RESUMO
The aim of our pilot study was to demonstrate the feasibility and dosimetric quality of MR-guided HDR prostate brachytherapy in a low-field 0.35T open MRI scanner and to present our initial clinical experiences. 16 patients with intermediate- to high-risk localized prostate cancer were treated with 46-60 Gy of external beam radiotherapy preceded and/or followed by an 8 Gy MR-guided HDR boost. For interventions an MR compatible custom-made system, coaxial needles and plastic catheters were used. Template reconstruction, trajectory planning, image guidance, contouring and treatment planning were exclusively based on MR images. For treatment planning, dose-point- and anatomy-based inverse planning optimization was used. Image quality was found to be good to excellent in almost all cases. The mean catheter placement accuracy modeled by Rayleigh distribution was 2.9 mm with a sigma value of 2.3 mm. The mean and standard deviation (SD) of the dosimetric results for the target volume were the following: V100: 94.2 ± 4.3%, V150: 43.9 ± 6.8%, V200: 18.5 ± 5.9%. The mean D(0.1), D(1) and D1 values for the intraprostatic urethra were 117.6 ± 12.5%, 98.5 ± 19.9% and 122.3 ± 16.4%, respectively. Regarding the rectal wall the mean D(0.1), D(1) and D(2) values were 77.3 ± 7.2%, 64.8 ± 7.5%, and 53.2 ± 9.1%, respectively. The mean maximum dose for the inner rectal surface was 53.5 ± 9.2%. No RTOG Grade 3 or worse acute toxicities were observed. Our method seems to be a promising approach for performing feasible, accurate and high-quality MR-guided HDR prostate brachytherapy. To determine the long term side effects and outcome higher number of patients, additional follow-up is needed.