Impact and evaluation of the use of tri-dimensional over bi-dimensional plan for the breast and axillary lymph node irradiation with tangential fields for conservative breast cancer treatment

ABSTRACT

BACKGROUND: A comparative study of dose distribution delivered to the anatomically defined breast, axillary levels I-III, supra clavicle nodal, cardiac and left lung volumes treated by standard tangent fields using conventional technique, planned by either two dimensional (2D) or tri-dimensional (3D) radiotherapy treatment-plan was performed to determine if the dosimetry for the breast, regional lymph nodes and normal tissues at risk can be improved.MATERIAL AND METHODS: Data of the charts and images of 10 consecutive patients who underwent breast-conserving surgery for left-sided breast cancer and received post-operative RT at the Department of Radiation Oncology, Hospital A.C. Camargo, São Paulo, Brazil were reviewed and re-planned. All sets of images used for the study were saved separately and no modification was performed to the initial programmed plan for each patient. For 2D irradiation plans, two opposed fields to treat the breast volume were used and one appositional field was used to treat the supra clavicle nodes. After 2D dosimetric planning, a second 3D treatment plan, with CT tomography at 5-mm intervals in the same position as predetermined in the 2D simulation, was used for plan dose coverage comparison.RESULTS: The breast CTV dose coverage evaluated by the D85%, D90% and D100% presented statically significant differences favoring the 3D plan (p = 0.017; 0.011 and 0.005), with correlation indexes ranging from 42.6% to 57.2%. The same was observed for the supra clavicle nodes (p = 0.003; < 0.001 and 0.045) with correlation indexes ranging from 19.4% to 37.4%. For the axillary levels, a statistical significant difference on dose coverage was observed only for the axillary level III D100%, p = 0.001 and correlation index of 72.5%. For the cardiac area there was a statistical significant difference between the maximum and median given, p = 0.002 and p = 0.01, favoring the 3D plan. CONCLUSION: The use of 3D plan is necessary to include....