Sep 29

SS 27 - Advances in Multimodal Therapy for Glioblastoma: From Phase I to Phase III Trials

238 - Targeting Recurrent Glioblastoma with Stereotactic Radiosurgery and Tumor Treating Fields Guided by 18F-FET-PET: Long-Term Results from a Prospective Phase 2 Trial (TTaRGeT)

12:40pm - 12:50pm ET

Room 153

Presenter(s)

Maciej Harat, MD, PhD - Franciszek Lukaszczyk Oncology Center, Bydgoszcz, Kujawsko-Pomorsk

M. Blok^1,2, M. Adamczak-Sobczak¹, I. Zarebska³, M. Marjanski^1,2, M. Harat^2,4, B. Malkowski^5,6, and M. Harat^1,2; ¹Department of Neurooncology and Radiosurgery, Franciszek Lukaszczyk Oncology Center, Bydgoszcz, Poland, ²Department of Clinical Medicine, Jan and Jedrzej Sniadecki University of Science and Technology, Bydgoszcz, Poland, ³Department of Radiotherapy, Franciszek Lukaszczyk Oncology Center, Bydgoszcz, Poland, ⁴Department of Neurosurgery, 10th Military Research Hospital, Bydgoszcz, Poland, ⁵Department of Diagnostics Imaging, Nicolaus Copernicus University, Torun, Poland, ⁶Department of Nuclear Medicine, Franciszek Lukaszczyk Oncology Center, Bydgoszcz, Poland

Purpose/Objective(s):

Recurrent glioblastoma (rGBM) is highly aggressive and optimal management remains undefined. The prospective TTaRGeT trial evaluated tumor treating fields (TTFields) combined with FET PET–guided stereotactic radiosurgery (SRS). Here we present for the first time a long-term outcomes of the trial.

Materials/Methods:

Forty patients with rGBM (WHO 2016) were treated with TTFields and FET PET–guided SRS in a prospective single-arm study. The primary endpoint was one-year overall survival (OS). Secondary endpoints included progression-free survival (PFS), radiographic response, clinical status, toxicity, and steroid use. Median SRS dose was 18 Gy (single fraction) or 25 Gy (5 fractions). Median TTFields duration was 11.7 months. Median time from enrollment till cut of date was 49.5 months.

Results:

We restricted long-term survival analysis to 35 patients with Glioblastoma IDH wild-type (WHO 2021). Five-year OS from study enrollment was 20.9 % (7.3 -39.2) and from primary diagnosis 31.3% (15.9 ; 48.0). Median OS was 16.8 months (95%CI 12.9-27.3). Median PFS was 5.9 (4–6.5). Biomarker and volumetric analyses of all patients suggested differential benefit. The 30-month OS was 35.1% in MGMT-methylated versus 29.2%, in unmethylated tumors (p=0.7). Patients with PTV <10.5 cm³ demonstrated significantly improved survival, the 30-month survival rate was 50.3% and 15%, respectively (p = 0.016). Treatment was well tolerated. Grade =3 treatment-related toxicity was uncommon, radiation-induced contrast enhancement was predominantly low grade, and no treatment-related mortality occurred. Thirty-five percent of patients were steroid-free at end of follow-up.

Conclusion:

TTFields combined with FET PET–guided SRS demonstrated encouraging survival and durable local control in rGBM, particularly in small volume recurrences regardless of MGMT status. These data provide a strong rationale for randomized evaluation of this multimodal strategy.