CyberKnife System Research Articles

The Role of Ultrasound-Based Monitoring of Bladder Volume in Patients with Prostate Cancer during CyberKnife Stereotactic Radiosurgery

(1) Background: For patients irradiated due to prostate cancer, monitoring of bladder volume (BV) is crucial for accuracy of radiation delivery and minimizing exposure to surrounding healthy tissues. Due to the limited imaging capabilities of the CyberKnife system, ultrasound imaging plays a vital role in the monitoring of bladder filling. (2) Methods: A study was carried out in 142 prostate cancer patients treated with the CyberKnife system. Bladder ultrasound (US) was performed before each RTH session to assess real BV (rBV). The double US assessment of rBV was performed by two independent operators or a single operator during 177 and 495 RTH sessions, respectively, giving, in total, 1344 BV assessments. (3) Results: The mean BV in the first and second US assessment was 214.7 mL and 218.1 mL, respectively, while the mean planning bladder volume (pBV) was 340.8 mL. A pBV was significantly higher than an rBV. The mean difference between the US and CT assessment of BV was the smallest in the 100–349 mL group and the largest in the group above 349 mL. The Passing–Bablok regression results confirmed the reliability of the ultrasound (US) measurements. (4) Conclusions: The introduction of US-based BV assessment in patients irradiated due to prostate cancer using CyberKnife seems to be a crucial element in controlling the reproducibility of the treatment plan and should be a standard procedure. The pBV should be within the range of 200–300 mL. The US examination prior to CT scanning for planning is recommended to ensure the optimal range of BV for CT.

Calculating Optic Nerve Planning Organ at Risk Volume Margins for Stereotactic Radiosurgery Using Optic Nerve Motion determined using MRI.

The combination of sharp dose gradients in stereotactic radiosurgery (SRS) and minute optic nerve motion may significantly increase dose to the optic nerves when treating perioptic lesions. The aim of this study was to calculate optic nerve planning organ at risk volume (PRV) margins for CyberKnife SRS treatment planning. MRI scans were taken of 10 healthy volunteers looking left, right, up, down, and straight ahead to measure optic nerve motion. The measured optic nerve motion and the uncertainties in the technical accuracy of CyberKnife were used to calculate optic nerve PRV margins. Two optic nerve PRV margins were calculated: a non-isotropic margin of mL/R,PRV=3mm, mSup/Inf,PRV=2mm and mAnt/Post,PRV=1mm which considers the full range of motion measured in a worst case scenario; and an isotropic margin of mPRV=1mm which considers a scenario where patients are asked to look neutrally during imaging and treatment. Applying these PRVs to 8 historical sphenoid wing meningioma CyberKnife plans showed tolerance levels may be exceeded due to optic nerve motion. Optic nerve PRV margins may be needed in CyberKnife planning to reduce risk to the optic nerves. The use of a mPRV=1mm PRV to account for organ motion, along with instructing patients to hold their gaze neutrally during imaging and treatment, may be a suitable organ sparing strategy. Measured optic nerve motion and the technical accuracy of the CyberKnife system have been used to calculate optic nerve PRV margins.

Treatment for paraganglioma with stereotactic radiotherapy.

Paragangliomas (PG) are rare neoplasms of neuroendocrine origin that tend to be highly vascularized, slow-growing, and usually sporadic. To date, common treatment options are surgical resection (SR), with or without radiation therapy (RT), and a watch-and-wait approach. To evaluate the local control and effectiveness of exclusive fractionated stereotactic RT (FSRT) treatment in unresectable PG (uPG). We retrospectively evaluated patients with uPG (medically inoperable or refused SR) treated with FSRT with a Cyberknife System (Accuray Incorporated, Sunnyvale, California). Toxicity and initial efficacy were evaluated. From May 2009 to January 2023, 6 patients with a median age of 68 (range 20-84) were treated with FSRT. The median delivered dose was 21 Gy (range 20-30 Gy) at a median isodose line of 75.5% (range 70%-76%) in 4 fractions (range 3-5 fractions). The median volume was 13.6 mL (range 12.4-65.24 mL). The median cumulative biological effective dose and equivalent dose in 2-Gy fractions were 70 Gy and 37.10 Gy respectively. Site of origin involved were the timpa-nojugular glomus (4/6), temporal bone, and cervical spine. In 1 of the 6 patients, the follow-up was insufficient; 5 of 6 patients showed a 5-year overall survival and 5-year progression-free survival of 100%. We observed negligible toxicities during and after RT. The majority of patients showed stable symptoms during follow-up. Only 1 patient developed spine metastases. Our preliminary results on this small cohort of patients suggest that FSRT could be an effective and safe alternative to SR.

