Abstract
BackgroundTo explore the interobserver variability in the delineation of the tumour bed using seroma and surgical clips based on the four-dimensional computed tomography (4DCT) scan for external-beam partial breast irradiation (EB-PBI) during free breathing.MethodsPatients with a seroma clarity score (SCS) 3 ~ 5 and ≥5 surgical clips in the lumpectomy cavity after breast-conserving surgery who were recruited for EB-PBI underwent 4DCT simulation. Based on the ten sets of 4DCT images acquired, the tumour bed formed using the clips, the seroma, and both the clips and seroma (defined as TBC, TBS and TBC+S, respectively) were delineated by five radiation oncologists using specific guidelines. The following parameters were calculated to analyse interobserver variability: volume of the tumour bed (TBC, TBS, TBC+S), coefficient of variation (COVC, COVS, COVC+S), and matching degree (MDC, MDS, MDC+S).ResultsThe interobserver variability for TBC and TBC+S and for COVC and COVC+S were statistically significant (p = 0.021, 0.008, 0.002, 0.015). No significant difference was observed for TBS and COVS (p = 0.867, 0.061). Significant differences in interobserver variability were observed for MDC vs MDS, MDC vs MDC+S, MDS vs MDC+S (p = 0.000, 0.032, 0.008), the interobserver variability of MDS was smaller than that of MDC and MDC+S (MDS > MDC+S > MDC).ConclusionsWhen the SCS was 3 ~ 5 points and the number of surgical clips was ≥5, interobserver variability was minimal for the delineation of the tumour bed based on seroma.
Highlights
To explore the interobserver variability in the delineation of the tumour bed using seroma and surgical clips based on the four-dimensional computed tomography (4DCT) scan for external-beam partial breast irradiation (EB-PBI) during free breathing
The volume of the tumour bed delineated based on clips (TBC) was similar to that of TBS for six patients during weeks 4-8, the TBC was less than TBS in two patients during weeks 0-3, and the TBC was larger than TBS for twelve patients during weeks 8-16
Most reports define the tumour excision cavity or postoperative seroma as the target volume in treatment planning [7,8,15]. These studies reported significant interobserver variation in delineating post-lumpectomy cavities. van Mourik et al [16] investigated breast target volume delineations among thirteen observers in eight patients. They reported that the presence of clips or seroma reduced interobserver variability but that significant volumetric and spatial interobserver variability was observed in clinical target volume (CTV) even with the help of delineation guidelines
Summary
To explore the interobserver variability in the delineation of the tumour bed using seroma and surgical clips based on the four-dimensional computed tomography (4DCT) scan for external-beam partial breast irradiation (EB-PBI) during free breathing. External-beam partial breast irradiation (EB-PBI) has recently garnered increasing interest [4,5]. Several studies reported that EB-PBI, which delivers radiotherapy to the postoperative tumour bed (TB) with a margin of adjacent breast tissue, could achieve. Surgical clips and seroma are important markers for delineating the TB for EB-PBI [7,8]. Kirby et al [7] reported that the number of implanted markers influences the accuracy of target delineation and that five to six surgical clips are preferable for TB delineation for PBI or breast boost radiotherapy. Landis et al [8] indicated that the shift of the centre of mass (COM) decreased and the percent volume overlap (PVO) increased significantly as the seroma clarity
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