Predictors of radiation necrosis in long-term survivors after Gamma Knife stereotactic radiosurgery for brain metastases

Leveraging radiomics and machine learning to differentiate radiation necrosis from recurrence in patients with brain metastases

OBJECTIVE

Radiation necrosis (RN) can be difficult to radiographically discern from tumor progression after stereotactic radiosurgery (SRS). The objective of this study was to investigate the utility of radiomics and machine learning (ML) to differentiate RN from recurrence in patients with brain metastases treated with SRS.

METHODS

Patients with brain metastases treated with SRS who developed either RN or tumor reccurence were retrospectively identified. Image preprocessing and radiomic feature extraction were performed using ANTsPy and PyRadiomics, yielding 105 features from MRI T1-weighted post-contrast (T1c), T2, and fluid-attenuated inversion recovery (FLAIR) images. Univariate analysis assessed significance of individual features. Multivariable analysis employed various classifiers on features identified as most discriminative through feature selection. ML models were evaluated through cross-validation, selecting the best model based on area under the receiver operating characteristic (ROC) curve (AUC). Specificity, sensitivity, and F1 score were computed.

RESULTS

Sixty-six lesions from 55 patients were identified. On univariate analysis, 27 features from the T1c sequence were statistically significant, while no features were significant from the T2 or FLAIR sequences. For clinical variables, only immunotherapy use after SRS was significant. Multivariable analysis of features from the T1c sequence yielded an AUC of 76.2% (standard deviation [SD] ± 12.7%), with specificity and sensitivity of 75.5% (± 13.4%) and 62.3% (± 19.6%) in differentiating radionecrosis from recurrence.

CONCLUSIONS

Radiomics with ML may assist the diagnostic ability of distinguishing RN from tumor recurrence after SRS. Further work is needed to validate this in a larger multi-institutional cohort and prospectively evaluate it's utility in patient care.

Assessment of Radiation Dosage to the Hippocampi during Treatment of Multiple Brain Metastases Using Gamma Knife Therapy

Background and Objectives: Brain metastases (BMs) pose significant clinical challenges in systemic cancer patients. They often cause symptoms related to brain compression and are typically managed with multimodal therapies, such as surgery, chemotherapy, whole brain radiotherapy (WBRT), and stereotactic radiosurgery (SRS). With modern oncology treatments prolonging survival, concerns about the neurocognitive side effects of BM treatments are growing. WBRT, though widely used for multiple BMs, has recognized neurocognitive toxicity. SRS, particularly Gamma Knife (GK) therapy, offers a minimally invasive alternative with fewer side effects, suitable for patients with a quantifiable number of metastases and better prognoses. Materials and Methods: A retrospective analysis was conducted on 94 patients with multiple BMs treated exclusively with GK at an academic medical center. Patients with prior WBRT were excluded. This study focused on the mean radiation dose received by the hippocampal area, estimated according to the 'Hippocampal Contouring: A Contouring Atlas for RTOG 0933' guidelines. Results: The precision of GK equipment results in mean doses of radiation that are lower than those suggested by RTOG 0933 and observed in other studies. This precision may help mitigate cognitive dysfunction and other side effects of hippocampal irradiation. Conclusions: GK therapy facilitates the administration of smaller, safer radiation doses to the hippocampi, which is advantageous even for lesions in the temporal lobe. It is feasible to treat multiple metastases, including cases with more than 10, but it is typically reserved for patients with fewer metastases, with an average of 3 in this study. This underlines GK's potential for reducing adverse effects while managing BMs effectively.

The Impact of Immune Checkpoint Inhibition on the Risk of Radiation Necrosis Following Stereotactic Radiotherapy for Metastatic Brain Cancer

