A prospective investigation into the clinical impact of 4D-PET/CT in the characterisation of solitary pulmonary nodules

Abstract

Background While the effects of respiratory motion on measuring metabolic signal in PET/CT scanning are well known, it is still standard practice in most centres to scan patients while breathing freely with no correction for the effects of respiratory motion. The aim of this study was to investigate the impact of 4D-PET/CT in classifying lesions in patients with a radiologically-indeterminate solitary pulmonary nodule. Methods Twenty consecutive patients with a solitary pulmonary nodule for investigation were prospectively recruited and completed a whole-body (WB)-PET/CT and 4D-PET/CT in the same session. The reporting physician initially classified the nodule using a 5-point scale (Definitely Malignant, Probably Malignant, Indeterminate, Probably benign, Definitely Benign) on the WB-PET/CT. The physician was then shown the 4D-PET/CT and asked if they would re-classify the lesion. Frequency, sensitivity, specificity and accuracy values were calculated for WB-PET/CT alone and then with the addition of the 4D-PET/CT. Results There were no changes in the classification for nodules initially classed as either benign or malignant with the addition of a 4D-PET/CT. However changes were observed between WB and 4D-PET/CT scans in lesions initially classified as indeterminate. When indeterminate lesions were defined as malignant there was a minor increase in sensitivity (from 73% to 75%), in specificity (56%-63%) and in accuracy (65%-70%) but these results do not reach statistical significance. When the Indeterminate lesions were defined as benign there was an increase in sensitivity (from 55% to 67%) but there was a reduction in the specificity (100%-75%) and accuracy (75%-70%) with the addition of the 4D-PET/CT but again the results did not reach statistical significance. Conclusion The addition of 4D-PET/CT is most likely to have an impact on those nodules initially classified as indeterminate on standard WB-PET/CT. In lesions classified as benign or malignant on standard WB-PET/CT the addition of a 4D-PET/CT is less likely to impact lesion classification. While 4D-PET/CT does improve the measurement of the metabolic signal, it does not overcome inherent limitations of FDG in differentiating a malignant lesion from inflammatory processes, correct for partial volume effects or compensate for the low intrinsic FDG-avidity of some malignancies.

Validation of Software Gating: A Practical Technology for Respiratory Motion Correction in PET

“…Such artifacts impede the provision of appropriate patient care. For example, use of fluorine 18 FDG PET/ CT for oncologic imaging is subject to the limitations and artifacts imposed by respiratory motion; subsequent corrections could affect initial staging and subsequent treatment response monitoring, thus altering patient management, as previously shown (33,34). The objective improvements we saw in image resolution (decreased lesion FWHM) and quantification of radiotracer uptake (increased FDG SUV max ) Note.-ND = lesion not definable with a FWHM measurement (eg, lesion-to-background ratio was too low), SD = standard deviation.…”

A modern review of the uncertainties in volumetric imaging of respiratory‐induced target motion in lung radiotherapy

“…179,180 Furthermore, 4D PET imaging with fluorodeoxyglucose (FDG) tracers is just as limited as 3D PET imaging, in terms of not having the ability to differentiate malignancies from inflammatory processes, correct for partial volume effects or correct for lesions that are inherently less FDG-avid. 181 Kruis et al 182 also demonstrated the importance of using a 4D-CT (vs a 3D CT) for the attenuation correction of the 4D PET because of the uncertainties that may be introduced into the SUV values due to respiratory-induced CT changes.…”

Quantification, improvement, and harmonization of small lesion detection with state-of-the-art PET

“…For the first method, to maintain image quality, respiratory gating requires a longer scan time and/or a higher injected activity. Therefore, respiratory gating is nowadays not routinely used for diagnostic imaging [ 49 , 50 ]. However, it is more commonly applied for radiotherapy planning, where an accurate delineation and quantification is even more important [ 51 – 53 ].…”