Diffusion abnormalities of the corpus callosum in patients receiving bevacizumab for malignant brain tumors: suspected treatment toxicity

The relationship between radiation dose and bevacizumab-related imaging abnormality in patients with brain tumors: A voxel-wise normal tissue complication probability (NTCP) analysis

PURPOSE

Bevacizumab-related imaging abnormality (BRIA), appearing as areas of restricted diffusion on magnetic resonance imaging (MRI) and representing atypical coagulative necrosis pathologically, has been observed in patients with brain tumors receiving radiotherapy and bevacizumab. We investigated the role of cumulative radiation dose in BRIA development in a voxel-wise analysis.

METHODS

Patients (n = 18) with BRIA were identified. All had high-grade gliomas or brain metastases treated with radiotherapy and bevacizumab. Areas of BRIA were segmented semi-automatically on diffusion-weighted MRI with apparent diffusion coefficient (ADC) images. To avoid confounding by possible tumor, hypoperfusion was confirmed with perfusion imaging. ADC images and radiation dose maps were co-registered to a high-resolution T1-weighted MRI and registration accuracy was verified. Voxel-wise normal tissue complication probability analyses were performed using a logistic model analyzing the relationship between cumulative voxel equivalent total dose in 2 Gy fractions (EQD2) and BRIA development at each voxel. Confidence intervals for regression model predictions were estimated with bootstrapping.

RESULTS

Among 18 patients, 39 brain tumors were treated. Patients received a median of 4.5 cycles of bevacizumab and 1-4 radiation courses prior to BRIA appearance. Most (64%) treated tumors overlapped with areas of BRIA. The median proportion of each BRIA region of interest volume overlapping with tumor was 98%. We found a dose-dependent association between cumulative voxel EQD2 and the relative probability of BRIA (β0 = -5.1, β1 = 0.03 Gy-1, γ = 1.3).

CONCLUSIONS

BRIA is likely a radiation dose-dependent phenomenon in patients with brain tumors receiving bevacizumab and radiotherapy. The combination of radiation effects and tumor microenvironmental factors in potentiating BRIA in this population should be further investigated.

The Use of Imaging in the Prediction and Assessment of Cancer Treatment Toxicity

Multimodal imaging is commonly used in the management of patients with cancer. Imaging plays pivotal roles in the diagnosis, initial staging, treatment response assessment, restaging after treatment and the prognosis of many cancers. Indeed, it is difficult to imagine modern precision cancer care without the use of multimodal molecular imaging, which is advancing at a rapid pace with innovative developments in imaging sciences and an improved understanding of the complex biology of cancer. Cancer therapy often leads to undesirable toxicity, which can range from an asymptomatic subclinical state to severe end organ damage and even death. Imaging is helpful in the portrayal of the unwanted effects of cancer therapy and may assist with optimal clinical decision-making, clinical management, and overall improvements in the outcomes and quality of life for patients.

Physiologic MRI for assessment of response to therapy and prognosis in glioblastoma

Aside from bidimensional measurements from conventional contrast-enhanced MRI, there are no validated or FDA-qualified imaging biomarkers for high-grade gliomas. However, advanced functional MRI techniques, including perfusion- and diffusion-weighted MRI, have demonstrated much potential for determining prognosis, predicting therapeutic response, and assessing early treatment response. They may also prove useful for differentiating pseudoprogression from true progression after temozolomide chemoradiation and pseudoresponse from true response after anti-angiogenic therapy. This review will highlight recent developments using these techniques and emphasize the need for technical standardization and validation in prospective studies in order for these methods to become incorporated into standard-of-care imaging for brain tumor patients.

Bevacizumab: radiation combination produces restricted diffusion on brain MRI

AIMS

The purpose of this paper is to investigate the effect of bevacizumab (BEV) on the diffusion properties of irradiated brain gliomas.

MATERIALS & METHODS

Neuroimaging studies and medical records of 44 patients undergoing treatment for cerebral gliomas were reviewed. MRIs were analyzed for presence of restricted diffusion, time to onset, pattern/location, duration of restriction, and persistence of restriction post-treatment with BEV.

RESULTS

Patchy confluent areas of diffusion restriction on MRI were found in 12 patients. All 12 patients received radiation therapy followed by BEV therapy. Diffusion restriction appeared 3 to 21 months after onset of radiation and 1 to 6 months after starting BEV therapy, increased in size over time, and persisted up to 23 months while on BEV. Restricted diffusion was observed in areas that received 60 Gy or more of radiation. Areas of restricted diffusion showed low T1 and increased T2 signal intensity, minimal or no contrast enhancement, and low cerebral blood volume. A thin perimeter of susceptibility outlined the restricted areas on susceptibility-weighted images in nine patients (75%). Small focal areas of tumor recurrence within larger regions of restricted diffusion were evident in only four patients (33%). In seven patients (58%) the area of restricted diffusion showed necrosis or radiation change on histology or no metabolic activity on MR spectroscopy or PET.

CONCLUSION

Restricted diffusion associated with BEV-treated cerebral gliomas occurs in regions of high-dose radiation and does not indicate high-cellularity of tumor recurrence.