and V-150 (40.3% vs. 42.9%, p = 0.69) coverage. However, the PTV V-200 was not attainable with SBRT (15.2% vs. 0.0%, p <0.001). The rectal D-max was significantly lower with BDR (94.2% vs. 99.42%, p = 0.05). The rectal D-2 (cc) was also lower (60.8% vs. 71.1%, p = 0.07). Difference in D-1 (cc) urethral dose was not significantly different (87.7% vs. 75.2%, p = 0.33). Comparing the PTV-prioritized plans, the rectal D-max (94.2% vs. 111.1%, p = 0.05) and mean dose (27.1% vs. 33.3%, p = 0.03) were significantly higher using SBRT, and the rectal D-2 (cc) was higher using SBRT (60.8% vs. 81.8%, p = 0.07). CONCLUSIONS: HDR achieves significantly higher intraprostatic doses while achieving a lower maximum rectal dose compared with our virtual SBRT treatment planning. Future studies should compare clinical outcomes and toxicity between these modalities. (C) 2013 American Brachytherapy Society. Published by Elsevier Inc. All rights reserved.