Pulmonary imaging after stereotactic radiotherapy—does RECIST still apply?

Abstract

The use of stereotactic ablative radiotherapy (SABR) for the treatment of primary lung cancer and metastatic disease is rapidly increasing. However, the presence of benign fibrotic changes on CT imaging makes response assessment following SABR a challenge, as these changes develop with an appearance similar to tumour recurrence. Misclassification of benign fibrosis as local recurrence has resulted in unnecessary interventions, including biopsy and surgical resection. Response evaluation criteria in solid tumours (RECIST) are widely used as a universal set of guidelines to assess tumour response following treatment. However, in the context of non-spherical and irregular post-SABR fibrotic changes, the RECIST criteria can have several limitations. Positron emission tomography can also play a role in response assessment following SABR; however, false-positive results in regions of inflammatory lung post-SABR can be a major clinical issue and optimal standardized uptake values to distinguish fibrosis and recurrence have not been determined. Although validated CT high-risk features show a high sensitivity and specificity for predicting recurrence, most recurrences are not detected until more than 1-year post-treatment. Advanced quantitative radiomic analysis on CT imaging has demonstrated promise in distinguishing benign fibrotic changes from local recurrence at earlier time points, and more accurately, than physician assessment. Overall, the use of RECIST alone may prove inferior to novel metrics of assessing response.

Image‐based management of empiric lung stereotactic body radiotherapy (SBRT) without biopsy: Predictors from a 10‐year single institution experience

“…As illustrated here and in other studies, RECIST is often difficult to interpret on the background of post‐radiation changes, but remains the gold standard for post‐treatment imaging surveillance . This study corroborates the suggestion that future iterations of RECIST account for the acute inflammatory and chronic fibrotic lung changes related to treatment .…”

“…The widely ranging defined criteria for lung nodule size, morphology, growth patterns, standard uptake value (SUV) thresholds, and treatment response are designed for standard management with biopsy and local therapy. The applicability of such criteria in the empiric SBRT setting with equivalent efficacy is probable but unproven, particularly in the United States (US) . We therefore report our experience of clinically diagnosed presumed early stage NSCLC treated with SBRT, with particular attention to imaging specifics for diagnosis and follow‐up.…”

Treatment outcomes and patterns of radiologic appearance after hypofractionated image-guided radiotherapy delivered with helical tomotherapy (HHT) for lung tumours

“…Novel metrics of assessing tumour response after SABR based on advanced quantitative radiomic analysis on CT imaging have demonstrated to be more accurate in distinguishing benign fibrotic changes from local recurrence than the use of RECIST alone or in combination with functional imaging. 41,42 Furthermore, we did not attempt to provide a differential diagnosis between recurrence and second primary lung cancers in patients who underwent HHT. Actually, owing to the short median FU of this series, we could not apply the criteria of Martini and Melamed, 43 and we assumed as a conventional wisdom that recurrences generally occur during the first 2 years after treatment.…”

Texture analysis of medical images for radiotherapy applications

“…75 In fact, the evaluation of treatment response is complicated by the possible presence of radiation-induced lung injuries (RILIs), such as radiation pneumonitis and fibrosis, which appear as an increase in lung density on CT, similar to tumour recurrence. 6 Although most parts of the works in this context faced the detection of RILI by the evaluation of simple CT ; Pota et al, 2015 103 CRT, chemoradiotherapy; DCE-MRI, dynamic contrast-enhanced MRI; EBRT, external beam radiotherapy; IMRT, intensity-modulated radiotherapy; mp-MRI, multiparametric MRI; PET, positron emission tomography; RT, radiotherapy; SABR, stereotactic ablative radiation therapy; SRT, stereotactic radiotherapy; T2w, T 2 weighted. density, [76][77][78] Mattonen et al [79][80][81] proposed texture analysis for an automatic classification of tumour recurrence and lung injuries.…”

“…3,[5][6][7][8][9] Despite the fact that it seems a promising technique, it has not been completely exploited, since some possible limitations, especially regarding factors that can reduce its repeatability and robustness, need to be explored in more detail.…”