Tiny differences in a patient’s position during radiotherapy for lung or oesophageal cancer can impact how likely they are to survive, according to research presented at the ESTRO 37 conference in Barcelona. The study found that differences of just a few millimetres can shift radiation targeted to the tumour fractionally closer to the heart, where it can cause unintentional damage and reduce survival chances. This finding suggests that survival could be improved by tightening up treatment guidelines to ensure patients are positioned more accurately.

Corinne Johnson, a medical physics PhD student at the Manchester Cancer Research Centre, and colleagues studied 780 patients with non-small cell lung cancer who were treated with radiotherapy. For each treatment, patients were positioned on the treatment system and an image taken to confirm that they lay within 5 mm of their original position.

The researchers used the data from these images to gauge how accurately radiotherapy dose was delivered over the course of treatment, and whether it was shifted slightly closer or slightly further away from the patient’s heart. Comparing these data with how likely patients were to survive showed that patients with slight residual shifts towards their hearts were around 30% more likely to die than those with similar sized shifts away from their hearts. Repeating the research in a group of 177 oesophageal cancer patients revealed an even greater difference, of around 50%.

“We already know that using imaging can help us to target cancers much more precisely and make radiotherapy treatment more effective,” Johnson explained. “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 tumours are close to a vital organ like the heart.”

She suggests that imaging patients more frequently, and reducing the threshold on the accuracy of their position, could help lower the radiation dose to the heart and avoid unnecessary damage. The researchers are now examining the data in more detail to see whether particular regions of the heart are more sensitive to radiation than others. They also hope to investigate the effect of differences in patient position in other types of cancer.