(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose:
To quantify the positional accuracy of electromagnetic tracking (EMT) as a QA tool in complex interstitial and intracavitary cervix brachytherapy (BT) implants.
Methods:
A CT scan was acquired of the Venezia™ applicator (70mm intrauterine tube, lunar ovoids F = 30mm, 8 needles; Elekta), embedded in silicon. The applicator was reconstructed using a library file containing the measured source path, while the needles were reconstructed manually. EMT measurements were performed using a prototype integrated EMT/BT afterloader (Elekta), (PhysMedBiol. 63(9) 095008). EMT-measured and planned dwell positions were rigidly registered and the residual errors, defined as the Euclidean distance, were analyzed. Besides registering all dwell positions together we also analyzed the needles and applicator channels separately: registering the applicator channels on the straight parts while evaluating the curved parts. Effects of the dwell time, distance d(FG) between implant and Field Generator (FG), and EM-field orientation were investigated.
Results:
Registering all dwell positions together (FG parallel to the applicators main axis, d(FG) = 200 mm) resulted in a median residual error of 0.88 mm (95%-CI maximum 2.66 mm). No differences were observed for dwell times down to 0.5 s. The residual error was larger for 300 mm dFG, as compared to 100 and 200 mm. When registering the needles only no differences in the residual error as a function of the EM-field orientation were found (range 0.5 – 0.7 mm). When registering the intracavitary channels only an orientation dependency was found when rotating the FG around the applicators left-right axis (median residual error 1.2 - 2.2 mm for the lunar ovoids; 2.1 - 2.9 mm for the intrauterine tube).
Conclusion:
EMT is a promising QA tool for complex cervix BT implants. A high accuracy is achieved for dwell position detection in the needles. Further research is needed for application in the intracavitary channels.
Funding Support, Disclosures, and Conflict of Interest: This work was in part funded by a research grant from Elekta AB, Stockholm, Sweden
Keywords
EM Reconstruction, HDR, Treatment Verification
Taxonomy
TH- Brachytherapy: Treatment verification and reconstruction
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