A comprehensive clinical 3-dimensional dosimetric analysis of forward planned IMRT and conventional wedge planned techniques for intact breast radiotherapy

Abstract 

A forward planned intensity modulated technique was initiated for intact breasts radiotherapy (FPIMRT). Forty-three patients were selected to compare dose distributions achieved by FPIMRT to dose distributions produced by conventional wedge techniques (CW). For the simulation process, the treatment field margins were clinically defined by a physician, and a set of fiducial reference markers was placed on the patient. A computed tomography (CT) scan was then performed and the images were transferred to a 3-dimensional (3D) treatment planning system (TPS). The breast tissue was then contoured to allow for a quantitative dose volume analysis. The treatment plan was initially generated with conventional tangential beam arrangements and open fields. Multiple multileaf collimator (MLC) shaped segments were created for each tangential beam in an effort to produce dose homogeneity throughout the breast. 6-MV photon beams were used for treatment unless acceptable dose homogeneity could not be achieved due to large breast size. In this case, the beam energies of selected segments were modified to 15-MV. Once the FPIMRT plan was created, additional plans were generated using the same beam geometry and 2 tangential open fields with CW techniques and 15° wedges (15DW), 30° wedges (30DW), 45° wedges (45 DW), and 60° wedges (60DW). The dose distributions generated by the CW plans were then compared to the FPIMRT plan. This process was repeated for each patient, and the patient group was divided into 3 categories based on breast volume (small, medium, and large). Both point dose relationships, which compared global hot spot (GHS) magnitude and location and dose volume relationships, which compared breast volume coverage of the 105% and 110% isodose lines (IDL) relative to the prescribed dose (PD), were explored. For the patient group in our study, FPIMRT produced the smallest average GHS and the most evenly distributed location of GHS for all breast size categories when compared to all CW techniques. FPIMRT also produced the smallest average breast volume receiving greater than 105% of the PD (V_a105) for the small- and medium-size breast patients and the smallest average breast volume receiving greater than 110% of the PD (V_a110) for all breast size categories when compared to all CW techniques.

Key Words: Breast, IMRT, Wedges, Dose distribution