Risk of radiation necrosis after hypofractionated stereotactic radiotherapy (HFSRT) for brain metastases: a single center retrospective study

Efficacy of hypofractionated Gamma Knife radiosurgery in treating surgical beds of metastatic brain tumors

OBJECTIVE

Surgery alone for metastatic brain tumors (METs) often results in local recurrence due to microscopic residual tumor tissue. While stereotactic radiosurgery (SRS) is commonly used post-surgery, hypofractionation may be required for large surgical beds. This study evaluated the efficacy and safety of hypofractionated Gamma Knife radiosurgery (hf-GKRS) for the first time as a post-operative adjuvant therapy.

METHODS

This retrospective study involved 24 patients (28 surgical beds) who underwent hf-GKRS within four weeks after surgery. The study primarily focused on local control (LC) rate and analyzed distant intracranial failure (DICF), intracranial progression-free survival (PFS), leptomeningeal disease (LMD), overall survival (OS), and radiation necrosis (RN).

RESULTS

During a median follow-up of 9 months, LC was achieved in 89.3 % of surgical beds. LC estimates at 6, 12, and 24 months were 96.4 %, 82.7 %, and 82.7 %, respectively. DICF was observed in 45.8 % of patients, and LMD was identified in two patients (8.3 %). At the end of the follow-up, 58.3 % of patients were alive, and the median OS was 20 months. RN occurred in only one surgical bed (3.6 %). No grade 5 toxicity was observed. The univariate analysis identified a longer interval to GKRS (HR 11.842, p = 0.042) and a larger treatment volume (HR 1.103, p = 0.037) as significant factors for local failure.

CONCLUSIONS

hf-GKRS shows potential as an effective and safe adjuvant treatment for surgical beds. It offers an alternative to SRS, SRT, or WBRT, particularly for larger volumes or tumors near critical structures. Further research is needed to confirm these results and optimize treatment approaches.

Regression of a melanoma brain metastasis that had appeared after immune checkpoint inhibitor discontinuation: a hypothesis-generating case

We present the case of a 50-year-old woman previously treated with nivolumab-ipilimumab combination therapy for a metastatic melanoma. Despite premature discontinuation of these immune checkpoint inhibitors (ICIs) after 2 cycles due to severe immune-related hepatitis, the patient achieved a complete response. Nine months later, brain magnetic resonance imaging (MRI) showed progression of a single cerebral lesion, and the patient was referred for stereotactic radiosurgery. Unexpectedly, the brain MRI acquired one month later as part of radiosurgery planning showed a spontaneous regression of this lesion, allowing for radiosurgery cancellation. Follow-up imaging showed a sustained response, although the patient did not receive any other oncological treatment. We discuss here the potential immune mechanisms involved in this unusual course and the importance of better understanding the behaviour of tumours in the era of ICIs.

Fractionated Stereotactic Radiotherapy with Helical Tomotherapy for Brain Metastases: A Mono-Institutional Experience

Background: The present study reports on the outcomes of our mono-institutional experience of Helical Tomotherapy (HT)-based SRT for brain metastases. The use of this linac is less frequently reported for this kind of treatment. Methods: This retrospective study displays a series of patients treated with HT-SRT. The eligibility of using SRT for brain metastases was defined by a Karnofsky performance status of >70, a life expectancy of >6 months, and controlled extra-cranial disease; no SRT was allowed in the case of a number of brain metastases larger than 10. All the cases were discussed by a multidisciplinary board. Toxicity assessments were performed based on CTCAE v5.0. Survival endpoints were assessed using the Kaplan-Meier method, and univariate and multivariate analyses were carried out to identify any potential predictive factor for an improved outcome. Results: Sixty-four lesions in 37 patients were treated using HT-SRT with a median total dose of 30 Gy in five fractions. The median follow-up was 7 months, and the 1- and 2-year LC rates were both 92.5%. The IPFS rates were and 56.75% and 51.35%. The OS rates were 54% and 40%. The UA showed better IPFS rates significantly related to male sex (p = 0.049), a BED₁₂ of ≥42 Gy (p = 0.006), and controlled extracranial disease (p = 0.03); in the MA, a favorable trend towards LC (p = 0.11) and higher BED (p = 0.11) schedules maintained a correlation with improved IPFS rates, although statistical significance was not reached. Conclusions: HT-based SRT for brain metastases showed safety and efficacy in our monoinstiutional experience. Higher RT doses showed statistical significance for improved outcomes of LC and OS.

