SBRT is an effective non-invasive method used to deliver high doses of ionizing radiation to a small tumor volume,
and has been increasingly used as the principal therapy specially in patients with poor performance status and stage I lung cancer,
who historically had a standard treatment with lobectomy or pneumonectomy[18].
SBRT resulted in a different pattern of lung actinic changes,
and its understanding is crucial to evaluate treatment response and recurrence.
The current classification of SBRT lung changes and recurrence findings was evaluated by three radiologists,
with strong agreement between the findings.
Our findings are in line with previous studies,
which demonstrated 64% of early changes and 98% of late changes among our population study,
compared to an overall incidence of early/late changes ranging from 54-79% to 80-100%[12].
The conventional modified pattern was the most common change in our population,
also agreeing with most SBRT imaging studies[14].
Furthermore, enlarging opacity,
bulging margins,
and loss of an air bronchogram were also imaging features related to recurrence.
Conversely,
we found a small percentage of diffuse consolidation (an early radiation pneumonitis finding) among the late CTs.
The finding was slightly more described among the junior and intermediate radiologists,
and may be related to the strictly following of the imaging classification disregarding the time of follow-up.
In our study,
this misclassification did not have statistical significance,
but diffuse consolidation and enlarging opacity are features that may be present in the same patient and need to be carefully evaluated and described for avoiding misdiagnosis.
Comparison between exams and to notice the time of follow-up is essential to prevent the mistake.
The clinical relevance of our results relies on our strong inter-reader agreement among almost all findings,
endorsing the present imaging classification.
We found only a single study which evaluates the agreement between radiologists considering the current SBRT pulmonary changes classification[19],
and all the previous studies about the subject include only the radiotherapist CT evaluation.
As an emerging radiological classification,
its recognizing and reproducibility by radiologists is extremely important to maintain or refine the findings. Indeed,
this current classification for inflammatory and recurrence post-SBRT changes is very didactical and turns to an excellent guide to follow imaging data.
There are some potential limitations of this study.
First,
this is a retrospective study and the timing of the CT evaluation was not controlled,
so patients with a short follow-up may have had a missed recurrence.
Also,
the study was performed with a small number of patients.
A larger sample would lead to more accurate data.
Therefore,
further studies,
especially prospective cohorts with a long follow-up,
are necessary to overcome these limitations and to provide a better generalization of our results.
In conclusion,
our study demonstrates that the current classification of pulmonary post-SBRT changes (including the recurrence findings) is easily reproducible by radiologists with different levels of expertise.
Additionally,
we also demonstrated that the presence of enlarging opacity,
bulging margin and loss of air bronchogram on CT were significantly correlated with recurrence.