Radiosurgery System Research Articles

Risk Assessment of ZAP-X→ Radiosurgery System in a Quaternary Care Hospital Using FMEA Approach

Background and Aims: The overarching goal of this study is to conduct a robust risk assessment using the Failure Modes and Effects Analysis (FMEA) approach. By identifying potential failure modes and their potential impacts on patient care and hospital operations, this research seeks to provide actionable insights and mitigation strategies for the safe and effective implementation of the ZAP-X Radiosurgery System. The swift integration of advanced medical technologies, exemplified by the ZAP-X→ Gyroscopic Stereotactic Radiosurgery System, a computer-controlled machine that delivers radiation to an intended target in the brain, necessitates a comprehensive proactive risk assessment before the launch of the system to ensure the safety of patients, staff and operational processes. Method: Applying the FMEA methodology, we meticulously mapped all processes and sub-processes associated with the ZAP-X Radiosurgery System implementation. Our multidisciplinary team, through a discussion on ‘what can go wrong’, identified failure modes. Risks were prioritised based on severity, likelihood and detectability giving them a Risk Priority Number (RPN). The team proposed mitigation strategies, deploying controls to enhance safety and reliability.

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.

Comparative analysis of plan quality and delivery efficiency: ZAP-X vs. CyberKnife for brain metastases treatment

Purpose/ObjectivesZAP-X, a novel and dedicated radiosurgery (SRS) system, has recently emerged, while CyberKnife has solidified its position as a versatile solution for SRS and stereotactic body radiation therapy over the past two decades. This study aims to compare the dosimetric performance and delivery efficiency of ZAP-X and CyberKnife in treating brain metastases of varying target sizes, employing circular collimation.Methods and materialsTwenty-three patients, encompassing a total of 47 brain metastases, were included in the creation of comparative plans of ZAP-X and CyberKnife for analysis. The comparative plans were generated to achieve identical prescription doses for the targets, while adhering to the same dose constraints for organs at risk (OAR). The prescription isodose percentage was optimized within the range of 97–100% for each plan to ensure effective target-volume coverage. To assess plan quality, indices such as conformity, homogeneity, and gradient (CI, HI, and GI) were computed, along with the reporting of total brain volumes receiving 12Gy and 10Gy. Estimated treatment time and monitor units (MUs) were compared between the two modalities in evaluating delivery efficiency.ResultsOverall, CyberKnife achieved better CI and HI, while ZAP-X exhibited better GI and a smaller irradiated volume for the normal brain. The superiority of CyberKnife’s plan conformity was more pronounced for target size less than 1 cc and greater than 10 cc. Conversely, the advantage of ZAP-X’s plan dose gradient was more notable for target sizes under 10 cc. The homogeneity of ZAP-X plans, employing multiple isocenters, displayed a strong correlation with the target’s shape and the planner’s experience in placing isocenters. Generally, the estimated treatment time was similar between the two modalities, and the delivery efficiency was significantly impacted by the chosen collimation sizes for both modalities.ConclusionThis study demonstrates that, within the range of target sizes within the patient cohort, plans generated by ZAP-X and CyberKnife exhibit comparable plan quality and delivery efficiency. At present, with the current platform of the two modalities, CyberKnife outperforms ZAP-X in terms of conformity and homogeneity, while ZAP-X tends to produce plans with a more rapid dose falloff.

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.

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.

Physical dose validation of dynamic treatment for Gamma Knife radiosurgery.

