Robotic Radiosurgery Research Articles

AAPM task group report 135.B: Quality assurance for robotic radiosurgery.

AAPM Task Group Report 135.B covers new technology components that have been added to an established radiosurgery platform and updates the components that were not well covered in the previous report. Considering the current state of the platform, this task group (TG) is a combination of a foundational task group to establish the basis for new processes/technology and an educational task group updating guidelines on the established components of the platform. Because the technology discussed in this document has a relatively small user base compared to C-arm isocentric linacs, the authors chose to emphasize the educational components to assist medical physicists who are new to the technology and have not had the opportunity to receive in-depth vendor training at the time of reading this report. The TG has developed codes of practice, introduced QA, and developed guidelines which are generally expected to become enduring practice. This report makes prescriptive recommendations as there has not been enough longitudinal experience with some of the new technical components to develop a data-based risk analysis.

Reducing treatment time for robotic radiosurgery by considering path efficiency during node selection.

Robotic radiosurgery treatments allow for precise non-coplanar beam delivery by utilizing a robot equipped with a linac that traverses through a set of predetermined nodes. High quality treatment plans can be produced but treatment times can grow large, with one substantial component being the robot traversal time. The aim of this study is to reduce the treatment time for robotic radiosurgery treatments by introducing algorithms for reducing the robot traversal time. The algorithms are integrated into a commercial treatment planning system. First, an optimization framework for robotic radiosurgery planning is detailed, including a heuristic optimization method for node selection. Second, two methods aimed at reducing the traversal time are introduced. One utilizes a centrality measure focusing on the structure of the node network, while the other is based on the direct computation of traversal times during optimization. A comparison between plans with and without the time-reducing algorithms is made for three brain cases and one liver case with basis in treatment time, plan quality, monitor units, and network structure of the selectednodes. Large decreases in traversal times are obtained by the traversal time reducing algorithms, with reductions of up to 49 % in the brain cases and 31 % in the liver case. The resulting reductions in treatment times are up to 30 % and 13 %, respectively. Small differences in plan quality are observed, with similar dose-volume histograms, dose distributions, and conformity/gradientindices. The total treatment time of the robotic radiosurgery treatments can be reduced by selecting nodes with more efficient robot traversal paths, while maintaining planquality.

A high-density multi-electrode platform examining the effects of radiation on in vitro cortical networks

Radiation therapy and stereotactic radiosurgery are common treatments for brain malignancies. However, the impact of radiation on underlying neuronal circuits is poorly understood. In the prefrontal cortex (PFC), neurons communicate via action potentials that control cognitive processes, thus it is important to understand the impact of radiation on these circuits. Here we present a novel protocol to investigate the effect of radiation on the activity and survival of PFC networks in vitro. Escalating doses of radiation were applied to PFC slices using a robotic radiosurgery platform at a standard dose rate of 10 Gy/min. High-density multielectrode array recordings of radiated slices were collected to capture extracellular activity across 4,096 channels. Radiated slices showed an increase in firing rate, functional connectivity, and complexity. Graph-theoretic measures of functional connectivity were altered following radiation. These results were compared to pharmacologically induced epileptic slices where neural complexity was markedly elevated, and functional connections were strong but remained spatially focused. Finally, propidium iodide staining revealed a dose-dependent effect of radiation on apoptosis. These findings provide a novel assay to investigate the impacts of clinically relevant doses of radiation on brain circuits and highlight the acute effects of escalating radiation doses on PFC neurons.

Technical note: MR image-based synthesis CT for CyberKnife robotic stereotactic radiosurgery

The purpose of this study is to investigate whether deep learning-based sCT images enable accurate dose calculation in CK robotic stereotactic radiosurgery. A U-net convolutional neural network was trained using 2446 MR-CT pairs and used it to translate 551 MR images to sCT images for testing. The sCT of CK patient was encapsulated into a quality assurance (QA) validation phantom for dose verification. The CT value difference between CT and sCT was evaluated using mean absolute error (MAE) and the statistical significance of dose differences between CT and sCT was tested using the Wilcoxon signed rank test. For all CK patients, the MAE value of the whole brain region did not exceed 25 HU. The percentage dose difference between CT and sCT was less than ±0.4% on GTV (D2(Gy), −0.29%, D95(Gy), −0.09%), PTV (D2(Gy), −0.25%, D95(Gy), −0.10%), and brainstem (max dose(Gy), 0.31%). The percentage dose difference between CT and sCT for most regions of interest (ROIs) was no more than ±0.04%. This study extended MR-based sCT prediction to CK robotic stereotactic radiosurgery, expanding the application scenarios of MR-only radiation therapy. The results demonstrated the remarkable accuracy of dose calculation on sCT for patients treated with CK robotic stereotactic radiosurgery.