Feasibility of a simultaneously integrated boost concept for hypofractionated stereotactic radiotherapy of unresected brain metastases

BACKGROUND

In stereotactic radiotherapy, dose is prescribed to an isodose surrounding the planning target volume (PTV). However, the desired dose inhomogeneity inside the PTV leaves the specific dose distribution to the gross tumor volume (GTV) unspecified. A simultaneously integrated boost (SIB) to the GTV could solve this shortcoming. In a retrospective planning study with 20 unresected brain metastases, a SIB approach was tested against the classical prescription.

METHODS

For all metastases, the GTV was isotropically enlarged by 3 mm to a PTV. Two plans were generated, one according to the classical 80% concept with 5 times 7 Gy prescribed (on D_2%) to the 80% PTV surrounding isodose (with D_98%(PTV) ≥ 35 Gy), and the other one following a SIB concept with 5 times 8.5 Gy average GTV dose and with D_98%(PTV) ≥ 35 Gy as additional requirement. Plan pairs were compared in terms of homogeneity inside GTV, high dose in PTV rim around GTV, and dose conformity and gradients around PTV using Wilcoxon matched pairs signed rank test.

RESULTS

The SIB concept was superior to the classical 80% concept concerning dose homogeneity inside GTV: Heterogeneity index of GTV was in the SIB concept (median 0.0513, range 0.0397-0.0757) significantly (p = 0.001) lower than in the 80% concept (median 0.0894, range 0.0447-0.1872). Dose gradients around PTV were not inferior. The other examined measures were comparable.

CONCLUSION

Our stereotactic SIB concept better defines the dose distribution inside PTV and can be considered for clinical use.

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.

Precision Radiation for Brain Metastases With a Focus on Hypofractionated Stereotactic Radiosurgery

There are multiple published randomized controlled trials supporting single-fraction stereotactic radiosurgery (SF-SRS) for patients presenting with 1 to 4 brain metastases, with the benefit of minimizing radiation-induced neurocognitive sequelae as compared to whole brain radiotherapy . More recently, the dogma of SF-SRS as the only means of delivering an SRS treatment has been challenged by hypofractionated SRS (HF-SRS). The ability to deliver 25-35 Gy in 3-5 HF-SRS fractions is a direct consequence of the evolution of radiation technologies to allow image guidance, specialized treatment planning, robotic delivery and/or patient positioning corrections in all 6 degrees-of-freedom, and frameless head immobilization. The intent is to mitigate the potentially devastating complication of radiation necrosis and improve rates of local control for larger metastases. This narrative review provides an overview of outcomes specific to HF-SRS in addition to the more recent developments of staged SRS, preoperative SRS, and hippocampal avoidance-whole brain radiotherapy with simultaneous integrated boost.

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.

Dosimetric and clinical analysis of pseudo-progression versus recurrence after hypo-fractionated radiotherapy for brain metastases

BACKGROUND

The main challenge in follow-up duration of patients with brain metastases after stereotactic radiotherapy is to distinguish between pseudo-progression and tumor recurrence. The objective of this study is to retrospectively analyze the predictive factors.

METHODS

The study included 123 patients with enlarged brain metastases after hypo-fractionated radiotherapy in our center from March 2009 to October 2019, and the baseline clinical features, radiotherapy planning parameters, and enhanced magnetic resonance imaging before and after radiation therapy were analyzed. Logistic regression was performed to compare the differences between groups. Independent risk factors with P < 0.05 and associated with recurrence were used to establish a nomogram prediction model and validated by Bootstrap repeated sampling, which was validated in an internal cohort (n = 23) from October 2019 to December 2021.