Dynamic treatment in Gamma Knife (GK) radiosurgery systems delivers radiation continuously with couch movement, as opposed to stationary step-and-shoot treatment where radiation is paused when moving between isocenters. Previous studies have shown the potential for dynamic GK treatment to give faster treatment times and improved dose conformity and homogeneity. However, these studies focused only on computational simulations and lack physicalvalidation. This study aims conduct dynamic treatment dosimetric validation with physical experimental measurements. The experiments aim to (1) address assumptions made with computational studies, such as the validity of treating a continuous path as discretised points, (2) investigate uncertainties in translating computed plans to actual treatment, and (3) determine ideal treatment planning parameters, such as interval distance for the path discretization, collimator change limitations, and minimum isocenter treatmenttimes. This study uses a GK ICON treatment delivery machine, and a motion phantom custom-made to attach to the machine's mask adapter and move in 1D superior-inferior motion. Phantom positioning is first verified through comparisons against couch motion and computed doses. For dynamic treatment experiments, the phantom is moved through a program that first reads the desired treatment plan isocenters' position, time, and collimator sizes, then carries out the motion continuously while the treatment machine delivers radiation. Measurements are done with increasing levels of complexity: varying speed, varying collimator sizes, varying both speed and collimator sizes, then extends the same measurements to simulated 2D motion by combining phantom and couch motion. Dose comparisons between phantom motion radiation measurements and either couch motion measurements or dose calculations are analyzed with 2 mm/2% and 1 mm/2% gamma indices, using both local and global gamma indexcalculations. Phantom positional experiments show a high accuracy, with global gamma indices for all dose comparisons 99%. Discretization level to approximate continuous path as discrete points show the good dose matches with dose calculations when using 1 and 2-mm gaps. Complex 1D motion, including varying speed, collimator sizes, or both, as well as 2D motion with the same complexities, all show good dose matches with dose calculations: the scores are 92.0% for the strictest 1 mm/2% local gamma index calculation, 99.8% for 2 mm/2% local gamma index, and 97.0% for all global gamma indices. Five simulated 2D treatments with optimized plans scored highly as well, with all gamma index scores 95.3% when compared to stationary treatment, and scores 97.9% when compared to plan calculateddose. Dynamic treatment computational studies are validated, with dynamic treatment shown to be physically feasible and deliverable with high accuracy. A 2-mm discretization level in treatment planning is proposed as the best option for shorter dose calculation times while maintaining dose accuracy. Our experimental method enables dynamic treatment measurements using the existing clinical workflow, which may be replicated in other centers, and future studies may include 2D or 3D motion experiments, or planning studies to further quantify potential indication-specificbenefits.

Long-term geometric quality assurance of radiation focal point and cone-beam computed tomography for Gamma Knife radiosurgery system.

To investigate the geometric accuracy of the radiation focal point (RFP) and cone-beam computed tomography (CBCT) over long-term periods for the ICON Leksell Gamma Knife radiosurgery system. This phantom study utilized the ICON quality assurance tool plus, and the phantom was manually set on the patient position system before the implementation of treatment for patients. The deviation of the RFP position from the unit center point (UCP) and the positions of the four ball bearings (BBs) in the CBCT from the reference position were automatically analyzed. During 544days, a total of 269 analyses were performed on different days. The mean ± standard deviation (SD) of the deviation between measured RFP and UCP was 0.01 ± 0.03, 0.01 ± 0.03, and -0.01 ± 0.01mm in the X, Y, and Z directions, respectively. The deviations with offset values after the cobalt-60 source replacement (0.00 ± 0.03, -0.01 ± 0.01, and -0.01 ± 0.01mm in the X, Y, and Z directions, respectively) were significantly (p = 0.001) smaller than those before the replacement (0.02 ± 0.03, 0.02 ± 0.01, and -0.02 ± 0.01mm in the X, Y, and Z directions, respectively). The overall mean ± SD of four BBs was -0.03 ± 0.03, -0.01 ± 0.05, and 0.01 ± 0.03mm in the X, Y, and Z directions, respectively. Geometric positional accuracy was ensured to be within 0.1mm on most days over a long-term period of more than 500days.

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.

