Room: Exhibit Hall | Forum 7
Purpose: To present an energy independent in vivo dosimeter with real-time positional information and characterized the sensor performance in terms of its effect on the dosimeter signal, its accuracy and precision.
Methods: A 3mm long and 0.5mm diameter BCF-60 (Saint-Gobain Crystals) plastic scintillation dosimeter was coupled to various 5 and 6 degrees of freedom (DOF) electromagnetic (EM) sensors read by the Aurora V3 system (NDI, Ontario, Canada). Four different sensors were tested by taking measurement at 120 kVp (Xsthrall orthovoltage unit). Acquisition of the scintillator signals was taken from 0Â° (parallel) to 90Â° (perpendicular) in 10Â° increments. For the optimal sensor, jitter error was characterized by statistical analysis of 9x 10 s measurements at a fixed position. Positional accuracy was tested by measuring the distance between known reference positions (Â±0.01mm), 3 in each XY (parallel to the EM generator), XZ and YZ planes. Measurements were carried out 4 times. The angular accuracy was also tested by varying the angle and comparing with the known changes.
Results: The selected EM sensor is a novel sensor, called 5DOFthin, 6 mm long and 0.45 mm diameter and has at most a constant -1% effect on the scintillation signals. Its jitter error is Â±0.06 mm with a repeatability of Â±0.008 mm. Those uncertainties would correspond to an average dose variation of 1.02 % at 10 mm from a 192Ir brachytherapy source. The EM system performance in terms of positional accuracy and precision was on average 0.012 mm from the expected values (= 0.007 mm). The maximum difference for rotation was 1.04Â°.
Conclusion: This work demonstrates that the sensor used has the accuracy and precision needed for real-time dosimeter tracking while having negligible impact on the signal. It opens up the possibility to increase the accuracy of in vivo dosimetry in brachytherapy.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the National Sciences and Engineering Research Council of Canada (NSERC) via the NSERC-Elekta Industrial Research Chair. grant No. 484144-15. Daline Tho further acknowledges partial support from the Medical Physics Training Network CREATE NSERC grant No. 432290.