ESTRO 2024 - Abstract Book

S5318

Radiobiology - Tumour biology

ESTRO 2024

Purpose/Objective:

Microbeam Radiation Therapy (MRT) and minibeam radiation therapy (MBRT) are two innovative preclinical concepts in radiotherapy that collimates X-ray radiation in micrometer-wide, planar beams. Previous research has shown that MRT substantially spares normal tissue, while being equally effective in tumor ablation. The aim of this study was to determine the tumor growth delay in an in vivo mouse xenograft model comparing MRT and MBRT with conventional radiotherapy.

Material/Methods:

The A549 lung cancer cell line was implanted subcutaneously in CD1-Foxn1nu mice. Groups of nine animals each were irradiated with either sham, conventional broadbeam, MRT or MBRT. All irradiations were performed at the small animal radiation research platform XenX. The spatially fractionated fields were created by using two specially designed collimators with a beam width of 50 μm and a center-to-center-distance (CTC) of 400 μm for MRT and a beam width of 500 μm and 2000 μm CTC for MBRT. The equivalent uniform dose (EUD) concept with 20 Gy was used to calculate radiation doses for MRT and MBRT. The peak-valley-dose-ratio (PVDR) for MBRT was 20, while for MRT 10 and 20. The tumor growth was recorded until the tumors reached at least 3-fold their initial volume.

Results:

There was a significant increase in tumor growth delay following all three irradiation modalities. A growth delay of 14.67 ± 3.57 (95% CI) days was observed for broadbeam compared to sham (p=0.0004) whereas MBRT showed 23.76 ± 3.15 days (p=1.6 x 10-6) while MRT with only a PVDR of 10 showed a trend with 6 ± 2 days (p=0.062). The most pronounced tumor growth delay was observed following MRT irradiation with a PVDR of 20 with 42.35 ± 18.75 days (p=0.0002).

Conclusion:

This study clearly demonstrates that MRT and MBRT lead to an increased tumor growth delay when compared to conventional irradiation at the same irradiation device.

Keywords: Xenograft microbeam minibeam

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