SU-E-T-624: Study of the Robustness of the Integrated Photon Boost Irradiation Technique for the Treatment of the Tumour Bed for Breast Patients

Abstract

Purpose: The treatment of the breast bed tumour using a simultaneous photon boost is a good alternative to the use of electrons. This technique is widely used and provides similar clinic results than the treatment of the bed tumour in a second phase with electrons. The purpose of this study is to evaluate the robustness of this technique. Methods: The homogenization of the dose distributions of the entire breast is accomplished using segments selected following an IMRT forward approach. The total dose to the breast is 50 Gy and 60 Gy to the tumour bed. The patient is positioned with the two arms elevated using the breast board from MED‐TEC. To evaluate the robustness of the technique a new CT to the patient is done by the end of the second week of treatment. The new CT is fused with the planning CT. The original structures and irradiation plan are associated to the new CT and a new calculation is done using the second CT as base. The dosimetric discrepancies between both plans and the possible movement of structures are then evaluated. Results: The comparison of contours between the planning CT and the verification CT shows good agreement in most cases. In some of them the deviations were significant but they were inside the margins of PTV. The recalculation of the original irradiation plan in the verification CT shows no significant differences with the original planning, the homogeneity in the CTVs continues being good, the covering of the CTVs is similar for both CTs and the OAR do not show significant increases. Conclusions: Results show that this technique is low dependent of small movements of the patient between fractions and that the clinical positioning protocol used allows a good reproducibility of the patient position taking into account the margins considered.