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The Dosimetric Evaluation of Cesium 131 Brachytherapy Permanent Implants for Resected Brain Tumors

R Badkul*, Y Butler-xu, H Jiang, N Demez, S Awan, H Saleh, F Wang, University of Kansas Medical Center, Kansas City, KS

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: The Cesium-131 seeds are implanted intra-operatively into the tumor bed after surgical resection of brain tumors to reduce the recurrences.Post implant plans for cavity volumes and dosimetric parameters were evaluated.


Methods: Fifteen patients were treated with Cs-131 permanent implants,8 patients previously had SRS treatment and 7 of them received no previous radiation. Total number of seeds were estimated based on Revard’s nomogram for prescription dose of 80Gy by contouring the tumor volume on pre-op MRI in Eclipse. Seeds with air kerma strength of 2.4U/seed were implanted at the tumor-bed with desired seed interspacing of 7-10mm. CT and MRI was performed on the second or third day from the implant. CT and MRI data sets were imported in the Eclipse system and tumor cavity was contoured. CT along with the contours were transferred to the VariSeed for post implant planning. Pre-Op tumor volume(POTV), Post implant Cavity volume(PICV), and other dose coverage parameters were analyzed and compared.


Results: The mean values of POTV, pre-op seed numbers and total air kerma strength were 14.2cc(SD 9.5;range 1.6-33), 30.9(SD 10.3;range 14-50) and 74.3U(SD 24.6;range 33.6-120) respectively. Mean values of PICV, number of seeds implanted and total air-kerma strength were 12.1cc(SD7.4;range 1.9-30.4), 22.7(SD 8.3, range 9-37) and 54.5U(SD 20; range 21.6-88.8) respectively. Nomogram estimated 33% more seeds than implanted. PICV volume were 15% smaller than POTV likely due to collapse of the surgical cavity. PICV mean of D90%, Dmax, Dmin, Dmean and V100% were 99.3Gy(SD 27.8;range 60-142), 904.7Gy(SD 170.4;range 647-1257), 51.9Gy(SD 17.2; range 27-84), 206.2(SD 42.6; range 141-277) and 92.9% (SD 7.8; range 77-100) respectively.


Conclusion: Treating tumor bed with Cs-131 seeds is an effective and safe treatment for recurrent as well as new brain metastatic lesions with good clinical outcome. Our implant procedure found to be satisfactory based on our post implant dosimetric analysis.

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