COMPARISON OF RADIOTHERAPY TREATMENT TECHNIQUES IN PATIENTS WITH LEFT BREAST CANCER BY ASSESSING ABSORBED DOSE IN DIFFERENT STRUCTURES OF THE HEART

The most common type of cancer among women is breast cancer. Due to the anatomical position of the breast, radiotherapy may cause side effects to adjacent normal tissues, especially the heart. The severity of radiation-induced toxicity is closely linked to volume and dose of radiation received by cardiac tissue and its substructures. The aim of this study is to evaluate the dose distribution received by the breast and by organs at risk, with emphasis on individual heart structures, for 2 different radiotherapy treatment techniques (Field-in-Field and 3D) in patients undergoing conservative surgery of left breast. After injection of iodinated contrast medium in 18 patients, tomographic images were acquired on a 64-channel multislice tomograph synchronized to the electrocardiogram. The following contours of the target volumes and heart substructures were outlined: pulmonary trunk, heart, right and left ventricles, right and left atria, left anterior descending artery (LAD), right coronary artery, circumflex artery and aorta. For each patient, treatment plans were performed using the 3D and Field-in-field (FiF) techniques in a treatment planning system. From the dose-volume histogram information, the volumes for different doses (V2, V5, V10, V20, V25 and V30) and the average and maximum doses received for each outlined structure were determined. Means and respective standard deviations were calculated. The FiF technique, in comparison to 3D, showed an 18% percentage reduction in the average dose received by the heart and 11% lower V25. The LAD and left ventricle substructures also presented lower irradiated volumes for the FiF technique. The average dose of LAD was much higher than that of the heart. It was concluded in the study that angiotomography effectively assists in the precise delineation of each heart substructure during the planning process. In addition, for dose distribution, benefits on FiF technique were found when compared to 3D for radiotherapy treatment of patients with left breast cancer. Almost all analyzed substructures were less irradiated with the FiF technique compared to 3D, and all p-values were significant. The average heart dose was not a representative parameter of the average LAD dose, and it is common for this substructure to receive high doses even though the heart dose limits are being respected.