Purpose: To evaluate planning quality and dosimetric differences of clinically deliverable 3D conformal plans generated from Tomotherapy with TomoDirectTM (TD) and conventional field-in-field approach in prone breast treatment. Materials and methods: Total of twelve randomly selected early stage left breast patients who went through lumpectomy and were previously treated on traditional Linear Accelerator (LINAC) have been re-planned and tested on Tomotherapy TomoDirect module. Baseline prescription dose was chosen at 50.4 Gy (1.8 Gy ¡Á 28 fractions) to cover ¡Ý95% of PTV for planning criteria with other critical structure dose constraints in the thoracic region. Planning outcomes such as D95 (95% of volume of PTV receiving the prescribed dose), D5 and D1, heart, both lungs as well as the contralateral breast were simultaneously evaluated. Conformity of the prescription isodose/volume to PTV was evaluated as conformity index (CI) and dose uniformity was also evaluated with homogeneity index (HI) in the same study series. All outcome parameters were analyzed and summarized to evaluate dosimetric impact of planning qualities between these two planning platforms. Results: The planning results indicate that CI, HI, D95, D5 and D1 of PTV, critical structures such as heart, ipsilateral and contralateral lungs as well as contralateral breast doses were comparable but with better overall statistical end points from TD plans. The D95, D5