The value of V/Q SPECT/CT lobar quantitation for pre-treatment assessment of lung malignancy

Background: Predicting post-treatment lung function is critical in selecting curative-intent therapies like surgery or stereotactic ablative body radiotherapy (SABR) for early-stage lung cancer. Current guidelines estimate predicted post-operative (PPO) function using lobar volume, ignoring regional variation in ventilation and perfusion, especially in diseased lungs. We aimed to assess the feasibility of ventilation/perfusion single photon emission computed tomography/computed tomography (V/Q SPECT/CT) lobar quantification for improved prediction of post-treatment lung function. Methods: We developed a novel index-Ventilation-Perfusion Capacity Differential Index (VQCDI)-using in-house software that quantifies lobar ventilation, perfusion and volume, reflecting each lobe's contribution to lung function. The software enables manual annotation of surgical margins and radiation fields, allowing regional quantification. Patients undergoing lobectomy, sub-lobar resection or SABR were prospectively enrolled. VQCDI and CT-based volumetric predictions (Vol%) of PPO forced expiratory volume in 1 second (FEV1), diffusing capacity of the lungs for carbon monoxide (DLCO) and haemoglobin-corrected DLCO (DLCOc) were compared to 6-month post-treatment measurements using Pearson correlation, intraclass coefficients (ICC) and Bland-Altman analysis. Results: Fifty-three of 60 sequentially enrolled participants completed post-treatment lung function. VQCDI predicted post-treatment FEV1 in surgical participants with a strong correlation (R=0.920, ICC =0.908, mean difference: -0.096 L) outperforming Vol%. For DLCO and DLCOc, VQCDI also showed strong correlation in surgical participants (R=0.899, ICC =0.874, and R=0.921, ICC =0.899). Performance remained high across participants undergoing lobectomy and sub-lobar resection and in smokers and those with emphysema. VQCDI may also be useful in the quantification of lung function changes in acute radiation pneumonitis post-SABR using 100%, 75%, 50% and 25% radiation dose isocontour zones. Conclusions: VQCDI is a feasible tool that appears to accurately predict post-treatment lung function, with novel capability in sub-lobar resection and post-SABR evaluation. Further multicentre studies with longer follow-up would be beneficial.