A mini review of plan quality and secondary cancer risk in CyberKnife M6 radiosurgery for benign intracranial tumors.

With advancements in medical technology, stereotactic radiosurgery (SRS) has become an essential option for treating benign intracranial tumors. Due to its minimal side effects and high local control rate, SRS is widely applied. This paper evaluates the plan quality and secondary cancer risk (SCR) in patients with benign intracranial tumors treated with the CyberKnife M6 system. The CyberKnife M6 robotic radiosurgery system features both multileaf collimator (MLC) and IRIS variable aperture collimator systems, providing different treatment options. The study included 15 patients treated with the CyberKnife M6 system, examining the differences in plan quality and SCR between MLC and IRIS systems. Results showed that MLC and IRIS plans had equal PTV (planning target volume) coverage (98.57% vs. 98.75%). However, MLC plans demonstrated better dose falloff and conformity index (CI: 1.81 ± 0.26 vs. 1.92 ± 0.27, P = 0.025). SCR assessment indicated that MLC plans had lower cancer risk estimates, with IRIS plans having average LAR (lifetime attributable risk) and EAR (excess absolute risk) values approximately 25% higher for cancer induction and 15% higher for sarcoma induction compared to MLC plans. The study showed that increasing tumor volume increases SCR probability, but there was no significant difference between different plans in PTV and brainstem analyses.

Exploring long-term outcomes following CyberKnife robotic radiosurgery for trigeminal neuralgia

Background and purposeRadiosurgery has been extensively studied for its efficacy and safety in the management of trigeminal neuralgia (TN). However, among the plethora of relevant studies in the literature, only a restricted number have been conducted targeting an elongated trigeminal nerve segment with the CyberKnife radiosurgery (CKRS) system. Herein, we report long-term clinical outcomes of TN patients treated with CKRS. Materials and methodsFifty patients treated with CKRS for medically refractory TN were analyzed. Pain response and sensory dysfunction post CKRS were assessed using the Barrow Neurological Institute (BNI) scale. Kaplan-Meier analysis was used to assess the maintenance of pain control and the risk of onset of facial numbness. The Cox proportional hazards regression model was employed for both univariate and multivariate analyses to identify predictive factors among the collected variables. ResultsThe median follow-up period was 63 months (range: 12–174 months). The median values of treated nerve volume, prescription dose, and integral dose were 59 mm3, 60 Gy and 3.9 mJ, respectively. Pain control (BNI I-III) was achieved in 37 patients (74%). Among them, the actuarial freedom from pain (FFP) rate was 82%, 78% and 74% at 24, 36 and beyond 48 months post-CKRS, respectively. A correlation of FFP rate with patient gender, treated nerve volume, and mean dose was revealed in multivariate analysis. Twenty-three patients (62%) reported onset of new or aggravation of pre-existing, facial numbness with twenty-one of them (57%) characterizing it as “mild facial numbness, not bothersome” (BNI-II) and two (5%) as “somewhat bothersome” (BNI-III). We did not encounter any case with very bothersome facial numbness (BNI-IV). ConclusionsLong-term results of this work contribute to the body of evidence supporting the safety and efficacy of CKRS in the treatment of TN patients, in view of excellent pain control for an acceptable toxicity profile.

Epileptic encephalopathies secondary to hypothalamic hamartomas treated with radiosurgery: A case series.

Hypothalamic hamartomas are congenital lesions that typically present with gelastic seizures, refractory epilepsy, neurodevelopmental delay, and severe cognitive impairment. Surgical procedures have been reported to be effective in removing the hamartomas, however, they are associated with significant morbidity. Therefore, it is not considered a safe therapeutic modality. Image-guided robotic radiosurgery (CyberKnife® Radiosurgery System) has been shown to provide good outcomes without lasting complications. This series of cases describes the clinical, radiological, radiotherapeutic, and postsurgical outcomes of five patients with epileptic encephalopathies secondary to hypothalamic hamartomas who were treated with CyberKnife®. All patients exhibited refractory epilepsy with gelastic seizures and were unsuitable candidates for surgical resection The prescribed dose ranged between 16 and 25 Gy, delivered in a single fraction for four patients and five fractions for one patient while adhering strictly to visual pathway constraints. After radiosurgery, four patients maintained seizure control (one with an Engel class Ia, three with an Engel class 1d), and another presented sporadic, nondisabling gelastic seizures (with an Engel class IIa). After 24-26 months of follow-up, in three patients, their intelligence quotient scores increased. No complications were reported. This report suggests that Cyberknife may be a good option for treating hypothalamic hamartoma, particularly in cases where other noninvasive alternatives are unavailable. Nevertheless, additional studies are essential in order to evaluate the effectiveness of the technique in these cases.

