Magnetic resonance imaging for precise radiotherapy of small laboratory animals.

AIMS: Radiotherapy of small laboratory animals (SLA) is often not as precisely applied as in humans. Here we describe the use of a dedicated SLA magnetic resonance imaging (MRI) scanner for precise tumor volumetry, radiotherapy treatment planning, and diagnostic imaging in order to make the experiments more accurate. METHODS AND MATERIALS: Different human cancer cells were injected at the lower trunk of pfp/rag2 and SCID mice to allow for local tumor growth. Data from cross sectional MRI scans were transferred to a clinical treatment planning system (TPS) for humans. Manual palpation of the tumor size was compared with calculated tumor size of the TPS and with tumor weight at necropsy. As a feasibility study MRI based treatment plans were calculated for a clinical 6MV linear accelerator using a micro multileaf collimator (µMLC). In addition, diagnostic MRI scans were used to investigate animals which did clinical poorly during the study. RESULTS: MRI is superior in precise tumor volume definition whereas manual palpation underestimates their size. Cross sectional MRI allow for treatment planning so that conformal irradiation of mice with a clinical linear accelerator using a µMLC is in principle feasible. Several internal pathologies were detected during the experiment using the dedicated scanner. CONCLUSION: MRI is a key technology for precise radiotherapy of SLA. The scanning protocols provided are suited for tumor volumetry, treatment planning, and diagnostic imaging.

Multifunctional polymer scaffolds with adjustable pore size and chemoattractant gradients for studying cell matrix invasion.

Transmigrating cells often need to deform cell body and nucleus to pass through micrometer-sized pores in extracellular matrix scaffolds. Furthermore, chemoattractive signals typically guide transmigration, but the precise interplay between mechanical constraints and signaling mechanisms during 3D matrix invasion is incompletely understood and may differ between cell types. Here, we used Direct Laser Writing to fabricate 3D cell culture scaffolds with adjustable pore sizes (2-10 µm) on a microporous carrier membrane for applying diffusible chemical gradients. Mouse embryonic fibroblasts invade 10 µm pore scaffolds even in absence of chemoattractant, but invasion is significantly enhanced by knockout of lamin A/C, a known regulator of cell nucleus stiffness. Nuclear stiffness thus constitutes a major obstacle to matrix invasion for fibroblasts, but chemotaxis signals are not essential. In contrast, epithelial A549 cells do not enter 10 µm pores even when lamin A/C levels are reduced, but readily enter scaffolds with pores down to 7 µm in presence of chemoattractant (serum). Nuclear stiffness is therefore not a prime regulator of matrix invasion in epithelial cells, which instead require chemoattractive signals. Microstructured scaffolds with adjustable pore size and diffusible chemical gradients are thus a valuable tool to dissect cell-type specific mechanical and signaling aspects during matrix invasion.