Interobserver variability of clinical target volume delineation of glandular breast tissue and of boost volume in tangential breast irradiation.

BACKGROUND AND PURPOSE To determine the interobserver variability of clinical target volume delineation of glandular breast tissue and of boost volume in tangential breast irradiation. PATIENTS AND METHODS Eighteen consecutive patients with left sided breast cancer treated by breast conserving surgery agreed to participate in our study. Volumes of the glandular breast tissue (CTV breast) and of the boost (CTV boost) were delineated by five observers. We determined 'conformity indices' (CI) and the ratio between the volume of each CTV and the mean volume of all CTVs (CTV ratio). Subsequently we determined the most medial, lateral, anterior, posterior, cranial and caudal extensions both of CTV breast and CTV boost for all observers separately. RESULTS The mean CI breast was 0.87. For one observer we noted the highest CTV ratio in 17 out of 18 cases. No association was noted between CI breast and menopausal status. The mean CI boost was 0.56. We did not find a relation between the presence or absence of clips and the CI boost. For another observer we noted the lowest CTV boost ratio in 10 out of 17 cases. CONCLUSIONS We recommend that each institute should determine its interobserver variability with respect to CTV breast and CTV boost before implementing the delineation of target volumes by planning CT in daily practice.