Optimization of dose distribution with multi-leaf collimator using field-in-field technique for parallel opposing tangential beams of breast cancers

摘要

3 Dimensional Conformal Radiotherapy (3D-CRT) planning software helps in displaying the 3D dose distribution at different levels in the planned target volume (PTV). Physical or dynamic wedges are commonly applied to obtain homogeneous dose distribution in the PTV. Despite all these planning efforts, there are about 10% increased dose hot spots encountered in final plans. To overcome the effect of formation of hot spots, a manual forward planning method has been used. In this method, two more beams with multi-leaf collimator (MLC) of different weights are added in addition to medial and lateral wedged tangent beams. Fifteen patient treatment plans were taken up to check and compare the validity of using additional MLC fields to achieve better homogeneity in dose distributions. The resultant dose distributions with and without presence of MLC were compared objectively. The dose volume histogram (DVH) of each plan for the PTV was evaluated. The 3D dose distributions and homogeneity index (HI) values were compared. The 3D dose maximum values were reduced by 4% to 7%, and hot spots assumed point size. Optimizations of 3D-CRT plans with MLC fields improved the homogeneity and conformability of dose distribution in the PTV. This paper outlines a method of obtaining optimal 3D dose distribution within the PTV in the 3D-CRT planning of breast cases.Keywords: 3D-CRT, dose volume histogram, homogeneity index, planned target volume