A new technique to reduce or eliminate breathing-related movement during radiotherapy and diagnostic imaging exams has been developed by researchers at the University Hospitals Birmingham NHS Foundation Trust. The technique increases oxygen levels in the lungs and removes carbon dioxide from the blood, enabling individuals to hold their breath safely for up to 6 min and for multiple times in a single session.
Movement in the thorax and abdomen during an MRI or PET scan can negatively impact the diagnostic quality of the exam. When movement occurs during radiotherapy, the target tumour may shift, causing under-delivery of the prescribed radiation dose and/or dose delivered to adjacent healthy tissues.
Currently, patients are taught deep-inspirational breath-hold techniques, typically achieving multiple (10 or more) short breath-holds each of about 20 s. However, when a breath-hold ends, a patient’s chest and internal organs move, requiring realignment.
Co-principal investigators Michael Parkes, Stuart Green, Qamar Ghafoor and Tom Clutton-Brock developed an approach in which individuals breathe oxygen-enriched air (60% oxygen) and halve blood carbon dioxide levels by mechanical ventilation through a face mask. They previously demonstrated that this method enables healthy volunteers and patients with breast cancer to achieve single prolonged breath-holds safely for longer than 5 min. In this study, they tested the feasibility and safety of multiple prolonged breath-holds (Radiother. Oncol. 10.1016/j.radonc.2019.06.014).
“Before we realised its applications for radiotherapy, the physiology of breath-holding had no medical application,” Parkes tells Physics World. “So this is not routinely taught at medical schools, and therefore clinicians just don’t yet know enough about the basics of breath-holding.”
Thirty healthy volunteers participated in the study, which consisted of initial training on how best to take a deep breath-hold of normal air (21% oxygen) and then of 60% oxygen, and in letting a mechanical ventilator take over their breathing via a face mask, enabling hyperventilation to halve their carbon dioxide levels. With practice over a few days, all 30 could perform single prolonged breath-holds safely for around 6 min.
For the experiments, subjects were told to break at roughly 80% through their 6-min breath-hold. They then either exhaled and took one breath of 60% oxygen, or were mechanically re-hyperventilated with 60% oxygen. The researchers then measured the duration of a second breath-hold. They discovered that after just one breath of 60% oxygen, 18 of 18 participants were able to breath-hold for another 3 min. After being re-hyperventilated, 18 of 18 could breath-hold again for the full 6 min.
In tests of multiple prolonged breath-holds, participants were stopped at about 4 min into their single breath-hold and were re-hyperventilated with oxygen before breath-holding again. The researchers note that, remarkably, 17 of 17 participants could perform nine such prolonged breath-holds in a row, with the first eight lasting approximately 4 min (until termination) and the ninth still lasting 6 min.
The study demonstrates for the first time that multiple prolonged breath-holds are feasible and safe, according to the authors. It also shows three major new features of their prolonged breath-holding technique.
First, if the radiotherapist or patient had to terminate a single prolonged breath-hold early, another 3-min breath-hold is possible just by taking one breath of 60% oxygen. Second, deliberately terminating a single prolonged breath-hold early, with just one breath of 60% oxygen, extends the potential treatment time (total breath-hold duration) to 8 min. And third, instead of using nine short breath-holds to build up a treatment time of, say, 3 min, the patient could perform a single prolonged breath-hold of 5 min. What’s more, it should be possible to use nine prolonged breath-holds to build up a treatment time of 41 min in a single session.
Parkes and Clutton-Brock invented the mechanical ventilator technique approximately 20 years ago. “It is the easiest and safest method of lowering blood carbon dioxide levels,” Parkes explains. “While voluntary hyperventilation is possible, it is too difficult for individuals to do reliably and safely.”
The authors note that their study cohort was limited to individuals aged 20 to 25, and that older or less healthy patients may not achieve the same breath-hold durations. “However, as far as we can tell, the ability to breath-hold safely with our technique for over 5 min is independent of age and gender,” says Parkes. “In our single prolonged breath-hold study with breast cancer patients, the eldest patient was a 74-year old woman who could hold her breath for over 5 min.”
The technique has not yet been introduced by any radiotherapy department, partly because radiation oncologists and radiologists are not generally aware of it. “We hope that this latest study will help convince more clinicians that our technique could help improve patient treatment. The achievements of our volunteers showed that multiple breath-holds are even easier than we dared think might be possible,” says Parkes.
“A challenge that does need to be addressed is to quantify the precise reductions we can achieve in internal movement of all organs in the chest and abdomen,” he adds. The researchers have developed a solution for this and are currently seeking funds to conduct research for clinical applications. They are also investigating the feasibility of using their single prolonged breath-hold technique for lung cancer patients.
