Purpose: Advances in early diagnosis in lung cancer have increased the interest in preserving post-radiotherapy lung function, especially with commonly used lung SBRT/SABR radiation treatment; therefore, lung function map is extra important for radiotherapy treatment planning. During treatment simulation for lung cancer radiation therapy, a CT scan with different phases/4DCT can be obtained for the evaluation of lung function. This project was to validate and utilize the new ventilation calculation prototype that Siemens provides in order to implement lung function sparing radiotherapy treatment planning.
Methods: Patients with lung disease treated with SBRT (total 50-55Gy) at a single institution between 2011-2019 were retrospectively identified from a prospectively collected database. Pretreatment and post-treatment 10-phase 4DCT scans were included that are compatible with the Siemens E-Xamine software (Siemens Healthineers, Germany). We imported secondary data from these 4D scans to create a CT ventilation and aeration map using the E-Xamine software. The ventilation map calculated based on Hounsfield Unit changes with deformable registration was used in the E-Xamine. Pre-treatment CT with isodose levels, ventilation levels and tumor contours (GTV, ITV and PTV) and delivered doses (20Gy and 5Gy) were registered to post-treatment CT. The coefficient of ventilation (variance of the whole lung map) and lung V20 and V5 were correlated with pre and post pulmonary function test (PFT) results.
Results: All 6 patients have pre/post PFTs within 5 months from the pre-treatment and post-treatment 4DCT scans. Relative changes in FEV1/FVC for V5Gy trended negatively with slope of -0.9 and r square value of 0.77. Relative changes in FVC for V20Gy trended positively with slope of 3.3 and r square = 0.61.
Conclusion: E-Xamine calculated ventilation maps have a medium acceptable level respective to the PFT value changes.