## 4 Discussion
[10] found that IMRT poses a higher risk for developing second malignant neoplasms relative to conformal treatment for most of the examined OARs including breast, skin, lungs, thyroid, and stomach. Our study reveals the superiority of IMRT over 3D-CRT to decrease the probability of radiation carcinogenesis for both breasts, esophagus, and thyroid. The above superiority of IMRT was not observed in the probability for developing radiotherapy-induced lung malignancies. Possible reasons for the discrepancy with previous reports [9; 10] might be related to differences in the IMRT planning and optimization strategies. The study of [PERSON] et al. [9] lacks information about the applied IMRT technique, whereas [PERSON] et al. [10] only reported the use of five-field IMRT without giving details about the gantry angles and number of control points. The dosimetric parameters of the whole heart, LAD, and LV derived from 3D-CRT plans were always more elevated than those from the intensity modulated radiotherapy techniques. The RRs for MCE and CHF associated with conformal treatment were significantly higher than those derived by IMRT and VMAT plans. These intensity modulated radiotherapy techniques for the management of thymoma were found to be significantly better than the conventional therapeutic irradiation in heart protection. No significant difference was observed in the risks for radiation-induced cardiac diseasesestimated by IMRT and VMAT. It should be mentioned that the RRs varied widely among patients. For example, the maximum RR for MCE was almost twice larger than the minimum value for all treatment techniques. This may be attributed to differences in the radiation exposure of the whole heart and cardiac substructures. In the case of two patients deemed inoperable due to tumor invasion of the pericardium, the expansion of the PTV necessitated the inclusion of a substantial portion of the heart and LV. Consequently, this expansion led to augmented radiation doses to cardiac structures and to elevated risks for cardiotoxicity. Limited data have been published about the risk for cardiac diseases following thymoma irradiation. The normal tissue control probability of the heart was previously calculated [30]. The considered endpoint for heart toxicity in this report was pericarditis [31]. [PERSON] et al. [8] found a mean RR of 1.6 for the presence of CHF following flattening-filter free VMAT. Our study found a smaller mean risk for CHF of 1.21 after VMAT with flattened beams. [PERSON] et al. [12] reported a risk increase for MCE of 135% after thoracic IMRT. A RR of 1.43 is given in our study for the above effects. The small number of subjects with thymoma examined in this work may be considered as a limitation. The infrequency of this malignant disease is mainly related to the small patient group. [PERSON] et al. [2] reported that the annual incidence of thymomas is 2.2 cases per million inhabitants in the United States of America. The respective incidence in Germany is 2.64 thymomas per million of the population [2]. Thymoma is most commonly presented among Asians/Pacific Islanders [18]. The population of this study consisted of European patients who constitute the vast majority of subjects referred for radiotherapy in our department. It should also be mentioned that only females with thymoma needing radiotherapy participated in this study. This selection criterion ensured a uniform patient group enabling the assessment of the second breast cancer risk. The presented probabilities for radiotherapy-induced second primary cancer may be limited by the uncertainties of the organ-dependent parameters of the model used. This model has been extensively employed in studies investigating the probability of carcinogenesis following radiation therapy for both malignant and benign diseases [24; 32; 33]. The second cancer risk estimates are solely related to the use of therapeutic irradiation. The risk of carcinogenesis may be also affected by the genetic susceptibility and lifestyle factors such as smoking [35].