Abstract PS01-09: Early Results of a Phase I Pre-Operative Single Fraction Ablative Trial for Early Stage Breast Cancer

Abstract Objective(s): To explore the impact of pre-operative single fraction stereotactic ablative partial breast irradiation (SPBI) dose escalation (30, 34, or 38Gy) on toxicity and tumor response for early-stage hormone receptor (HR)+ breast cancer in an interim analysis of an expanded cohort phase I dose escalation study (NCT04040569). Methods: Eligible patients (pts) have < 3 cm, HR+, Her2 -, cN0 invasive breast carcinomas not requiring chemotherapy. Patients are treated on either MR LINAC, robotic radiosurgery, or cobalt stereotactic breast units. Endocrine therapy is started two weeks after SPBI. Surgery is completed 2-12 months after SPBI. The primary objective is to escalate single fraction SPBI to an ablative dose without exceeding maximum tolerable dose (MTD). Secondary endpoints include pathologic complete response (pCR), local control, toxicity, cosmesis, and distant disease-free survival. Near complete response (nCR) is defined as RCB 1 and Miller-Payne 4/5. Dose limiting toxicity (DLT) is defined as grade ≥3 toxicity or any grade 4/5 toxicity attributed to SPBI. Each dose cohort enrolls 7-15 pts. Dose escalation is permitted if 0/7, 2/9, ≤3/12, or ≤4/15 patients experienced a DLT within 90 days of SPBI. MTD is exceeded if more DLTs occur in any cohort. Results: From 12/2019 to 6/2023, 11 and 15 pts were treated with 30Gy and 34Gy, respectively. Rates of pCR/nCR are 37.5% for 30Gy versus 92.8% 34 Gy (p=0.01). At 30Gy, 8/11 pts (73%) underwent surgery with a median 4.3 (range 2.8-5.9) month interval from SPBI to surgery: 0/8 (0%) had a pCR and 3/8 (37.5%) had a nCR. At dose level 34Gy, 14/15 pts (93%) underwent surgery with a median 7.3 (range 5.9-12) month interval from SPBI to surgery: 6/14 (42.8%) had a pCR while 7/14 (50%) had a nCR. Of the 8 pts with a nCR, 50% had only 1-3mm of residual disease. The mean ki67 for the entire cohort was 12.0% +/- 6.9% at diagnosis and decreased to 1.4 +/-2.3% at surgery. 13/14 (92.8%) pts with residual disease had a ki67 < 3% after surgery and SPBI. There were 33 acute grade 1; 2 acute grade 2 (breast pain and dermatitis); and 10 late grade 1 [1 grade 2 (breast pain), and 1 grade 3 (slow healing wound) in an uncontrolled diabetic] toxicities. Conclusion: First study to show pre-operative SPBI up to 34Gy in a single fraction was safe and effective for early-stage HR+ breast cancer. Escalating the dose has achieved a dramatic improvement in pCR/nCR (92.8%) suggesting this is an exciting approach for potentially eliminating tumor with radiation/endocrine therapy alone in early stage breast cancer and potentially paving a path towards non-surgical management in highly selected patients. Citation Format: Asal Rahimi, A Marilyn Leitch, Baṣak Dogan, Prasanna Alluri, Deborah Farr, Mona Arbab, Stephen Seiler, Nathan Kim, Rachel Wooldridge, Nisha Unni, Chika Nwachukwu, Ina Patel, You Zhang, David Parsons, Anvy Nguyen, Howard E Morgan, Heather McArthur, Sunati Sahoo, Robert Timmerman. Early Results of a Phase I Pre-Operative Single Fraction Ablative Trial for Early Stage Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS01-09.

Long-term clinical outcomes of hypofractionated stereotactic radiotherapy using the CyberKnife robotic radiosurgery system for jugular foramen schwannomas.

