Reducing interobserver variation of boost-CTV delineation in breast conserving radiation therapy using a pre-operative CT and delineation guidelines☆

Abstract 

Aims

To investigate whether using a pre-operative CT scan (Preop-CT) (1) decreases interobserver variation of boost-CTV delineation in breast conserving therapy (BCT), and (2) influences the size of the delineated volumes.

Patients and methods

Thirty cT1-2N0-1 breast cancer patients underwent a CT-scan in radiation treatment position, prior to and after lumpectomy. Five observers delineated a boost-CTV, both with and without access to the Preop-CT. For each patient and for each observer pair, the conformity index (CI) and the distance between the centres of mass (COMd) for both boost volumes were calculated. In addition, all delineated volumes including the standard deviation (SD) with respect to the median delineation were calculated.

Results

Using a Preop-CT reduced the mean COMd of the boost-CTV from 1.1cm to 1.0cm (p<0.001). No effect was seen on the CI, but the boost-CTV volume reduced from 42cc to 36cc (p=0.005), implying a reduction of interobserver variation. We saw no significant change in the SD.

Conclusion

Use of a Preop-CT in BCT results in a modest but statistically significant reduction in interobserver variation of the boost-CTV delineations and in a significant reduction in the boost-CTV volume.

Keywords: Breast conserving therapy, Tumourbed delineation, Pre-operative CT, Interobserver variation