Technical Note: Identification of an optimal electromagnetic sensor for in vivo electromagnetic-tracked scintillation dosimeter for HDR brachytherapy.

Purpose: Brachytherapy is a treatment modality which delivers large doses of radiation in a reduced number of visits. Since a small number of large dose-per-fraction is administered in high dose rate brachytherapy, ensuring the right dose is delivered is highly critical. In this work, a scintillation detector is coupled to an electromagnetic (EM) sensor (NDI, Waterloo, ON, Canada) having submillimeter positional accuracy for real-time tracking of the dosimeter position. However, adding an EM sensor adds materials in the path to the scintillator and thus could potentially perturb the dose measurements. This study assesses four different sensors for a plastic scintillation detector-EM sensor coupled dosimeter.

Methods: To confirm the perturbation presence, different sensors were placed in front of the scintillator so the radiation does not arrive to it directly. Variation of the distance between the sensor and the scintillator was used to quantify the effect on the signal at and . To test the signal's angular dependence for each sensor, the signal measurement was taken from to with increment.

Results: The Aurora 5DOF-610090 sensor showed an increased signal of almost 20% with increasing beam angle. Sensors Aurora 5DOF-610099, Aurora 5DOF-610157, and Aurora Micro 6DOF-610059 showed no significant angle dependance. The Aurora Micro 6DOF-610059 and Aurora 5DOF-610157 sensors' cable signal revealed no extra signal attenuation. The latter gives a smaller overall attenuation. Therefore, the Aurora 5DOF-610157 sensor is chosen to be part of the novel dosimeter construction. It has a jitter error (average standard deviation of each individual measurement) of ±0.06 mm and a reproducibility of ±0.008 mm. In the optimal operating range, the average positional uncertainty is less than 0.2 mm. Average angle errors are not higher than .

Conclusion: It is feasible to integrate an EM tracking sensor to a plastic scintillation dosimeter with minimal impact to the collected signal as well as sufficient positional accuracy to keep dose uncertainty below 5%.