Program Information
Dosimetric Coverage Evaluation of Personalized MR/CT Guided Ring and Tandem HDR Brachytherapy for Cervical Cancer
Z Kang1*, M Gopalakrishnan2 , Z Grelewicz3 , B Lee4 , V Sathiaseelan5 , H Zhang6 , (1) Northwestern Memorial Hospital, Chicago, IL, (2) Northwestern Memorial Hospital, Chicago, IL, (3) Northwestern Memorial Hospital, Chicago, IL, (4) Northwestern Memorial Hospital, Chicago, IL, (5) Northwestern Memorial Hospital, Chicago, IL, (6) Northwestern Memorial Hospital, Chicago, IL
Presentations
TU-RPM-GePD-TT-1 (Tuesday, August 1, 2017) 3:45 PM - 4:15 PM Room: Therapy ePoster Theater
Purpose: Adequate dose coverage to the high risk clinical target is essential to HDR brachytherapy planning for cervical cancer treatments. This study aims to evaluate whether the HR-CTV_MR (MR defined volume at the first fraction) were adequately treated during the subsequent fractions where the targets were CT-defined (HR-CTV_CT). The study also investigates the dosimetry impacts from MR-CT fusion strategies based on pelvic anatomy and implanted applicator features.
Methods: 7 patients were treated with ring and tandem for 4 or 5 fractions (total 34). Personalized plans were delivered in all treatments. For the first fraction, the attending radiation oncologist delineated the HR-CTV_MR on the T2 weighted sequence acquired immediately after applicator insertion. For the subsequent fractions, HR-CTV_CTs were delineated on the CT images acquired after insertion, by the same physician with visual references to the MR. In the current study, the MR was retrospectively fused with the CTs using rigid registration algorithms weighting on either the pelvic bony anatomy or applicators. The HR-CTV_MR was then mapped to the CTs and the volumes were compared to the HR-CTV_CTs. The target dose coverage, measured by HR-CTV_MR V90 (target covered by 90% of the prescription dose), were then evaluated.
Results: Although all daily plans achieved V90>90% for the respective volumes, the HR-CTV_MRs were covered 68.8-100% on the CTs based on applicator based registration. The cases where V90<90% were well correlated with the HR-CTV_CT volume reduction. The coverage varied 11.3-100% if the MR was fused to CT based on anatomical features.
Conclusion: The variations in V90 among all fractions are correlated with the differences in the volume. If the MR were not accessible for all HDR treatment fractions, employing the applicator based registration for target delineation may lead to more consistent results.
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