Functional lung volume mapping with perfusion SPECT scan for radiotherapy planning in patients with locally advanced NSCLC

Objectives. Radical chemo-radiotherapy (CHT-RT) represents the standard treatment for locally-advanced Non Small Cell Lung Cancer (NSCLC). Conventional RT achieves limited local tumour control, but dose escalation to the primary tumour is prevented by RT-induced toxicity. Aim of this study was to evaluate feasibility of a tailored Intensity-Modulated RT (IMRT) planning based on lung SPECT perfusion data and to compare functional and conventional dose-volume parameters. Methods. 21 patients were prospectively enrolled. Patients underwent IMRT treatment with 2Gy/fraction (median total dose 60Gy). Lung perfusion SPECT images were acquired before RT and 3 and 6 months after RT completion. SPECT and planning CT images were co-registered using MIM-MAESTRO™ software with 3D-PET EDGE™ algorithm. Lung volumes were defined anatomically as Total Lung and functionally as Total Not Functional Lung and Total Functional Lung. Dose-Volume Histograms (DVH) were calculated using QUANTEC constraints (MLD<20Gy, V20<20%). For each patient, conventional and functional RT plans were generated and compared. Results. 19 of 21 NSCLC patients were included (mean age 66y, 11 stage IIIA, 8 stage IIIB), 12/19 patients completed the 6-months follow-up. A significant reduction of mean V20 was observed in functional RT planning compared to conventional plan (405.9 cc, p<0.001). Mean MLD was also lower in the SPECT-based plans, but the difference was not statistically relevant (0.8 Gy, p=0.299). G2 radiation pneumonitis was observed in 2 patients. Conclusions. Functional RT planning allowed to decrease functional lung irradiation compared to conventional planning. The possibility to limit RT-induced toxicity could allow to perform an effective dose-escalation to target volume.