Room: AAPM ePoster Library
To determine the accuracy of EMT-measured dwell positions in prostate HDR brachytherapy (BT) patients using a prototype of an integrated EMT/BT afterloader (Flexitron with an integrated EMT sensor; Elekta).
Twenty prostate patients with up to 26 needles, treated with 2 fractions of US/CT guided HDR-BT, were included in a prospective study. EMT measurements, in which the EMT sensor was automatically moved by the afterloader through the implant, were performed and registered to implant reconstruction from CT images. We analyzed 21 data sets (belonging to 12 patients) in which the positions of 3 external and 1 internal reference sensor were measured concurrently to correct for patient motion. At each time point the 3D deviation of the reference sensors from its mean position was subtracted from the position of the moving sensor. Next, the corrected EMT-measured and planned dwell positions were registered and the residual error, i.e. the distance between the EMT-measured and planned dwell positions, was calculated and compared to a registration of the uncorrected EMT-measured and planned dwell positions.
The mean residual error, without correction from reference sensors, was 1.8 mm (range 1.1 – 4.4 mm). However, maximum residual errors per data set ranged from 2.5 to 9.5 mm. When using the correction based on external or internal reference sensors the mean residual errors were, respectively, 1.9 mm (range 1.4 – 3.0 mm) with maximum errors between 3.6 mm and 8.7 mm, and 1.7 mm (range 1.1 – 2.2 mm) with maximum errors between 2.2 mm and 7.7 mm.
The determined accuracy of EMT-based treatment verification in HDR-BT prostate patients using the integrated EMT/BT afterloader is comparable to the previously reported accuracy for HDR-BT breast verification (RadiotherOncol 2019 141:p312-320). Reference sensors do not decrease mean residual errors but may reduce large errors in individual cases.
Funding Support, Disclosures, and Conflict of Interest: This work was in part funded by a research grant from Elekta AB, Stockholm, Sweden