ESTRO 2024 - Abstract Book

S5438

Radiobiology - Tumour biology

ESTRO 2024

with either MRT or uniform doses ranging from 15 Gy – 40 Gy with 5 mice per dose group. All irradiations were performed using a self-developed setup within the small animal irradiator XenX platform. For microbeams the radiation dose was determined using the concept of the equivalent uniform dose (EUD) based on the linear quadratic model (LQM) for which the radiobiological parameters were retrieved with colony formation assays beforehand. The dosimetry for both radiation modalities was carried out using Gafchromic EBT3 films at different time points during the irradiation period and a daily quality assurance protocol was established utilizing the PTW microdiamond detector.

Results:

The microbeam dose distribution is shown in figure 1. The valley dose rate was found to be stable throughout the irradiation period at (0.185±0.0005) Gy/min, whereas the peak dose showed fluctuations of <5% being on average at (4.6±0.1) Gy/min and leading to a mean peak-to-valley-dose-ratio (PVDR) of (24.8±0.6). Furthermore, the uniform dose rate was found to be stable at (4.64±0.005) Gy/min. The preliminary data of the tumor control fractions in the individual dose groups is shown in figure 2. Fitting the data using logistic regression shows a significant shift in the TCD 50 value, where 50% of the tumors are controlled. For MRT the TCD 50 value was found to be (19.6±1) Gy, whereas the value for conventional treatment was (28.8±4.6) Gy. Furthermore, the slope of tumor control probability increase is steeper for MRT than for uniform dose.