Jugular foramen schwannomas (JFSs) are rarely seen, benign tumors with slow growth. Today, management options for JFSs include observation, surgery, and radiation. However, the optimal treatment strategy remains controversial. Stereotactic radiosurgery serves as a minimally invasive alternative or adjuvant therapeutic regimen of microsurgery. Gamma Knife radiosurgery is suitable for patients with JFS who have small- and medium-sized tumors and normal cranial nerve (CN) function. Hypofractionated stereotactic radiotherapy (HSRT) offers a potential radiobiological advantage and may result in better preservation of normal structures compared to single-fraction stereotactic radiosurgery. The aim of the article was to review the clinical and radiographic outcomes of patients with JFS who were treated using HSRT. The authors retrospectively analyzed 74 patients with JFS who received HSRT between January 2009 and January 2020 in the authors' center. Among them, 53 patients were newly diagnosed with JFS, 19 patients had a previous history of microsurgical resection, and the other 2 patients underwent CyberKnife because of tumor recurrence after Gamma Knife radiosurgery. A total of 73 patients had preexisting CN symptoms and signs. The median tumor volume was 14.8 cm3 (range 0.5-41.2 cm3), and most of them (70.3%) were ≥ 10 cm3. The radiation dose regimen was prescribed depending on the tumor size, and more fractions were used in larger tumors. The median margin doses prescribed were 18.2 Gy/2 fractions, 21.0 Gy/3 fractions, and 21.6 Gy/4 fractions. The median follow-up was 103 months (range 18-158 months). After treatment, 42 (56.8%) patients had tumor regression, 27 (36.5%) patients had stable tumors, and 5 (6.8%) experienced tumor progression. Among them, MRI revealed that 1 patient had a complete response. Three patients received surgery at a median of 25 months because of tumor progression. One patient underwent ventriculoperitoneal shunt insertion for hydrocephalus that developed after HSRT independent of tumor progression. The 5-year progression-free survival rate was 93.2%. Preexisting cranial neuropathies improved in 46 patients, remained stable in 14, and worsened in 14. HSRT proved to be a safe and effective primary or adjuvant treatment strategy for JFSs, although 14 patients (18.9%) experienced some degree of delayed symptomatic deterioration posttreatment. This therapeutic option was demonstrated to provide both excellent tumor control and improvement in CN function.

Dosimetric Comparison of Dedicated Radiosurgery Platforms for the Treatment of Essential Tremor: Technical Report.

Essential tremor (ET) is one of the most common adult movement disorders. As the worldwide population ages, the incidence and prevalence of ET is increasing.Although most cases can be managed conservatively, there is a subset of ET that is refractory to medical management. By virtue of being "reversible", deep brain stimulation (DBS) of the ventral intermediate nucleus (VIM) of the thalamus is one commonly accepted intervention. As an alternative to invasive and expensive DBS, there has been a renaissance in treating ET with lesion-based approaches, spearheaded most recently by high-intensity focused ultrasound (HIFU), the hallmark of which is that it is non-invasive. Meanwhile, stereotactic radiosurgical (SRS) lesioning of VIM represents another time-honored lesion-based non-invasive treatment of ET, which is especially well suited for those patients that cannot tolerate open neurosurgery and is now also getting a "second look". While multiple SRS platforms have been and continue to be used to treat ET, there is little in the way of dosimetric comparison between different technologies. In this brief technical report we compare the dosimetric profiles of three major radiosurgical platforms (Gamma Knife, CyberKnife Robotic Radiosurgery, and Zap-X Gyroscopic Radiosurgery (GRS)) for the treatment of ET. In general, the GRS and Gamma Knife were shown to have the best theoretical dosimetric profiles for VIM lesioning. Nevertheless the relevance of such superiority to clinical outcomes requires future patient studies.

Co-relation of Portal Vein Tumour Thrombus Response With Survival Function Following Robotic Radiosurgery in Vascular Invasive Hepatocellular Carcinoma

