Radiosurgery System Research Articles

Comparison of Single and Multiple Treatment Plans Made in CyberKnife® Radiosurgery System on Phantom

While the use of CyberKnife® radiosurgery systems is increasing, the choice of treatment plan is also important. In this study, it was aimed to determine the more advantageous application by comparing the irradiation of all metastases at once and the protocols of irradiation of metastases separately in multiple brain metastases. For this, on an entirely new head phantom; 6 brain metastases and 3 critical organs, including the spinal cord, brain stem, and chiasm, were determined over the spaces where the dosimeters were placed. Computed tomography (CT) images of the head phantom were taken and these 6 tumors and 3 critical organs were drawn (contouring) on the image. In the treatment planning system, the dose we wanted to give was written and irradiation plans were created to be done separately with a single irradiation. Luminescence (OSL) dosimeters with BeO optical excitation were removed from the phantom after each irradiation and the count value obtained from the dosimeter reader device was recorded. Homogeneity index (HI), conformity index (CI), new conformity index (nCI), duration of treatment, and gradient index (GI) values of irradiation at one time and separately were compared. While it was found that irradiation of tumors with a separate treatment plan was more advantageous in terms of conformity index (CI), new conformity index (nCI), homogeneity index (HI), and coverage values, it was seen that a single plan was more suitable in terms of gradient index and duration.

Commissioning and clinical evaluation of the IDENTIFYTM surface imaging system for frameless stereotactic radiosurgery.

To commission and assess the clinical performance of a new commercial surface imaging (SI) system by analyzing intra-fraction motion from the initial cohort of patients treated with frameless stereotactic radiosurgery (fSRS). The IDENTIFYTM SI system was commissioned for clinical use on an Edge (Varian Medical Systems, Palo Alto, CA) linear accelerator. All patients who received intracranial radiotherapy with HyperArcTM (Varian Medical Systems, Palo Alto, CA) were immobilized with the EncompassTM (Qfix, Avondale, PA) thermoplastic mask and monitored for intra-fraction motion with SI. IDENTIFYTM log files were correlated with trajectory log files to correlate treatment parameters with SI-reported offsets. IDENTIFYTM reported offsets were correlated with gantry and couch angles to assess system performance for obstructed and clear camera field of view. Data were stratified by race to evaluate performance differences due to skin tone. All commissioning data were found to meet recommended tolerances. IDENTIFYTM was used to monitor intra-fraction motion on 1164 fractions from 386 patients. The median magnitude of translational SI reported offsets at the end of treatment was 0.27mm. SI reported offsets were shown to increase when camera pods are blocked by the gantry with larger increases seen at non-zero couch angles. With camera obstruction, the median magnitude of the SI reported offset was 0.50 and 0.80mm for White and Black patients, respectively. IDENTIFYTM performance during fSRS is comparable to other commercially available SI systems where offsets are shown to increase at non-zero couch angles and during camera pod blockage.

Cosmetic Outcome and Toxicity After Stereotactic Accelerated Partial Breast Irradiation in Early Breast Cancer: A Prospective Observational Cohort Study

The aim of this work was to prospectively evaluate the toxicity and cosmetic outcomes of 5-fraction, stereotactic, accelerated partial breast irradiation (APBI). This prospective observational cohort study enrolled women who underwent APBI for invasive carcinoma or carcinoma in situ of the breast. APBI was delivered using a CyberKnife M6 robotic radiosurgery system at 30 Gy in 5 nonconsecutive, once-daily fractions. Women undergoing whole breast irradiation (WBI) were also enrolled for comparison. Patient-reported and physician-assessed adverse events were recorded. Breast fibrosis was measured using a tissue compliance meter, and breast cosmesis was assessed using BCCT.core (an automatic, computer-based software). Outcomes were collected until 24 months posttreatment according to the study protocol. In total, 204 patients (APBI, n=103; WBI, n=101) were enrolled. Regarding patient-reported outcomes, the APBI group reported significantly less skin dryness (6.9% vs 18.3%; P=.015), radiation skin reaction (9.9% vs 23.5%; P=.010), and breast hardness (8.0% vs 20.4%; P=.011) at 6 months than the WBI group. On physician assessment, the APBI group had significantly less dermatitis at 12 months (1.0% vs 7.2%; P=.027) than the WBI group. Any severe toxicities after APBI were rare in patient-reported outcomes (score ≥3, 3.0%) and physician assessments (grade ≥3, 2.0%). In the uninvolved quadrants, measured fibrosis in the APBI group was significantly lower than that in the WBI group at 6 (P=.001) and 12 (P=.029) months but not at 24 months. In the involved quadrant, measured fibrosis in the APBI group was not significantly different from that in the WBI group at any time. Cosmetic outcomes in the APBI group were mostly excellent or good (77.6%) at 24 months, and there was no significant cosmetic detriment from the baseline. Stereotactic APBI was associated with less fibrosis in the uninvolved breast quadrants than WBI. Patients showed minimal toxicity and no detrimental effects on cosmesis after APBI.

