Dynamics of metabolic changes in intracranial metastases and distant normal-appearing brain tissue after stereotactic radiosurgery: a serial proton magnetic resonance spectroscopy study

A systematic review on the use of quantitative imaging to detect cancer therapy adverse effects in normal-appearing brain tissue

Cancer therapy for both central nervous system (CNS) and non-CNS tumors has been previously associated with transient and long-term cognitive deterioration, commonly referred to as 'chemo fog'. This therapy-related damage to otherwise normal-appearing brain tissue is reported using post-mortem neuropathological analysis. Although the literature on monitoring therapy effects on structural magnetic resonance imaging (MRI) is well established, such macroscopic structural changes appear relatively late and irreversible. Early quantitative MRI biomarkers of therapy-induced damage would potentially permit taking these treatment side effects into account, paving the way towards a more personalized treatment planning.This systematic review (PROSPERO number 224196) provides an overview of quantitative tomographic imaging methods, potentially identifying the adverse side effects of cancer therapy in normal-appearing brain tissue. Seventy studies were obtained from the MEDLINE and Web of Science databases. Studies reporting changes in normal-appearing brain tissue using MRI, PET, or SPECT quantitative biomarkers, related to radio-, chemo-, immuno-, or hormone therapy for any kind of solid, cystic, or liquid tumor were included. The main findings of the reviewed studies were summarized, providing also the risk of bias of each study assessed using a modified QUADAS-2 tool. For each imaging method, this review provides the methodological background, and the benefits and shortcomings of each method from the imaging perspective. Finally, a set of recommendations is proposed to support future research.

Dynamic contrast-enhanced MR imaging pharmacokinetic parameters as predictors of treatment response of brain metastases in patients with lung cancer

OBJECTIVES

To determine the diagnostic accuracy of pharmacokinetic parameters measured by dynamic contrast-enhanced (DCE) magnetic resonance imaging (MRI) in predicting the response of brain metastases to antineoplastic therapy in patients with lung cancer.

METHODS

Forty-four consecutive patients with lung cancer, harbouring 123 newly diagnosed brain metastases prospectively underwent conventional 3-T MRI at baseline (within 1 month before treatment), during the early (7-10 weeks) and midterm (5-7 months) post-treatment period. An additional DCE MRI sequence was performed during baseline and early post-treatment MRI to evaluate baseline pharmacokinetic parameters (K ^trans, k _ep, v _e, v _p) and their early variation (∆K ^trans, ∆k _ep, ∆v _e, ∆v _p). The objective response was judged by the volume variation of each metastasis from baseline to midterm MRI. ROC curve analysis determined the best DCE MRI parameter to predict the objective response.

RESULTS

Baseline DCE MRI parameters were not associated with the objective response. Early ∆K ^trans, ∆v _e and ∆v _p were significantly associated with the objective response (p = 0.02, p = 0.001 and p = 0.02, respectively). The best predictor of objective response was ∆v _e with an area under the curve of 0.93 [95% CI = 0.87, 0.99].

CONCLUSIONS

DCE MRI and early ∆v _e may be a useful tool to predict the objective response of brain metastases in patients with lung cancer.

KEY POINTS

• DCE MRI could predict the response of brain metastases from lung cancer • ∆v _e was the best predictor of response • DCE MRI could be used to individualize patients' follow-up.

Differentiation of tumor progression and radiation-induced effects after intracranial radiosurgery

A number of intracranial tumors demonstrate some degree of enlargement after stereotactic radiosurgery (SRS). It necessitates differentiation of their regrowth and various treatment-induced effects. Introduction of low-dose standards for SRS of benign neoplasms significantly decreased the risk of the radiation-induced necrosis after -management of schwannomas and meningiomas. Although in such cases a transient increase of the mass volume within several months after irradiation is rather common, it usually followed by spontaneous shrinkage. Nevertheless, distinguishing tumor recurrence from radiation injury is often required in cases of malignant parenchymal brain neoplasms, such as metastases and gliomas. The diagnosis is frequently complicated by histopathological heterogeneity of the lesion with coexistent viable tumor and treatment-related changes. Several neuroimaging modalities, namely structural magnetic resonance imaging (MRI), diffusion-weighted imaging, diffusion tensor imaging, perfusion computed tomography (CT) and MRI, single-voxel and multivoxel proton magnetic resonance spectroscopy as well as single photon emission CT and positron emission tomography with various radioisotope tracers, may provide valuable diagnostic information. Each of these methods has advantages and limitations that may influence its usefulness and accuracy. Therefore, use of a multimodal radiological approach seems reasonable. Addition of functional and metabolic neuroimaging to regular structural MRI investigations during follow-up after SRS of parenchymal brain neoplasms may permit detailed evaluation of the treatment effects and early prediction of the response. If tissue sampling of irradiated intracranial lesions is required, it is preferably performed with the use of metabolic guidance. In conclusion, differentiation of tumor progression and radiation-induced effects after intracranial SRS is challenging. It should be based on a complex evaluation of the multiple clinical, radiosurgical, and radiological factors.