Purpose or ObjectiveProspective evaluation of stereotactic body radiotherapy (SBRT) with Robotic Radiosurgery in hepatocellular carcinoma patients with macrovascular invasion (HCC-PVT). Materials and MethodsPatients with inoperable HCC-PVT, good performance score (PS0-1) and preserved liver function (up to Child Pugh B7) were accrued after ethical and scientific committee approval [CTRI: 2022/01/050234] for treatment on Robotic Radiosurgery (M6) and planned with Multiplan (iDMS V2.0). Triple-phase contrast computed tomography (CT) scan was done for contouring and gross tumor volume (GTV) included contrast enhancing mass within main portal vein and adjacent parenchymal disease. Dose prescription was as per risk stratification protocol (22- 50Gy in 5 fractions) while achieving the constraints of mean liver dose <15Gy, 800 cc liver <8Gy and the duodenum max of <24 Gy). Response assessment done at 2 months follow up for recanalization. Patient and treatment related factors evaluated for influence in survival function. ResultsBetween Jan 2017 till May 2022, 317 consecutive HCC with PVT patients were screened and 219 patients were accrued [male 92%, CP score 5-7 90%, mean age 63 years (38-85yrs), CLIP <3: 84 (40%), 3-6 117 (56%), infective etiology 9.5%, Performance status (PS) 0-37%; 1-56%]. Among 209 consecutive patients after accrual SBRT treatment done (10 patients were excluded after accrual due to ascites and decompensation), 139 were evaluable for response assessment (>2 mo follow up). At mean follow up of 10.2 months (SD 8.43), 88 (63%) patients expired and 51 (36%) were alive. 82 (59%) patients had recanalization of PVT (response), 57 (41%) pts did not recanalize, 28 (17%) had progressive disease had progressive/metastatic disease prior to response evaluation (<2 months). Mean overall survival in responders and non-responders were 18.4 (SE 2.52) and 9.34 month (SE 0.81) respectively (p<0.001). Mean survival in patients with PS0, PS1 and PS2 were 17, 11.7 and 9.7 months (p- 0.019) respectively. Overall survival (OS) in partial recanalization, bland thrombus and complete recanalization was 12.4, 14.1, 30.3 months respectively (p-0.002). Adjuvant sorafenib, Barcelona Clinic Liver Classification (BCLC) stage, gender, age, RT dose did not influence response to treatment. Recanalization rate was higher in good PS patients (p-0.019). OS in patients with response to treatment, no response to treatment, fit but not accrued and not suitable patients were 18.4, 9.34, 5.9, 2.6 months respectively (p-<0.001). 36/139 patients (24%) had RILD [10 (7.2%) had Classic Radiation induced liver disease (RILD) & 26 (19%) had non-classic RILD]. Derangement in Child Pugh Score (CP score change) by more than 2 was seen in 30 (24%) within 2-month period after Robotic Radiosurgery. 18 (13%) had unplanned admissions, two patients required embolization due to fiducial related bleeding, 20 (14%) had ascites of which 9 (6%) patients required abdominocentesis. ConclusionPVT response or recanalization after SBRT is a statistically significant prognostic factor for survival function in HCC-PVT.

Robust and optimal dose distribution for brain metastases with robotic radiosurgery system: recipe for an inflection point.

Purpose.This study aims to establish a robust dose prescription methodology in stereotactic radiosurgery (SRS) and stereotactic radiotherapy (SRT) for brain metastases, considering geometrical uncertainty and minimising dose exposure to the surrounding normal brain tissue.Methods and Materials.Treatment plans employing 40%-90% isodose lines (IDL) at 10% IDL intervals were created for variously sized brain metastases. The plans were constructed to deliver 21 Gy in SRS. Robustness of each plan was analysed using parameters such as the near minimum dose to the tumour, the near maximum dose to the normal brain, and the volume of normal brain irradiated above 14 Gy.Results.Plans prescribed at 60% IDL demonstrated the least variation in the near minimum dose to the tumour and the near maximum dose to the normal brain under conditions of minimal geometrical uncertainty relative to tumour radius. When the IDL-percentage prescription was below 60%, geometrical uncertainties led to increases in these doses. Conversely, they decreased with IDL-percentage prescriptions above 60%. The volume of normal brain irradiated above 14 Gy was lowest at 60% IDL, regardless of geometrical uncertainty.Conclusions.To enhance robustness against geometrical uncertainty and to better spare healthy brain tissue, a 60% IDL prescription is recommended in SRS and SRT for brain metastases using a robotic radiosurgery system.

Evaluation of a novel patient-specific quality assurance phantom for robotic single-isocentre, multiple-target stereotactic radiosurgery, and stereotactic radiotherapy.

To evaluate patient-specific quality assurance (PSQA) of 3 targets in a single delivery using a novel film-based phantom. The phantom was designed to rotate freely as a sphere and could measure 3 targets with film in a single delivery. After identifying the coordinates of 3 targets in the skull, the rotation angles about the equator and meridian were computed for optimal phantom setup, ensuring the film plane intersected the 3 targets. The plans were delivered on the CyberKnife system using fiducial tracking. The irradiated films were scanned and processed. All films were analysed using 3 gamma criteria. Fifteen CyberKnife test plans with 3 different modalities were delivered on the phantom. Both automatic and marker-based registration methods were applied when registering the irradiated film and dose plane. Gamma analysis was performed using a 3%/1 mm, 2%/1 mm, and 1%/1 mm criteria with a 10% threshold. For the automatic registration method, the passing rates were 98.2% ± 1.9%, 94.2% ± 3.7%, and 80.9% ± 6.3%, respectively. For the marker-based registration approach, the passing rates were 96.4% ± 2.7%, 91.7% ± 4.3%, and 78.4% ± 6.2%, respectively. A novel spherical phantom was evaluated for the CyberKnife system and achieved acceptable PSQA passing rates using TG218 recommendations. The phantom can measure true-composite dose and offers high-resolution results for PSQA, making it a valuable device for robotic radiosurgery. This is the first study on PSQA of 3 targets concurrently on the CyberKnife system.

