Phase I study of vandetanib (ZD6474) administered during and after irradiation (RT) in children with diffuse intrinsic pontine glioma (DIPG)

10020

Background: Children with DIPG have a dismal prognosis despite use of RT, which is the mainstay of therapy. All chemotherapy regimens used so far demonstrated no benefit. EGFR and VEGFR pathways are considered important in tumorigenesis of DIPG. Methods: We conducted a traditional phase I study combining oral vandetanib (VEGFR-2 and EGFR inhibitor) during and after local RT in children with DIPG. Five dosage levels were tested (50, 65, 85, 110, and 145mg/m2 per day). Vandetanib and RT started on the same day. The first 6 weeks of therapy constituted the dose-limiting toxicity (DLT)-evaluation period. Correlative studies consisted of pharmacokinetic analysis (PK), pharmacodynamic studies in blood, and standard and investigational imaging (before and 1, 3, and 6 weeks after start of therapy). Results: Twenty-one patients were enrolled on study (50 [n = 3], 65 [n = 3], 85 [n = 3], 110 [n = 6], and 145mg/m2 [n = 6]). Two patients experienced DLT consisting of rash/mucositis (level 4) and diarrhea (level 5). The maximum-tolerated dose (MTD) of vandetanib was not reached. Other significant toxicities included lymphopenia grade 3/4 (n = 10), grade 3 neutropenia and hypophosphatemia (one each), grade 2 proteinuria (n = 2), grade 2 hypertension (n = 4), and mild QTc prolongation (n = 7) .Once the phase I component was completed, two extra patients were enrolled at dosage level 5; one of them developed grade 4 seizure secondary to posterior reversible encephalopathy syndrome. PK (n = 21) showed similar drug clearance and volume of distribution compared to adults. However, drug exposure at steady state normalized by dose seemed higher in children. Increased tumor perfusion during the first 6 weeks of therapy was observed in the first 12 patients analyzed. Conclusions: Although MTD was not reached, we recommend administration of vandetanib at a dose of 110mg/m2 per day during and after local RT in children. Further combination studies of vandetanib in children with DIPG are planned.

No significant financial relationships to disclose.

Magnetic resonance imaging-guided renal artery stent placement in a Swine model: comparison of two tracking techniques

BACKGROUND

Magnetic resonance (MR)-guided interventions have evolved from a pure research application to a preclinical method over the last decade. Among the device-tracking techniques, susceptibility artifact-based tracking relies on the contrast between the surrounding blood and the device, and radiofrequency coil-based tracking relies on the local gradient field amplification in a resonating circuit attached to the interventional device.

PURPOSE

To evaluate the feasibility and precision of susceptibility artifact-based and microcoil-based MR guidance methods for renal artery stent placement in a swine model.

MATERIAL AND METHODS

MR imaging-guided renal artery stent placements were performed in six fully anesthetized pigs using a 1.5T short-bore MR scanner. Susceptibility artifact-based tracking with manual scan-plane adjustments and microcoil tracking with automatic scan-plane adjustments were used for renal artery stent placements in three pigs in each group. With both methods, near real-time steady-state free-precession (SSFP) imaging was used. Differences between the two tracking approaches on stenting time, total procedure time, and stent position were measured.

RESULTS

The microcoil-based approach yielded a shorter mean procedure time (17 vs. 23 min). There was no relevant difference for the mean stenting time (12 vs. 13 min). The mean stent deviation from the aortic wall with the susceptibility approach was larger than with the microcoil approach (10 vs. 4.0 mm).

CONCLUSION

For MRI-guided renal artery stent placement, the microcoil-based technique had a shorter procedure time and a higher stent placement precision than the susceptibility artifact-based approach.

MR CAT scan: a modular approach for hybrid imaging

In this study, a modular concept for NMR hybrid imaging is presented. This concept essentially integrates different imaging modules in a sequential fashion and is therefore called CAT (combined acquisition technique). CAT is not a single specific measurement sequence, but rather a sequence design concept whereby distinct acquisition techniques with varying imaging parameters are employed in rapid succession in order to cover k-space. The power of the CAT approach is that it provides a high flexibility toward the acquisition optimization with respect to the available imaging time and the desired image quality. Important CAT sequence optimization steps include the appropriate choice of the k-space coverage ratio and the application of mixed bandwidth technology. Details of both the CAT methodology and possible CAT acquisition strategies, such as FLASH/EPI-, RARE/EPI- and FLASH/BURST-CAT are provided. Examples from imaging experiments in phantoms and healthy volunteers including mixed bandwidth acquisitions are provided to demonstrate the feasibility of the proposed CAT concept.

