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Session: Best of Professional [Return to Session]

Patient Dosimetry Statistics From Permanent Cs-131 Low Dose Rate Brachytherapy Implants in the Brain

A Turner*, D Brachman, GT Medical Technologies, Inc, Phoenix, AZ


MO-E115-BOP-F1-2 (Monday, 7/11/2022) 1:15 PM - 1:45 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 1

Purpose: To evaluate patient dosimetry from low dose rate intracavitary brachytherapy in the brain using permanently implanted collagen tiles embedded with Cs-131 seeds (GammaTile, GT Medical Technologies, Tempe, AZ). GammaTiles contain four 3.5U seeds to deliver a nominal (Rx) dose of 60Gy to a depth of 5mm.

Methods: For 12 patients receiving GammaTile implants a commercial TPS (MIM Symphony, MIM Software Inc, Cleveland, OH) was used to delineate surgical cavity and CTV and calculate dose distributions using the AAPM TG43 2-D formalism. CTV was defined as the region of brain parenchyma adjacent to tile placement to a depth of 5mm, excluding the cavity. The following dose statistics were tabulated: maximum isodose covering 90% and 95% of the CTV (D90%, D95%), percent volume of the CTV receiving 90% and 95% of 60Gy (V90%, V95%), dose gradient index (DGI=V30Gy/V60Gy), and maximum dose at depths ranging from 0 - 29mm in the brain in 1mm increments. The mean, standard deviation, and range were calculated across all patients.

Results: Volume ranges (cc) of the cavity and CTV were 3.3-49.9 and 6.9-27.1. Mean D90% and D95% (Gy) were 59.2 (45.5–73.8) and 53.0 (36.3–67.1). Mean V90% and V95% (%) were 90.5 (77.6–99.8) and 87.6 (72.6–99.4). Mean DGI was 2.3 (2.2-2.5). Mean maximum dose at depths of 0 – 29mm decreased with distance from the cavity, with mean values (Gy) of 385.3, 95.0, 53.1, 32.7, 21.5, and 14.6 at depths of 0, 5, 10, 15, 20, and 25mm, respectively.

Conclusion: Dose statics derived from actual GammaTile patient dosimetry has been presented. This data can be used for pre-planning (e.g. determining potential maximum doses to organs at risk) and as benchmarks for postoperative dosimetry evaluation. Future work will include increasing the patient sample size and comparisons of these dose statics to other targeted radiation modalities, such as SRS/SRT.

Funding Support, Disclosures, and Conflict of Interest: Authors are employees and stock holders of GT Medical Technologies, Inc.


Brain, Brachytherapy, Dosimetry


TH- Brachytherapy: Low Energy Seed Brachytherapy

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