Forward-planned intensity modulated radiation therapy using a cobalt source: A dosimetric study in breast cancer

This analysis evaluates the feasibility and dosimetric results of a simplified intensity-modulated radiotherapy (IMRT) treatment using a cobalt-therapy unit for post-operative breast cancer. Fourteen patients were included. Three plans per patient were produced by a cobalt-60 source: A standard plan with two wedged tangential beams, a standard tangential plan optimized without the use of wedges and a plan based on the forward-planned “field-in-field” IMRT technique (Co-FinF) where the dose on each of the two tangential beams was split into two different segments and the two segments weight was determined with an iterative process. For comparison purposes, a 6-MV photon standard wedged tangential treatment plan was generated. D(mean), D(98%), D(2%), V(95%), V(107%,) homogeneity, and conformity indices were chosen as parameters for comparison. Co-FinF technique improved the planning target volume dose homogeneity compared to other cobalt-based techniques and reduced maximum doses (D(2%)) and high-dose volume (V(110%)). Moreover, it showed a better lung and heart dose sparing with respect to the standard approach. The higher dose homogeneity may encourage the adoption of accelerated-hypofractionated treatments also with the cobalt sources. This approach can promote the spread of breast conservative treatment in developing countries.