Is the use of a preoperative computed tomography beneficial to reduce the interobserver variability of the CTV delineation for breast radiation therapy?

Purpose: To determine whether the use of a preoperative (preop) computed tomography (CT) reduces (1) the clinical target volume boost (CTV) and (2) the interobserver variability (IOV) of the delineated CTV in breast radiation therapy.

Methods And Materials: In patients treated with breast-conserving therapy, 3 CT scans in treatment position were performed: (1) preop; (2) after surgery, prechemotherapy (postop); and (3) postchemotherapy (postchemo). Six radiation-oncologists delineated the tumor bed and CTV before and after fusion of the preop CT. To assess the IOV, the Jaccard index was used. Linear mixed models were performedfor all analyses.

Results: Eighty-two lumpectomy cavities were evaluated in 22 patients. No difference in CTV using the fusion of the preop CT (50.0 cm; 95% confidence interval [CI], 35.6-64.4) compared with no fusion (49.0 cm; 95% CI, 34.6-63.4) (P = .6) was observed. A significant increase in IOV was shown with the fusion of the preop CT; the mean Jaccard index of the CTV delineation of postop and postchemo CT together without the fusion of the preop CT was 0.53 (95% CI, 0.49-0.57) versus 0.50 (95% CI, 0.46-0.53) with fusion (P < .0001).

Conclusions: There is no benefit of using a preop CT to reduce the volume or the interobserver variability of the delineated CTV for breast radiation therapy.