Interobserver Variability in Clinical Target Volume Delineation in Tangential Breast Irradiation: a Comparison between Radiation Oncologists and Radiation Therapists

Abstract

Aims The delineation of target volumes has been radiation oncologist led. If radiation therapists were to undertake this task, work processes may be more efficient and the skills set of radiation therapy staff broadened. This study was undertaken to quantify interobserver variability of breast target volumes between radiation oncologists and radiation therapists. Materials and methods The planning computed tomography datasets of 30 patients undergoing tangential breast radiotherapy were utilised. Four radiation oncologists and four radiation therapists independently contoured the clinical target volume (CTV) of the breast on planning computed tomography using a written protocol. The mean CTV volumes and the mean distance between centres of volume (COV) were determined for both groups to determine intergroup variation. Each of the radiation oncologists’ readings in turn has been used as the gold standard and compared with that of the radiation therapists. The concordance index for each patient’s CTV was determined relative to the gold standard for each group. A paired t-test was used for statistical comparison between the groups. An intraclass correlation coefficient was calculated to measure the agreement between the radiation oncologist and radiation therapist groups. Results The mean concordance index was 0.81 for radiation oncologists and 0.84 for radiation therapists. The intraclass correlation coefficient for the mean volume was 0.995 (95% confidence interval 0.981–0.998) between radiation oncologist- and radiation therapist-contoured volumes. The intraclass correlation for the mean difference between radiation oncologists’ and radiation therapists’ COV was 0.999 (95% confidence interval 0.999–1.000). Conclusions Interobserver variability between radiation oncologists and radiation therapists was found to be low. Radiation therapists could potentially assume the role of CTV voluming for breast radiotherapy provided a standardised contouring protocol is in place.