Purpose/objective Forty percent of cancer patients develop brain metastases (BM) and are often treated with stereotactic radiation (SRS/SRT). Checkpoint inhibitor (CI) use is suspected of increasing the risk of radiation necrosis (RN). Our aim is to determine whether treatment with CI is associated with an increased risk of RN in BM patients treated with SRS/SRT. Methods We retrospectively identified the medical records of BM patients treated with SRS/SRT between 1/2017 and 12/2021 using an institutional database. RN was defined by MRI imaging read by neuroradiologists and/or surgical pathology. V12GY of patients with and without RN was compared using the Mann-Whitney test. The chi-square test was used to see if RN was associated with CI use, histology, particular CI agent used, > 1 course SRS/SRT, SRS/SRT dose, chemotherapy, whole brain radiotherapy (WBRT), age, or sex. Results Two hundred and fifty-nine patients treated with 455 courses of SRS/SRT were analyzed. The most common primary histologies were lung 56% (N=146), breast 14% (N= 37), melanoma 9% (N=24), and renal cancer 7% (N=18). A total of 53.8% (N = no. of patients) were treated with CI. The overall rate of any RN was 21.8% (N=27) in the CI group compared to 14.8% (N=141) in the non-CI group (p=0.174). Mean V12Gy was 15.525 cc and 9.419 cc in patients with and without RN (p=0.02768). Mean number of SRS/SRT courses was 2 and 1.53 for patients with and without RN, and >1 course of SRS/SRT was a predictor of RN (p <0.01). Other features analyzed were not significant. Conclusion RN was higher in the BM patients treated with SRS/SRT receiving CI compared to non-CI patients (21.8%, N=27, versus 14.6%, N= 16), but failed to reach statistical significance. V12Gy and > 1 course of SRS/SRT was associated with RN. Caution should be taken in treating patients with SRS/SRT and CI there might be an increased risk of RN.

Novel Mechanisms and Future Opportunities for the Management of Radiation Necrosis in Patients Treated for Brain Metastases in the Era of Immunotherapy

Radiation necrosis, also known as treatment-induced necrosis, has emerged as an important adverse effect following stereotactic radiotherapy (SRS) for brain metastases. The improved survival of patients with brain metastases and increased use of combined systemic therapy and SRS have contributed to a growing incidence of necrosis. The cyclic GMP-AMP (cGAMP) synthase (cGAS) and stimulator of interferon genes (STING) pathway (cGAS-STING) represents a key biological mechanism linking radiation-induced DNA damage to pro-inflammatory effects and innate immunity. By recognizing cytosolic double-stranded DNA, cGAS induces a signaling cascade that results in the upregulation of type 1 interferons and dendritic cell activation. This pathway could play a key role in the pathogenesis of necrosis and provides attractive targets for therapeutic development. Immunotherapy and other novel systemic agents may potentiate activation of cGAS-STING signaling following radiotherapy and increase necrosis risk. Advancements in dosimetric strategies, novel imaging modalities, artificial intelligence, and circulating biomarkers could improve the management of necrosis. This review provides new insights into the pathophysiology of necrosis and synthesizes our current understanding regarding the diagnosis, risk factors, and management options of necrosis while highlighting novel avenues for discovery.

What effective technique to differentiate radiation brain necrosis from a tumor progression in patients treated with radiation: A monocentric retrospective study combining the MRI TRAMs technique and the (18F)-dopa PET/CT

PURPOSE

Brain necrosis after radiotherapy is a challenging diagnosis, since it has similar radiological appearance on standard MRI to tumor progression. Consequences on treatment decisions can be important. We compare recent imaging techniques in order to adopt a reliable diagnostic protocol in doubtful situations.

PATIENTS AND METHOD

This is a retrospective study comparing the performance of three imaging techniques after radiotherapy of brain metastasis: Perfusion-MRI, TRAMs technique and F-dopa PET-CT. The evolution of the treated metastasis volume was also analyzed by contouring all patients MRIs. All included patients were suspected of relapse and had the three exams once the volume of treated metastasis increased.

RESULTS

The majority of our patients were treated by stereotactic radiotherapy. Suspicion of relapse was on average around 17months after treatment. Four cases of radionecrosis were diagnosed and six cases of real tumor progression. Neurological symptoms were less present in radionecrosis cases. All of our radionecrosis cases had relative cerebral blood volume below 1. F-dopa PET-CT succeeded to set the good diagnosis in eight cases, although we found one false positive and one false negative exam. The TRAMs technique failed in one case of false negative exam.

CONCLUSIONS

Perfusion-MRI showed high performance in the diagnosis of radionecrosis, especially when calculating relative cerebral blood volume rate. The TRAMs technique showed interesting results and deserves application in daily routine combined with the perfusion-MRI. F-dopa CT might induce false results because of different metabolic uptake according to tumor type, medication and brain blood barrier leak.

Radiation necrosis and therapeutic outcomes in patients treated with linear accelerator-based hypofractionated stereotactic radiosurgery for intact intracranial metastases

INTRODUCTION

Balancing disease control and treatment-related toxicities can be challenging when treating higher-risk brain metastases (BMs) that are larger in size or eloquent anatomical locations. Hypofractionated stereotactic radiosurgery (hfSRS) is expected to offer superior or equal efficacy with lower toxicity profile compared with single-fraction SRS (sfSRS). We report the efficacy and toxicity profiles of hfSRS in a consecutive cohort of patients to support this predicted benefit from hfSRS for high-risk BMs.