Abstract PD3-06: Robotic Stereotactic APBI for Early-Stage Breast Cancer: 2-year Outcomes of a Prospective Multi-Institutional Trial

Abstract Purpose: Outcomes following adjuvant accelerated partial breast irradiation (APBI) in select women with early-stage breast cancer are comparable to whole breast irradiation. Robotic stereotactic accelerated partial breast irradiation (RSAPBI) with fiducial tracking is an attractive treatment option, but limited outcomes data are available for this approach. We report 2-year outcomes for a prospective multi-institutional trial treating select women with RSAPBI. Materials and Methods: Post-menopausal women with DCIS and Stage IA breast cancer were treated over a five-year period extending from November 2015 to November 2020 and were followed for a minimum of 18 months. Treatments were delivered with a robotic radiosurgery system. Four gold fiducials were implanted around the lumpectomy cavity prior to the start of treatment for tumor bed delineation and target tracking. The CTV was defined as the lumpectomy cavity with a uniform 5-15 mm expansion confined to the breast tissue and the PTV was defined as the CTV with a 0-5 mm uniform expansion. The PTV was prescribed 30 Gy in 5 fractions. Disease status assessments were completed at 4 weeks, 3 months, 6 months, 12 months, 18 months, 24 months and yearly intervals thereafter for five years. Results: Eighty-one patients (median age 68 years) with hormone receptor-positive tumors were treated over a median 9 days (range, 5-15). Sixty-eight women had invasive ductal carcinoma (84%) and thirteen had DCIS (16%). The median treated PTV was 108 cm3 (IQR 66-156) and the median prescription isodose line was 81% (IQR 79-83). The median CTV expansion was 10 mm (range 5-10) and the median PTV expansion was 3 mm (range 0-5). At a median follow up of 2 years there was one new ipsilateral breast tumor diagnosed. There were no local, regional, or distant treatment failures. Conclusions: Two-year results suggest that RSAPBI with fiducial tracking is an effective technique for the adjuvant treatment of post-menopausal women with hormone receptor-positive early-stage breast cancer. Additional follow-up is planned to confirm this preliminary finding. Citation Format: Jonathan M. Cantalino, David D’Ambrosio, Arica Hirsch, Brian Collins, Malika Danner, Dawn Matsanka, Sonali Rudra, Simeng Suy, Sean Collins, Monica Pernia Marin, Michael Good, Jing Feng, John Lamond, Deborah Markiewicz, Rachelle Lanciano, Olusola Obayomi-Davies. Robotic Stereotactic APBI for Early-Stage Breast Cancer: 2-year Outcomes of a Prospective Multi-Institutional Trial [abstract]. In: Proceedings of the 2022 San Antonio Breast Cancer Symposium; 2022 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2023;83(5 Suppl):Abstract nr PD3-06.

Benchmarking a New Circular Cone-based Radiosurgery System against Clinically Tested Radiosurgery System on the same Novel Digital Linear Accelerator Platform.

To examine the dosimetric characteristics of circular cones, the accuracy of dose modeling and overall treatment delivery of two radiosurgery systems integrated on a linear accelerator (Linac). The dosimetric characteristics of circular cones (4-17.5 mm) from Varian (VC) and BrainLAB (BLC) were measured for 6 MV flattening filter free beam from Edge linac using stereotactic field diode and 0.65 cc ionization chamber following established protocols. The Eclipse and iPlan modeled dose distribution for VCs and BLCs were validated with EBT3-film measurement. End-to-end tests were performed using stereotactic phantom having PTW 60008 diode connected to a Dose-1 electrometer. The depth at dose maximum, TRP2010 and dose at 10cm depth of the same size VC and BLC agree within ± 0.7 mm, ± 0.71% and ± 0.81% respectively. Full width at half maximum (FWHM) of any cone beyond 15 mm depth increases at 1% of nominal cone size per 10 mm depth. The penumbra of 4mm and 17.5mm VC at 15 mm depth was 1.1 mm and 1.50 mm. At 300 mm depth, penumbra increased by around 0.4 mm for 4 mm cone and up to 1 mm for cone size ≥12.5 mm. The VCs penumbra values were within ±1mm of the corresponding BLCs. Scatter factors for VCs varies from 0.609 to 0.841 and were within ± 1.0% of corresponding values of BLCs. Agreement between the Eclipse and iPlan computed dose fluence and the EBT3-film measured dose fluence was >98% (γ: 1%@1 mm), and the absolute dose difference was ≤ 2.2%, except for the 4 mm cone in which it was >96% and ≤4.83%. Target localization using cone-beam computed tomography was accurate within ± 0.8 mm and ± 0.3° in translation and rotation. The end-to-end dose delivery accuracy for both radiosurgery systems was within ± 3.62%. The dosimetric characteristics of Varian and BLC cones of same diameter was comparable. Both Eclipse and iPlan cone planning system modeled dose fluences agree well with the EBT3 film measurement. The end-to-end tests revealed an excellent target localization accuracy of Edge linac with satisfactory and comparable absolute dose agreement between Varian and BLC radiosurgery systems and hence these can be interchanged on edge linac.

