ESTRO 2023 - Abstract Book

S1967

Digital Posters

ESTRO 2023

Three real HDR-BT breast treatments are reproduced on the 3D-printed template, fixed inside a water tank. The treatment needles are connected to the Elekta Flexitron afterloader with a 192-Ir source. Following the calibration geometry, three additional needles are inserted in the middle of an equilateral triangle of the treatment one for the microMOSFET detectors TN-502RDM of Best Medical Canada (figure 1). A CT scan is performed on each distribution, the needles are reconstructed and a treatment plan similar to that of real patients in the Treatment Planning System (TPS) Oncentra Brachy is calculated. The treatment plan is delivered and the measured dose by microMOSFETs, which is the product of its calibration factor in cGy/mV and its read signal or voltage, is recorded.

The difference between the measured dose by the microMOSFETs and the calculated dose in the TPS is evaluated.

Results Figure 2 shows the percentage difference between measured dose by three microMOSFETs and calculated dose in the TPS for three real HDR-BT breast treatments (cases A, B and C). The average percentage difference between measured and calculated dose with and without applying correction factors is 1.5±5.8% and 3.6±5.6%, respectively. The response of the microMOSFETs underestimates the calculated dose in the TPS and the correction factors improve the results in a 2%.

Conclusion The proposed method to perform IVD in HDR-BT breast cancer treatments with microMOSFETs is consistent with the results of bibliography [1, 2]. Therefore, it can be carried out in clinical practice in order to monitor the delivered dose. In future studies, the IVD methodology should be evaluated in real patients in order to establish error detection thresholds to distinguish between dosimetric deviations and false alarms. REFERENCES

[1] RUIZ-ARREBOLA, S. et al. Characterization of microMOSFET detectors for in vivo dosimetry in high-dose-rate brachytherapy with 192-Ir. Medical Physics, 2020, 47 (5), 2242-2253.