RESULTS

The median follow-up time was 68.4 months (range, 8.9-146.2 months). A total of 76 (61.8%) patients were evaluated as pseudo-progression, 47 patients (38.2%) were evaluated as tumor recurrence. The median time to pseudo-progression and tumor recurrence were 18.3 months (quartile range, 9.4-27.8 months) and 12.9 months (quartile range, 8.7-19.6 months) respectively. Variables associated with tumor recurrence included: gross tumor volume ≥ 6 cc, biological effective dose < 60 Gy, target coverage < 96% and no targeted therapy. The area under curve values were 0.730 and 0.967 in the training and validation cohorts, respectively. Thirty-one patients received salvage therapy in the tumor recurrence group. The survival time in pseudo-progression and tumor recurrence groups were 66.3 months (95% CI 56.8-75.9 months) and 39.6 months (95% CI 29.2-50.0 months, respectively; P = 0.001).

CONCLUSIONS

Clinical and dosimetry features of hypo-fractionated radiation therapy based on enhanced brain magnetic resonance can help distinguish pseudo-progression from tumor recurrence after hypo-fractionated radiotherapy for brain metastases. Gross tumor volume, biological effective dose, target coverage, and having received targeted therapy or not were factors associated with the occurrence of tumor recurrence, and the individual risk could be estimated by the nomogram effectively.

Five-Fraction Stereotactic Radiotherapy for Brain Metastases-A Retrospective Analysis

PURPOSE

To determine the safety and outcome profile of five-fraction stereotactic radiotherapy (FSRT) for brain metastases (BM), either as a definitive or adjuvant treatment.

METHODS

We assessed clinical data of patients receiving five fractions of 7 Gy each (cumulative physical dose of 35 Gy) to BM or surgical cavities. The primary endpoints were toxicity and radiation necrosis (RN) rates. Secondary endpoints were 1-year cumulative local control rate (LCR) and estimated overall survival (OS).

RESULTS

A total of 36 eligible patients receiving FSRT to a total of 49 targets were identified and included. The median follow up was 9 (1.1-56.2) months. The median age was 64.5 (34-92) years, the median ECOG score was 1, and the median Diagnostic-Specific Graded Prognostic Assessment (DS-GPA) score was 2. Treatment was well tolerated and there were no grade 3 adverse events or higher. The overall RN rate was 14.3% and the median time to RN was 12.9 (1.8-23.8) months. RN occurrence was associated with immunotherapy, young age (≤45 years), and large PTV. The cumulative 1-year local control rate was 83.1% and the estimated median local progression free-survival was 18.8 months. The estimated median overall survival was 11 (1.1-56.2) months and significantly superior in those patients presenting with RN.

CONCLUSIONS

FSRT with 5 × 7 Gy represents a feasible, safe, and efficient fast track approach of intensified FSRT with acceptable LC and comparable RN rates for both the adjuvant and definitive RT settings.

Gamma knife icon based hypofractionated stereotactic radiosurgery (GKI-HSRS) for brain metastases: impact of dose and volume

OBJECTIVE

Gamma Knife Icon-based hypofractionated stereotactic radiosurgery (GKI-HSRS) is a novel technical paradigm in the treatment of brain metastases that allows for both the dosimetric benefits of the GKI stereotactic radiosurgery (SRS) platform as well as the biologic benefits of fractionation. We report mature local control and adverse radiation effect (ARE) outcomes following 5 fraction GKI-HSRS for intact brain metastases.

METHODS

Patients with intact brain metastases treated with 5-fraction GKI-HSRS were retrospectively reviewed. Survival, local control, and adverse radiation effect rates were determined. Univariable and multivariable regression (MVA) were performed on potential predictive factors.

RESULTS

Two hundred and ninety-nine metastases in 146 patients were identified. The median clinical follow-up was 10.7 months (range 0.5-47.6). The median total dose and prescription isodose was 27.5 Gy (range, 20-27.5) in 5 daily fractions and 52% (range, 45-93), respectively. The median overall survival (OS) was 12.7 months, and the 1-year local failure rate was 15.2%. MVA identified a total dose of 27.5 Gy vs. ≤ 25 Gy (hazard ratio [HR] 0.59, p = 0.042), and prior chemotherapy exposure (HR 1.99, p = 0.015), as significant predictors of LC. The 1-year ARE rate was 10.8% and the symptomatic ARE rate was 1.8%. MVA identified a gross tumor volume of ≥ 4.5 cc (HR 7.29, p < 0.001) as a significant predictor of symptomatic ARE.