Developing Robust Safety Protocols for Radiosurgery within Patient Positioning System Framework

This paper offers a comprehensive examination of the development and implementation of advanced safety protocols in the Patient Positioning System (PPS) for radiosurgery. In an era where precision and safety are increasingly crucial in medical procedures, particularly radiosurgery, the implementation of sophisticated safety measures in PPS is vital. This research delves into the detailed design of the system, emphasizing the sensor and controller mechanisms employed. A significant focus is placed on comparing single-loop and dual-loop control systems, assessing their impact on the precision, accuracy, and repeatability of the PPS. The study showcases how dual-loop control demonstrates superior performance in these areas, leading to enhanced patient safety and treatment outcomes. Additionally, the paper discusses the integration of these safety protocols within the system’s architecture, underscoring the practical implications of these advanced measures in augmenting patient safety and treatment effectiveness.

Determination of output factor for CyberKnife using scintillation dosimetry and deep learning

Objective. Small-field dosimetry is an ongoing challenge in radiotherapy quality assurance (QA) especially for radiosurgery systems such as CyberKnifeTM. The objective of this work is to demonstrate the use of a plastic scintillator imaged with a commercial camera to measure the output factor of a CyberKnife system. The output factor describes the dose on the central axis as a function of collimator size, and is a fundamental part of CyberKnife QA and integral to the data used in the treatment planning system. Approach. A self-contained device consisting of a solid plastic scintillator and a camera was build in a portable Pelicase. Photographs were analysed using classical methods and with convolutional neural networks (CNN) to predict beam parameters which were then compared to measurements. Main results. Initial results using classical image processing to determine standard QA parameters such as percentage depth dose (PDD) were unsuccessful, with 34% of points failing to meet the Gamma criterion (which measures the distance between corresponding points and the relative difference in dose) of 2 mm/2%. However, when images were processed using a CNN trained on simulated data and a green scintillator sheet, 92% of PDD curves agreed with measurements with a microdiamond detector to within 2 mm/2% and 78% to 1%/1 mm. The mean difference between the output factors measured using this system and a microdiamond detector was 1.1%. Confidence in the results was enhanced by using the algorithm to predict the known collimator sizes from the photographs which it was able to do with an accuracy of less than 1 mm. Significance. With refinement, a full output factor curve could be measured in less than an hour, offering a new approach for rapid, convenient small-field dosimetry.

Stereotactic radiotherapy for ventricular tachycardia: A study protocol.

Currently, the standard curative treatment for ventricular tachycardia (VT) and ventricular fibrillation (VF) is radiofrequency catheter ablation. However, when the VT circuit is deep in the myocardium, the catheter may not be delivered, and a new, minimally invasive treatment using different energies is desired. This is a protocol paper for a feasibility study designed to provide stereotactic radiotherapy for refractory VT not cured by catheter ablation after at least one catheter ablation. The primary end point is to evaluate the short-term safety of this treatment and the secondary endpoint is to evaluate its efficacy as assessed by the reduction in VT episode. Cyberknife M6 radiosurgery system will be used for treatment, and the prescribed dose to the target will be 25Gy in one fraction. The study will be conducted on three patients. Since catheter ablation is the only treatment option for VT that is covered by insurance in Japan, there is currently no other treatment for VT/VF that cannot be cured by catheter ablation. We hope that this feasibility study will provide hope for patients who are currently under the stress of ICD activation. The study has been registered in the Japan Registry of Clinical Trials (jRCTs042230030).

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.

Lexicographic Optimization-Based Planning for Single and Multiple Brain Metastasis Radiosurgery with Coplanar Arcs

