2607 - Occurrence of Rapid Early Progression (REP) and Rapid Early Response (RER) in Patients with Newly Diagnosed GBM Undergoing Resection and Immediate Post Resection Brachytherapy: A Preliminary Report fr

L. Sloan¹, C. Chen², C. Ferreira¹, E. Neil³, D. J. McCracken⁴, J. Wanebo⁵, K. Smith⁶, O. Bloch⁷, M. Shah⁸, A. Richardson⁸, J. David⁹, K. S. Lee¹⁰, M. S. Peach¹¹, E. L. Chang¹², G. Zada¹³, M. A. Garcia¹⁴, A. C. Turner¹⁴, and D. G. Brachman¹⁴; ¹University of Minnesota: Department of Radiation Oncology, Minneapolis, MN, ²Department of Neurosurgery at the Warren Alpert Medical School of Brown University and Lifespan Health System, Providence, RI, ³University of Minnesota: Department of Neurology, Minneapolis, MN, ⁴Piedmont Healthcare, Atlanta, GA, ⁵Ivy Brain Tumor Center, Barrow Neurological Institute, Phoenix, AZ, ⁶Barrow Neurological Institute, Phoenix, AZ, ⁷UC Davis Brain Tumor Program, Sacramento, CA, ⁸Department of Neurological Surgery, Indiana University School of Medicine, Indianapolis, IN, ⁹Tampa General Hospital, Tampa, FL, ¹⁰ECU Health Medical Center, Greenville, NC, ¹¹Department of Radiation Oncology, East Carolina University, Greenville, NC, ¹²U, Los Angeles, CA, ¹³University of Southern California, Los Angeles, CA, ¹⁴GT Medical Technologies, Tempe, AZ

Purpose/Objective(s): In newly-diagnosed glioblastoma (nGBM) rapid early progression (REP) is defined as tumor progression/regrowth between resection and start of external beam radiation (EBRT) with temozolomide (EBRT+TMZ). This occurs in 45% of patients per a recent multi-institutional meta-analysis. We hypothesized the rate of REP may be decreased in the setting of immediate post-resection brachytherapy (BT) in newly diagnosed GBM. We also describe rapid early response (RER), which is regression of residual tumor in the setting of BT. Materials/

Methods: Occurrence of REP and RER were investigated by record and imaging review of patients with nGBM who enrolled pre-operatively on an ongoing single arm multi-center prospective trial (NCT05342883) of resection and intraoperative placement of cesium-131 collagen tile brachytherapy (CTBT)(GT Medical Technologies, Tempe AZ, USA), and subsequent EBRT+ temozolomide. Records were analyzed for demographics, resection type, methylation status, and occurrence of REP/RER.

Results: From 8/22 to 2/24, 22 patients with nGBM (all IDH wild type) underwent resection and CTBT. All patients had both a post-operative MRI and a pre-EBRT MRI for treatment planning with a median inter-MRI interval of 17 days (range 12-56). 14 patients (64%) had MRI-confirmed gross total resections (GTR). MGMT was methylated in 7 and unmethylated in 15. Overall, 6/22 (27%) had evidence of REP at a median inter-MRI interval of 16.5 days (range 13-20). REP was adjacent to the cavity in 5 patients and distant in 1. In 3/8 (38%) cases of sub-total resection or near total resection the residual tumor showed a RER on MRI (median inter-MRI interval 17 days, range 12-22). At time of analysis, median follow-up was 5.9 months (range 0.5-16).

Conclusion: In the setting of post-resection brain BT, we found an REP rate of 27% and RER rate 38% (3/8 <GTR patients). To our knowledge, this is the first report on the incidence of REP and the first description of RER in nGBM patients treated with post-resection BT. The trial is continuing to accrue to a total of 61 participants. Additional enrollment and follow-up will provide further data on REP, RER, and impact on other outcomes as well as data on the primary endpoints of feasibility and safety. Abstract 2607 – Table 1

Demographics, Resection type, Methylation status, and REP/RER
Subjects	Age median (range)	Sex (F:M)	Max. Pre-op Diameter (cm) median (range)	Resection type number (%)		Methylation status number (%)
				GTR	<GTR	MGMT+	MGMT-
All: N=22	62 (42-77)	7:15	4.6 (3.0-6.7)	14/22 (64%)	8/22 (36%)	7/22 (32%)	15/22 (68%)
REP: 6 (27%)	68 (57-76)	2:4	4.0 (3.2-6.7)	3/14 (21%)	3/8 (38%)	2/7 (29%)	4/15 (27%)
No REP: (73%)	61 (42-77)	5:11	4.9 (3.0-6.4)	11/14 (79%)	5/8 (62%)	5/7 (71%)	11/15 (73%)
RER: 3 (17%)	67 (49-71)	2:1	5.3 (5.0-5.8)	n/a	3/8 (38%)	2/7 (29%)	1/15 (7%)