Inter observer variation in delineating lumpectomy cavity and CTV for patients undergoing APBI using intra-operative implants and its impact on implant dosimetry

Abstract

Introduction 3D conformal brachytherapy utilized limited source positions in catheters and thus may impact dosimetry for inter observer variation in target delineation. Purpose To investigate the inter observer variations in lumpectomy cavity (LC) and clinical target volume (CTV) delineation and their dosimetric impact. Material and methods Delineation of LC and CTV was done by five radiation oncologists on 20 patients of interstitial breast implant. Cavity visualization index (CVI), four point scale ranging from (0-excellent) to (3-poor) was developed for open cavity technique and assigned for each patient. Total 200 contours for all five observers and 100 geometrical optimized plans were made. Spatial concordance (CI), average shift in the center of mass (COM) and SD of structure volume were quantified among all observers and statistically analyzed. Variation in source dwell positions for each tube and volume encompassing prescription isodose (Vmax/Vmin) among observers was estimated. Results The mean ± SD CI of LC and CTV was 0.54 ± 0.08 and 0.58 ± 0.08. Mean assigned CVI was 0.85 ± 0.81. CI tends to decrease and shift in COM increase significantly ( p Conclusion Significant correlation of CVI was observed with CI and COM shift. Inter observer variations have shown the impact on the source positions along catheters and thus have dosimetric impact on irradiation of breast tissue with prescription isodose.