1158 - Optimizing Target and Diaphragmatic Configuration, and Dosimetric Benefits Using Continuous Positive Airway Pressure (CPAP) in Stereotactic Ablative Radiotherapy for Lung Tumors

J. B. Park^1,2, J. H. Lee¹, J. H. Chang³, J. Son⁴, S. Kwon⁵, S. Y. Choi⁵, H. W. Shin⁶, T. Yu^2,7, and H. J. Kim⁴; ¹Department of Radiation Oncology, Seoul National University Hospital, Seoul, Korea, Republic of (South), ²Department of Radiation Oncology, Seoul National University College of Medicine, Seoul, Korea, Republic of (South), ³Department of Radiation Oncology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea, Seoul, Korea, Republic of (South), ⁴Department of Radiation Oncology, Seoul National University Hospital, Seoul National University College of Medicine, Seoul, Korea, Republic of (South), ⁵Seoul National University College of Medicine, Seoul, Korea, Republic of (South), ⁶Obstructive Upper Airway Research Laboratory, Department of Pharmacology, Seoul National University College of Medicine, Seoul, Korea, Republic of (South), ⁷Department of Radiation Oncology, Dongnam Institute of Radiological & Medical Sciences, Gijang-gun, Busan, Korea, Republic of (South)

Purpose/Objective(s): Continuous positive airway pressure (CPAP), a treatment for sleep apnea, is considered an alternative respiratory motion management strategy for stereotactic ablative radiation therapy (SABR) for lung tumors, replicating lung inflation and stabilization similar to deep inspiratory breath hold technique. This study aimed to evaluate the impact of CPAP in resolving target delineation uncertainties in lung SABR. Materials/

Methods: We performed a prospective single-institutional trial of patients who were diagnosed with either primary lung cancer or lung metastases and received SABR with a dose of 40 to 60 Gy in 4 fractions. Patients with a history of pneumothorax, recent cranial surgery, and any clinical conditions unsuitable for lung SABR or CPAP were excluded. 4D-CT simulations were conducted for each patient, once without CPAP and again with CPAP. To understand differences associated with target delineation, we measured the tumor’s proximity to the diaphragm and tumor excursion. To assess the extent of tumor proximity to the diaphragm, we measured the planning target volume (PTV) volumes that overlapped with the diaphragm or the amplitude of the tumor from the diaphragm. Adverse events were examined on the simulation day, the start date of the treatment, the end date of the treatment, and 2 months after the treatment through patient interviews and physical examinations. Tumor proximity and excursion, as well as volumetric and dosimetric values were compared using a paired Student’s t-test and a Wilcoxon signed-rank test.
Results: 32 patients with 39 tumors were analyzed, after the withdrawal of 5 patients due to discomfort. The median age was 67.3 years old, and all patients showed tolerable pulmonary function, with the mean of FEV1/FVC at 70.6, FEV1 at 95.9%, and DLCO at 83.5%. For 26 tumors separated from the diaphragm, CPAP significantly reduced the supero-inferior (SI) distance between the tumor and the diaphragm (5.96 cm vs. 8.06 cm; p < .001). For 13 tumors located adjacent to the diaphragm, CPAP decreased the overlap of PTV with the diaphragm significantly (6.32 cm³ vs. 4.09 cm³; p = .002). In dosimetric analyses, CPAP expanded lung volume by 58.4 % with a significant reduction in mean dose and V5 to V40 (all p < .05). No more than grade 2 adverse events were reported.
Conclusion: This study was the first to evaluate the potential benefit of CPAP in facilitating target delineation by separating adjacent organs and managing respiratory motion. Lung expansion and separation from the diaphragm with CPAP were associated with a favorable anatomic configuration, contributing to significant critical organ savings from radiation exposure with dosimetric benefits. CPAP proved a favorable safety profile and tolerability for elderly patients. With the limitation of a single institutional cohort, further investigations in diverse clinical settings might be necessary to validate our findings. Our findings strongly support the role of CPAP as a novel strategy for respiratory motion management.