Technical Note: A Novel Electromagnetic-Tracked Scintillation Dosimeter for Accurate In Vivo Dosimetry in HDR Brachytherapy

Since large dose are administrated to the patient in brachytherapy treatment, ensuring the right dose is delivered is highly critical. This study presents a first step in solving the standing issue of accurately knowing the dosimeter position at all time during in vivo dosimetry. In this work, an energy independent dosimeter, namely plastic scintillation detector, is coupled to an electromagnetic (EM) sensor having sub-mm 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.To confirm the perturbation presence, 4 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 0{\deg} and 90{\deg}.To test the dependence for each sensor, the signal measurement were taken from 0{\deg} to 90{\deg} with 10${\deg}$ increment. The 5PCBDOF sensor showed an increased signal of almost $20{\%}$ with increasing beam angle. Sensor 5DOF, 5DOFthin and 6DOFshowed no significant angle dependance.The 6DOF and 5DOFthin sensor's cable revealed no extra signal attenuation. The latter gives a smaller overall attenuation. Therefore, the 5DOFthin is chosen to be part of the novel dosimeter construction. It has a jitter error of $\pm$ 0.06 mm and a reproductibility of$ {\pm}$ 0.008 mm. In the optimal operating range, the average positional uncertainty is less than 0.2 mm. Average angle errors are at most of 1.1${\deg}$. It is feasible to integrate an EM tracking sensor to an energy independent plastic scintillation dosimeter with minimal impact to the collected signal as well as sufficient positional accuracy to keep dose uncertainty below 5${\%}$.