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  5. Use of a Tandem and Ring Applicator Reference-CT to Improve Digitization in MR-Based Brachytherapy Planning

Use of a Tandem and Ring Applicator Reference-CT to Improve Digitization in MR-Based Brachytherapy Planning

I Malajovich1*, B Teo2 , O Dolney3 , W Arscott4 , N Taunk5 , S Anamalayil6 , (1) University of Pennsylvania, Philadelphia, PA, (2) UNIVERSITY OF PENNSYLVANIA, Philadelphia, PA, (3) University Of Pennsylvia Hospital, Philadelphia, PA, (4) Univ. of Pennsylvania, Philadelphia, ,(5) University of Pennsylvania, Philadelphia, PA, (6) University of Pennsylvania, Philadelphia, PA

Presentations

(Sunday, 7/14/2019) 2:00 PM - 3:00 PM

Room: 301

Purpose: Eliminating the patient-Computed Tomography (CT) scan for patients undergoing tandem and ring (T&R) brachytherapy procedures reduces time with the applicator in place and eliminates imaging dose. However, visualizing titanium applicators in a patient-Magnetic Resonance Imaging (MR) is difficult. We evaluated the reproducibility of an MR-only based digitization, and assessed the feasibility of a new workflow where a reference-CT of the T&R applicator (without a patient) is used in lieu of a patient-CT.

Methods: For the MR-only workflow, 8 physicists replanned a case to assess reproducibility. We used PD weighted TSE-sequence with a 1.5T-Siemens and BrachyVisionâ„¢ solid-applicator library for contouring and digitization, respectively. For the reference-CT workflow, 8 physicists registered the reference-CT to the T2-weighted patient-MR. The patient-MR was used for planning, with the registered reference-CT displayed during digitization to assist in applicator reconstruction. We evaluated dwell positions and plan quality differences among the plans in terms of the high-risk-CTV (HRCTV) V100, D100 and D90, and D2cc of the rectum, sigmoid, bladder, and small bowel.

Results: MR-Only workflow: Comparison of MR-Only digitization showed a mean variation between plans of 1.3mm in the tandem (range:0.34-3.74mm), and 2mm in the ring dwell positions (range:0.27-3.68mm). Coverage of the HRCTV changed as much as 14%, and dose to OARs up to 19%. Reference CT workflow: The uncertainty in dwell positions was reduced by 30% in the tandem and 10% in the ring. Mean dwell-position variation between plans was 0.9mm (range:0.2-1.6mm) in the tandem and 1.8mm (range:0.5-3.4mm) in the ring. The standard deviation of resulting dose distributions decreased for the HRCTV V100 (6.6%to3.3%), and Rectum-D2cc (8%to3.3%).

Conclusion: Registering the reference-CT for applicator reconstruction to the patient-MR prior to digitization decreased the uncertainty in dwell position placement in MR-based planning, resulting in improved reproducibility and reduction of plan deviations.

Keywords

MR, HDR, Intracavitary Brachytherapy

Taxonomy

TH- Brachytherapy: Registration

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