Catheter-based delineation of lumpectomy cavity for accurate target definition in partial-breast irradiation with multicatheter interstitial brachytherapy

PURPOSE: In partial-breast irradiation (PBI), accurate lumpectomy cavity (LC) delineation is critical. Seroma-based delineation (SBD) using computed tomography (CT) with clips remains uncertain, causing an expansion of the LC and planning target volume (PTV). In catheter-based delineation (CBD), the implanted catheters were used as reference markers for LC delineation in multicatheter interstitial brachytherapy (MIB). MATERIAL AND METHODS: Between October 2008 and October 2018, 513 patients who underwent MIB-PBI were examined. In CBD, anatomical relations of LC to catheters were recorded. In randomly selected 22 CBD cases, the LC volume and PTV were retrospectively recontoured on SBD, and the relationship between the contribution of CBD and cavity visuality was evaluated. The LC volume and PTV before and after the introduction of CBD were compared. RESULTS: The mean LC volumes based on SBD and CBD were 19.1 cm(3) and 14.1 cm(3), respectively (p < 0.001). The mean PTVs based on SBD and CBD were 47.9 cm(3) and 35.7 cm(3), respectively (p < 0.0001). More reductions in the LC volume (5.1 cm(3)) (p < 0.05) and PTV (7.7 cm(3)) (p = 0.13) were observed in the poorly visible LC than in the visible LC. The LC volume and PTV before the introduction of CBD (n = 411) were compared with those after introduction (n = 102). Significant reductions were observed in the LC volume (5.9 cm(3)) (p < 0.0001) after the introduction of CBD; moreover, PTV tended to be reduced (3.9 cm(3)) (p = 0.17). CONCLUSIONS: CBD may help to establish the standardized procedure for MIB-PBI and prevent unnecessary radiation exposure to the normal breast tissue.