Discussion
pneumonitis, tumor, malignancy, inflammation, non-tumor, fibrosis
PNEUMONITIS, TUMOR, RECURRENCE, INFLAMMATION, SOLID TUMORS, FIBROSIS, SECONDARY, TUMOR RECURRENCE
The superiority of PET/CT over CT for the detection of malignancy in lung nodules, mediastinal staging [Inflammatory changes in fibrotic tissue after radiation. Axial fused PET/CT image (General approaches to read PET/CT include visual and quantitative assessment strategies. Visual evaluation is the most common method to interpret FDG-avid findings in daily routine. Appropriate strategies for recurrence detection include definitions where focal FDG uptake above liver uptake likely reflects tumor and diffuse uptake lower than liver signal rather reflects post therapeutic changes such as inflammation or fibrosis. The definition of Peter Mac criteria and Hopkins criteria represent this approach and intend to define reproducible study criteria for solid tumors [With the potential of imaging derived uptake quantification in PET/CT, quantitative parameters have long been hoped to allow fixed definitions of imaging findings. SUVmax as a commonly used parameter in daily routine represents a single voxel with the highest uptake value and is therefore easy to use. However, with the improvement of scanners, smaller voxel sizes and variation of matrix sizes, SUVmax is not preferable. Single voxel values are not as reproducible as larger region of interests (ROI) [SULpeak which is corrected for lean body mass and describes a ROI rather than a single voxel, is the fundamental parameter in PERCIST [Intercriteria agreement (ICA) between our visual and quantitative evaluation was consistently substantial and even showed almost perfect agreement in relapse assessment of more than 6 months after therapy. Differences exist in the evaluation of different timepoints after therapy: rigid threshold-based assessments are more likely to fail in differentiating inflammation and tumor recurrence. This is one possible explanation for our observation of lower ICA within the first 6 months after therapy and higher ICA after 6 months. This interpretation is supported by the very low and only slight agreement between visual and quantitative evaluation of the lung parenchyma within the first 6 months (ĸ = 0.11) when post-radiation inflammation confounds PET/CT reading. Our findings in the early post therapeutic phase support the superiority of the visual assessment in differentiating between radiation pneumonitis and locoregional tumor recurrence. Nevertheless, quantitative parameters are highly reproducible and especially unexperienced readers might benefit from the implementation of quantitative criteria [With liver-normalized SUL thresholds defined, discrimination between tumor and non-tumor uptake is well possible particularly at time-points later than 6 months after irradiation. Tools for this kind of semi-automated evaluation are already available from the well-known software developers and could easily be implemented in every software environment. After being started, the algorithm runs in the background during the visual assessment and especially the workflow of unexperienced readers could benefit from it.Yet, inflammatory changes within the first 6 months seem to confound threshold-based assessments. In this period, visual assessments show a higher sensitivity. However, it comes at cost of a low specificity, which states that the visual assessment might be conducted too carefully.Even experienced readers tend to be too sensitive and their assessment is overcalling inflammatory changes as recurrence, consecutively resulting in a low specificity and a higher false positive rate. These findings are supported by the low IOA in this time period and line up with the results of studies investigating local therapy response in the lungs after radiotherapy [One strength of the study is the well-controlled primary endpoint of the PET-Plan trial, which was time to locoregional progression; secondary endpoints included time to out-of-field progression and time to distant progression amongst others [