Intraoperative radiotherapy (IORT) for surgically resected brain metastases: outcome analysis of an international cooperative study

Abstract

Background and objective: The ideal delivery of radiation to the surgical cavity of brain metastases (BMs) remains the subject of debate. Risks of local failure (LF) and radiation necrosis (RN) have prompted a reappraisal of the timing and/or modality of this critical component of BM management. IORT delivered at the time of resection for BMs requiring surgery offers the potential for improved local control (LC) afforded by the elimination of delay in time to initiation of radiation following surgery, decreased uncertainty in target delineation, and the possibility of dose escalation beyond that seen in stereotactic radiosurgery (SRS). This study provides a retrospective analysis with identification of potential predictors of outcomes.

Methods: Retrospective data was collected on patients treated with IORT immediately following surgical resection of BMs at three institutions according to the approval of individual IRBs. All patients were treated with 50kV portable linear accelerator using spherical applicators ranging from 1.5 to 4.0 cm. Statistical analyses were performed using IBM SPSS with endpoints of LC, DBC, incidence of RN, and overall survival (OS) and p < 0.05 considered significant.

Results: 54 patients were treated with IORT with a median age of 64 years. The most common primary diagnosis was non-small cell lung cancer (40%) with the most common location in the frontal lobe (38%). Median follow-up was 7.2 months and 1-year LC, DBC, and OS were 88%, 58%, and 73%, respectively. LMD was identified in 2 patients (3%) and RN present in 4 patients (7%). The only predictor of LC was extent of resection with 1-year LC of 94% for GTR versus 62% for STR (p = 0.049).

Conclusions: IORT is a safe and effective means of delivering adjuvant radiation to the BM resection cavities with high rates of LC and low incidence of RN. Further studies are warranted directly comparing LC outcomes to SRS.

Keywords: Brain metastases; IORT; Intraoperative radiotherapy.

Conflict of interest statement

Conflict of interest All other authors have no disclosures relevant to the submitted work.

Figures

Fig. 1

Kaplan–Meier estimations following IORT. Local control (LC) at 1-year was 88% (top panel); Distant Brain Control (DBC) was 58% at 1-year (middle panel); Overall survival (OS) was 73% percent at 1-year post IORT treatment (bottom panel). Numbers of patients at risk are listed at the bottom of each graph with 54 patients for LC and DBC and 51 patients in OS, accounting for 3 patients lacking survival status data at the time of collection

Fig. 2

Kaplan–Meier estimation of LC between GTR and STR cohorts. At 1-year, the LC rate remained at 94% for patients with post-operative imaging demonstrating a GTR, while the LC rate at 1-year for STR patients was only 62%. GTR gross total resection, STR sub-total resection

Fig. 3

Dosimetric representation of IORT versus SRS plan in a sample patient. The pre-operative navigation CT scan was used for dose map development for an IORT plan using a 2.0 cm applicator and a surface prescription dose of 30 Gy (left panel) while the same images were used for the creation of a potential SRS plan using GammaPlan® with a prescription dose of 16 Gy at the margin (middle panel). Both plans were imported into independent dose calculation software with the generation of the dose map according the scale shown (right panel)