CONCLUSION

Moderate total doses in 5 daily fractions of GKI-HSRS were associated with high rates of LC and a low incidence of symptomatic ARE.

Radiation-induced neuropathological changes in the oligodendrocyte lineage with relevant clinical manifestations and therapeutic strategies

PURPOSE

With technological advancements in radiation therapy for tumors of the central nervous system (CNS), high doses of ionizing radiation can be delivered to the tumors with improved accuracy. Despite the reduction of ionizing radiation-induced toxicity to surrounding tissues of the CNS, a wide array of side effects still occurs, particularly late-delayed changes. These alterations, such as white matter damages and neurocognitive impairments, are often debilitative and untreatable, significantly affecting the quality of life of these patients, especially children. Oligodendrocytes, a major class of glial cells, have been identified to be one of the targets of radiation toxicity and are recognized be involved in late-delayed radiation-induced neuropathological changes. These cells are responsible for forming the myelin sheaths that surround and insulate axons within the CNS. Here, the effects of ionizing radiation on the oligodendrocyte lineage as well as the common clinical manifestations resulting from radiation-induced damage to oligodendrocytes will be discussed. Potential prophylactic and therapeutic strategies against radiation-induced oligodendrocyte damage will also be considered.

CONCLUSION

Oligodendrocytes and oligodendrocyte progenitor cells (OPCs) are radiosensitive cells of the CNS. Here, general responses of these cells to radiation exposure have been outlined. However, several findings have not been consistent across various studies. For instance, cognitive decline in irradiated animals was observed to be accompanied by obvious demyelination or white matter changes in several studies but not in others. Hence, further studies have to be conducted to elucidate the level of contribution of the oligodendrocyte lineage to the development of late-delayed effects of radiation exposure, as well as to classify the dose and brain region-specific responses of the oligodendrocyte lineage to radiation. Several potential therapeutic approaches against late-delayed changes have been discussed, such as the transplantation of OPCs into irradiated regions and implementation of exercise. Many of these approaches show promising results. Further elucidation of the mechanisms involved in radiation-induced death of oligodendrocytes and OPCs would certainly aid in the development of novel protective and therapeutic strategies against the late-delayed effects of radiation.

Hypofractionated versus single-fraction stereotactic radiosurgery for the treatment of brain metastases: A systematic review and meta-analysis

OBJECTIVE

This systematic review and meta-analysis aimed to synthesize the latest evidence on the hypofractionated stereotactic radiosurgery (HF-SRS) compared to single-fraction stereotactic radiosurgery (SF-SRS) for the treatment of brain metastases.

METHODS

We systematically searched PubMed, Scopus, EuropePMC, ProQuest, and Cochrane Central Databases. Original research articles investigating patients with brain metastasis receiving HF-SRS or SF-SRS reporting the local control/failure and/or radionecrosis during follow-up were included.

RESULTS

There were 1100 patients from 7 studies. 616 lesions were allocated to HF-SRS group and 777 lesions were allocated to SF-SRS group. Pooled rate of local control was 88% (95% CI 84%, 91%) in HF-SRS group and 81% (95% CI 74%, 88%) in the SF-SRS groups. Local control was higher in patients receiving HF-SRS compared to SF-SRS (OR 1.53 [95% CI 1.08, 2.18], p = 0.018; I²: 0%). Pooled rate of radionecrosis was 7% (95% CI 3%, 12%) in HF-SRS group and 15% (95% CI 8%, 23%) in the SF-SRS groups. Similar rate of radionecrosis was observed in both HF-SRS and SF-SRS (OR 0.82 [95% CI 0.31, 2.21], p = 0.698; I²: 61.3%). Grading of Recommendations, Assessment, Development and Evaluations (GRADE) qualification showed a low level of certainty for the higher local control in patients receiving HF-SRS compared to SF-SRS and a very low level of certainty for similar risk of radionecrosis between the two groups.

CONCLUSION

This meta-analysis showed that HF-SRS was associated with higher local control and similar rate of radionecrosis compared to SF-SRS in patients with brain metastases.

PROSPERO ID

CRD42020210469.