Room: Exhibit Hall | Forum 2
Purpose: To clinically implement MR-based treatment planning and dose accumulation for cervical brachytherapy with QFix-Symphony-patient-transport-system (â€œSymphonyâ€?) and RayStation V6.1.
Methods: 3D turbo-spin-echo (TSE) pulse-sequence (Siemens SPACE) is optimized with 1.3-mm3 isotropic voxels and 3D distortion-correction. End-to-end testing of image-registration between T2-MRI and CT is performed for typical MRI-compatible GYN applicators with MR-markers in water and MR gel phantoms. Applicator placement is performed on the Symphony-table in MRI preparation-area at the 1st HDR fraction. Patient is subsequently transferred to the Siemens MAGNETOM-Aera (1.5T) scanner using the dockable table for MRI, followed by CT-imaging to evaluate applicator position movement due to transport. Routine brachytherapy planning is done on CT for the subsequent 4 fractions utilizing the high risk CTV (HR-CTV) contour from 1st fraction MRI as a guide. Smit-sleeve is used as the reference contour for CT/MR rigid-image-registration, and the biomechanical-deformable-registration in RayStation v6.1 is validated for dose accumulation to HR-CTV and OARs.
Results: Better than 0.5-mm 1st dwell position accuracy in all channels is achievable with 3D T2-SPACE MRI for both shielded ovoids-tandem and interstitial-ring applicators when using the applicator library in the Oncentra-TPS. The position of applicator relative to smit-sleeve and OARs is reproducible with the aid of Symphony-patient-transport-system. Total procedure time, including MR imaging, planning and fraction delivery is less than 2 hours with this single optimized 7-min T2 SPACE planning scan, as it allows the physician to accurately delineate HR-CTV/soft-tissue in Raystation without referring to prior diagnostic MRI, while simultaneously allowing the physicist to start applicator reconstruction and planning in Oncentra. Biomechanical-deformable-registration in Raystation might be a useful tool to sufficiently register the HR-CTV/rectum/bladder contour and dose-distribution between 1st fraction MR and subsequent fraction CT, on-going validation is pending.
Conclusion: MRI-based brachytherapy planning could be efficiently implemented without dedicated MRI simulator as the new standard for cervical brachytherapy.