Mid-term outcomes after stereotactic arrhythmia radioablation for refractory ventricular tachycardia

Abstract Introduction stereotactic arrhythmia radioablation (STAR) is used as a rescue treatment for refractory ventricular tachycardia (VT) originating from unreachable myocardial substrate following unsuccessful radiofrequency catheter ablation (RFCA). The mid-term outcomes of STAR, however, remain poorly known. Objective to report the mid-term efficacy and safety outcomes in our series of 21 patients (pts) treated by STAR over 6 years. Methods Inclusion of consecutive pts treated by STAR with a Cyberknife system between 2017 and 2023. 3D-electroanatomical maps (EAM) of the VT substrate during unsuccessful RFCA were used to delineate the planned target volumes (PTV) on a 4D CT scan. Patients were followed up at least every 6 months by echocardiography and ICD interrogation at the outpatient clinic. Results 21 pts [16 (76 %) male, age 66±8 years] with a mean LVEF of 40±15% were included. The underlying substrate was ischemic in 7 (33 %); non-ischemic dilated in 7 (33 %); inflammatory in 4 (19%); hypertrophic in 1 (5%); neoplasic in 1 (5%); and malignant mitral valve prolapse in 1 (5%). A dose of 21±2 Gray was delivered to the PTV (26 ml, IQR 18-43 ml). After a median follow-up of 39 [IQR, 14-48] months, 12 pts (57%) remained in stable condition, 1 (5%) underwent a heart transplantation, 1 (5%) a left ventricular assistance device, 1 (5%) was in an incessant slow VT and 6 (29%) pts died (3 from end stage heart failure). 15 (71%) pts presented VT recurrences [7 (33%) ATPs; 3 (14%) shocks; 4 (19%) VT storm and 1 (5%) with a well-tolerated slow VT (100 bpm) with an LVAD till transplantation, of whom 9 (43%) required redo RFCA. The median value of total ventricular arrhythmic burden (defined as any arrhythmia requiring ICD therapies) decreased significantly from 31 (IQR, 4-100) to 7 (IQR, 1-23) (p<0.05); for nsVT from 57 (IQR, 1.5- 1196) to 41 (IQR, 0.5-584) (p ns); or ICD shocks from 1.5 (IQR, 0-5.5) to 0 (IQR, 0-2) (p<0.05); for ATPs from 21 (IQR, 2.5-94) to 4 (IQR, 0.5-13) (p<0.05). Figure 1 shows a graphic representation of arrhythmic burden before and after STAR. Conclusion in this cohort of highly selected pts with refractory VT, STAR significantly reduced the arrhythmic burden by a factor of 4 over a 3-year follow-up. Death rate remained high (29%), mostly by terminal heart failure. Nevertheless, a high proportion of pts had VT recurrences that were successfully managed by redo RFCA.VT burden before and after STAR

Primary Stereotactic Body Radiotherapy for Spinal Bone Metastases From Lung Adenocarcinoma

ObjectiveThis study aimed to assess the results of primary stereotactic body radiotherapy (SBRT) for spinal bone metastases (SBM) originating from lung adenocarcinoma (ADC). We considered the revised Tokuhashi score (rTS), Spinal Instability Neoplastic Score (SINS), and genetic characteristics. MethodsWe examined adult patients with lung ADC who underwent primary SBRT (using the CyberKnife System) for SBM between March 2012 and January 2023. ResultsWe analyzed data from 99 patients, covering 152 SBM across 194 vertebrae. The overall local control (LC) rate was 77.6% for SBM from lung ADC, with a LC rate of 90.7% at 1 year. The median period for local progression (LP) occurrence was recorded at 10.0 (3-52) months. Additionally, Asian patients demonstrated higher LC rates than White patients. Utilizing the rTS and SINS as predictive tools, we revealed that a poor survival prognosis and an unstable spinal structure were associated with increased rates of LP. Furthermore, the presence of osteolytic bone destructions and pain complaints were significantly correlated with the occurrence of LP. In the cohort of this study, 108 SBM underwent analysis to determine the expression levels of programmed cell death ligand 1 (PD-L1). Additionally, within this group, 60 showed mutations in the epidermal growth factor receptor (EGFR) alongside PD-L1 expression. Nevertheless, these genetic differences did not result in statistically significant differences in the LC rate. ConclusionThe one-year LC rate for primary SBRT targeting SBM from lung ADC stood at 90.7%, particularly with the use of the CyberKnife System. Patients achieving LC exhibited significantly longer survival times compared to those with LP.

