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

Abstract

Purpose Variation in target volume delineation represents a significant hurdle in clinical trials involving conformal radiotherapy. We sought to determine the impact of a consensus guideline-based visual atlas on contouring of target volumes. Methods A representative case and target volume delineation instructions derived from a proposed rectal cancer clinical trial involving conformal radiotherapy were contoured (Scan1) by 14 physician observers and a reference expert. Gross tumor volume (GTV), and 2 clinical target volumes (CTVA, comprising internal iliac, pre-sacral, and peri-rectal nodes, and CTVB, external iliac nodes) were contoured. Observers were randomly assigned to receipt (Group_A) /non-receipt (Group_B) of a consensus guideline and atlas for anorectal cancers, then instructed to re-contour the same case/images (Scan2). Observer variation was analyzed volumetrically using conformation number (CN, where CN=1 equals a total agreement). Results In 14 evaluable contour sets (1 expert, 7 Group_A, 6 Group_B), there was greater agreement for GTV (mean CN 0.75) than CTVs (mean CN 0.46–0.65). Atlas exposure for Group_A led to a significant increased inter-observer agreement for CTVA (mean initial CN 0.68, post-atlas 0.76; p=0.03), as well as increased agreement with the expert reference (initial mean CN 0.58, 0.69 post-atlas; p=0.02). For GTV and CTVB, neither inter-observer nor expert agreement was altered after atlas exposure. Conclusion Consensus guideline atlas implementation resulted in a detectable difference in inter-observer agreement and greater approximation of expert volumes for CTVA, but not GTV or CTVB, in the specified case. Visual atlas inclusion should be considered as a feature in future clinical trials incorporating conformal radiotherapy.

Human–Computer Interaction in Radiotherapy Target Volume Delineation: A Prospective, Multi-institutional Comparison of User Input Devices

“…The collected data also reveal no statistically detectable difference between pen-tablet and mouse-keyboard entry GTV ROI volume(s) for paired measurements (Table 4). Likewise, intra-observer and interobserver CN values were roughly comparable to those seen in a previous series [26], suggesting that the ROI volumes designated were only minimally altered in a systematic manner based on data entry UID.…”

Interobserver variation in parotid gland delineation: a study of its impact on intensity-modulated radiotherapy solutions with a systematic review of the literature

“…Contrary to prevalent belief, the introduction and use of contouring guidelines did not consistently lead to a reduction in interobserver variation in target volume definition among radiation oncologists [63][64][65]. This may be secondary to interclinician differences in guideline and imaging interpretation.…”

Critical discussion of evaluation parameters for inter-observer variability in target definition for radiation therapy

“…Inter-observer studies are necessary in order to quantify delineation uncertainties within an institutional contouring protocol or clinical trial, to validate delineation guidelines, and to evaluate automatic segmentation tools or new image modalities for analysis of tumor behavior [1,6,8,9,35,46].…”