An optimized small animal tumour model for experimentation with low energy protons

Abstract

BackgroundThe long-term aim of developing laser based particle acceleration towards clinical application requires not only substantial technological progress, but also the radiobiological characterization of the resulting ultra-short and ultra-intensive particle beam pulses. After comprehensive cell studies a mouse ear tumour model was established allowing for the penetration of low energy protons (~20 MeV) currently available at laser driven accelerators. The model was successfully applied for a first tumour growth delay study with laser driven electrons, whereby the need of improvements crop out.MethodsTo optimise the mouse ear tumour model with respect to a stable, high take rate and a lower number of secondary tumours, Matrigel was introduced for tumour cell injection. Different concentrations of two human tumour cell lines (FaDu, LN229) and Matrigel were evaluated for stable tumour growth and fulfilling the allocation criteria for irradiation experiments. The originally applied cell injection with PBS was performed for comparison and to assess the long-term stability of the model. Finally, the optimum suspension of cells and Matrigel was applied to determine applicable dose ranges for tumour growth delay studies by 200 kV X-ray irradiation.ResultsBoth human tumour models showed a high take rate and exponential tumour growth starting at a volume of ~10 mm3. As disclosed by immunofluorescence analysis these small tumours already interact with the surrounding tissue and activate endothelial cells to form vessels. The formation of delimited, solid tumours at irradiation size was shown by standard H&E staining and a realistic dose range for inducing tumour growth delay without permanent tumour control was obtained for both tumour entities.ConclusionThe already established mouse ear tumour model was successfully upgraded now providing stable tumour growth with high take rate for two tumour entities (HNSCC, glioblastoma) that are of interest for future irradiation experiments at experimental accelerators.

Spectral and spatial shaping of laser-driven proton beams using a pulsed high-field magnet beamline

“…One particular aim, which is further used as an example for the beamline optimisation, is the irradiation of a volumetric tumour on a mouse ear, according to Oppelt et al 48,49 . This tumour model was specifically designed to match the capabilities of a laser-driven proton beamline.…”

“…In the following work we present the design and optimisation of a compact laser-driven proton beamline based on two pulsed high-field solenoid lenses and its implementation at the Draco laser facility for dose-controlled irradiation studies of three-dimensional biological samples. This appears in the context of an extensive translational research programme focusing on radiobiological in-vivo studies [47][48][49] via irradiation of 3D tumour entities with low-energy high-dose-rate proton bunches. With the presented beamline the generation of volumetrically homogeneous SOPB dose distributions in a single shot is demonstrated for target volumes of up to 5 × 5 × 5 mm 3 to be irradiated with a dose of about 1 Gy per shot.…”

Analysing Tumour Growth Delay Data from Animal Irradiation Experiments with Deviations from the Prescribed Dose

“…Conventionally, growth data from xenograft subcutaneous tumours were obtained for dedicated, pre-defined treatment groups [13,14,15,16,17] with a sufficient number of animals. Since the allocation in different groups took place before treatment, deviations from the treatment schedule and censoring of animals during follow-up must be taken into account.…”

“…However, despite standardized handling procedures, subtle changes, i.e., in the number of tumour cells inoculated in the mice [12], in the position of inoculation, in the stress status of the individual mouse etc., might result in variations in the tumour radiation response, as visible in Figure 1a. This biological variability is hard to predict and must be taken into account by a sufficient number of animals per group and improved tumour models [16].…”

“…While the dose delivery of the clinical Linac was stable and reproducible, leading to a maximum deviation from the prescribed dose of about 2%, beam-intensity fluctuations of the laser-accelerated electrons were not fully compensated by online dosimetry, which resulted in deviations of more than 10 % from the prescribed dose as measured by retrospective absolute film dosimetry. The common methods for evaluating tumour-growth data, however, are based on grouping of animals treated with a similar dose (e.g., [13,14,15,16]). Consequently, 20 of 47 animals treated with laser-driven electrons were excluded from analysis, reducing the statistical power to detect significant differences between the beam qualities.…”