Analysis of Irradiated Lung and Heart Volumes using Virtual Simulation in Postoperative Treatment of Stage I Breast Carcinoma

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Abstract
Aims and Background: The aim of the study was to assess the usefulness of virtual simulation in postoperative radiotherapy treatment planning of early-stage breast cancer and to evaluate its potential to reduce the volume of critical structures exposed compared to treatment plans produced by a conventional 2D system. Methods and Study Design: Eighteen patients undergoing breast radiotherapy following conservative surgery for small breast carcinomas were studied. Scans from spiral CT equipment (with the patient in the treatment position) were transferred to a virtual simulator. From the screen images the operator contoured breast, lung and heart. Calculations were made of the extent to which the heart and lung were included in the irradiation fields (50% isodose line of tangential fields). Results: Manual contouring was time-consuming, but when virtual simulation was used, the mean volume of the lung included in the radiation fields was significantly reduced compared to the 2D treatment plan (4.5% vs 5.4%, P = 0.034); in addition, a slight reduction was observed for the heart (0.5% to 1.2%), but this was not statistically significant. Conclusions: With a 3D system we obtained optimal target coverage and a reduction of the dose to critical structures (statistically significant only for the lung). From a clinical point of view, this 0.9% reduction in the mean irradiated lung volume is probably not significant, as the percentage irradiated with a 2D system is considerably below the recommended value. Furthermore, our analysis was performed in a relatively small group of patients; for a reliable estimate larger series would be required. Consequently, the 3D system should not be considered in routine treatment after breast conserving surgery for early stage carcinomas; for the time being it should be reserved for selected cases.

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