ESTRO 2024 - Abstract Book

S5277

Radiobiology - Normal tissue radiobiology

ESTRO 2024

Figure 1. Dicentrics and rings, and total chromosoma aberrations after using different numbers of CBCT with a therapeutic dose of 2 Gy, measured in the CTDI phantom in the central read out point. Blue line shows the average dicentrics and rings aberration for 2 Gy therapeutic dose, only.

Very small difference could be found between the 9 read out points when the CBCT profile was measured, however higher value was found in one side, what could predict the actual CBCT profile (Figure 2).

Figure 2. Effect of CBCT profile on chromosoma aberrations measured in 9 read out points in a CTDI phantom. T Top, U-UP, C-Center, BE-Below, BO-Bottom, FL-Far left, L-Left, R-Right, FR-Far Right

Conclusion:

Based on our in vitro phantom investigation, we found that the biological effect of the combined CBCT and therapeutic beam is higher than the summarized physical dose. It is essential to collect the summarized dose from imaging and treatment for the patient, but the biological effect could be greater than we predicted before. We recommend, that young patients should not be treated with high frequency CBCT based radiotherapy, like Ethos, because of the increased risk of developing secondary cancer. The biological measurement could be sensitive enough to measure small differences like in a CBCT profile, if relatively high linear energy transfer (LET) beams are used.