ESTRO 2025 - Abstract Book

S4016

Radiobiology - Tumour radiobiology

ESTRO 2025

3924

Mini-Oral Microbeam Radiation Therapy (MRT) enhances tumour growth delay in a syngeneic mouse lung tumour model Aleksandra Čolić 1,2 , Marina Santiago Franco 1,2 , Narayani Subramanian 1,2 , Mabroor Ahmed 1,2 , Susanne Raulefs 1,2 , Stephanie E. Combs 1,2 , Stefan Bartzsch 1,2 , Thomas E. Schmid 1,2 1 Institute of Radiation Medicine, Helmholtz Munich, Neuherberg, Germany. 2 Department of Radiation Oncology, Technical University of Munich, School of Medicine and Health, TUM University Hospital, Munich, Germany Purpose/Objective: Microbeam Radiation Therapy (MRT), a form of spatially fractionated radiation therapy (SFRT) is a pre-clinical concept which is based on arrays of highly collimated, quasi-parallel microbeams. Such inhomogeneous dose deposition allows for the dose in the target to be distributed in high-dose “peak” and low-dose “valley” regions (1). Previous studies have shown that MRT elicits a better tumour control compared to the conventional broad beam (BB) radiation therapy (2). The aim of this study was to compare the tumour growth delay (TGD) in an in vivo syngeneic subcutaneous lung model between MRT and BB. Material/Methods: Two murine lung cancer cell lines Lewis Lung Carcinoma (LLC) and CMT167 were subcutaneously injected in the right hind leg of 6–8-week-old C57BL/6J mice. Once the tumours reached 60-100 mm 3 mice were irradiated either with MRT or BB doses ranging from 5-20 Gy. All irradiations were performed at a XenX small animal irradiation device (X-Strahl Limited, Camberley, UK). The device was equipped with a custom-made tungsten collimator with a slit-width of 50 µm and a center-to-center (CTC) distance of 400 µm, while the peak-to-valley-dose ratio (PVDR) was 20. To determine the radiation doses for MRT, the concept of the equivalent uniform dose (EUD) was applied. The termination criteria was reached once the tumours reached three times their original volume. Results: The data is shown in Fig. 1. For the CMT167 cell line the TGD for the 20 Gy BB group was 10.18±7.7 days (p=0.0584) while the MRT 15 Gy group already showed a significant enhanced TGD of 15.7±8.8 (p=0.0019). In addition, 10 Gy BB and 10 Gy MRT showed a similar TGD with 5.3±6.6 and 5.6±4.9 days respectively. For LLC cell line the 15 Gy MRT group exhibited a stronger effect than 15 Gy BB with 26.73±8.3 and 9.43±3.41 days, respectively (p<0.0001). A small discrepancy in TGD was observed between 10 Gy BB with 5.13±1.67 days and equivalent dose of MRT with 8.55±2.98 (p=0.009) days.