Abstract
This study aimed to assess the relationship between radiation dose and changes in the irradiated myocardial F-18 fluorodeoxyglucose (FDG) uptake after radiotherapy (RT) in breast cancer patients. The data of 55 patients with left and 48 patients with right breast cancer who underwent curative surgical resection and adjuvant three-dimensional conformal RT and staging (PET1), post-adjuvant chemotherapy (PET2), post-RT (PET3), and surveillance (PET4) FDG positron emission tomography/computed tomography (PET/CT) were retrospectively reviewed. The median interval between PET1 and curative surgical resection, between the end of adjuvant chemotherapy and PET2, between the end of RT and PET3, and between the end of RT and PET4 were five days, 13 days, 132 days, and 353 days, respectively. The myocardial-to-blood pool uptake ratio was measured in all patients. For patients with left breast cancer, the 30 Gy- (30 Gy) and 47.5 Gy-irradiated myocardium-to-low-irradiated myocardium (47.5 Gy) FDG uptake ratios were additionally measured. There were no differences in the myocardial-to-blood pool uptake ratios between left and right breast cancer on all PET scans. For left breast cancer, higher 30 Gy and 47.5 Gy uptake ratios were observed on PET3 than on PET1 and PET2. Both uptake ratios decreased on PET4 compared to PET3, but, were still higher compared to PET1. On PET3 and PET4, the 47.5 Gy were higher than the 30 Gy uptake ratios, while there were no differences between them on PET1 and PET2. Although the whole myocardium FDG uptake showed no significant change, the irradiated myocardium FDG uptake significantly increased after RT and was related to radiation dose to the myocardium in breast cancer patients. These results might be an imaging evidence that supports the increased risk of heart disease after RT in patients with left breast cancer.
Highlights
Breast conserving surgery followed by adjuvant radiotherapy (RT) is widely accepted as an essential part of breast cancer treatment [1,2]
For patients with left breast cancer, some territory of the heart is often included in the RT field, which could result in radiation-induced damage to the myocardium and coronary artery [4,5], and previous clinical studies have reported increased risk of ischemic heart disease, myocardial infarction, and cardiac disease-related mortality in patients with left breast cancer compared to those with right breast cancer [6,7,8]
We retrospectively enrolled patients with breast cancer who had undergone both staging and post-RT positron emission tomography/computed tomography (PET/CT) and measured the FDG uptake of the whole and of the irradiated myocardium on both staging and post-RT PET/CT images by fusing FDG PET/CT images with dose-distribution maps on RT simulation CT images. Using these myocardial FDG uptake values, we aimed to investigate whether FDG uptake of the whole and irradiated myocardium changes after adjuvant three-dimensional conformal radiotherapy (3D-CRT) and whether the changes in myocardial FDG uptake are related to the radiation dose to the myocardium in patients with breast cancer
Summary
Breast conserving surgery followed by adjuvant radiotherapy (RT) is widely accepted as an essential part of breast cancer treatment [1,2]. For patients with left breast cancer, some territory of the heart is often included in the RT field, which could result in radiation-induced damage to the myocardium and coronary artery [4,5], and previous clinical studies have reported increased risk of ischemic heart disease, myocardial infarction, and cardiac disease-related mortality in patients with left breast cancer compared to those with right breast cancer [6,7,8]. In a previous dosimetry study, patients with left breast cancer had absorbed a dose of 2.3 ± 0.7 Gy to the heart and the left anterior descending coronary artery showed the highest radiation dose (7.6 ± 4.5 Gy) among the coronary arteries, while all patients with right breast cancer had absorbed a dose lower than 2.0 Gy [5] These results emphasize the need to develop advanced RT techniques that can reduce the radiation dose to the heart and to screen patients with left breast cancer for radiation-induced heart disease [4,9,10]. Most previous studies have evaluated myocardial FDG uptake by visual analysis or by measuring the maximum FDG uptake of certain myocardial portions, and only few have measured and compared myocardial FDG uptake according to dose-distribution maps for RT [20,21,23,24,25]
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