Breast cancer is considered as the most common malignant tumor of the woman. In addition to surgical interventions and the treatment with systemic therapy, radiotherapy is an important component in the treatment of this disease. Despite the latest technical innovations, the radiation exposure of the organs at risk such as the heart and lung remains an essential part. In order to minimize late toxicities of radiation treatment of the left breast, breathing techniques are used. One of the breath hold techniques deals with the deep inspiration during the irradiation of the left breast, named deep inspiration breath hold (DIBH). The goal is to move the heart away from the thoracic wall and thus from the area to be irradiated, as opposed to free breathing (FB). These two methods are used at the University Hospital Krems to treat patients with left sided breast cancer. The aim of the work is to find out, if there is a difference between the irradiation with DIBH and the irradiation in FB concerning the risk organ load in the teletherapeutic treatment of the left breast. The data collected at the University Hospital Krems, such as the average and maximum heart dose, maximum cardiac distance, maximum dose of the left anterior descending coronary (LAD), average dose of the ipsilateral lung and central lung distance are evaluated. The approach to data collection will be explained, as well as the criteria for patient selection. The evaluation of the collected parameters is done with the statistics and analysis program SPSS. In order to be able to carry out the verification of the significance, the data were checked in advance for normal distribution. In order to be able to demonstrate a comparability of the values. Averages, minimum and maximum values were calculated. A significant difference in favor of DIBH compared to FB could be determined for all planning parameters. In the present work, the process of search after studies is also mentioned, which are compared in the discussion chapter with the results of the bachelor thesis. This is followed by a comparison of the data with other studies. The work ends with a summary of the individual chapters.