✅ Respiratory Motion Management Series ② - Expanding the Chest Without Holding the Breath: CPAP
📍Introduction
In the previous issue, we explored how oxygen supplementation and controlled hyperventilation can make breath-holding easier and help patients sustain it for longer. This issue introduces another respiratory motion management technique discussed at the BRIC Symposium: continuous positive airway pressure, or CPAP.
CPAP was the subject of considerable discussion at the BRIC Symposium held in Birmingham, UK, last April. During the meeting, I had the opportunity to meet Dr. Zvi Symon of Sheba Medical Center in Israel, who led one of the earliest prospective studies to systematically apply CPAP in radiation therapy.
CPAP is already widely used in patients with sleep apnea. By continuously delivering positive airway pressure, it helps prevent the upper airway from narrowing or closing during sleep.
Dr. Symon explained that the idea of applying CPAP to radiation therapy arose during a conversation over lunch with a pulmonologist colleague. The question was simple: if CPAP could expand the lungs, could it also reduce tumor motion and lower the dose to surrounding normal organs during radiation therapy?
That question led to a prospective study using CPAP as a respiratory motion management technique and helped establish the basis for further research in this field.
DIBH expands the lungs by asking the patient to take a deep breath and hold it, thereby increasing the distance between the heart and the treatment field. CPAP aims to achieve a similar anatomical effect through a different mechanism. Rather than requiring a breath-hold, it delivers positive pressure throughout the respiratory cycle and increases lung volume while allowing the patient to continue breathing.
This is one of its main practical advantages.
An early prospective study published in 2015 enrolled 11 patients with thoracic tumors who underwent 4D CT under both free-breathing and CPAP conditions. Among 10 evaluable patients with 18 lesions, CPAP increased lung volume by an average of 32%, reduced internal target volume by 27%, and lowered mean lung and heart doses by 22% and 29%, respectively. Pressures of 10 to 15 cmH₂O were used, and most patients completed treatment without significant difficulty (Goldstein et al., 2015).
A subsequent prospective study involving 49 patients showed similar findings. CPAP increased lung volume by an average of 37% and reduced the planning target volume of lung tumors by 19% (Jacobson et al., 2021).
However, the effect was not consistent in every patient. Tumor motion increased in four patients whose tumors were located close to the diaphragm. CPAP can expand the lungs with reasonable consistency, but it does not directly control the rate or depth of spontaneous breathing.
📍From Lung Tumors to Breast Cancer
The application of CPAP soon expanded to breast cancer radiotherapy.
By increasing lung volume, CPAP can increase the distance between the heart and the chest wall and move the heart farther away from the treatment field. This raised the possibility that CPAP could provide a heart-sparing effect similar to DIBH in patients who have difficulty holding their breath.
A research group in Tel Aviv prospectively evaluated CPAP in patients with left-sided breast cancer. Lung volume increased by approximately 60%, while the mean heart dose decreased from 3.02 Gy to 1.60 Gy (Allen et al., 2020).
Around the same time, Dr. Hoonjong Kil, who was practicing in the United States, published a series of studies showing that CPAP could provide heart-sparing effects comparable to those of DIBH in breast cancer treatment (Kil et al., 2018; Kil et al., 2019).
I first encountered CPAP at the 2018 ASTRO Annual Meeting. While attending the meeting with Professor Ik-Jae Lee, I met Dr. Kil, who explained that his hospital did not have a dedicated breath-hold system and had therefore begun using CPAP as an alternative. He described the method as simple and highly effective and strongly recommended that we consider it.
After returning from the meeting, we obtained CPAP equipment for both Gangnam Severance Hospital and Severance Hospital in Sinchon and began applying it in clinical practice.
📍Our Research on CPAP
When we first introduced CPAP, our initial question was straightforward.
“Does CPAP actually reduce the heart dose?”
In our first study, patients with left-sided breast cancer underwent simulation CT under both free-breathing and CPAP conditions, and the resulting treatment plans were compared. CPAP substantially reduced the heart dose with both 3D conformal radiation therapy and volumetric modulated arc therapy (Ko et al., 2021).
Our second question was: “How does CPAP compare directly with DIBH?”
