ESTRO 2021 Abstract Book

S1608

ESTRO 2021

Figure 1: An example (CTV1) of a conventional radiotherapy compared to VMAT RapidPlan.

Conclusion ABAS and KBP show promise for generating plans that will deliver improved conformity and homogeneity across the spine metastases CTV.

PO-1888 Dosimetric comparision of heart substructures for left lung cancer with 3 different radiation plans S. Aytac 1 , G. guler avcı 2 1 memorial hospital , radiation oncology, ankara, Turkey; 2 tokat gop university, radiation oncology, tokat, Turkey Purpose or Objective In the era of positive results of immunotherapy and targeted therapies, the fate of locally advanced lung cancer has changed and survival rates considerably have increased. Cardiotoxicity can negatively affect survival outcomes, especially when mediastinal irradiation is required. The aim of this study is to determine the doses exposed to heart substructures and coronary arteries by different radiotherapy (RT) techniques in patients with lung cancer when mediastinal irradiation is performed or not. Materials and Methods Twenty patients who received RT with any T or any N, located centrally in the left lung, were selected retrospectively. The proximal tracheobronchial tree was determined according to the RTOG guideline, and tumors in the volume formed by expanding 3 cm were defined as central tumors. In addition to the target volume and critical organs, the heart chambers (left atrium, right atrium, left ventricle, right ventricle) coronary arteries (left main (LMCA), left anterior descending (LAD), circumflex (CX) and right coronary arteries (RCA)) were delineated by the same physician. The doses of 60 Gy external RT was prescribed in 30 fractions using 3D-CRT, static (s)-IMRT and dynamic (d) -IMRT techniques in all patients. The following parameters were evaluated in RT plans with three different techniques; D mean ,D max ,V 30 ,V 45 for whole heart, left-right atriums and ventricles; D mean , D max for LMCA, LAD, CX and RCA; D mean ,D max ,V 95 ,V 107 , conformity (CI) and homogeneity index (HI) for PTV. Patients were divided into subgroups as N (node) positive (n = 11) and N negative (n = 9). The doses of the heart structures in centrally located tumors without nodal irradiation were assessed. Statistically, all data were evaluated using the Friedman test, initially. Post-hoc analyzes were performed with the Wilcoxon test in significant ones. Results As PTV D mean , D max , V 95 and V 107 , CI and HI, the d-IMRT plans were the best, and the s-IMRT plans significantly superior to 3D- CRT. Right atrium D max and V 45 were not different between the three techniques. The d-IMRT technique was significantly better in other heart substructures and coronary arteries. In the subgroup analysis, there was no difference between the techniques only in left atrium D max in the N positive group. The D mean of right atrium and left ventricle, V 45 of right ventricle and coronary of LMCA D max , RCA D mean , RCA D max were significantly better in d-IMRT technique in the N positive group irradiated in the mediastinum (Table 1). In the remaining parameters, there were no statistical differences between the N positive and negative groups.

Conclusion In lung cancer radiotherapy, when primary tumor or mediastinal irradiation due to node positivity is carried out, heart substructures receive a substantial amount of dose. With different techniques, the doses to these structures are exposed may vary. In the present study, the heart substructures were best preserved with the d-IMRT technique.