P32: Comparing radiotherapy with free breathing and deep inspiration breath hold for thymic cancers

Background: Patients with thymic epithelial tumours (TET) have an excellent prognosis. Radiotherapy (RT) is used in the treatment of thymomas as adjuvant treatment after surgery or, if surgery is not possible, as the primary local treatment. High doses of radiation delivered to normal tissue may result in increased morbidity and mortality. We investigated whether RT with deep inspiration breath hold (DIBH) reduces the radiation dose to normal tissues compared to RT in free breathing (FB).

Methods: Seventeen patients with TETs and a treatment planning scan done both with FB and DIBH are included in the study. Treatment plans will be calculated in both FB and DIBH. We will estimate the mean dose to the heart, and lung, and the relative volumes of heart, and lung receiving 20 and 30 Gy. The differences in these dose characteristics are tested with Wilcoxon signed-rank test.

Results: We have identified 17 patients with TETs who have been treated with RT in doses of at least 50 Gy and who had a therapy planning CT scan with both FB and DIBH. Five patients were treated with curative intent and 12 in the adjuvant setting. All patients were treated in 2 Gy 
fractions. Ten patients received doses of 50–54 Gy and seven patients received 60–66 Gy. The mean doses to the heart and lung are estimated as well as the relative volumes of heart, and lung receiving 20 and 30 Gy. A full dataset will be presented at the meeting.

Keywords: Radiation therapy; deep inspiration breath hold (DIBH); radiotherapy (RT)