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Development and Verification of the Three-Dimensional Evaluation System for the Tip Position Accuracy in Brachytherapy

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T Kikuchi

T Kikuchi1*, S Kabuki2 , T Hiroki3 , H Todaka4 , E Kunieda5 , (1) Tokai University Hospital, Isehara, Kanagawa, (2) Tokai University, Isehara, Kanagawa, (3) Tokai University Hospital, Isehara, Kanagawa, (4) Tokai University Hospital, Isehara, Kanagawa, (5) Tokai University, Isehara-shi, Kanagawa


SU-I-GPD-T-10 (Sunday, July 30, 2017) 3:00 PM - 6:00 PM Room: Exhibit Hall

Purpose: In high dose rate brachytherapy, an error of a source dwell position influences therapeutic effects and probabilities of normal tissue complication. Therefore, periodical QA is essential for safe and high quality treatment. In this study, we report an evaluation system which we built to capable of verifying the source dwell position and dose distribution by the treatment plan using CT images (Image Guided Brachytherapy).

Methods: We designed and optimized a jig capable of fixing two orthogonal films and the Fletcher applicators for gynecology using a 3D printer. After that, we prepared a treatment plan using jig’s CT images, and irradiation was carried out by 192-Ir remote afterloading system. The analysis method of this system can reconstruct the three-dimensional dwell position and the dose distribution by calculating the peak position of film of the axial and the coronal side, and can measure the error from the treatment plan. Dose distribution was also acceptable.

Results: The uncertainty of this system was estimated to be 0.14mm. The main part of this uncertainty is considered to be the difference in origin coordinates between treatment plan and film. Since this value is small enough, we verified the accuracy of the tip position in brachytherapy. The quantity of displacement of the three-dimensional direction was all less than 2mm in each applicator. There are three major causes was considered that mechanical variation (~0.4 mm) in the transfer direction which is measured at the daily QA, position error (~1.0 mm) in the radial direction because of inner diameter of applicator, and the reconstruction error of the applicators in the CT treatment plan.

Conclusion: This system that we developed possible to perform highly accuracy total three-dimensional tip position and dose distribution verification in IGBT easily and simply. This leads to the assurance of the accuracy of patient treatment.

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