Dosimetric comparison of conventional and field-in-field techniques in early stage breast cancer radiotherapy

Introduction: Breast conserving surgery followed by adjuvant radiotherapy (RT) of the whole breast is accepted as the treatment of choice in early stage breast cancer. Due to breast irregularities, it is difficult to access homogenous dose distribution with conventional techniques. Currently, it is possible to use varied breast irradiation techniques, such as field- in-field (FIF), to apply a more homogenous distribution of doses within target volumes, and organs at risk (OAR) sparing which lead to achieve better treatment outcome. This study aimed to compare conventional and FIF techniques dosimetrically Materials and Methods: Twenty patients with early-stage breast cancer underwent computed tomography (CT) with a 16 Slice CT simulator; datasets were transferred to the treatment planning system (TPS) via a digital imaging communications in medicine (DICOM). Two different treatment plans were created for each patient by the same medical physicist: a wedge base (conventional) plan and a FIF plan. Then, dosimetric and monitor unit (MU) results were compared. Results: Dosimetric indices in the planning target volume (PTV) were more satisfying with the FIF technique than with three dimensional-conformal RT (3D-CRT). FIF reduced the maximum doses of PTV and MU. In addition, the FIF technique reduced doses to the heart (in left-side irradiation cases) and ipsilateral lung by 7% and 8%, respectively. FIF also significantly reduced V40 (volume receiving 40 Gy) of heart in left side breast irradiation. V20 of lung (volume receiving 20 Gy), and also doses to the contralateral lung did not differ significantly. Conclusion: FIF can produce more homogenous doses within the PTV, and reduce doses to the OAR. Moreover, by using the FIF technique in breast irradiation, MUs required for therapy are significantly decreased compared with that required by 3D-CRT.