Robotic stereotactic radiosurgery for intracranial meningiomas in elderly patients: assessment of treatment efficacy and safety.

Stereotactic radiosurgery (SRS) has been increasingly used to treat intracranial pathologies in elderly patients. The treatment efficiency of SRS has been demonstrated in meningiomas, with excellent local control. We aimed to analyze the safety of robotic SRS in elderly patients with meningiomas. We searched for patients with suspected WHO °I meningioma ≥ 60 years old, who underwent CyberKnife (CK) SRS from January 2011 to December 2021. Tumor localization was categorized using the "CLASS" algorithmic scale. Tumor response was evaluated using the Response Assessment in Neuro-Oncology (RANO) criteria for meningiomas. Adverse effects were graded using the Common Terminology Criteria for Adverse Events (CTCAE) version 5.0 and a cox regression was performed to investigate possible predictors. We identified 82 patients with 102 CK-treated lesions that matched the criteria for the first SRS. The median age was 70 [IQR 64-75] years, and 24.3% of the patients were aged > 75 years. Multiple lesions (up to six) were treated in 14.1% of the SRS-sessions. A previous surgery was performed in 57.3% of lesions, with a median time interval of 41 [IQR 10 - 58] months between the initial surgical procedure and the SRS treatment. In 47.9% of cases, CLASS 3 meningiomas at high-risk locations were irradiated. Single fraction radiosurgery was applied to 62.5% of the lesions, while in the remaining cases multi-session SRS with three to five fractions was used. During the median follow-up period of 15.9 months, lesion size progression was observed in 3 cases. Karnofsky Performance Status (KPS) declined by ≥ 20 points in four patients. Adverse effects occurred in 13 patients, while only four patients had CTCAE ≥2 toxicities. Hereby only one of these toxicities was persistent. The occurrence of complications was independent of age, planned target volume (PTV), high-risk localization, and surgery before SRS. The data indicates that SRS is a safe, efficient, and convenient treatment modality for elderly patients with meningioma, even at high-risk locations.

Evaluation of the Effect of Radiosurgery for Target and Non-Target Lesions in Patients with Brain Metastases Using RANO-BM Criteria.

The current therapeutic indications of radiosurgery are constantly expanding. Magnetic resonance imaging (MRI) has an important role in the diagnostic and post-therapeutic period of primary and secondary brain tumor formations. A total of 66 patients with verified cancer disease and brain metastases were separated into two groups. The first group includes 34 patients with primary non-small cell lung cancer and the second one 32 patients with other types of primary cancer. All of them received high-dose radiotherapy in 1-5 fractions. The number, size, and location of the treated lesions responded to robotic stereotactic radiosurgery criteria. The Response Assessment Criteria for Brain Metastases (RANO-BM) is an international multidisciplinary group of experts who developed acceptable criteria for assessing brain metastases. Before treatment and on the first, third, sixth month after radiosurgery, a MRI and blood tests were performed. Treated lesions were separated into four groups depending on the results - complete response, partial response, progressive disease, and stable disease. In both groups of patients, the percentage of complete or partial response had increased in the third and sixth months. The results give us a reason not to recommend an MRI 1 month after treatment if the patient doesn't have any new neurological symptoms, because there may be a pseudo-progression. MRI results valued by RANO-BM criteria give us a good option to evaluate brain metastases on the third and sixth month after after stereotactic radiosurgery.

Patient Cranial Angle and Intrafractional Stability in CyberKnife Robotic Radiosurgery: A Retrospective Analysis.

