Room: Track 2
Purpose: Normal lung gas exchange requires ventilation and perfusion to be present, however, surrogate measures, namely 4DCT ventilation and perfusion SPECT, are often used in functional radiation treatment planning. In this study, pre-treatment ventilation and perfusion (V/Q) metrics were compared in non-small lung cancer (NSCLC) patients that received radiotherapy to better understand the functional distribution in this patient population. Dose to combined V/Q functional categorizations were analyzed for their correlation with radiation-induced lung toxicity (RILT).
Methods: V/Q SPECT scans were acquired from 88 NSCLC patients prior to receiving conventionally fractionated radiotherapy as part of two separate IRB-approved studies. Rigid registration was used to spatially align SPECT scans to the treatment planning CT. SPECT intensities were normalized to the mean intensity in the low-dose (<5 Gy), normal-functioning region of the contralateral lung. Three functional lung categorizations were defined: low-functioning (LF<15% of max), normal-functioning (15%=F<70% of max), and high-functioning (HF=70% of max). RILT was defined as grade2+ radiation pneumonitis and/or fibrosis (n=15). Spearman correlation coefficient and dice similarity coefficient (DSC) were used to compare perfusion and ventilation. Univariable logistic regression was applied to assess the association between combined V/Q SPECT dose-function metrics and incidence of RILT.
Results: The patient-averaged Spearman correlation calculated based on voxelwise V/Q intensities was found to be 0.73. Patient-averaged percent of lung with V/Q functional categorization overlap (and DSCs) of 16%(0.65), 59%(0.83), and 2%(0.29) were calculated for the low-functioning, normal-functioning, and high-functioning lung, respectively. Patients that incurred RILT tended to have large volumes of V/Q overlap in low-functioning lung [p=0.004], less overlap in normal-functioning lung [p=0.02] and received =20Gy to a large portion of low-functioning lung [p<0.001].
Conclusion: This study suggests a large presence and irradiation of V/Q functional defects in NSCLC patients undergoing radiotherapy, which may contribute to the onset of RILT and should be further investigated.
Funding Support, Disclosures, and Conflict of Interest: This work was partially funded by NIH grants (P01-CA059872/R01-142840). Dr. Matuszak reports funding from Varian Medical Systems outside the scope of this work.