Initial evaluation of the performance of novel inorganic optical fibre dosimeters using the CyberKnife system

Initial evaluation of the performance of novel inorganic optical fibre dosimeters using the CyberKnife 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.

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.

Optimization of stereotactic radiotherapy (SRT) planning for brain metastases from lung cancer by Cyberknife system: reducing dose distribution inner ear.

Objective: Through retrospective statistical analysis of radiation distribution in inner ear avoidance for brain metastases from lung cancer by the CyberKnife (CK) system, it can provide a reference for stereotactic radiotherapy (SRT) planning and treatment optimization. Methods: Computed tomography/magnetic resonance imaging data of 44 patients with one brain metastases lesion from lung cancer were used to re-plan and analyze, who had been treated by CK system from April 2021 to April 2022. The prescribed doses of 14-30 Gy in 1-3 fractions was simultaneously delivered to the metastatic lesions. The SRT plans for the same patients were replaned under with and without inner ear avoidance setting. The plan parameters and dose distribution differences were compared between plans. Results: All plans met the dose restrictions. There were no significant differences in the coverage (Coverage), conformity index (CI), mean dose (Dmean), the maximum dose (Dmax) and minimum dose (Dmin) of planning target volume (PTV). With inner ear avoidance setting, the Dmax and Dmean of inner ear area decreased by 13.76% and 12.15% (p<0.01), respectively. The total number of machine nodes and monitor units (MU) increased by 4.63% and 1.06%. Conclusions: During the SRT plan designing for brain metastases from lung cancer, the dose distribution in inner ear area could be reduced by avoidance setting, and the patient's hearing would be well protected.

Evaluation of intracranial stereotactic treatment plans: a comparison study of CyberKnife and TrueBeam systems

Abstract Background: Stereotactic radiotherapy (SRT) for patients with intracranial tumours are delivered using a dedicated platform or a conventional linear accelerator with a flattening filter-free beam. Materials and methods: This study compares treatment plans with intracranial tumours. A total of 29 patients were treated on CyberKnife and planned using the Accuray Precision. The same structure sets ws then exported to Varian Eclipse, and plans were made using a 6 MV FFF beam. Both plans were compared for parameters of target coverage, homogeneity index (HI), new conformity index (nCI), gradient index, selectivity index (SI), volumetric and OAR doses. Results: The treatment plans made for CyberKnife exhibit better results in terms of nCI (1·168 ± 0·08 versus 1·173 ± 0·077), SI (0·885 ± 0·05 versus 0·877 ± 0·05) and GI (3·64 ± 0·5 versus 4·45 ± 1·25), while HI values are better for TrueBeam. For OAR doses, in 65·5% and 72% of treatment plans, brainstem and optic pathways received lower doses on CyberKnife, respectively. In terms of dose spillage, Truebeam plans are better for very low doses (V5%), while for V10%, V20% and V50% CyberKnife plans are better. Conclusion: CyberKnife is a better modality for the delivery of SRS/SRT to intracranial tumours except for dose homogeneity where TrueBeam offered better results.

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).

Dosimetric impact of rotational errors in trigeminal neuralgia radiosurgery using CyberKnife.

Trigeminal neuralgia (TN) can be treated on the CyberKnife system using two different treatment delivery paths: the general-purpose full path corrects small rotations, while the dedicated trigeminal path improves dose fall-off but does not allow rotational corrections. The study evaluates the impact of uncorrected rotations on brainstem dose and the length of CN5 (denoted as Leff) covered by the prescription dose. A proposed model estimates the delivered dose considering translational and rotational delivery errors for TN treatments on the CyberKnife system. The model is validated using radiochromic film measurements with and without rotational setup error for both paths. Leff and the brainstem dose is retrospectively assessed for 24 cases planned using the trigeminal path. For 15 cases, plans generated using both paths are compared for the target coverage and toxicity to the brainstem. In experimental validations, measured and estimated doses agree at 1%/1mm level. For 24 cases, the treated Leff is 5.3±1.7mm, reduced from 5.9±1.8mm in the planned dose. Constraints for the brainstem are met in 23 cases for the treated dose but require frequent treatment interruption to maintain rotational corrections<0.5° using the trigeminal path. The treated length of CN5, and plan quality metrics are similar for the two paths, favoring the full path where rotations are corrected. We validated an analytical model that can provide patient-specific tolerances on rotations to meet plan objectives. Treatment using the full path can reduce treatment time and allow for rotational corrections.