Hybrid cardiac imaging with MR-CAT scan: a feasibility study

We demonstrate the feasibility of a new versatile hybrid imaging concept, the combined acquisition technique (CAT), for cardiac imaging. The cardiac CAT approach, which combines new methodology with existing technology, essentially integrates fast low-angle shot (FLASH) and echoplanar imaging (EPI) modules in a sequential fashion, whereby each acquisition module is employed with independently optimized imaging parameters. One important CAT sequence optimization feature is the ability to use different bandwidths for different acquisition modules. Twelve healthy subjects were imaged using three cardiac CAT acquisition strategies: a) CAT was used to reduce breath-hold duration times while maintaining constant spatial resolution; b) CAT was used to increase spatial resolution in a given breath-hold time; and c) single-heart beat CAT imaging was performed. The results obtained demonstrate the feasibility of cardiac imaging using the CAT approach and the potential of this technique to accelerate the imaging process with almost conserved image quality.

High-resolution diffusion imaging using a radial turbo-spin-echo sequence: implementation, eddy current compensation, and self-navigation

This work describes a segmented radial turbo-spin-echo technique (DW-rTSE) for high-resolution multislice diffusion-weighted imaging and quantitative ADC mapping. Diffusion-weighted images with an in-plane resolution of 700 microm and almost free of bulk motion can be obtained in vivo without cardiac gating. However, eddy currents and pulsatile brain motion cause severe artifacts when strong diffusion weighting is applied. This work explains in detail the artifacts in projection reconstruction (PR) imaging arising from eddy currents and describes an effective eddy current compensation based on the adjustment of gradient timing. Application of the diffusion gradients in all three orthogonal directions is possible without degradation of the images due to eddy current artifacts, allowing studies of the diffusional anisotropy. Finally, a self-navigation approach is proposed to reduce residual nonrigid body motion artifacts. Five healthy volunteers were examined to show the feasibility of this method.

Signal intensities in FLASH-EPI-hybrid sequences

Theoretical considerations on the signal-to-noise ratio (SNR) in FLASH-EPI-Hybrid imaging were published previously. The purpose of this work was to investigate in vivo the signal intensities in Hybrid images as a function of sequence specific parameters. In detail, the SNR as a function of the number of echoes m per RF excitation, the excitation flip angle alpha, and the dependence on the tissue relaxation times T1 and T2* were studied. In eight healthy subjects brain and abdominal Hybrid images were acquired where m and alpha were changed independently. Signal intensities in human brain, liver, and kidney were evaluated for each Hybrid experiment. Additionally, T1 and T2* values of these tissue types were quantified to allow for a comparison with the theory. An excellent agreement between calculated and measured signal behavior was found. The theory was therefore validated in vivo and can thus be used to optimize the signal-to-noise in Hybrid experiments.

Quantitative magnetic resonance imaging of capillary water permeability and regional blood volume with an intravascular MR contrast agent

A novel method is presented to simultaneously measure the permeability surface area product of water (PS), also known as capillary diffusion capacity, and the regional blood volume (RBV). It is based on magnetic resonance imaging of the longitudinal relaxation times of tissue and blood at different concentrations of an intravascular MR contrast agent. PS and RBV were measured in vivo in different regions of the brain and the skeletal muscle of the rat. The average PS values (n = 5) obtained in cerebral cortex, corpus callosum, hippocampus, thalamus, jaw muscle, and tongue muscle were 3.31 +/- 0.20, 1.81 +/- 0.25, 3.37 +/- 0.36, 3.68 +/- 0.44, 10.6 +/- 1.1, and 14.1 +/- 2.51 ml x min(-1) x g(-1), respectively. The corresponding average RBV values were 1.63 +/- 0.18, 1.22 +/- 0.25, 3.30 +/- 0.37, 3.03 +/- 0.36, 1.66 +/- 0.30, and 1.38 +/- 0.33 ml x 100 g(-1). These results are in good agreement with previously reported literature values obtained by means of autoradiography.

Calorimetric measurement of optical absorption

Airborne particles are drawn into a chamber. After closing the chamber the particles are irradiated with broadband shortwave radiation. The mean shortwave volume absorption coefficient of the particles is calculated from the measured pressure change with time within the chamber. The method has been calibrated using water vapor. The detection limit is +/-2 x 10(-6)/m in terms of the volume absorption coefficient. There is very good agreement between the calorimetric and a new photometric absorption measurement. Advantages and disadvantages of both methods are discussed at the end of the paper.

Light absorption measurements: new techniques

A new radiometer is described which simplifies measurement of the radiation supply of solar wavelengths. Two methods of measuring the radiant energy absorbed by aerosol particles are described: A photometric technique is used for particles collected on filters, and a calorimetric technique is used for in situ measurements. Data collected with the radiometer and the light absorption techniques yield the heating rate of the atmosphere due to light absorption by the particles. Sample measurements show substantial atmospheric temperature increases due to absorption, especially in industrial regions.