Preliminary dosimetric comparison between fixed and rotating source stereotactic radiosurgery systems.

The Akesis Galaxy RTi (AK) is a novel rotational 60 Co-based cranial stereotactic radiosurgery (SRS) system. While similar systems have been compared against the fixed-source Leksell Gamma Knife (GK) system using stylized phantoms, dosimetric plan quality with realistic anatomy has yet to be characterized for this or any other rotating system versus GK. This study aims to benchmark AK dosimetric performance against GK by retrospectively replanning previously-treated GK patients at our institution. Thirteen patients, previously treated on a GK Icon, were re-planned on the AK treatment planning system using the same prescription doses and isodoses as the original GK plans. The cohort includes patients treated for brain metastases, schwannomas, pituitary adenomas, trigeminal neuralgias, and arteriovenous malformations. Plans are evaluated with target coverage metrics (Dmin , Dmean , D95% , V150% ) and dose conformality indices: Radiation Therapy Oncology Group conformity index (CI), selectivity, Paddick CI (PCI), gradient index (GI). AK plans use fewer shots and larger collimation compared to GK plans, resulting in statistically significant reductions in treatment time (p=0.047) by as much as 88.4 minutes while maintaining comparable target V100% . For most metastatic cases, GK produces higher Dmin (16.0-25.9 vs. 12.5-24.3Gy, p=0.008) while AK produces higher V150% (0.03-14.92 vs. 0.02-11.59 cc, p=0.028). For non-metastatic cases, GK provides superior CI (p=0.025) and GI (p=0.044). No statistically significant differences were found in the remaining metrics. This cohort demonstrates that the AK system is able to achieve largely comparable dosimetric results to GK, typically with shorter treatment times. Further investigation with a larger cohort is underway.

A novel Monte Carlo (MC) dose model for small MLC fields of the cyberknife® M6TM radiosurgery system using the EGSnrc.

The multi-leaf collimator (MLC)-equipped CyberKnife® M6 radiosurgery system (CKM6) (Accuray Inc., Sunnyvale, CA) has been increasingly employed for stereotactic radiosurgery (SRS) to treat relatively small lesions. However, achieving an accurate dose distribution in such cases is usually challenging due to the combination of numerous small fields≤(30×30)mm2 . In this study, we developed a new Monte Carlo (MC) dose model for the CKM6 system using the EGSnrc to investigate dose variations in the small fields. The dose model was verified for the static MLC fields ranging from (53.8×53.9) to (7.6×7.7) mm2 at 800mm source to axis distance in a water phantom, based on the computed doses of Accuray Precision® (Accuray Inc.) treatment planning system (TPS). We achieved a statistical uncertainty of ≤4% by simulating 30-50 million incident particles/histories. Then, the treatment plans were created for the same fields in the TPS, and the corresponding measurements were performed with MapCHECK2 (Sun Nuclear Corporation), a standard device for patient-specific quality assurance (PSQA). Results of the MC simulations, TPS, and MapCHECK2 measurements were inter-compared. An overall difference in dosimetric parameters such as profiles, tissue maximum ratio (TMR), and output factors (OF) between the MC simulations and the TPS results was found ≤3% for (53.8×53.9-15.4×15.4) mm2 MLC fields, and it rose to 4.5% for the smallest (7.6mm×7.7mm) MLC field. The MapCHECK2 results showed a deviation ranging from -1.5% to + 4.5% compared to the TPS results, whereas the deviation was within±2.5% compared with the MC results. Overall, our MC dose model for the CKM6 system showed better agreement with measurements and it could serve as a secondary dose verification tool for the patient-specific QA in small fields.