This study validated a not yet commercially available fully-automated lexicographic optimization planning system (LOps) for single and multiple lesions intracranial stereotactic radiosurgery (SRS). Forty-four consecutive SRS treatment plans (21 Gy/1 fx) delivered between November 2019 and August 2022 were retrospectively selected and automatically re-planned by LOps: 25 of them has 1 lesion, 13 had 2 lesions, 4 had 3 lesions, and 2 had 4 lesions. An a-priori assigned priority list, Wish List (WL), was used to define the sequential LO: 4 patient sets (tuning set) were necessary to tune each WL, for single lesion-plans (SLp) and multiple lesion-plans (MLp). While in manual plans (MP), the arc setup is freely chosen, the WL was tuned to use 2 coplanar arcs of 140° and 360° for SLp and MLp, respectively. A 0° and 90° collimator rotation were set for counter-clockwise and clockwise arcs, respectively. The fluence optimization is followed by a Monte Carlo calculation (MCc) with 1 mm-dose grid and 0.5%-statistical uncertainty. A target coverage as high as possible was requested, with at least 80% of the prescription dose covering 99% of the PTV. The main criteria for SLp approval were a brain V12Gy <10 cm3. In MLp this criterion can be overcome to get the minimum target coverage. The remaining 36 SRS plans (21 SL and 15 MLp) were automatically re-planned (testing set). Testing plans were compared in terms of dose-volume constraints, conformality, and monitor units (MUs). Statistical significance was assessed by performing the Wilcoxon test and plan delivery accuracy was verified by pre-treatment QA. WLs-tuning took 3 days. Overall manual and automatic MCc time can be estimated at 8 hours and 3 hours, respectively. Statistically significant increases in SLp and MLp target coverage (GTV_D98%: +3.0% SL, +5.7% ML, PTV_D98%: +4.4% SL, +13.4% ML) and conformity index were registered. Automatic plans showed acceptably higher median brain V12Gy (SL: MP 7.2 cm3, SLp 7.6 cm3; ML: MP 8.7 cm3, MLp 10.3 cm3). The SLp registered a lower median MU number (-4.2%) while MLp were obtained with a higher median number of MU (+9.8%). This not statistically significant difference did not affect gamma passing rates. The novel LOps produced high-quality clinically acceptable SRS SL and ML plans with coplanar arcs according to institutional-specific planning protocols, significantly reducing the overall planning time from about one working day for one MP to about 3 hours for one automatic plan. Together with comparable OAR sparing, the target coverage was significantly increased and the plan deliverability preserved.

RBE Model Based Proton Planning of Stereotactic Body Radiotherapy for Spine Metastasis: A Dosimetric Analysis

Study of proton stereotactic body radiotherapy (SBRT) for spine metastasis is limited, largely due to theorized increased risk of spinal cord injury with higher end of range RBE. Though the 1.1 RBE constant for proton beam is clinically used, data indicate that proton RBE is variable and dependent on technical-, tissue-, and patient-factors. To better understand safety of proton SBRT for spine metastasis, we performed a dosimetric analysis comparing plans delivered by photon robotic technique versus intensity modulated proton therapy (IMPT) and accounting for RBE weighted dose. A total of 9 patients with spine metastasis (3 cervical, 3 thoracic, 3 lumbar) previously treated with a frameless robotic radiosurgery system (Sunnyvale, CA) were identified. Each level contained a case with paraspinal extension, a reirradiation case, and a case with epidural extension (Bilsky grade ≥1c) as such cases in current practice often require planning target volume (PTV) under-coverage in order to meet organ at risk (OAR) dose constraints. Given these challenges, selected cases were clinically treated with 30 Gy in 5 fractions despite an institutional preference of further dose escalation. Comparative IMPT plans were generated using 30 GyE in 5 fractions and 1.1 RBE constant. IMPT plans were then made using 1.1 RBE and 45 GyE in 5 fractions: a prescription dose associated with a 2-yr local control rate of 95% on prior tumor control probability modelling. A treatment planning system was used to separately generate and optimize RBE weighted plans based on Carabe-, McNamara-, or Wedenberg models for prescription doses of 30 GyE and 45 GyE. IMPT plans used robust optimization parameters of ± 3.5% range and 2-mm setup uncertainties. PTV coverage and OAR sparing were compared using Wilcoxon signed-rank tests. PTV coverage (PTV volume receiving prescription dose) was significantly improved with IMPT at 30 GyE / 1.1 RBE (median PTV V30: 93%) compared to CK at 30 Gy (median: 88.5%, p = .02). PTV coverage was similar when comparing CK at 30 Gy with IMPT at 45 GyE / 1.1 RBE (median PTV V45: 90%, p = .23). When comparing maximum spinal cord dose (cord Dmax), there was improved OAR sparing with IMPT at 30 GyE / 1.1 RBE (median: 17.6 GyE, p = .04) and IMPT at 45 GyE / 1.1 RBE (median: 16.1 GyE, p = .04) when respectively compared to CK at 30 Gy (median: 18 Gy). No difference was seen in cord Dmax when comparing CK at 30 Gy to RBE weighted plans at 30 GyE using Carabe- (median: 17.3 GyE, p = .22), McNamara- (median: 17.4 GyE, p = .22), or Wedenberg (median: 17.0 GyE, p = .08) model. Median cord Dmax values for RBE weighted plans at 45 GyE were numerically equivalent. The average increase in variable RBE plans' maximum dose compared to fixed RBE plans was 105.3% +/- 3.5%. We report the first dosimetric analysis of proton SBRT for spine metastasis using variable RBE dose models. IMPT may provide improved target coverage and better sparing of adjacent OARs compared to CK though fixed RBE computation may underestimate maximum dose to adjacent OARs.

