Target volume delineation variation in radiotherapy for early stage rectal cancer in the Netherlands

Abstract 

Purpose

The aim of this study was to measure and improve the quality of target volume delineation by means of national consensus on target volume definition in early-stage rectal cancer.

Methods and materials

The CTV’s for eight patients were delineated by 11 radiation oncologists in 10 institutes according to local guidelines (phase 1). After observer variation analysis a workshop was organized to establish delineation guidelines and a digital atlas, with which the same observers re-delineated the dataset (phase 2). Variation in volume, most caudal and cranial slice and local surface distance variation were analyzed.

Results

The average delineated CTV volume decreased from 620 to 460cc (p<0.001) in phase 2. Variation in the caudal CTV border was reduced significantly from 1.8 to 1.2cm SD (p=0.01), while it remained 0.7cm SD for the cranial border. The local surface distance variation (cm SD) reduced from 1.02 to 0.74 for anterior, 0.63 to 0.54 for lateral, 0.33 to 0.25 for posterior and 1.22 to 0.46 for the sphincter region, respectively.

Conclusions

The large variation in target volume delineation could significantly be reduced by use of consensus guidelines and a digital delineation atlas. Despite the significant reduction there is still a need for further improvement.

Keywords: Delineation variation, Rectal cancer, Delineation atlas, Clinical target volume