DESIGN OF AN IN VITRO IRRADIATION PROTOCOL WITH DOSIMETRIC CONTROL APPLIED TO THE STUDY OF PULMONARY SURFACTANT

Pulmonary surfactant (PS) is a lipoprotein complex essential for respiratory mechanics, composed of approximately 10% specific proteins (SP-A, SP-B, SP-C, and SP-D) and 90% lipids, with dipalmitoylphosphatidylcholine (DPPC) as its main component. Its fundamental physical function is to regulate the alveolar air–liquid interface, reducing surface tension and preventing lung collapse. This work presents the design and validation of an experimental protocol to evaluate the perturbation induced by ionizing radiation (IR) in this system under clinical radiotherapy conditions. Pulmonary surfactant was obtained by bronchoalveolar lavage of porcine lungs and subsequently prepared for use under controlled experimental conditions. From the standpoint of the physics of radiation–matter interactions, IR induces water radiolysis, generating reactive species (such as hydroxyl radicals, .OH, and aqueous electrons, e-aq) that trigger lipid peroxidation processes. Previous preclinical studies show that different irradiation schemes induce comparable effects; however, they generally lack a detailed, quantitative, and reproducible dosimetric characterization. In this context, we propose an experimental protocol that integrates physical control and methodological standardization. The experimental protocol is implemented using a clinical linear accelerator (Elekta) and includes a geometric simulation phase by computed tomography, ensuring reproducible conditions with a defined source-to-surface distance (SSD). Three-dimensional dosimetric planning is performed in a treatment planning system (TPS), where the volume of interest is delineated and the desired doses are prescribed. Irradiation is delivered using fields conformed to the sample volume, with energies between 6 MV and 10 MV, prioritizing homogeneity in dose deposition. Validation is carried out through rigorous dosimetric quality control, using high-resolution detectors to verify the agreement between prescribed and delivered dose, as well as the homogeneity of the dose distribution. This protocol makes it possible to isolate the direct effects of irradiation from biological variables, providing a standardized experimental tool of great value for analyzing interfacial dynamics in biophysical systems. As future work, we plan to study the alterations of irradiated surfactant, ranging from its structural level to the impact on its biophysical properties.