Assessing Radiation Pneumonitis Through Functional Lung Imaging: A Single Photon Emission Computed Tomography (SPECT)-Based Approach in Lung Cancer.

[PURPOSE] To develop models to assess the risk of symptomatic radiation pneumonitis (SRP) (Common Terminology Criteria for Adverse Events 4.03 grade ≥ 2) in lung cancer patients by utilizing single-photon emission computed tomography (SPECT) for functional lung volume identification and dosimetric analysis.

[MATERIALS AND METHODS] This retrospective study included 71 lung cancer patients who underwent SPECT before radiotherapy from 2018 to 2024. Perfusion and ventilation SPECT images were co-registered with planning CT to define functional and anatomical lung volumes. Functional lung was defined as voxels with ≥ 20% of the maximum intensity on SPECT. Models to assess the risk of SRP were constructed using Cox regression and evaluated using corrected Akaike Information Criterion (AICc) and time-dependent receiver operating characteristic analysis.

[RESULTS] At a median follow-up of 16.8 months, 19 of 71 patients (26.8%) developed SRP. Factors significantly associated with SRP risk included planning target volume ≥ 150 mL, percentage of total perfusion-defined functional lung receiving ≥ 10 Gy (pVf10) exceeding that of total anatomical lung receiving ≥ 10 Gy (V10), percentage of total ventilation-defined lung receiving ≥ 10 Gy (vVf10) ≥ 45%, and ipsilateral vVf10 ≥ 60% (p=0.004, 0.004, 0.024, and 0.007, respectively). Among the three models, the model incorporating additional ventilation-based parameters demonstrated the best performance (AICc = 85.81, area under the curve = 0.819).

[CONCLUSION] SPECT-based dosimetric parameters derived from perfusion and ventilation are significantly associated with the risk of SRP. Incorporating SPECT may improve risk stratification and enable lung-sparing strategies.