PPP04 Expanding Treatment Options for Reirradiation: The First Case of Gammatile Implantation in the Spine

Document Type

Conference Proceeding

Publication Date

7-1-2025

Publication Title

Brachytherapy

Abstract

Purpose: GammaTile® surgically targeted radiation therapy is a form of low dose rate brachytherapy in which Cs-131 seeds are embedded into a resorbable collagen-based matrix, allowing the seeds to be easily placed along a resection cavity during surgery. GammaTile has been used in several intracranial applications including the treatment of recurrent glioblastomas, meningiomas, and brain metastases as well as newly diagnosed brain metastases. However, it has not been used extracranially. This study describes the first use of GammaTile in the spine, for a patient who had rectosigmoid adenocarcinoma with recurrent metastatic disease in the sacrum. They received their first course of radiation in 2022 with external beam (54Gy in 30 fractions), followed by fractionated stereotactic radiation therapy to the recurrent lumbosacral disease in 2023 (30Gy in 5 fractions), and presented with pain in the legs and progressive disease in the sacrum. Given the patient's two prior courses of external beam radiation therapy, off-label use of GammaTile was pursued due to its ability to minimize dose to the nearby thecal sac, cauda equina and sacral nerve roots. Methods: GammaTile workflow for cranial applications involves estimating the surface area of the resection cavity to calculate the expected number of tiles needed. However, for this novel application, the number of tiles was estimated using a mock-up of the anticipated tile configuration based on the patient's MRI (Figure 1b), as well as a personalized 3D-printed replica of the patient's spine (Figure 1a).Following surgical resection, which included a partial L5 laminectomy and partial sacrectomy (Figure 1c), four tiles (16 sources) were placed “upside down” from the typical orientation, i.e., with the larger 3mm spacing facing toward the thecal sac to maximize separation and minimize dose to the cauda. Additionally, Fibrin sealant and absorbable gelatin were placed in between the tiles and the thecal sac to create further separation. Immediately after surgery, CT images were acquired in the OR for post-implant dosimetry and to verify the desired tile placement. These images were then used to calculate the delivered dose to the patient using the Eclipse planning system, and MIM was used to convert physical dose to biological effective dose to the thecal sac (BED3Gy) using the linear quadratic model for a permanent LDR implant and published values for the repair time, potential doubling time, and alpha values.1 Results: The post-implant calculated BED3Gy distribution is shown in Figure 1d. The D0.035cc physical dose and BED3Gy dose to the thecal sac was 89.8Gy and 106.4Gy respectively. At a 3-month post-operative appointment, the patient reported improved pain and was able to ambulate for longer distances with a walker. Conclusions: This study presents our institution's experience with the first use of Gammatile for the spine, highlighting the ability of our multi-disciplinary team to offer a novel treatment technique for a patient faced with either disease progression or a more extensive, life-altering surgery.

Volume

24

Issue

4

First Page

S20

Last Page

S21

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