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Use of Invivo Dosimeters for Catching Guide Tube Errors in HDR Prostate Brachytherapy

B Ravindranath*, G Cohen , K Episcopia , A Damato , Memorial Sloan-Kettering Cancer Center, NY


(Tuesday, 7/31/2018) 9:30 AM - 10:00 AM

Room: Exhibit Hall | Forum 7

Purpose: To determine how optimization at the time of planning of the number and position of real time invivo dosimetry detectors placed within urethra and/or rectum can improve identification of treatment errors in prostate HDR brachytherapy.

Methods: 13 previously delivered single fraction (15Gy) HDR prostate plans were used in this retrospective simulation study. We simulated two guidetube error scenarios (1) Discrepancy between reconstructed and actual needle tips of +/- 3 and +/- 6 mm; rectal and urethra volume where errors are detectable after delivery of the first dwell position was determined; (2) Swap in guidetube connection. Up to three invivo dosimeters were simulated in the rectum and urethra; their position were optimized to identify the maximum number of unique errors. The fraction of errors caught was determined for dosimeter detection accuracy (DA) of 1%, 5% and 10%.

Results: (1)For a DA of 1%, 73% of rectum and 92% of urethra voxels capture shift errors after 1 dwell delivery (3% treatment time). This drops to 40% and 81% for rectum and urethra resp. for a DA of 5% and to 16% and 48% for DA of 10%. (2)For a DA of 1%, 3 detectors with optimized location can identify (average and range) 96% (94-100%) of swap errors, for DA of 5% identification is 63% (57-74%) and for DA 10% identification is 39%( 20-50%). 5 of the 13 plans resulted in institutional threshold violations due to swaps; for these plans,a DA of 5%, detected 91% (73 - 100%) errors and DA of 10% detected 80% (41 - 100%) of errors.

Conclusion: Our studies show that invivo dosimeters could be used to capture treatment errors in a time sensitive manner if their number and positions are optimized for each patient at the time of treatment planning.


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