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

Abstract

To determine whether the use of a preoperative (preop) computed tomography (CT) reduces (1) the clinical target volume boost (CTV_boost) and (2) the interobserver variability (IOV) of the delineated CTV_boost in breast radiation therapy. 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_boost before and after fusion of the preop CT. To assess the IOV, the Jaccard index was used. Linear mixed models were performedfor all analyses. Eighty-two lumpectomy cavities were evaluated in 22 patients. No difference in CTV_boost using the fusion of the preop CT (50.0 cm³; 95% confidence interval [CI], 35.6-64.4) compared with no fusion (49.0 cm³; 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_boost 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). There is no benefit of using a preop CT to reduce the volume or the interobserver variability of the delineated CTV_boost for breast radiation therapy.