Implementation of a Patient Specific QA Protocol for a Novel Dedicated Stereotactic Radiosurgery Linear Accelerator

To describe the patient specific QA (Quality Assurance) protocol implemented for plan integrity verification, in stereotactic radiosurgery (SRS) and radiotherapy (SRT) treatments performed on a novel dedicated frameless image guided radiosurgery system using conical collimator, and a combination of yoked gimbals to cover near2pi solid angle. Startup and commissioning results obtained for planned vs measured dose distributions with several detectors are presented. The patient specific QA protocol includes: A) Review of the approved plan based on AAPM TG 275 report recommendations B) 1D verification using small volume ionization chambers inside an anthropomorphic head phantom C) 2D dose verification of a coronal and sagittal dose plan performed with high resolution 2D Array and respective phantom apparatus D) In-house independent MU (Monitor Unit) calculation using the same formalism of the vendor TPS (Treatment Planning Systems) RayTracing dose-calculation algorithm E) Monte Carlo based secondary dose check & plan QA. A retrospective analysis of the results of the first 15 patients treated is presented, focusing on plan complexity vs QA results. The 1D results obtained for the 15 SRS plans were within ±5% for all reported cases, with a mean percent difference of -1,25%, confirming an overall good agreement and, as expected, a partial volume effect in plans with smaller collimators. For the 2D dose verifications, with a 10% dose threshold, gamma passing rates of 97,5% (coronal) and 96,78 (sagittal) with 3% 1mm criteria, 95,1% (coronal) and 94,3% (sagittal) for 2% 1 mm criteria and 90,7% (coronal) and 90,0% (sagittal) for 1% 1mm criteria were obtained. Moreover, the results showed a correlation between lesion volume or number of collimators used with gamma passing rates. All MU verification results were within ±0,3% and provides an efficient risk mitigation approach for this new delivery technique. The verification results of the first 15 treated SRS plans confirmed point dose and planar measurements in agreement with TPS calculations, with superior results for planes with smaller lesions and fewer collimators. This also represents an integral validation of the image-based alignment system and fine treatment couch movements, as treatments are intrinsically multi-isocentric.

Difference in Radiotherapeutic Plan of HyperArc-Based and CyberKnife-Based Stereotactic Radiotherapy (SRT) Techniques for Multiple Brain Metastases

