Session Item

The use of stereotactic body radiotherapy (SBRT) remains a challenge in the treatment of central lung lesions. We report the dose to heart substructures and its related toxicity.

From Abril'18 to December'20, 28 patients were treated with SBRT.Central lung lesions were defined according to RTOG 0813 criteria. Immobilization systems were used. ITV was defined by 4D RPM-Varian™.PTV was generated by a 5mm isotropic expansion of the ITV.Two regimens were used: 7.5Gy in 8 fractions or 10-11Gy in 5 fractions.We contoured and retrospectively reviewed the dosimetry of 17 heart substructures according to Feng et al. heart atlas and cardiac toxicity based on CTCAE v5.0. UK constraints were applied.

10 patients with early-stage non-small cell lung cancer, 5 non-biopsed lesions and 14 lung metastases were analysed. 21 were central and 4 ultra-central. Mean follow-up was 16 months(3-33). Mean age was 70y (52-89). Mean GTV/PTV size was 26/57.6cc (0.8-100/6.1-219). Local control was 96% at 12 months. 

In the 8 fractions group, median D0,5cc at each substructure was: right and left atrium, 7.5Gy(1-20) and 17,2Gy(1-48); right and left ventricle, 6.5Gy(1-12) and 3.5Gy(1-17); superior vena cava, 48Gy(6.8-52.8); pulmonary artery, 17Gy(1-43); ascending and descending aorta, 17.1Gy(1-39) and 18.8Gy(1-54.8); aortic valve, 2Gy(0-19.5); pulmonic valve, 4.5Gy(0-10); mitral valve, 0.5Gy(0- 14); tricuspid valve, 0.5Gy(0-13.5); left main coronary artery, 7Gy(0-13.8); left anterior descending artery, 5Gy(0-15.6); left circumflex, 3Gy(0-18.5); right coronary artery, 2.5Gy(0-10) and AV node, 1.5Gy(1-12.6). Median D0,5cc and mean dose in heart were 47Gy(1-51.5) and 2,9Gy(0.1-10.8) respectively.

In the 5 fractions group, median D0,5cc at each substructure was: right and left atrium, 3Gy(1-39) and 5Gy(1-31.5); right and left ventricle, 1.5Gy(1-14.3) and 3Gy(1-37.5); superior vena cava, 12Gy(1.7-53.1); pulmonary artery, 13.75Gy(0,7-28.8); ascending and descending aorta, 12.2Gy(5-33) and 13.3Gy(5.9-49.6); aortic valve, 0.5Gy(0-15.5); pulmonic valve, 1.5Gy(0.3-13); mitral valve, 0.5Gy(0-11); tricuspid valve, 0.4Gy(0-12); left main coronary artery, 0.9Gy(0.1-10); left anterior descending artery, 0.6Gy(0.1-8.8); left circumflex, 0.6Gy(0.1-15.7); right coronary artery, 0.5Gy(0-12.8) and AV node, 0.4Gy(0.2-9.8). Median D0,5 cc and heart mean dose were 16Gy(0.8-43.1) and 1.1Gy(0.1-10) respectively.

Six deaths were reported at the time of the analysis. No > G3 toxicities were found.

No cardiovascular related deaths were observed with the doses reported above. Heart dose constraint used were safe. No consensus for each heart substructure constrains have been met yet. Knowing the dose that each substructure of the heart can tolerate might be useful for the treatment of central and ultracentral lesions in certain clinical situations (e.g. multiple lesions or re-irradiation). Prospective trials are needed to elucidate cardiac toxicity at each heart substructure. We are performing one at our center.