3D-Quantitated lung perfusion ^99mTc-MAA SPECT/CT: Impact on intended management in comparison to planar (2D) lung perfusion scan in lung cancer patients

Objectives: Prior to lung resection, predicting the postoperative lung function is of paramount importance. The current practice uses planar (2D) scintigraphy. We have previously shown that 3D quantitated SPECT is more accurate than 2D in determining lobar perfusion. We aim to assess the impact of 3D-quantitated lung perfusion SPECT/CT on the operability of lung cancer patients.

Methods: Post-hoc, single centre study in consecutive patients with suspected or known lung cancer, undergoing pre-operative evaluation with lung perfusion imaging and pulmonary function tests (PFT). ^99mTc-MAA planar and SPECT/CT lung perfusion scans were performed on a single imaging system (Intevo, Siemens). The lobar contribution to the total lung perfusion was assessed using the established 2D-projection method and the 3D-anatomical method (CT Pulmo 3D and xSPECT-Quant - Siemens). The accuracy of the two evaluation methods was tested against a computational anthropomorphic chest phantom (XCAT). Predictive post-operative PFT (PPO PFT) was calculated according to the established formula: PPO PFT =pre-operative PFT[asterisk](1-fraction of lung perfusion to be resected). According to current guidelines, patients were deemed operable with a PPO PFT >40% of the predicted.

Results: From 10/2016 to 10/2017, we enrolled 50 patients (20 females) with the following baseline demographics (mean±Std deviation): age 69.2y±8.2, FEV1 (forced expiratory volume in one second) 69.9%±21.5, DLCO (diffusing capacity of the lung for CO) 58.0%±19.3, VO2max (maximum rate of oxygen consumption during exercise) (% of the normal predicted value). There were significant differences between the lobar perfusion when comparing the percentage lobar perfusion with the two methods, with 22/50 patients (44%) having >10% difference in at least one lobe. 3D-method was highly accurate in estimating the lobar contribution of the XCAT phantom compared to the standard 2D, with a mean absolute bias of 0.4% and 9.6%, respectively. When integrated into the clinical decision, SPECT/CT-based (3D) evaluation of the lung perfusion would have modified the intended surgical management in 7/50 patients (14%) - from operable to non-operable (n=4) or from non-operable to operable (n=3).

Conclusions: 3D Quantification of lung perfusion is significantly different and substantially more accurate than the currently used 2D-method. Evaluation of oncological patient cohort demonstrates a change in the intended surgical management in 14% of patients when this 3D method is integrated in the clinical decision algorithm.