Multi-Institutional Study of Stereotactic Radiosurgery for Recurrent WHO Grade 2/3 Meningiomas: An Interim Analysis

PURPOSE/OBJECTIVE(S)

Meningiomas are the most common tumors of the central nervous system (CNS). Approximately 80% are classified as World Health Organization (WHO) grade 1, while 20% correspond to grade 2 or grade 3. In those with grade 2/3 disease, local recurrence is not uncommon. Salvage treatment options vary widely and include resection, external beam radiation therapy (EBRT), stereotactic radiosurgery (SRS), and/or clinical trials. Although retrospective studies have reported on the use of upfront SRS in grade 2/3 meningiomas, large-scale outcomes with SRS in the recurrent setting are lacking. The objective of this study was to report on oncologic outcomes for patients with recurrent grade 2/3 meningioma treated with SRS.

MATERIALS/METHODS

This is an ongoing multi-institutional retrospective cohort study. Eligibility criteria include patients >18 years old with pathologically confirmed WHO grade 2 or 3 meningioma treated with SRS monotherapy at the time of first recurrence. Patients require pathologic confirmation only at time of diagnosis; those with upfront grade 1 disease must have pathologic confirmation of grade 2/3 disease at time of first recurrence. Patients with multifocal disease upfront were excluded from this study.

RESULTS

A total of 60 patients met eligibility criteria. Baseline demographics at time of initial diagnosis are shown in table 1. At the time of first recurrence, 57 (95%) were WHO grade 2, and 3 (5%) were grade 3. Median follow up time from first recurrence was 5.02 years. Median marginal SRS dose was 16 Gy (IQR 14-17) to a 2.67cc planning treatment volume (IQR 1.4-5.1). 92% of patients received single fraction SRS. Median time to second recurrence was 5.92 years. 1, 3, and 5-year progression-free survival (PFS) was 95%, 68%, and 51%, respectively. 1, 3, and 5-year overall survival (OS) was 100%, 98%, and 96%, respectively. On multivariate analysis, grade 3 disease was independently associated with worse PFS (HR 15.7, p = 0.03). Median SRS dose and treatment volume did not correlate with PFS. 1 patient (1.7%) experienced symptomatic radiation necrosis requiring steroids, 3 (5.0%) experienced new seizure activity, and 2 (3.3%) additional patients showed clinical evidence of post-treatment neurocognitive decline.

CONCLUSION

Based on this interim analysis, primary SRS for recurrent grade 2/3 meningioma appears safe and feasible, with outcomes comparable to prospective data on high-risk grade 2/3 patients treated with post-operative fractionated EBRT. We look forward to further analysis with a larger cohort which may help guide further prospective studies.

CT-Guided Online Adaptive Stereotactic Body Radiotherapy for Pancreas Ductal Adenocarcinoma: Dosimetric and Initial Clinical Experience

PURPOSE/OBJECTIVE(S)

Retrospective analysis suggests that dose escalation to a biologically effective dose of more than 70 Gy may improve overall survival in patients with pancreatic ductal adenocarcinoma (PDAC), but such treatments in practice are limited by proximity of organs at risk (OARs). We hypothesized that CT-guided online adaptive radiotherapy (OART) can account for interfraction movement of OARs, reduce dose to OARs, and improve coverage of targets.

MATERIALS/METHODS

This is a single institution retrospective analysis of patients with PDAC treated with OART on a CBCT-based OART platform. All patients were treated to 40 Gy in 5 fractions. PTV overlapping with a 5 mm planning risk volume expansion on the stomach, duodenum and bowel received 25 Gy. Initial treatment plans were created conventionally. For each fraction, PTV and OAR volumes were recontoured with AI assistance after initial cone beam CT (CBCT). The adapted plan was calculated, underwent QA, and then compared to the scheduled plan. A second CBCT was obtained prior to delivery of the selected plan. Total treatment time (first CBCT to end of radiation delivery) and active physician time (first to second CBCT) were recorded. PTV_4000 V95%, PTV_2500 V95%, and D0.03 cc to stomach, duodenum and bowel were reported for scheduled (S) and adapted (A) plans. CTCAEv5.0 toxicities were recorded. Statistical analysis was performed using a two-sided T test and α of 0.05.

RESULTS

Seven patients with unresectable or locally-recurrent PDAC were analyzed, with a total of 35 fractions. Average total time was 33:00 minutes (22:25-49:40) and average active time was 22:48 minutes (14:15-39:34). All fractions were treated with adapted plans. All adapted plans met PTV_4000 V95.0% > 95.0% coverage goal and OAR dose constraints. Dosimetric data for scheduled and adapted plans per fraction are in Table 1. Median follow up was 1.7 months. 5 (71%) patients experienced either Grade 1 or 2 toxicities. No patients experienced Grade 3+ toxicities.

CONCLUSION

Daily OART significantly reduced dose OARs while achieving superior PTV coverage. Treatment was generally well tolerated with no grade 3+ acute toxicity, and required only 22:48 minutes on average of active physician time. Our initial clinical experience demonstrates OART allows for safe dose escalation in the treatment of PDAC.