ESTRO 2024 - Abstract Book

S289

Brachytherapy - Head & neck, skin, eye

ESTRO 2024

100

Digital Poster

GammaTile® Brachytherapy in Treatment of Glioblastoma: A Report of Three Cases

Erin McCammack, Kathryn Dusenbery, Clara Ferreira

University of Minnesota, Radiation Oncology, Minneapolis, USA

Purpose/Objective:

GammaTile® is a surgically targeted, FDA approved radiation source for use in brachytherapy (BT) of brain tumors. When GBM recurs quickly after initial resection prior to standard of care chemoradiotherapy (CRT), another treatment option is repeat resection with GammaTile® BT followed by CRT. We report 3 such cases including dosimetric considerations and patient outcomes.

Material/Methods:

To determine how many 2 x 2 cm² tiles were needed, the T1 contrast enhancement on pre-op MRI was contoured and the surface area was calculated. Tiles were ordered to cover the entire surface area. A neurosurgeon then performed maximal safe tumor resection with 5 ALA and intraoperative MRI and implanted the tiles. On POD 1, MRI and CT were obtained to identify the surgical cavity (SC) and locate each seed. Using Eclipse software, the SC and individual seeds were contoured. 60 Gy was prescribed 5 mm deep to the SC surface. A plan was created to evaluate target coverage. After 3 half-lives or 30 days, MRI was obtained to plan CRT. Using inverse planning and including physical dose contribution from BT, cumulative dose of 50 Gy was prescribed to T2 FLAIR and 60 Gy to T1 contrast. Radiation was delivered over 20 once-daily fractions via IMRT technique. Dose was delivered in a gradient, decreasing near the SC. Concurrent Temozolomide (Tem) 75 mg/m2 was taken during CRT. 1 month after CRT, adjuvant Tem and Tumor Treating Fields (TTF) were recommended and MRI was obtained. Thereafter, MRI was followed every 2 months. If radiologic recurrence was observed, MRI was fused with DICOMs from BT and CRT to retrospectively calculate cumulative biological equivalent dose (BED) to the area of recurrence.

Results:

Patient A lacked MGMT promoter methylation which contributed to overall poor response to CRT. Also, she did not tolerate Tem which was discontinued during CRT. 1.6 months after surgery in the midst of CRT, she developed intractable dystonia. Diagnostic MRI at that time showed disease recurrence in an area that had received BED 50 Gy. She survived 7.9 months from diagnosis. Patient B had MGMT promoter methylation. She tolerated CRT well, completed adjuvant Tem and TTF, and is still living with no evidence of recurrence 19.8 months after diagnosis. Patient C had MGMT promoter methylation. He recurred 2.6 months after surgery and 1 month after completion of CRT. Recurrence was in an area that had received BED 60 Gy. The recurrence was proven by biopsy and treated with laser interstitial thermal therapy. He later developed multifocal recurrence, surviving 15.2 months from diagnosis.

Conclusion:

In our 2 patients with recurrence, we retrospectively calculated BED to areas of recurrence, as BED accounts for low dose rates at the BT and CRT junction. The BED was adequate in both occasions. BED will be used in place of