Very small differences in the way a patient lies during radiotherapy treatment for lung or esophageal cancer can have an impact on survival, according to research presented at the European Society for Radiotherapy & Oncology (ESTRO) 37 Conference (Abstract OC-0322). These differences of only a few millimeters can mean that the radiation treatment designed to target a patient's tumor can move fractionally closer to a patient's heart, where it can cause unintentional damage and as a result impact survival.
Radiotherapy plays an important role in cancer care in a number of tumor types, including hard-to-treat tumors such as those in the lung and esophagus. However, it can cause side effects, and previous research shows that radiotherapy to the chest can have negative long-term effects on the heart, for example, increasing the risk of heart disease.
When planning radiotherapy treatment, cancer specialists create a computed tomography (CT) image of a patient. This reveals the exact position and size of the tumor within the body. At each subsequent treatment, another image is created and used to check that the patient and, therefore, the tumor is in the same position, within a certain threshold, before the treatment is delivered.
The new research was presented by Corinne Johnson, a medical physics PhD student at the Manchester Cancer Research Centre, part of the Christie NHS Foundation Trust and the University of Manchester, UK.
Methods and Findings
Ms. Johnson and her colleagues studied a group of 780 patients with non–small cell lung cancer who were treated with radiotherapy. For each treatment, patients were positioned on the treatment machine and an image was taken to confirm that they lay within 5 mm of their original position. Data from these images were used to gauge how accurately the radiotherapy dose was delivered over the course of treatment, and whether it was shifted slightly closer to, or slightly further away from, a patient’s heart. When these data were compared with how likely patients were to survive, researchers found that patients who experienced slight shifts in position toward their hearts were around 30% more likely to die than those with similar slight shifts in position away from their hearts.
Researchers repeated the study with a group of 177 patients with esophageal cancer and reported an even greater difference in survival related to positioning. In both groups, the pattern of effect on survival was consistent, even when other factors were taken into account, such as the patient’s age.
Ms. Johnson explained, “We already know that using imaging can help us to target cancers much more precisely and make radiotherapy treatment more effective. This study examines how small differences in how a patient is lying can affect survival, even when an imaging protocol is used. It tells us that even very small remaining errors can have a major impact on patients’ survival chances, particularly when tumors are close to a vital organ like the heart.”
“By imaging patients more frequently and by reducing the threshold on the accuracy of their position, we can help lower the dose of radiation that reaches the heart and avoid unnecessary damage,” she concluded.
Ms. Johnson and her colleagues are now looking at the data in more detail to see whether particular regions of the heart are more sensitive to radiation than others, and they hope to investigate the effect of differences in patient position in other types of cancer.
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