Program Information
Dosimetric Evaluation of MR-Guided HDR Brachytherapy Planning for Cervical Cancer
Y Kamio*, M Barkati, D Beliveau-Nadeau, CHUM Notre Dame Hospital, Montreal, QC, CA
Presentations
TH-AB-BRA-4 (Thursday, August 4, 2016) 7:30 AM - 9:30 AM Room: Ballroom A
Purpose: To perform a retrospective study on 16 patients that had both CT and T2-weighted MR scans done at first fraction using the Utrecht CT/MR applicator (Elekta Brachytherapy) in order to evaluate uncertainties associated with an MR-only planning workflow.
Methods: MR-workflow uncertainties were classified in three categories: reconstruction, registration and contouring. A systematic comparison of the CT and MR contouring, manual reconstruction and optimization process was performed to evaluate the impact of these uncertainties on the recommended GEC ESTRO DVH parameters: D90% and V100% for HR-CTV as well as D2cc for bladder, rectum, sigmoid colon and small bowel. This comparison was done using the following four steps:
1. Catheter reconstruction done on MR images with original CT-plan contours and dwell times.
2. OAR contours adjusted on MR images with original CT-plan reconstruction and dwell times.
3. Both reconstruction and contours done on MR images with original CT-plan dwell times.
4. Entire MR-based workflow optimized dwell times re-imported to the original CT-plan.
Results: The MR-based reconstruction process showed average D2cc deviations of 4.5 ± 3.0%, 1.5 ± 2.0%, 2.5 ± 2.0% and 2.0 ± 1.0% for the bladder, rectum, sigmoid colon and small bowels respectively with a maximum of 10%, 6%, 6% and 4%. The HR-CTV's D90% and V100% average deviations was found to be 4.0 ± 3.0%, and 2.0 ± 2.0% respectively with a maximum of 10% and 6%. Adjusting contours on MR-images was found to have a similar impact. Finally, the optimized MR-based workflow dwell times were found to still give acceptable plans when re-imported to the original CT-plan which validated the entire workflow.
Conclusion: This work illustrates a systematic validation method for centers wanting to move towards an MR-only workflow. This work will be expanded to model based reconstruction, PD-weighted images and other types of applicators.
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