The purpose of this study is to compare the dosimetric quality and dose to surrounding normal tissue of HyperArc-based stereotactic radiotherapy (SRT) technique with a frameless robotic radiosurgery system for patients with multiple brain metastases. Nineteen patients with multiple brain metastases (2-5 lesions) treated in our center were enrolled. The prescribed dose was 2100 cGy to 3250 cGy in three to five fractions. In order to determine the dosimetric quality, we compared the conformity index (CI), Gradient radius (GR), homogeneity index (HI), dose distribution in planning target volume, and dose to several organs at risk (OARs). All of the data were compared using pair-T test. Both planning systems have prescribed dose coverage to GTV and PTV with no significant difference (P = 0.243; P = 0.312). The conformity index (CI), and homogeneity index (HI) were 1.27 ±0.022, and 1.08 ±0.006, respectively, for HyperArc plan and 1.76 ±0.065 and 1.22 ±0.009, respectively, for the CK plan (both, P< 0.001). The Gradient radius (GR) was 0.732 ±0.056 cm for HyperArc plan and 0.847 ±0.762 cm for CK plan (P = 0.002). These indicated that HyperArc plan had better CI, HI, and GR when compared to CK plan. Maximum dose to brainstem for HyperArc and CK plans were 485.1 ±128.65 and 723.6 ±126.93 cGy, respectively (P < 0.001). Moreover, HyperArc plan had less mean dose to optic chiasm, bilateral eyes, bilateral lens, and bilateral optic nerves (all, P < 0.05). Brain V5, V12, V24 were all much smaller in HyperArc plan (all, P < 0.05), indicating that HyperArc plan delivered less dose to normal brain tissue. For patients with two to five brain metastases, HyperArc-based SRT provide excellent dosimetric quality and less dose to normal tissue.

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

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. 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). 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. 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.

Comparison of dynamic tumor tracking error measurement methods for robotic radiosurgery.

Dynamic tumor motion tracking is used in robotic radiosurgery for targets subject to respiratory motion, such as lung and liver cancers. Different methods of measuring tracking error have been reported, but the differences among these methods have not been studied, and the optimal method is unknown. The purpose of this study was to assess and compare tracking errors encountered with individual patients using different evaluation methods for method optimization. We compared the beam's eye view (BEV), machine learning (ML), log (addition error: AE), and log (root sum square: RSS) methods. Log (AE) and log (RSS) were calculated from log files. These tracking errors were compared, and the optimal evaluation method was ascertained. A t-test was performed to evaluate statistically significant differences. Here, the significance level was set at 5%. The mean values of BEV, log (AE), log (RSS), and ML were 2.87, 3.91, 2.91, and 3.74mm, respectively. The log (AE) and ML were higher than BEV (p<0.001), and log (RSS) was equivalent to the BEV, suggesting that the log (RSS) calculated with the log file method can substitute for the BEV calculated with the BEV method. As RSS error calculation is simpler than BEV calculation, using it may improve clinical practice throughput. This study clarified differences among three tracking error evaluation methods for dynamic tumor tracking radiotherapy using a robotic radiosurgery system. The log (RSS) calculated by the log file method was found to be the best alternative to BEV method, as it can calculate tracking errors more easily than the BEV method.

Stereotactic radiotherapy for ventricular tachycardia: A study protocol

Background: Currently, the standard curative treatment for ventricular tachycardia (VT) and ventricular fibrillation (VF) is radiofrequency catheter ablation. However, when the VT circuit is deep in the myocardium, the catheter may not be delivered, and a new, minimally invasive treatment using different energies is desired. Methods: This is a protocol paper for a feasibility study designed to provide stereotactic radiotherapy for refractory VT not cured by catheter ablation after at least one catheter ablation. The primary end point is to evaluate the short-term safety of this treatment and the secondary endpoint is to evaluate its efficacy as assessed by the reduction in VT episode. Cyberknife M6 radiosurgery system will be used for treatment, and the prescribed dose to the target will be 25Gy in one fraction. The study will be conducted on three patients. Conclusion: Since catheter ablation is the only treatment option for VT that is covered by insurance in Japan, there is currently no other treatment for VT/VF that cannot be cured by catheter ablation. We hope that this feasibility study will provide hope for patients who are currently under the stress of ICD activation. Trial registration: The study has been registered in the Japan Registry of Clinical Trials (jRCTs042230030).