Purpose Radiation therapy has shown to be an effective treatment of brain arteriovenous malformations (bAVMs).^{1 2} Target delineation is commonly performed on volumetric image data, such as MRI or CT data. However, the nidi of micro-AVMs may not be visualized adequately by these modalities due to their limited image resolution. In this report, we show a novel usage of high-resolution contrast-enhanced cone-beam computed tomography (CBCT) imaging and multi-modal image registration³ for radiation target delineation of a micro-AVM, a technique previously suggested for larger AVMs.⁴

Case A 42-year-old male presented with intraparenchymal hemorrhage in the mesencephalic tectum and left posterior thalamus. Conventional angiography revealed a left superior collicular AVM with a nidus of 3 mm. The AVM was successfully embolized but follow-up angiography examinations at 36 months demonstrated a small re-growth of the AVM (Abstract P-017 figure 1A). The patient was thus referred to radiosurgery. Thin slice contrast and non-contrast MRI acquired for target delineation did not show the AVM nidus. Therefore, the patient was transferred to the angiography suite for high resolution contrast-enhanced CBCT. Data was acquired using the angiography c-arm system with a reduced detector size of 22 cm. Contrast was injected with 2 ml/s for a total of 64 ml and a 2 sec delay) using a coupled power injector into the left vertebral artery with a 5Fr catheter. Volumetric CBCT data (FOV: 70³ mm³, matrix: 0.14³ mm³) was generated using a non-binned reconstruction algorithm. Lesion and nidus were visualized with CBCT. MRI, CT-simulator and CBCT data was then transferred to the radiation planning software and mutually co-registered. The nidus was delineated on CBCT data by an experienced neurointerventional radiologist for radiation therapy and dose/treatment plan was completed. Due to image registration, the target area could be directly transferred to MRI and CT data (Abstract P-0017 figure 1B). The patient received a total of 4 radiation sessions.

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Abstract P-017 Figure 1

Discussion and Conclusion Radiation target delineation of micro AVMs can be challenging with conventional 3D imaging techniques as their spatial resolution is relatively low for the application of visualization of the nidus. We were able to demonstrate the complementary value of high resolution contrast enhanced CBCT in radiation target delineation of a micro brain AVM. Multi-modal image registration of CBCT with MRI and CT-simulator has shown to be an effective method for radiation target delineation.

Competing interests I van der Bom: None. A Wakhloo: Philips Healthcare. A Kuhn: None. L Ding: None. D Goff: None. M Gounis: None.

References 1. AJNR 1995;16:299.

2. J Neurosurg 2002;97:779–84.

3. vanderBom IMJ, et al. J NeuroIntervent Surg 2011. In press.

4. Radvany MG, et al. J NeuroIntervent Surg 2011. In press.