Program Information
Feasibility Study of CBCT On a Linac for Vaginal Cylinder HDR Brachytherapy Simulation
M Ashenafi*, C Mart , J Peng , L Cooper , K Vanek , Medical University of South Carolina, Charleston, SC
Presentations
PO-BPC-Exhibit Hall-5 (Saturday, March 18, 2017) Room: Exhibit Hall
Purpose: To establish the acceptability of using the kV imaging capabilities of the TrueBeam linear accelerator to plan vaginal cylinder High Dose Rate brachytherapy treatments. Cone-beam computed tomography (CBCT) images acquired with the TrueBeam's OnBoard Imaging system were tested from both an image quality and geometric accuracy point of view. Planar kV images were also evaluated for their ability to replace a CT scout image for applicator insertion verification on subsequent fractions treated with the same initial plan.
Methods: A vaginal cylinder was placed in a water phantom with an x-ray marker in the intravaginal tube and anterior and lateral kV images and a kV CBCT were acquired on a TrueBeam. Geometric accuracy was tested by measuring the cylinder dimensions and relative source position depicted by the x-ray marker compared to the true physical dimensions. CBCT and planar images were acquired of a patient with cylinder and x-ray marker inserted and evaluated for image quality by the physician. Data transfer and treatment planning were tested by creating a plan from the patient’s CBCT using the virtual cylinder model provided in the treatment planning system and using dwell times from the helical CT plan of the same patient. Quality was analyzed by comparing the difference in the metrics used for plan evaluation.
Results: The geometric accuracy of the CBCT and planar images was found to be within 1mm of true values. The image quality was adequate to reconstruct the applicator in the treatment planning system and to contour the target and OARs. The plan quality based on CBCT images was in excellent agreement (0.5%/0.5cc) with the plan on helical CT images.
Conclusion: This study demonstrated the feasibility of CBCT-based cylinder HDR brachytherapy treatment planning. It also showed that kV planar images can replace the CT scout for applicator insertion verification.
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