Extending the EclipseTM AcurosXB output factor table for small field radiosurgery.

To investigate the necessity of extending the output factor table (OF Table) of the Varian EclipseTM Treatment Planning System for small field stereotactic radiosurgery (SRS) and stereotactic body radiosurgery (SBRT) treatments. A new AcurosXB 15.6 beam model was created in the Eclipse Beam Configuration, which is identical to the one that has been used in the clinic with a default 3×3cm to 40×40cm OF Table, except the OF Table in the new model was extended to cover the range from 1×1cm to 40×40cm. 80 small square and rectangular output factors were measured on a Varian TrueBeam utilizing a Standard Imaging Exradin W2-1×1 scintillator detector, inside a PTW BeamScan water tank with 95cm SSD at 5cm depth. Cerenkov contamination was corrected using a rectangular field method (2cm×15cm field). Nine Radiosurgery plans with primary jaw setting ranging from 0.7cm to 2.0cm were evaluated by both beam models. The monitor unit (MU) differences between the two beam models were calculated for identical 3-dimensional (3D) absolute dose distributions. Output factors, measured versus Eclipse calculated, were compared down to 0.5×0.5cm primary jaw setting. For the 6FFF beam, the difference between the two beam models was ∼ 6% for 1×1cm jaw settings and 4% at 1.5×1.5cm, with the extended OF Table requiring higher MUs for the same dose prescription and same 3-dimensional isodose distribution. For the 6MV beam, the corresponding difference is ∼7.5% for 1×1cm, 5% for 1.5×1.5cm, and 3% for 2×2cm jaw settings, with the extended OF Table requiring higher MUs. For jaw settings smaller than 1×1cm, measured dose can be considerably smaller than Eclipse predicted dose, even with the OF Table extension. This is reflected by the fact that the output factor for 0.5×0.5cm, calculated via Eclipse external beam, was more than 30% greater than that measured for both 6FFF and 6MV beams. Eclipse does a satisfactory job for primary jaw sizes down to 2cm. For jaw settings smaller than 1.5cm, the OF Table in Eclipse should be extended to improve the dose calculation accuracy.

Machine performance and stability of the first clinical self-shielded stereotactic radiosurgery system: Initial 2-year experience.

This study provides insight into the overall system performance, stability, and delivery accuracy of the first clinical self-shielded stereotactic radiosurgery (SRS) system. Quality assurance procedures specifically developed for this unit are discussed, and trends and variations over the course of 2-years for beam constancy, targeting and dose delivery are presented. Absolute dose calibration for this 2.7MV unit is performed to deliver 1 cGy/MU at dmax =7mm at a source-to-axis-distance (SAD) of 450mm for a 25mm collimator. Output measurements were made with 2-setups: a device that attaches to a fixed position on the couch (daily) and a spherical phantom that attaches to the collimating wheel (monthly). Beam energy was measured using a cylindrical acrylic phantom at depths of 100 (D10 ) and 200 (D20 )mm. Beam profiles were evaluated using Gafchromic film and compared with TPS beam data. Accuracy in beam targeting was quantified with the Winston-Lutz (WL) and end-to-end (E2E) tests. Delivery quality assurance (DQA) was performed prior to clinical treatments using Gafchromic EBT3/XD film. Net cumulative output adjustments of 15% (pre-clinical), 9% (1st year) and 3% (2nd year) were made. The mean output was 0.997±0.010 cGy/MU (range: 0.960-1.046cGy/MU) and 0.993±0.029 cGy/MU (range: 0.884-1.065cGy/MU) for measurements with the daily and monthly setups, respectively. The mean relative beam energy (D10 /D20 ) was 0.998±0.004 (range: 0.991-1.006). The mean total targeting error was 0.46±0.17mm (range: 0.06-0.98mm) for the WL and 0.52±0.28mm (range: 0.11-1.27mm) for the E2E tests. The average gamma pass rates for DQA measurements were 99.0% and 90.5% for 2%/2mm and 2%/1mm gamma criteria, respectively. This SRS unit meets tolerance limits recommended by TG-135, MPPG 9a., and TG-142 with a treatment delivery accuracy similar to what is achieved by other SRS systems.

