Title page for ETD etd-07052012-174103

Type of Document Master's Thesis
Author Kemp, Jeffrey Roger
Author's Email Address jkempj1@tigers.lsu.edu
URN etd-07052012-174103
Title The Feasibility of Using Megavoltage CT for the Treatment Planning of HDR Cervical Brachytherapy with Shielded Tandem and Ovoid Applicators
Degree Master of Science (M.S.)
Department Physics & Astronomy
Advisory Committee
Advisor Name Title
Price, Michael J Committee Chair
Gibbons, John P Committee Member
Gifford, Kent A Committee Member
Jin, Rongying Committee Member
Matthews, Kip Committee Member
Keywords
  • surrogate structure
  • centroid-to-perimeter
  • treatment planning
  • megavoltage computed tomography
  • MVCT
  • kVCT
  • water phantom
  • ovoid shielding
  • applicator modeling plugin
  • tandem and ovoid applicators
  • Nucletron
  • cervical cancer
  • intracavitary brachytherapy
Date of Defense 2012-05-31
Availability unrestricted
Abstract
Purpose/Objectives: A drawbackof tandem and ovoid (T&O) ICBT is exposure of the posterior bladder and anterior rectal walls to relatively high isodoses. To mitigate this effect, intra-ovoid shielding may be used to reducedose to these OARs. However, metal artifactspresent in images acquired via kVCT make anatomy segmentation and catheter localization difficult for the purpose of 3D treatment planning. We present a method that combines MVCT-based imaging and applicator modeling to increase the quality of 3D treatment plans for shielded T&O ICBT.

Materials/Methods: Using Oncentra’s TPS, 9 participants from multiple institutions performed organ segmentation and catheter reconstruction for KVCT and MVCT data sets acquired of a water phantom containing bladder and rectum surrogatesand various HDR T&O applicators: Nucletron’s CT/MR compatible(CTMR),Nucletron’s shielded Fletcher Williamson (FW) and (3) Varian’s shielded Fletcher-Suit-Delclos style(FSD).The dimensions of OAR structures were determined using in-air kVCT and physical measurements. By comparing the 3D volumes andcentroid-to-perimeter (C2P) measurements of individual OAR contours, segmentation accuracy was assessed in regions exhibiting artifact under kVCT (1cm superior and inferior to shielding). Comparing the TPS-defined coordinate of the most distal dwell position to that of the true position (determined using radiographs of a fiducial affixed to the applicators), assessed catheter reconstruction accuracy. For Nucletron devices, this metricwas also quantified using an applicator-model for localization.

Results:The percentage of points for C2P measurements that differ (greater than 2mm) from the true contour extentsdecreased underMVCT for the shielded T&Os (78.4 vs. 71.3%), while the converse is observed for the CTMR. Similarly, the volume of the OAR surrogates follows the same trend. This is attributed to the lack of metal artifacts as well as the decrease in the contrast of low Z materials observed when utilizing MVCT. Catheter reconstruction accuracy improved by 26% under MVCT for shielded T&Os, was invariant for the CTMR and within 2.29mm of the true position using applicator modeling.

Conclusions:The quality of MVCT 3D ICBT treatment plans of shielded T&O is comparable to MVCT CTMR treatment plans. Further improvements were observed when using an applicator model for catheter reconstruction.
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