Purpose: The aim of this study was to investigate whether variations in cranial angles and treatment accuracy during CyberKnife robotic radiosurgery necessitate adjustment of the margins of the planning target volume. Patients and Methods: Data from 66 patients receiving CyberKnife treatment for brain tumors were retrospectively analyzed. Patients were immobilized using a thermoplastic mask and headrest. The cranial angle was measured on planning CT and patients were divided into 2 groups: ≤10° (Group A) and >10° (Group B). Intrafractional motion was recorded using the CyberKnife tracking system over 50 min. Translational and rotational errors were compared between groups, and planning target volume margins were calculated. Results: In Group A, significant translational error differences were found along with the X-axis over time (P < .02). In Group B, significant differences occurred along with the Z-axis (P < .03). No significant rotational or 3-dimensional vector differences were found in either group. Group A had significantly lower Y-axis (P < .045) and roll axis (P < .005) errors compared to Group B. Estimated planning target volume margins in Group A were 0.56 mm (X), 0.46 mm (Y), and 0.47 mm (Z). In Group B, margins were 0.62 mm (X), 0.48 mm (Y), and 0.46 mm (Z). Margins covering 95% of intrafraction motion were 0.49 to 0.50 mm (X, Y, Z) and 0.69 mm (3-dimensional vector) for Group A, and 0.48 to 0.60 mm and 0.79 mm for Group B. With a 1-mm margin, complete coverage was achieved in Group A while 2.1% of vectors in Group B exceeded 1 mm. Conclusion: Adjusting cranial angle to ≤10° during thermoplastic mask molding provided better or similar intrafractional stability compared to >10°.

Robotic stereotactic radiosurgery with CyberKnife - brain metastases and fibrinolysis.

Deviations in haemostasis are found in about 50% of patients with cancer and up to 90% of those with metastatic disease. Many studies investigate the dynamics of the processes of coagulation and fibrinolysis and their role as apredictor of therapeutic response, early relapse, or metastasis risk. To investigate the serum levels of urokinase plasminogen activator (uPA) in patients with brain metastases treated with robotic stereotactic radiosurgery (SRS) with CyberKnife. Serum levels of urokinase plasminogen activator (uPA) were measured in 66patients with solid tumours, divided into two groups, with oligometastatic disease and brain metastases. In this prospective longitudinal study, the serum levels of uPA were measured before starting the therapy and at the first, third, and sixth months after patients were irradiated with the CyberKnife system. Analysis of serum uPA levels in the post-treatment period showed astatistically significant decrease between the baseline and the 6 months post-treatment time point in both patient groups. The baseline value of serum uPA in the group with lung cancer decreased by 62.7%, and in the group with other types of cancer - by 60%. Despite the significant reduction of serum uPA levels 6 months after the treatment, the levels remained significantly higher in both groups than in healthy controls. Ongoing research on uPA and cancer will enrich our knowledge and expand the possibilities for clinical utilization of the marker in the oncology setting (Tab. 2, Ref. 18).

End-to-end validation of fiducial tracking accuracy in robotic radiosurgery using MRI-only simulation imaging.

Image-guided radiation-therapy (IGRT)-based robotic radiosurgery using magnetic resonance imaging (MRI)-only simulation could allow for improved target definition with highly conformal radiotherapy treatments. Fiducial marker (FM)-based alignment is used with robotic radiosurgery treatments of sites such as the prostate because it aids in accurate target localization. Synthetic CT (sCT) images are generated in the MRI-only workflow but FMs used for IGRT appear as signal voids in MRIs and do not appear in MR-generated sCTs, hindering the ability to use sCTs for fiducial-based IGRT. In this study we evaluate the fiducial tracking accuracy for a novel artificial fiducial insertion method in sCT images that allows for fiducial marker tracking in robotic radiosurgery, using MRI-only simulation imaging (MRI-only workflow). Artificial fiducial markers were inserted into sCT images at the site of the real marker implantation as visible in MRI. Two phantoms were used in this study. A custom anthropomorphic pelvis phantom was designed to validate the tracking accuracy for a variety of artificial fiducials in an MRI-only workflow. A head phantom containing a hidden target and orthogonal film pair inserts was used to perform end-to-end tests of artificial fiducial configurations inserted in sCT images. The setup and end-to-end targeting accuracy of the MRI-only workflow were compared to the computed tomography (CT)-based standard. Each phantom had six FMs implanted with a minimum spacing of 2cm. For each phantom a bulk-density sCT was generated, and artificial FMs were inserted at the implantation location. Several methods of FM insertion were tested including: (1) replacing HU with a fixed value (10000HU) (voxel-burned); (2) using a representative fiducial image derived from a linear combination of fiducial templates (composite-fiducial); (3) computationally simulating FM signal voids using a digital phantom containing FMs and inserting the corresponding signal void into sCT images (simulated-fiducial). All tests were performed on a CyberKnife system (Accuray, Sunnyvale, CA). Treatment plans and digital-reconstructed-radiographs were generated from the original CT and sCTs with embedded fiducials and used to align the phantom on the treatment couch. Differences in the initial phantom alignment (3D translations/rotations) and tracking parameters between CT-based plans and sCT-based plans were analyzed. End-to-end plans for both scenarios were generated and analyzed following our clinical protocol. For all plans, the fiducial tracking algorithm was able to identify the fiducial locations. The mean FM-extraction uncertainty for the composite and simulated FMs was below 48% for fiducials in both the anthropomorphic pelvis and end-to-end phantoms, which is below the 70% treatment uncertainty threshold. The total targeting error was within tolerance (<0.95mm) for end-to-end tests of sCT images with the composite and head-on simulated FMs (0.26, 0.44, and 0.35mm for the composite fiducial in sCT, head-on simulated fiducial in sCT, and fiducials in original CT, respectively. MRI-only simulation for robotic radiosurgery could potentially improve treatment accuracy and reduce planning margins. Our study has shown that using a composite-derived or simulated FM in conjunction with sCT images, MRI-only workflow can provide clinically acceptable setup accuracy in line with CT-based standards for FM-based robotic radiosurgery.