A dosimetric study comparing Cyberknife and LINAC-based stereotactic radiotherapy or radiosurgery treatments

BackgroundWhile Gamma Knife and CyberKnife are commonly used for Stereotactic radiosurgery (SRS), their availability is limited. In contrast, linac-based SRS using linear accelerators (linacs) is more accessible and widely used. PurposeOur study aims to evaluate Linac-based SRS with the Varian RapidArc technique for treating brain metastases. The primary objective is to compare the quality of treatment plans between RapidArc and CyberKnife modalities. Materials & methodsTen patients with a single brain metastasis were treated using the CyberKnife machine with prescribed doses ranging from 18 to 25 Gy. Treatment plans utilized Multiplan software for CyberKnife and Eclipse for RapidArc plans. The plans were evaluated based on dose metrics for the target and critical structures, treatment time, and brain tissue volume. ResultsBoth techniques provided acceptable Gross tumor volume coverage and organs at risk sparing. CyberKnife delivered a higher integral dose to the Gross tumor volume and brain tissues compared to RapidArc (p < 0.05). The conformity index was slightly better in RapidArc (1.14 ± 0.25) compared to CyberKnife (1.22 ± 0.12), but the difference was not statistically significant (p > 0.05). However, CyberKnife exhibited a better dose gradient index (4.52 ± 0.99) compared to RapidArc (8.6 ± 7.28). The treatment time in RapidArc was significantly lower compared to CyberKnife, p < 0.05. RapidArc demonstrated lower minimum and maximum doses to some organs at risk, although some differences were not statistically significant. For normal brain tissues, V12Gy was significantly lower with RapidArc (3.27 ± 2.92) compared to CyberKnife (4.09 cc ± 3.27). ConclusionThe RapidArc technique is capable of achieving similar treatment quality as CyberKnife systems for SRS treatments. It offers improved target coverage, higher conformity, and homogeneous dose distribution within the Planning target volume if homogeneity is desirable in some intuitions or cases. In addition, it can also achieve low integral doses to organs at risk and brain tissues.

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.

Stereotactic body radiotherapy with CyberKnife® System for low- and intermediate-risk prostate cancer: clinical outcomes and toxicities of CyPro Trial.

Stereotactic body radiotherapy (SBRT) of 35-36.25 Gy in five fractions with the CyberKnife System yields excellent control with low toxicity in low-intermediate-risk prostate cancer patients. We found no differences in biochemical control and overall survival in relation to dose. There were no significant differences in toxicity or quality of life between the two groups. Stereotactic body radiotherapy (SBRT) is an emerging therapeutic approach for low- and intermediate-risk prostate cancer. We present retrospective data on biochemical control, toxicity, and quality of life of CyPro Trial. A total of 122 patients with low- and intermediate-risk prostate cancer were treated with the CyberKnife System at a dose of 35 Gy or 36.25 Gy in five fractions. Biochemical failure (BF)/biochemical disease-free survival (bDFS) was defined using the Phoenix method (nadir + 2 ng/ml). Acute/late rectal and urinary toxicities were assessed by the Radiation Therapy Oncology Group (RTOG) toxicity scale. Quality of life (QoL) was assessed by the European Organisation for Research and Treatment of Cancer (EORTC) QLQ C30 and PR25. International Erectile Function Index-5 (IIEF5) and International Prostate Symptom Score (IPSS) questionnaires were administered at baseline, every 3 months after treatment during the first years, and then at 24 months and 36 months. The 1-, 2-, and 5-year DFS rates were 92.9%, 92.9%, and 92.3%, respectively, while the 1-, 2-, and 5-year bDFS rates were 100%, 100%, and 95.7%, respectively. With regard to risk groups or doses, no statistically significant differences were found in terms of DFS or bDFS. Grade 2 urinary toxicity was acute in 10% and delayed in 2% of patients. No Grade 3 acute and late urinary toxicity was observed. Grade 2 rectal toxicity was acute in 8% and late in 1% of patients. No Grade 3-4 acute and late rectal toxicity was observed. Grade 2 acute toxicity appeared higher in the high-dose group (20% in the 36.25-Gy group versus 3% in the 35-Gy group) but was not statistically significant. Our study confirms that SBRT of 35-36.25 Gy in five fractions with the CyberKnife System produces excellent control with low toxicity in patients with low-intermediate-risk prostate cancer. We found no dose-related differences in biochemical control and overall survival. Further confirmation of these results is awaited through the prospective phase of this study, which is still ongoing.

