CyberKnife for Recurrent Malignant Gliomas: A Systematic Review and Meta-Analysis

Three-dimensional dose prediction based on deep convolutional neural networks for brain cancer in CyberKnife: accurate beam modelling of homogeneous tissue

Objectives

Accurate beam modelling is essential for dose calculation in stereotactic radiation therapy (SRT), such as CyberKnife treatment. However, the present deep learning methods only involve patient anatomical images and delineated masks for training. These studies generally focus on traditional intensity-modulated radiation therapy (RT) plans. Nevertheless, this paper aims to develop a deep CNN-based method for CyberKnife plan dose prediction about brain cancer patients. It utilized modelled beam information, target delineation, and patient anatomical information.

Methods

This study proposes a method that adds beam information to predict the dose distribution of CyberKnife in brain cases. A retrospective dataset of 88 brain and abdominal cancer patients treated with the Ray-tracing algorithm was performed. The datasets include patients' anatomical information (planning CT), binary masks for organs at risk (OARs) and targets, and clinical plans (containing beam information). The datasets were randomly split into 68, 6, and 14 brain cases for training, validation, and testing, respectively.

Results

Our proposed method performs well in SRT dose prediction. First, for the gamma passing rates in brain cancer cases, with the 2 mm/2% criteria, we got 96.7% ± 2.9% for the body, 98.3% ± 3.0% for the planning target volume, and 100.0% ± 0.0% for the OARs with small volumes referring to the clinical plan dose. Secondly, the model predictions matched the clinical plan's dose-volume histograms reasonably well for those cases. The differences in key metrics at the target area were generally below 1.0 Gy (approximately a 3% difference relative to the prescription dose).

Conclusions

The preliminary results for selected 14 brain cancer cases suggest that accurate 3-dimensional dose prediction for brain cancer in CyberKnife can be accomplished based on accurate beam modelling for homogeneous tumour tissue. More patients and other cancer sites are needed in a further study to validate the proposed method fully.

Advances in knowledge

With accurate beam modelling, the deep learning model can quickly generate the dose distribution for CyberKnife cases. This method accelerates the RT planning process, significantly improves its operational efficiency, and optimizes it.

Re-irradiation with stereotactic radiotherapy for recurrent high-grade glial tumors

Background

Despite the radical treatments applied, recurrence is encountered in the majority of high-grade gliomas (HGG). There is no standard treatment when recurrence is detected, but stereotactic radiotherapy (SRT) is a preferable alternative. The aim of this retrospective study is to evaluate the efficacy of SRT for recurrent HGG, and to investigate the factors that affect survival.

Materials and methods

From 2013 to 2021, a total of 59 patients with 64 lesions were re-irradiated in a single center with the CyberKnife Robotic Radiosurgery System. The primary endpoints of the study were overall survival (OS), progression free survival (PFS) and local control rates (LCR).

Results

The median time to first recurrence was 13 (4-85) months. SRT was performed as a median prescription dose of 30 Gy (range 15-30), with a median of 5 fractions (1-5). The median follow-up time was 4 months (range 1-57). The median OS was 8 (95% CI: 4.66-11.33) months. Age, grade 3, tumor size were associated with better survival. The median PFS was 5 [95% confidence interval (CI): 3.39-6.60] months. Age, grade 3 and time to recurrence > 9 months were associated with improved PFS. Grade 3 gliomas (p = 0.027), size of tumor < 2 cm (p = 0.008) remained independent prognostic factors for OS in multivariate analysis.

Conclusion

SRT is a viable treatment modality with significant survival contribution. Since it may have a favorable prognostic effect on survival in patients with tumor size < 2 cm, we recommend early diagnosis of recurrence and a decision to re-irradiate a smaller tumor during follow-up.

Dose reduction of hippocampus using HyperArc planning in postoperative radiotherapy for primary brain tumors

To compare dosimetric parameters for the hippocampus, organs at risk (OARs), and targets of volumetric modulated arc therapy (VMAT), noncoplanar VMAT (NC-VMAT), and HyperArc (HA) plans in patients undergoing postoperative radiotherapy for primary brain tumors. For 20 patients, HA plans were generated to deliver 40.05 to 60 Gy for the planning target volume (PTV). In addition, doses for the hippocampus and OARs were minimized. The VMAT and NC-VMAT plans were retrospectively generated using the same optimization parameters as those in the HA plans. For the hippocampus, the equivalent dose to be administered in 2 Gy fractions (EQD₂) was calculated assuming α/β = 2. Dosimetric parameters for the PTV, hippocampus, and OARs in the VMAT, NC-VMAT, and HA plans were compared. For PTV, the HA plans provided significantly lower D_max and D_1% than the VMAT and NC-VMAT plans (p < 0.05), whereas the D_99% and D_min were significantly higher (p < 0.05). For the contralateral hippocampus, the dosimetric parameters in the HA plans (8.1 ± 9.6, 6.5 ± 7.2, 5.6 ± 5.8, and 4.8 ± 4.7 Gy for D_20%, D_40%, D_60% and D_80%, respectively) were significantly smaller (p < 0.05) than those in the VMAT and NC-VMAT plans. Except for the optic chiasm, the D_max in the HA plans (brainstem, lens, optic nerves, and retinas) was the smallest (p < 0.05). In addition, the doses in the HA plans for the brain and skin were the smallest (p < 0.05) among the 3 plans. HA planning, instead of coplanar and noncoplanar VMAT, significantly reduces the dosage to which the contralateral hippocampus as well as other OARs are exposed without compromising on target coverage.

