Dosimetric Comparison between Conventional 2D and 3D Conformal Radiotherapy in the Treatment of Intact Breast Cancer

摘要

Background: Radiotherapy (RT) techniques after Conservative Breast Surgery (CBS) vary. Three Dimension (3D) planning allows for better plan optimization compared to 2 Dimension (2D) plans and also allowing for creating Dose Volume Histograms (DVHs) for both Planning Target Volume (PTV) and Organs at Risk (OAR). Patients and Methods: Twenty consecutive patients with CBS planned for whole breast and supraclavicular (SCV) RT at the National Cancer Institute (NCI), Egypt between January and June 2016 were included in this study. All patients were planned clinically in 2D fashion with no more than 2 cm of ipsilateral lung allowed in the tangential fields “Limited 2D” (Limit-2D) then Target and OAR volumes were drawn according to the Radiation Therapy Oncology Group (RTOG) guidelines and 3D plans and a central slice PTV-based 2D plan, “Modified 2D” (Mod-2D), were performed in the same Computerized Tomography (CT) slices for each patient. Mono-Iso-Centeric technique (MIT) was used in 3D plans. DVH parameters were used to compare the three plans. Results: In 3D plans, compared to Limit-2D, coverage improved for the intact breast (V95% = 95% versus (Vs) 69%, p = 0.036) and SCVPTV (V90% = 90% Vs 65%, p = 0.01). The breast and SCV V 107%, V112% and Dmax were better with 3D plan however not statistical significant (NS). Junctional hot spots were 120% and 107% in the Limit-2D and 3D plans respectively (p = 0.04). The dose to the heart, mean (333 Vs 491 cGy), V10 (5% Vs 10%) and V20 (3% Vs 7%), Ipsilateral lung V20 (19% Vs 26%), and contra lateral breast D-max (205 Vs 462 cGy) were higher in 3D plans however NS, and the dose to the cord was the same. Comparison between 3D and Mod-2D showed better OAR sparing with 3D with mean heart dose (491 cGy Vs 782 cGy, p = 0.025) and Ipsilateral lung V20 (26% Vs 32%, p = 0.07% with statistically comparable target coverage. Conclusion: This study demonstrated that application of 3D plan using MIT improves coverage of breast and SCVPTVs with minimizing hot spot at the junctional area if compared with Limit-2D plans with comparable dose to OAR. When compared with Mod-2D plans, 3D plans not only had better target coverage but also better sparing of OAR, the latter was statistically significant.