ESTRO 2023 - Abstract Book

S1470

Digital Posters

ESTRO 2023

standard laboratory. The reference point for pMC was placed at a 50 cm plane from the source and 15 cm off axis. The X ray irradiation setting was 10 mA and 250 kV, for a Thoraeus I filtration and a circular cone beam with an open angle 20º relative to the beam axis. The absolute dose calibration was performed in a single session following these steps: a) The IC was placed in the reference site as pMC for the cell culture irradiation setup. b) The IC was irradiated a few times until the X-ray tube gave a stable response. c) The IC was place in the beam axis to measure an established absolute dose at a 2 cm depth in a plastic phantom. d) The IC was placed in the pMC reference point and was irradiated a few times to check the stability response of the cell culture configuration related to the initial measurements. e) EBT3 film was calibrated and used to establish the absolute dose in cell plates taking into account the pMC response. Cell cultured plates were irradiated at different doses (0-15 Gy for clonogenic studies. Survival fraction (SF) was fitted to the Linear Quadratic Model taken into account both the irradiation doses based in the time calculation doses (A) and the ones corrected using the pMC measurements (B). The SF(A)/SF(B) ratio was determined for four cell lines. Results A calibration factor (0.071 ± 0.002) Gy/nC was established for the measurements in the pMC point. The uncertainty introduced in the pMC measurements due to the phantom dispersion for film calibration was estimated at 0.1 %. The maximum dose deviation to the expected dose without pMC correction was 5 % with a total standard deviation of 1.5 % for all the cases (Figure 1). SF(A)/SF(B) ratio showed that the differences between both considerations can imply big differences in the analysis results of the clonogenic curves (Figure 2).

Conclusion The use of an IC as a pMC can correct and enhance the clonogenic assays and it is a simple solution when the equipment does not have a Monitor Chamber. These corrections should be taken into account because the SF interpolation results have high dependency of this small variation, especially for high doses.

PO-1751 Correlation between tolerances for EPID metrics and CI dose deviation for patient-specific VMAT QA