ESTRO 2024 - Abstract Book

S1688

Clinical - Lung

ESTRO 2024

of continuous positive airway pressure (CPAP) in patients undergoing stereotactic ablative radiation therapy (SABR) for lung tumors, by managing respiration-induced tumor motion.

Material/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 were trained to utilize a CPAP device using a facial mask with pressures ranging from 6 to 20 cm H2O. Two separated 4D-CT simulations were conducted for each patient: once without CPAP (WO) and again with CPAP (WC) ( Figure 1 ). Anatomical and radiologic factors associated with target delineation, as well as dosimetric parameters, were analyzed statistically. 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.

Results:

A total of 39 patients were enrolled in this study, with 5 withdrawn due to discomfort during simulation and 3 were excluded for not receiving SABR. The final analysis included 32 patients with 39 tumors. Among the tumors, 11 (28.2%) were primary lung cancer, 28 (71.8%) lung metastases from other primary origins were included, and 30 (76.9%) tumors were located in the lower lobes. For 26 tumors separated from the diaphragm in all respiratory phases, supero-inferior (SI) distance between the tumor and the diaphragm was significantly reduced when using CPAP (5.96 cm vs. 8.06 cm in the WO group vs. WC group, respectively; p <.001). For 13 tumors located adjacent to the diaphragm, the planning target volume (PTV) overlapped with the diaphragm significantly decreased with the use of CPAP (mean, 6.32 cm 3 vs. 4.09 cm 3 ; p = .002) ( Figure 2 ). Significant differences in SI motion amplitudes were observed in both the tumors (mean, 1.08 cm vs. 0.65cm; p < .001) and the diaphragm (mean, 1.28 cm vs. 1.08cm; p = .036). Planning target volume (PTV) showed a significant reduction in the WC group (25.06 cm 3 vs. 22.52 cm 3 , p = .017). The average lung density measured -668.92 Housefield Units (HU) in the WO group and -776.835 HU in the WC group. In dosimetric and volumetric analysis, CPAP increased lung volume by 58.4 % (mean, 2974.7 cm3 to 4712.9 cm3; p < .001) and decreased heart volume by 7.3% (mean, 709.0 cm3 to 657.4 cm3; p < .001). In the lung, V 5 , V 10 , V 20 , V 30 , V 40 (V x = the percentage of the structure volume exceeding x Gy) and mean dose revealed significant dosimetric benefit (all p < .001), showing V 20 reduction from 3.14 % to 2.4 %. In the trial, grade 1 dry mouth (35%) was the most common adverse event, which was followed by dyspnea (20%), cough (20%), and hiccup (5%). No more than grade 2 adverse events were reported.