We acquired CT scans under free-breathing, CPAP, and DIBH conditions in the same patients and compared the results. The mean heart dose was 1.05 Gy with both CPAP and DIBH. Lung doses and the distance between the heart and the target were also similar.
The final treatment technique was selected by considering the degree of heart separation observed on imaging, the clinical team’s judgment, and the patient’s ability to tolerate each approach. CPAP was ultimately selected in approximately 90% of the patients.
Treatment time was also substantially shorter. The median treatment time was 385 seconds with DIBH, compared with 110 seconds with CPAP (Choi et al., 2024).
Our third question was: “Is the patient’s position stable during treatment and from one fraction to the next?”
We analyzed 2,273 cone-beam CT scans from 57 patients. Overall, the inter- and intrafractional geometric deviations observed with CPAP were comparable to those seen with DIBH or free breathing.
However, a small number of patients showed greater-than-expected motion during treatment. These patients may require closer monitoring or an alternative respiratory motion management technique (Lee et al., 2021).
Our fourth question was: “How well can CPAP be applied in routine clinical practice?”
In an analysis of 237 consecutive patients, CPAP was successfully applied in 221 patients, or 93%. The remaining 7% either had difficulty tolerating CPAP or did not receive it based on the clinical team’s judgment.
In an analysis of 300 daily cone-beam CT scans, the average error in heart position was approximately 2 mm. Respiratory motion of the breast target measured on 4D CT also remained within a few millimeters in most patients (Choi et al., 2022).
📍CPAP Adoption at Other Hospitals
CPAP has since been studied and adopted at several other hospitals.
Kangbuk Samsung Hospital recently conducted a series of studies combining CPAP with surface-guided radiation therapy, or SGRT. The results showed stable positioning reproducibility, while the overall treatment time was not substantially different from that of patients treated without SGRT (Cho et al., 2025).
A more recent study compared DIBH and CPAP, with both techniques combined with SGRT. Mean heart doses were similar between the two groups, while CPAP showed advantages in left anterior descending coronary artery dose, setup time, and beam-delivery time (Han et al., 2026).
Seoul National University Hospital also conducted a prospective phase I/II study using a target pressure of 20 cmH₂O. Four of the 20 enrolled patients withdrew during simulation because of discomfort.
Among the patients who were able to proceed with treatment, CPAP reduced the mean heart dose by 33.8% compared with free breathing. Lung doses were also significantly reduced (Park et al., 2026).
📍What Is the Appropriate CPAP Pressure?
One practical consideration is how much pressure should be applied.
In a lung stereotactic ablative radiotherapy study that used a relatively low mean pressure of approximately 6.9 cmH₂O, lung volume increased by only 8%, and no clear reduction was observed in tumor motion or heart dose (Di Perri et al., 2018).
By contrast, the early Sheba studies and several subsequent studies generally used pressures between 10 and 15 cmH₂O.
A study comparing different pressure levels found that lung volume and dosimetric parameters improved as the pressure increased. Taking the heart-sparing effect into account, the investigators suggested that approximately 14 cmH₂O could be an appropriate target (Park et al., 2022).
In the Seoul National University Hospital study, which used a relatively high pressure of 20 cmH₂O, approximately 20% of the participants had difficulty tolerating the treatment.
At our hospital, we currently aim for 13 to 15 cmH₂O in most patients with breast cancer. The patient puts on the mask in the simulation room, and the pressure is gradually increased. After approximately five minutes of adaptation, CT simulation proceeds if the patient is able to tolerate the pressure comfortably.
For patients who find the pressure difficult to tolerate, it is reduced to between 10 and 13 cmH₂O.
Patients generally adapt more comfortably when the procedure is explained thoroughly and sufficient time is provided for training. Dr. Symon told me that patients at Sheba Medical Center receive approximately one hour of training before treatment.
📍Conclusion
CPAP is not necessarily superior to DIBH, nor does it reduce tumor motion in every patient. However, it may provide a practical and effective alternative when DIBH is difficult to implement or when patients are unable to hold their breath reliably.
This may be particularly relevant in Korea, where there is no separate reimbursement for respiratory motion management and DIBH remains underused in breast cancer treatment. In such a clinical environment, CPAP may be one of the most practical alternatives available. | 