Stereotactic reirradiation with CyberknifeR for locally recurrent prostate cancer, long-term toxicity and clinical outcomes from a monocentric cohort.

Up to 47% of patients with localized prostate cancer (PCa) treated with radiotherapy (EBRT) eventually develop local recurrence. To date, no clear consensus exists on optimal management. A growing body of interest supports the use of stereotaxic re-irradiation (rSBRT), with promising oncological outcomes and low toxicity profile. We collected a single-center case series of locally recurrent PCa who underwent re-irradiation after a previous course of postoperative or definitive radiotherapy. Data from 101 patients treated at our institution for locally recurrent PCa from June 2012 to June 2021 were retrospectively collected. Patients underwent rSBRT with CyberKnife system (Accuray Inc., Sunnyvale, CA, USA), delivered to intraprostatic or macroscopic recurrences within the prostate bed, for a total dose of 30Gy in 5 fractions. All patients received prior EBRT. The median EQD2 total dose was 75.0Gy (range, 60-80Gy). Thirty-two (32%) patients were receiving androgen deprivation therapy (ADT) after prior biochemical recurrence. After a median follow-up of 57.8months, BR occurred in 55 patients (54.5%), with a median BR-free survival (BRFS) of 40.4months (95% C.I. 34.3-58.3). Thirty-two patients (31.7%) developed metastatic disease, with a median metastasis-free survival (MFS) not reached. PSA ≥ 2.5ng/ml and ADT were associated with worst BRFS (26.06 vs. 39.3months, p = 0.03 and 22.7 vs. 27months, p = 0.01, respectively). Castration-resistant status and ADT were found to be predictive of worst MFS (34.1 vs. 50.5months, p = 0.02 and 33.5 vs. 53.1months, p = 0.002, respectively). Concomitant ADT was confirmed as an independent factor for MFS (HR 4.8, 95% CI 1.5-10.6, p = 0.007). No grade > /2 adverse were recorded. After almost 5years of follow-up, with a median BRFS of 40.4months and no grade ≥ 2 AEs, CyberknifeR rSBRT proved effective and safe in a cohort of 101 patients affected by locally recurrent PCa.

Predicting successful clinical candidates for fiducial-free lung tumor tracking with a deep learning binary classification model.

The CyberKnife system is a robotic radiosurgery platform that allows the delivery of lung SBRT treatments using fiducial-free soft-tissue tracking. However, not all lung cancer patients are eligible for lung tumor tracking. Tumor size, density, and location impact the ability to successfully detect and track a lung lesion in 2D orthogonal X-ray images. The standard workflow to identify successful candidates for lung tumor tracking is called Lung Optimized Treatment (LOT) simulation, and involves multiple steps from CT acquisition to the execution of the simulation plan on CyberKnife. The aim of the study is to develop a deep learning classification model to predict which patients can be successfully treated with lung tumor tracking, thus circumventing the LOT simulationprocess. Target tracking is achieved by matching orthogonal X-ray images with a library of digital radiographs reconstructed from the simulation CT scan (DRRs). We developed a deep learning model to create a binary classification of lung lesions as being trackable or untrackable based on tumor template DRR extracted from the CyberKnife system, and tested five different network architectures. The study included a total of 271 images (230 trackable, 41 untrackable) from 129 patients with one or multiple lung lesions. Eighty percent of the images were used for training, 10% for validation, and the remaining 10% for testing. For all five convolutional neural networks, the binary classification accuracy reached 100% after training, both in the validation and the test set, without any falseclassifications. A deep learning model can distinguish features of trackable and untrackable lesions in DRR images, and can predict successful candidates for fiducial-free lung tumortracking.

Evaluation of computed tomography metal artifact and CyberKnife fiducial recognition for novel size fiducial markers.