Predictors of local control after robotic stereotactic radiotherapy for brain metastases: 10-years-experience after Cyberknife installation.

To evaluate the factors influencing brain metastases (BM) local control (LC) after stereotactic radiotherapy (SRT). Between 2010 and 2020, a cohort of 145 patients (246 BM) treated consecutively with robotic radiosurgery was analysed. Median age was 61 years (range, 29-90 years). Median radiological follow-up of the lesions was 21.7 months (range, 3-115 months). The mean overall survival and LC were 33.0 and 82.7 months, respectively. On univariate analysis, sex, primary cancer site, histological type, use of systemic steroids, maximum diameter, volume, early MRI response, isodose line, number of fractions, BED10 value, and BED10 value proportional to volume and maximum diameter were significant factors for LC. On multivariate analysis, female sex (hazard ratio [HR]: 2.10 P: 0.035), adenocarcinoma histology (HR: 6.54 P: 0.001), no steroid use (HR: 3.60 P: 0.001), maximum diameter (≤1 cm) (HR: 2.64 P: 0.018), complete response of lesion at first follow-up MRI compared to stable or progressive disease (HR: 4.20, P = 0.024; HR: 19.15, P < 0.001), isodose line (≥90%) (HR: 2.00 P: 0.036), and tumour volume (PTV ≤2 cc) (HR: 5.19 P: 0.001) were independent factors improving LC. SRT is an effective treatment for patients with a limited number of BM with a high LC rate. There are many factors related to the patient, tumour, and radiotherapy plan that have an impact on LC after SRT in brain metastases. These results warrant further investigation in a prospective setting.

Noninvasive cardiac radioablation for ventricular tachycardia: dosimetric comparison between linear accelerator- and robotic CyberKnife-based radiosurgery systems

BackgroundFew dosimetric comparisons have been published between linear accelerator (LA)-based systems and CyberKnife (CK)-based robotic radiosurgery systems for cardiac radio-ablation in ventricular tachycardia. This study aimed to compare the dosimetry of noninvasive cardiac radio-ablation deliverable on LA with that on CK.MethodsThirteen patients who underwent noninvasive cardiac radio-ablation by LA were included. The prescribed dose was 25 Gy in 1 fraction, and the average planning target volume was 49.8 ± 31.0 cm3 (range, 14.4–93.7 cm3). CK plans were generated for comparison.ResultsBoth the CK and LA plans accomplished appropriate dose coverage and normal tissue sparing. Compared with the LA plans, the CK plans achieved significantly lower gradient indices (3.12 ± 0.71 vs. 3.48 ± 0.55, p = 0.031) and gradient measures (1.00 ± 0.29 cm vs. 1.17 ± 0.29 cm, p < 0.001). They had similar equivalent conformity indices (CK vs. LA: 0.84 ± 0.08 vs. 0.87 ± 0.07, p = 0.093) and maximum doses 2 cm from the planning target volume (PTV) in any direction (CK vs. LA: 50.8 ± 9.9% vs. 53.1 ± 5.3%, p = 0.423). The dosimetric advantages of CK were more prominent in patients with a PTV of ≤ 50 cm3 or a spherical PTV. In patients with a PTV of > 50 cm3 or a non-spherical PTV, the LA and CK plans were similar regarding dosimetric parameters. CK plans involved more beams (232.2 ± 110.8 beams vs. 10.0 ± 1.7 arcs) and longer treatment times (119.2 ± 43.3 min vs. 22.4 ± 1.6 min, p = 0.007).ConclusionsBoth CK and LA are ideal modalities for noninvasive cardiac radio-ablation. Upfront treatment should be considered based on clinical intent.