Impact of fractionated stereotactic radiotherapy on activity of daily living and performance status in progressive/recurrent glioblastoma: a retrospective study

BACKGROUND

The prognosis of recurrent glioblastoma (GBM) is poor, with limited options of palliative localized or systemic treatments. Survival can be improved by a second localized treatment; however, it is not currently possible to identify which patients would benefit from this approach. This study aims to evaluate which factors lead to a lower Karnofsky performance status (KPS) score after fractionated stereotactic RT (fSRT).

METHODS

We retrospectively collected data from patients treated with fSRT for recurrent GBM at the Institut de Cancérologie de Lorraine between October 2010 and November 2017 and analyzed which factors were associated with a lower KPS score.

RESULTS

59 patients received a dose of 25 Gy in 5 sessions spread over 5-7 days (80% isodose). The median time from the end of primary radiotherapy to the initiation of fSRT was 10.7 months. The median follow-up after fSRT initiation was 8.8 months. The incidence of KPS and ADL impairment in all patients were 51.9% and 37.8% respectively with an adverse impact of PTV size on KPS (HR = 1.57 [95% CI 1.19-2.08], p = 0.028). Only two patients showed early grade 3 toxicity and none showed grade 4 or late toxicity. The median overall survival time, median overall survival time after fSRT, median progression-free survival and institutionalization-free survival times were 25.8, 8.8, 3.9 and 7.7 months, respectively. Initial surgery was associated with better progression-free survival (Hazard ratio (HR) = 0.48 [95% CI 0.27-0.86], p = 0.013).

CONCLUSIONS

A larger PTV should predicts lower KPS in the treatment of recurrent GBM using fSRT.

Boron neutron capture therapy and add-on bevacizumab in patients with recurrent malignant glioma

BACKGROUND

Although boron neutron capture therapy has shown excellent survival data, previous studies have shown an increase in radiation necrosis against recurrent malignant glioma. Herein, we proposed that bevacizumab may reduce radiation injury from boron neutron capture therapy by re-irradiation. We evaluated the efficacy and safety of a boron neutron capture therapy and add-on bevacizumab combination therapy in patients with recurrent malignant glioma.

METHODS

Patients with recurrent malignant glioma were treated with reactor-based boron neutron capture therapy. Treatment with bevacizumab (10 mg/kg) was initiated 1-4 weeks after boron neutron capture therapy and was administered every 2-3 weeks until disease progression. Initially diagnosed glioblastomas were categorized as primary glioblastoma, whereas other forms of malignant glioma were categorized as non-primary glioblastoma.

RESULTS

Twenty-five patients (14 with primary glioblastoma and 11 with non-primary glioblastoma) were treated with boron neutron capture therapy and add-on bevacizumab. The 1-year survival rate for primary glioblastoma and non-primary glioblastoma was 63.5% (95% confidence interval: 33.1-83.0) and 81.8% (95% confidence interval: 44.7-95.1), respectively. The median overall survival was 21.4 months (95% confidence interval: 7.0-36.7) and 73.6 months (95% confidence interval: 11.4-77.2) for primary glioblastoma and non-primary glioblastoma, respectively. The median progression-free survival was 8.3 months (95% confidence interval: 4.2-12.1) and 15.6 months (95% confidence interval: 3.1-29.8) for primary glioblastoma and non-primary glioblastoma, respectively. Neither pseudoprogression nor radiation necrosis were identified during bevacizumab treatment. Alopecia occurred in all patients. Six patients experienced adverse events ≥grade 3.

CONCLUSIONS

Boron neutron capture therapy and add-on bevacizumab provided a long overall survival and a long progression-free survival in recurrent malignant glioma compared with previous studies on boron neutron capture therapy alone. The add-on bevacizumab may reduce the detrimental effects of boron neutron capture therapy, including pseudoprogression and radiation necrosis. Further studies of the combination therapy with a larger sample size and a randomized controlled design are warranted.