A Brief Report on the Role of SPECT/TC in the Optimization of Radiotherapy Treatment with Radical Intent for Unresectable Stage III NSCLC

Background: The standard treatment for locally advanced non-small cell lung cancer (LA-NSCLC) is represented by concomitant chemo-radiotherapy followed by consolidation with durvalumab that ensures a 5-year survival of 46%. However, the risk of radiotherapy-induced pneumonia (RIP) is almost 10-15%. Complete cardiological examination is also usually performed during the cardiopulmonary pre-treatment evaluation and pulmonary function testing is one of the most used tool to predict the risk of RIP development. Aim: The aim of this study is to investigate the impact of Tc-99 macroaggregated albumin (MAA) lung perfusion scan with single photon emission-computed tomography/computed tomography (SPECT/CT) in the preliminary assessment of lung functions and its potential role for the optimization of the radiotherapy treatment planning. Methods: Descriptive and statistical analysis were performed on eight patients affected by unresectable stage III LA-NSCLC treated with chemo-radiotherapy. Before starting radiotherapy, patients underwent lung perfusion SPECT/CT. The SPECT/CT images were firstly co-registered with the simulation CT scan ones, then a specific region of interest (ROI) of lung volumes was created to represent the areas with a perfusion of at least 20% 40%, 60% and 80% of maximum perfusion, respectively. Finally, optimization of the standard treatment plan was performed with the aim of preserving the better perfused lung volumes. The dosimetric correlations of both plans were made comparing pulmonary V20 and V5, mean pulmonary, esophagus and heart dose. Results: From the DVH comparative analysis of the two treatment plans (standard one versus SPECT optimized one) obtained for each patient, the data confirmed an equal coverage of the target volume while respecting all lungs, heart and esophagus dose constraints. At the same time, SPECT-optimized plans allowed to reduce the average dose to the better perfused lung volumes. Conclusions: Lung perfusion scintigraphy could be considered a preliminary assessment tool to explore lung functions and stratify the risk of RIP development. SPECT/TC may also be proposed as a dose painting tool to optimize radiotherapy treatment plans. Only prospective analysis will be enable us to confirm the real reduction of RIP risk in lung areas with an optimal perfusion.