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Effect of Applicator Reconstruction Shifting on Dosimetric Dose-Volume Histogram Parameters during Magnetic Resonance Imaging in Brachytherapy for Cervical Cancer Patients

Affiliations

  • Medical Physicist, Department of Radiology, King Chulalongkorn Memorial Hospital, 1873, Rama IV Road, Pathumwan, Bangkok 10330, Thailand
  • Department of Radiology, Chulalongkorn University, Rama IV Road, Pathumwan, Bangkok 10330, Thailand

Abstract


Objective: This study observed the dose-volume histogram (DVH) parameter changes caused by applicator shifting that result from patient movement during image acquisition for magnetic resonance imaging guided brachytherapy for cervical cancer patients.

Materials and Methods: Nine cervical cancer plans with insertion of a Fletcher computed tomography (CT)/magnetic resonance (MR) applicator were retrospectively studied. The MR sequences were T2 fast spin echo on parasagittal, para-axial, and para-coronal planes, respectively. The applicator library was used for applicator reconstruction in each image data set. The tip of the applicator (2 ovoids + 1 tandem) was identified, and the difference from the reference image (axial view) was recorded. The DVH parameters were as follows: D90 of high-risk clinical target volume (HR-CTV) and D2cc of the bladder and rectum for each image data set were compared with the reference image.

Results: The tandem showed less applicator shift on the coronal plane than the reference image. The applicator shifts for tandem were 0.0 ± 0.4, 0.0 ± 1.0, and -0.5 ± 1.0 mm in the left-right, superior-inferior, and anterior-posterior directions, respectively. The mean percentage dose differences in DVH parameters on the coronal and sagittal planes were 3.04% and 1.23% for D90 of HR-CTV, 2.73% and 3.88% for D2cc of the bladder, and 2.60% and 3.49% for D2cc of the rectum, respectively.

Conclusion: An image acquisition time of approximately 15 minutes for three-dimensional MR brachytherapy provided a mean applicator reconstruction shift within 1.3 mm, with minor effects on the DVH parameter of approximately 3%.


Keywords

Applicator Reconstruction, MRI-Brachytherapy, Uncertainty, Applicator Library.

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References


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