Comparative study between two-dimensional and three dimensional planning for external irradiation after breast conservation surgery

ABSTRACT

The aim of this work is to compare between 2-dimensional [2-D] and 3-dimentional [3-D] treatment planning in female patients who are undergoing radical irradiation after breast conservation surgery [BCS]. The treatment plans of 10 consecutive patients receiving radical breast irradiation after BCS were studied for various dosimetric parameters. In 2-D planning the chest and breast contours were taken using rigid tape at midplane of the two tangential fields. The Planned Target Volume [PTV] included the whole breast and one centimetre of the underlying lung tissue. The contour and the PTV were fed to the computer via a scanner and 95% isodose line was made to cover the PTV and as a Mean Tumour Dose [MTD]. In 3-D planning, the patient was put on Computed Tomography [CT] flat table in the same position of simulation and the chest was scanned from supra-sternal notch to 5cm below the inferior margin of the intact breast PTV and organs at risk [i.e. heart and both lungs] were contoured at each 5mm CT cut as well as the PTV which included the whole breast with 2cm margin below. Isodose distribution, dose volume histograms [DVH] of various tangential fields were studied in coronal and sagital sections aiming to obtain maximum dose at Organs at Risk [OAR]. Results of 2-D and 3-D plans were compared regarding dose homogeneity within the PTV. The plans of ten patients were compared, the PTV received 95%, however analysis of dose distribution showed the mean dose homogeneity in the PTV was +/- 9.0% [range 6.4-11.4%] for the 2-D plans and 5.6% [range 4.5-10.3%] for the 3-D technique. The dose to the heart and lungs was minimal in the 3-D planning and could not be assessed in the 2-D plans. Three-dimensional treatment planning for the intact breast results in better dose homogeneity in the PTV and ensures minimal dose to OAR