Dosimetric comparison of radiation techniques for comprehensive radiation therapy for left-sided breast cancer: A treatment planning study

Introduction: The purpose of the study was to determine forward-planned intensity-modulated radiotherapy which improves the sparing of organs at risk (OAR), heart, lungs, and contralateral breast, when compared with multi-field inverse-planned intensity-modulated radiation therapy (RT). The anatomy of the chest wall is curved, which makes it difficult to achieve a homogeneous dose; therefore, it is essential to know the technique by which we can render a better treatment. Methods: The three-dimensional field-in-field (FIF) technique for radiotherapy is an advanced state-of-the-art method that uses multileaf collimators to generate a homogeneous and conformal dose distribution through segmental subfields. The planning computer tomography (CT) scans of 30 women with left-sided breast cancer previously treated with whole breast RT on an inclined breast board with both arms supported above the head were retrieved. The whole-breast planning target volume (PTV) was defined by clinical markup and contoured on all relevant CT slices as were the OARs. For each patient, two plans were generated using FIF and five-field inverse-planned IMRT, with a prescription dose of 50 Gy in 25 fractions to the whole breast. The mean and maximum doses to the OARs, conformity index, and homogeneity index (HI) of the whole-breast PTV were compared. Results: The FIF technique significantly reduced the maximum dose of the PTV as well as the mean doses of the heart, ipsilateral lung, contralateral lung, esophagus, and contralateral breast (P < 0.001 for each). When the organ at risk volumes irradiated with 10, 20, 30, and 40 Gy were compared, the results were in favor of the FIF technique. The volume receiving <20 Gy of the prescription dose for the ipsilateral lung was significantly decreased using the FIF technique (P < 0.001). The FIF technique allowed us more homogenous dose distribution. Conclusions: FIF resulted in a lower mean heart and contralateral breast dose with comparable HI of the whole-breast PTV compared to inverse-planned IMRT using five fields. These results with significantly fewer monitor units essential for therapy in FIF suggest that this technique may be more advantageous during breast irradiation.