Real-world dosimetric comparison between CyberKnife SBRT and HDR brachytherapy for the treatment of prostate cancer.

Purpose: High-dose-rate (HDR) brachytherapy (BRT) and stereotactic body radiotherapy (SBRT) are currently the two treatment options for definitive radiotherapy of prostate cancer, employing extreme hypofractionation. There are only very few studies comparing their dosimetry, all using computed tomography for treatment planning. We present here a real-word dosimetric comparison between SBRT and ultrasound-based virtual HDR-BRT, with both imaging modalities coming from the same patient.

Methods And Materials: Patients with prostate cancer on a prospective trial evaluating the toxicity of robotic-based SBRT were treated to a total dose of 35 Gy in 5 fractions. Fifteen patients were included in this analysis. During ultrasound-based fiducial implantation, a three-dimensional data set as in real HDR-BRT procedure was acquired. Virtual HDR-BRT plans were generated and various organs at risk and prostate dosimetric parameters were evaluated.

Results: Concerning prostate, SBRT achieved significant higher D, V Gy, and V Gy coverage, whereas virtual HDR-BRT achieved significant higher intratumoral doses reflected in the V Gy and V Gy. Rectal D, V Gy, and V Gy were significantly lower for HDR-BRT with no difference as for V Gy. SBRT was significantly inferior regarding bladder dosimetry (D, V Gy, V Gy), whereas urethra D and V Gy where significantly higher at the expense of HDR-BRT.

Conclusions: HDR-BRT is superior regarding rectum and bladder dosimetry, with SBRT being superior relative to urethra dosimetry. A randomized study is warranted to define the best extreme hypofractionated modality.