ESTRO 2016: SBRT in Early-Stage Lung Cancer Linked to Increased Risk of Noncancer Deaths
Researchers have found that treating patients who have early-stage non–small cell lung cancer (NSCLC) with stereotactic body radiation therapy (SBRT) is associated with a small but increased risk of death from causes other than cancer, according to findings presented at the European Society for Radiotherapy & Oncology (ESTRO 35) in Turin, Italy (Abstract OC-0339). In particular, they found that high doses to the left atrium of the heart and the superior vena cava had the strongest association and increased risk of noncancer death.
Barbara Stam, PhD, from the Netherlands Cancer Institute, explained that, as a result of these findings, she and other researchers would be investigating ways to deliver radiotherapy while sparing these crucial heart structures as much as possible.
“Our results show that even within a few years, a radiation dose to the heart is associated with an increased risk of noncancer death for early-stage lung cancer patients, and they indicate which regions of the heart possibly play a role. Validation and further investigations into the exact mechanisms and which heart structures are critical is warranted, but clinically, this could mean that patients might benefit from heart-sparing radiotherapy. For early-stage lung cancer patients treated with SBRT, we still need to investigate if heart sparing is possible, what compromises need to be made, and whether it can increase survival. Further research and a wider discussion on heart sparing at the cost of possibly higher average lung doses is required,” Dr. Stam said.
Study Findings
Dr. Stam and colleagues analyzed data from 565 patients diagnosed with early NSCLC between 2006 and 2013 at five institutions in Europe and North America who were treated with SBRT. In order to calculate how much radiation was delivered to which substructures of the heart, the researchers created a “template” image of the heart and its substructures on to which they could map the anatomy of each of the 565 patients—a process called deformable image registration. Information on the radiation doses for the patients was added, and this enabled the researchers to work out the dose parameters (such as minimum, average, and maximum doses) for the right and left atria, right and left ventricles, superior vena cava, descending aorta, and left pulmonary artery.
“Then we determined the association between these dose parameters and noncancer death for each substructure and for each dose parameter,” said Dr. Stam. “Finding if there is a relation between dose to substructures and noncancer death is only relevant if this relation still exists when other factors that are known to be related to noncancer death are also taken into account. Therefore, we performed a second statistical analysis, including factors such as age, lung function, and performance status.”
After a median follow-up of 28 months, 58% of the patients were still alive. “We found that dose to all substructures of the heart were associated with noncancer death for this group of patients. Two substructures had the strongest association with noncancer death: the maximum dose on the left atrium and the dose to a small area of the superior vena cava. Patients with low doses on the left atrium combined with low doses on the superior vena cava have a higher chance of survival than patients with high doses on the left atrium combined with high doses on the superior vena cava. This association remained after adjustments for the factors included in the second analysis,” Dr. Stam said.
The associations between higher radiation doses to the left atrium and the superior vena cava and deaths from causes other than cancer were small but significant for the investigated patient group: in the left atrium, for every 1 Gy above the average dose of 7.9 Gy, the risk increased by 1.5%, while for other structures, the risk increased by 1% to 2%.
The researchers do not know what were the causes of the noncancer deaths as these lung cancer patients were already elderly (on average, 73 years old) and usually died at home with no autopsies being performed. However, it’s hypothesized that the deaths were related to heart problems, as research in breast cancer patients, who have a much longer life expectancy than lung cancer patients, has shown that radiotherapy can affect the heart adversely.
Corrections were made to this article on May 3, 2016.
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