METHODS

We retrospectively analysed 185 consecutive individual lesions from 152 patients with intact BMs treated with hfSRS between 1 July 2016 and 31 October 2019 and followed up to 30 April 2022 with serial brain magnetic resonance imaging (MRI). The primary endpoint was the event of radiation necrosis (RN). Local control (LC) rate and distant brain failure (DBF) were reported as secondary outcomes. Kaplan-Meier method was used to report the cumulative incidence of RN and overall survival and the incidence of DBF. Potential risk factors for RN were assessed using univariable Cox regression analysis.

RESULTS

The median follow-up was 38.0 months, and the median survival post-SRS was 9.5 months. The cumulative incidence rate of RN was 13.2% (95% CI: 7.0-24.7%), and 18.1% of patients with confirmed RN were symptomatic. Higher mean dose delivered to planning target volume (PTV) (HR 1.22, 95% CI: 1.05-1.42, P = 0.01), higher mean BED₁₀ (biological equivalent dose assuming a tissue α / β $$ \alpha /\beta $$ ratio of 10) (HR 1.12, 95% CI: 1.04-1.2, P < 0.001), and higher mean BED₂ (HR 1.02, 95% CI: 1-1.04, P = 0.04) delivered to the lesion was associated with increased risk of RN. LC rate was 86% and the cumulative incidence of DBF was 36% with a median onset of 28.4 months.

CONCLUSIONS

Our results support the predicted radiobiological benefit of the use of hfSRS in high-risk BMs to limit treatment-related toxicity with low risk for symptomatic RN comparable with lower risk population receiving sfSRS while achieving satisfactory local disease control.

Long-Term Survival after Linac-Based Stereotactic Radiosurgery and Radiotherapy with a Micro-Multileaf Collimator for Brain Metastasis

Background: this study aimed to evaluate the prognostic factors associated with long-term survival after linear accelerator (linac)-based stereotactic radiosurgery (SRS) and fractionated stereotactic radiotherapy (fSRT) with a micro-multileaf collimator for brain metastasis (BM). Methods: This single-center retrospective study included 226 consecutive patients with BM who were treated with linac-based SRS or fSRT with a micro-multileaf collimator between January 2011 and December 2018. Long-term survival (LTS) was defined as survival for more than 2 years after SRS/fSRT. Results: The tumors originated from the lung (n = 189, 83.6%), breast (n = 11, 4.9%), colon (n = 9, 4.0%), stomach (n = 4, 1.8%), kidney (n = 3, 1.3%), esophagus (n = 3, 1.3%), and other regions (n = 7, 3.1%). The median pretreatment Karnofsky performance scale (KPS) score was 90 (range: 40–100). The median follow-up time was 13 (range: 0–120) months. Out of the 226 patients, 72 (31.8%) were categorized in the LTS group. The median survival time was 43 months and 13 months in the LTS group and in the entire cohort, respectively. The 3-year, 4-year, and 5-year survival rate in the LTS group was 59.1%, 49.6%, and 40.7%, respectively. Multivariate regression logistic analysis showed that female sex, a pre-treatment KPS score ≥ 80, and the absence of extracranial metastasis were associated with long-term survival. Conclusions: female sex, a favorable pre-treatment KPS score, and the absence of extracranial metastasis were associated with long-term survival in the current cohort of patients with BM.

Radiation Necrosis from Stereotactic Radiosurgery-How Do We Mitigate?

OPINION STATEMENT

Intracranial stereotactic radiosurgery (SRS) is an effective and convenient treatment for many brain conditions. Data regarding safety come mostly from retrospective single institutional studies and a small number of prospective studies. Variations in target delineation, treatment delivery, imaging follow-up protocols and dose prescription limit the interpretation of this data. There has been much clinical focus on radiation necrosis (RN) in particular, as it is being increasingly recognized on follow-up imaging. Symptomatic RN may be treated with medical therapy (such as corticosteroids and bevacizumab) with surgical resection being reserved for refractory patients. Nevertheless, RN remains a challenging condition to manage, and therefore upfront patient selection for SRS remains critical to provide complication-free control. Mitigation strategies need to be considered in situations where the baseline risk of RN is expected to be high-such as large target volume or re-irradiation. These may involve reduction in the prescribed dose or hypofractionated stereotactic radiation therapy (HSRT). Recently published guidelines and international meta-analysis report the benefit of HSRT in larger lesions, without compromising control rates. However, careful attention to planning parameters and SRS techniques still need to be adhered, even with HSRT. In cases where the risk is deemed to be high despite mitigation, a combination approach of surgery with or without post-operative radiation should be considered.