Dosimetric evaluation of various boluses for electron therapy of the chest wall with an inward defect

Introduction: Matched electron fields is a method for post-mastectomy radiotherapy. Chest-wall defects can cause dose inhomogeneity inside the target volume. In this study dose profiles of specific anatomical sites of an anthropomorphic phantom with a surface defected is assessed using nonconformal bolus application. The proposed method extends the capability of film dosimetry for assessing dose uniformity in a fixed distance from the source at a desired beam angle. Materials and Methods: Data of the DICOM file of the patient was directly used for designing the anthropomorphic phantom. Radiation with 12 MeV and 15 MeV electrons were delivered in various settings including no bolus, a bolus that filled the inward defect ,and one and two layers of uniform 5mm boluses. Film dosimetry was performed at the base of the defect, inside the target volume and lung and also the surface of the heart. Results: Defects cause high dose areas at the corners and low dose areas at the center of the defect base. Filling the defect with thermoplastic bolus caused the dose profile became more homogeneous and the double 5mm bolus decreased the dose homogeneity. Discussion: Surface defects change the shape of electron isodoses. Thermoplastic bolus that compensates a defect increased the homogeneity of dose in a fixed depth from the surface. From a practical view point, bolus application has a risk of underdosing the target volume.

کلیدواژه ها:

Radiotherapy ، electron ، phantom ، mastectomy ، bolus