Improving the diagnosis of radiation necrosis after stereotactic radiosurgery to intracranial metastases with conventional MRI features: a case series

Abstract

Background The distinction between true disease progression and radiation necrosis after stereotactic radiosurgery to intracranial metastases is a common, but challenging, clinical scenario. Improvements in systemic therapies are increasing the importance of this distinction. A variety of imaging techniques have been investigated, but the value of any individual technique is limited. Case presentation Assessment should extend beyond simply the appearances of the lesion at a given timepoint, but also consider local anatomy and lesion evolution. Firstly, enlargement of a metastasis is affected by local anatomical boundaries, such as the dural reflections or cerebrospinal fluid spaces. In contrast, the radiation dose administered with stereotactic radiosurgery does not respect these anatomical boundaries and is largely concentric around the treated lesion. Therefore, new, non-contiguous enhancement across such a boundary can be confidently attributed to radiation necrosis. Secondly, the dynamic nature of radiation necrosis may result in a change in lesion shape, with different portions of the lesion simultaneously enlarging and regressing. Regression of part of a lesion indicates radiation necrosis, even if the overall lesion enlarges. This case series describes these two features and provides illustrative clinical examples in which these features allowed a confident diagnosis of radiation necrosis. Conclusions The distinction between true disease progression and radiation necrosis should extend beyond just the appearances of the lesion. More nuanced interpretation incorporating a relationship to anatomical boundaries and a change in shape can improve accurate diagnosis of radiation necrosis.

Diagnostic Value of 18F-FACBC PET/MRI in Brain Metastases

“…This indicates that lesion enlargement may represent reactive immune response instead of tumor regrowth, showing that increase in size is not necessarily a good indicator for recurrence. Thus, other features such as enlargement across anatomical boundaries, type of contrast enhancement, conspicuity of tumor margins, and complex evolution such as simultaneous regression and enlargement have been suggested indicative of radiation necrosis rather than tumor progression, 57,58 but this has not been considered in this study. Biopsy is the criterion standard for distinguishing tumor recurrence from radiation necrosis but was not included in this study because it is invasive and may cause complications.…”

Growth dynamics of brain metastases differentiate radiation necrosis from recurrence

“…Different discrimination methods have been proposed in the literature based on either perfusion MR imaging, 8 positron emission tomography, 9 the use of AI, 10 radiomics, 11 , 12 or changes in the shape or anatomical boundaries. 13 However, many of those methods have not been validated or require complex computational methodologies. Moreover, many of the AI-based studies require extensive validation before clinical implementation due to the limitations of using these multivariate methods on small patient datasets.…”

“…In this sense, other methods have been used to differentiate both entities, including perfusion MR imaging, 8 positron emission tomography, 9 the use of artificial intelligence (AI) 10 and radiomic methods, 11 , 12 or changes in the shape of anatomical boundaries. 13 However, many of those methods have not been validated by independent groups and additional studies are required, or they are based on complex computational methodologies. There is a need for diagnostic techniques based on routinely used imaging methods, such as post-contrast T1-weighted images (T1–WI).…”

“…There is a need for diagnostic techniques based on routinely used imaging methods, such as post-contrast T1-weighted images (T1–WI). 13 …”

Radiation necrosis after radiation therapy treatment of brain metastases: A computational approach

“…Conventional MRI is not appropriate for discriminating between both conditions since they share similar characteristics. Several alternative methods have been employed to differentiate tumor progression and RN, including perfusion MR imaging [15], positron emission tomography [16], the use of artificial intelligence [17] and radiomic methods [18,19], or changes in anatomical boundaries [20]. However, many of these methods lack independent validation, require complex computational methodologies, or are in need of further study.…”