Clinical Investigation
Prospective Randomized Double-Blind Pilot Study of Site-Specific Consensus Atlas Implementation for Rectal Cancer Target Volume Delineation in the Cooperative Group Setting

Portions of the data were selected for a Poster Recognition Award at the 2009 American Society for Radiation Oncology Annual Meeting, November 1–5, 2009, Chicago, IL.
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Purpose

Variations in target volume delineation represent a significant hurdle in clinical trials involving conformal radiotherapy. We sought to determine the effect of a consensus guideline-based visual atlas on contouring the target volumes.

Methods and Materials

A representative case was contoured (Scan 1) by 14 physician observers and a reference expert with and without target volume delineation instructions derived from a proposed rectal cancer clinical trial involving conformal radiotherapy. The gross tumor volume (GTV), and two clinical target volumes (CTVA, including the internal iliac, presacral, and perirectal nodes, and CTVB, which included the external iliac nodes) were contoured. The observers were randomly assigned to receipt (Group A) or nonreceipt (Group B) of a consensus guideline and atlas for anorectal cancers and then instructed to recontour the same case/images (Scan 2). Observer variation was analyzed volumetrically using the conformation number (CN, where CN = 1 equals total agreement).

Results

Of 14 evaluable contour sets (1 expert and 7 Group A and 6 Group B observers), greater agreement was found for the GTV (mean CN, 0.75) than for the CTVs (mean CN, 0.46–0.65). Atlas exposure for Group A led to significantly increased interobserver agreement for CTVA (mean initial CN, 0.68, after atlas use, 0.76; p = .03) and increased agreement with the expert reference (initial mean CN, 0.58; after atlas use, 0.69; p = .02). For the GTV and CTVB, neither the interobserver nor the expert agreement was altered after atlas exposure.

Conclusion

Consensus guideline atlas implementation resulted in a detectable difference in interobserver agreement and a greater approximation of expert volumes for the CTVA but not for the GTV or CTVB in the specified case. Visual atlas inclusion should be considered as a feature in future clinical trials incorporating conformal RT.

Introduction

Interobserver differences in target volume delineation are a demonstrated source of potential treatment variability in the context of clinical trials that incorporate conformal radiotherapy (RT) approaches 1, 2. Recent publications have suggested that target delineation consensus documentation is highly desirable for clinical trials (3) and that specific instructional or educational interventions might afford a measurable effect in terms of physician contouring 4, 5.

As a part of efforts to improve RT implementation for the Southwest Oncology Group (SWOG) trials and consistent with its focus on quality improvement in cooperative studies, the SWOG Radiation Oncology Committee authorized the present study as a pilot project to achieve the following primary specific aims: the feasibility of centralized target volume delineation evaluation as a pretrial adjunct to a SWOG-sponsored study (SWOG S0713), and the determination of the effect of implementation of a consensus anatomic atlas on target volume variability.

Section snippets

Methods and Materials

This prospective institutional review board-exempt study was conducted under the auspices of the University of Texas Health Science Center at San Antonio institutional review board. The present study was designed as a double-blind, randomized hypothesis-generating pilot study (Fig. 1). Statistical power for agreement analysis was estimated for a non–Bonferroni-corrected paired-measures Wilcoxon test (assuming a minimum asymptotic relative efficiency of ≥0.863 compared with a paired t test),

Results

Eight SWOG institutions had at least one user submitting contours, as well as a single non–SWOG-affiliated participant. Of the 26 observers directly asked to participate, 15 submitted contour set pairs, of which 14 were technically evaluable (1 expert, 7 in Group A, and 6 in Group B). The nonevaluable contour set consisted of nonconnected, nonoverlapping contours that precluded ready analysis with the cohort at large. The survey results were pooled and tabulated (Table 2).

All 14 remaining

Discussion

Despite the well-known consequences of geometric inaccuracy in target volume delineation 15, 16, 17, interobserver variability in target definition has been demonstrated in a host of studies and at various anatomic sites (18). Simply put, “interobserver variability in the definition of GTV and CTV is a major—for some tumor locations probably the largest—factor contributing to the global uncertainty in radiation treatment planning” (18). Consequently, efforts to implement solutions to possible

Conclusion

The addition of a visual atlas and consensus treatment guidelines to a written protocol increased CTV delineation conformance with the expert-derived contours and increased contour agreement among the participants for the CTVA, but not the GTV or CTVB, for the included rectal cancer case. The detected interobserver (both with and without the atlas) and intraobserver variation in contouring target structures was substantial. Visual atlas-based supplementary target volume specification materials

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  • Cited by (0)

    C. D. Fuller was supported by a training grant from the National Institutes of Health/National Institute of Biomedical Imaging and Bioengineering, “Multidisciplinary Training Program in Human Imaging” (Grant 5T32EB000817-04), a Technology Transfer Grant from the European Society for Therapeutic Radiology and Oncology, and the Product Support Development Grant from the Society for Imaging Informatics in Medicine.

    The funders played no role in the study design, collection, analysis, interpretation of data, manuscript writing, or decision to submit the report for publication.

    Conflict of interest: none.

    1

    C.D.F. and J.N. contributed equally to this work.

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