This study aimed to compare fiducial markers used in CyberKnife treatment in terms of metal artifact intensity observed in CT images and fiducial recognition in the CyberKnife system affected by patient body thickness and type of marker. Five markers, ACCULOC 0.9mm×3mm, Ball type Gold Anchor (GA) 0.28mm×10mm, 0.28mm×20mm, and novel size GA 0.4mm×10mm, 0.4mm×20mm were evaluated. To evaluate metal artifacts of CT images, two types of CT images of water-equivalent gels with each marker were acquired using Aquilion LB CT scanner, one applied SEMAR (SEMAR-on) and the other did not apply this technique (SEMAR-off). The evaluation metric of artifact intensity (MSD ) which represents a variation of CT values were compared for each marker. Next, 5, 15, and 20cm thickness of Tough Water (TW) was placed on the gel under the condition of overlapping the vertebral phantom in the Target Locating System, and the live image of each marker was acquired to compare fiducial recognition. The mean MSD of SEMAR-off was 78.80, 74.50, 97.25, 83.29, and 149.64 HU for ACCULOC, GA0.28mm×10mm, 20mm, and 0.40mm×10mm, 20mm, respectively. In the same manner, that of SEMAR-on was 23.52, 20.26, 26.76, 24.89, and 33.96 HU, respectively. Fiducial recognition decreased in the order of 5, 15, and 20cm thickness, and GA 0.4×20mm showed the best recognition at thickness of 20cm TW. We demonstrated the potential to reduce metal artifacts in the CT image to the same level for all the markers we evaluated by applying SEMAR. Additionally, the fiducial recognition of each marker may vary depending on the thickness of the patient's body. Particularly, we showed that GA 0.40×20mm may have more optimal recognition for CyberKnife treatment in cases of high bodily thickness in comparison to the other markers.

Rare solitary pituitary metastasis of maxillary ameloblastic carcinoma: illustrative case.

Ameloblastic carcinoma (AC) is a rare odontogenic carcinoma with histological features resembling ameloblastoma. Metastasis to distant organs and direct expansion into the skull base structures are associated with a poor clinical outcome. This rare case of AC metastasis to the pituitary gland presented without local recurrence at the primary focus of the maxilla. A 47-year-old man had a 2-year history of AC in the right maxilla. Computed tomography for his regular checkup incidentally demonstrated pituitary tumor, rapidly growing over 2 months. He presented with the recent onset of panhypopituitarism and visual field defect. Magnetic resonance imaging showed a large, irregularly shaped intrasellar and suprasellar lesion with chiasmal compression. Endoscopic endonasal transsphenoidal surgery was performed for decompression of the optic apparatus to avoid intracranial spread. Histopathology confirmed metastatic AC, and a genetic panel test confirmed BRAF V600E mutation. Stereotactic radiotherapy (SRT) with the CyberKnife system was administered to the residual tumor. Remarkable tumor shrinkage was obtained, and panhypopituitarism was resolved 12 months later. A multidisciplinary treatment strategy including maximal safe resection to avoid dissemination in combination with SRT may be crucial for local control with the preservation of pituitary and visual functions in patients with solitary pituitary metastatic AC.

Evaluation of a planar diode matrix for SRS patient-specific QA in comparison with GAFchromic films.

We validate the routine use of a two-dimensional (2D) diode matrix for patient specific pre-treatment verification for Cyberknife (CK) stereotactic radiosurgery and to compare it with film dosimetry. A total of 46 patients were selected according to the most frequent diseases treated at our institution with the CK system, that is, brain metastases, meningiomas, spine metastases, and prostate tumors. All cases were evaluated with GAFChromic EBT-3 films and SRS MapCHECK for Fixed cone, IRIS, and MLC collimators of the CK. The highest mean passing rate was observed for the SRS MapCHECK system compared to films. In order to assess if the two techniques provide statistically different results, a Wilcoxon Signed-Rank non-parametric test was performed (p<0.05) and we found gamma values significantly lower for EBT-3 films with respect to the SRS MapCHECK. We noticed a moderately significant association between the two techniques using Spearman's rank correlation coefficient (rs>0.4). We also performed the Bland-Altman statistical method: less than 5% of the differences resulted outside the range (mean±1.96×SD), so the two methods can be considered interchangeable within the combined inaccuracy. The use of SRS MapCHECK for CK patient specific quality assurance (QA) is feasible for a variety of clinical districts and could be reliably used as a replacement for radiochromic films.