Small field output factor measurement and verification for CyberKnife robotic radiotherapy and radiosurgery system using 3D polymer gel, ionization chamber, diode, diamond and scintillator detectors, Gafchromic film and Monte Carlo simulation

The dosimetry of small fields has become tremendously important with the advent of intensity-modulated radiation therapy (IMRT) and stereotactic radiosurgery, where small field segments or very small fields are used to treat tumors. With high dose gradients in the stereotactic radiosurgery or radiotherapy treatment, small field dosimetry becomes challenging due to the lack of lateral electronic equilibrium in the field, x-ray source occlusion, and detector volume averaging. Small volume and tissue-equivalent detectors are recommended to overcome the challenges. With the lack of a perfect radiation detector, studies on available detectors are ongoing with reasonable disagreement and uncertainties. The joint IAEA and AAPM international code of practice (CoP) for small field dosimetry, TRS 483 (Alfonso et al., 2017) provides guidelines and recommendations for the dosimetry of small static fields in external beam radiotherapy. The CoP provides a methodology for field output factor (FOF) measurements and use of field output correction factors for a series of small field detectors and strongly recommends additional measurements, data collection and verification for CyberKnife (CK) robotic stereotactic radiotherapy/radiosurgery system using the listed detectors and more new detectors so that the FOFs can be implemented clinically. The present investigation is focused on using 3D gel along with some other commercially available detectors for the measurement and verification of field output factors (FOFs) for the small fields available in the CK system. The FOF verification was performed through a comparison with published data and Monte Carlo simulation. The results of this study have proved the suitability of an in-house developed 3D polymer gel dosimeter, several commercially available detectors, and Gafchromic films as a part of small field dosimetric measurements for the CK system.

Dosimetric Comparison between a Frameless Robotic Radiosurgery System and HyperArc Treatment Plans for Trigeminal Neuralgia: Cone-Based Robotic System vs. High-Definition MLC Based Linac System

<h3>Purpose/Objective(s)</h3> SRS is an effective and safe treatment option for trigeminal neuralgia (TN). Good dosimetric distribution has made HyperArc (HA) an attractive SRS/FRST technique for treating benign brain lesions. This study aims to evaluate the feasibility of HA for TN by comparing it with the dose distribution of frameless robotic radiosurgery systems. <h3>Materials/Methods</h3> Twenty patients with TN treated by cone-based CK were enrolled. The treatment location was targeted on the whole trigeminal nerve root entry zone (REZ) segment, leaving a 2-mm sparing from the brainstem. The prescription dose was 65 Gy in a single fraction, prescribing to the 80% isodose line with the highest dose of 81.25 Gy in the REZ. The segment of the trigeminal nerve encompassed by the 80% isodose line averaged 7.2 mm in length. Dose to brainstem surface was constrained with a maximum dose of 40 Gy. The corresponding HA plans were generated for the 20 patients to meet the same CK treatment plan criteria, using the high-definition MLC (2.5mm at the center) and SRS NTO optimization algorithm. The CK and HA treatment plans were compared with target coverage, sparing of organs at risk (OARs), and dose distribution metrics. <h3>Results</h3> All the OAR constraints were met in the HA treatment plans. The HA plans exhibited higher coverage of the PTVs than the CK plans, with statistically significant differences (HA vs. CK, 97.2% vs. 92.2%, P = 0.008). The HA plans consistently demonstrate better sparing of the OARs than the CK plans. The mean brain doses were 0.83 Gy and 1.15 Gy for HA and CK (P < 0.001), respectively. The brain V12 was significantly smaller with HA plans than with CK plans (5.9 c.c. in HA vs. 6.9 c.c. in CK, P = 0.019). Significant differences in the maximal and mean doses of the ipsilateral/contralateral CN VII/VIII were observed between the HA and CK plans. The HA plans exhibited a significantly greater conformity index than the CK plans (HA vs. CK, 1.59 vs. 1.71, P = 0.001). The dose gradient radius was similar in the CK and HA plans (HA, 0.28 vs. CK, 0.29). <h3>Conclusion</h3> Excellent sparing of OARs and good dosimetric distribution demonstrated HA is a feasible SRS technique for the treatment of TN. Further clinical studies using HA for TN would be necessary to confirm the therapeutic benefits and toxicity profiles.

Evaluation of Early Cosmetic Outcome and Toxicity after 5-Fraction Stereotactic Partial Breast Irradiation in Early-Stage Breast Cancer: A Prospective Cohort Study

<h3>Purpose/Objective(s)</h3> Partial breast irradiation (PBI) is a promising approach to minimize the patient burden by reducing irradiated volumes with accelerated schedules. Stereotactic-PBI (S-PBI) using a robotic stereotactic radiation system is a less invasive modality. However, prospective data are limited regarding the course of breast fibrosis and cosmesis as objective measures. We prospectively evaluated early toxicity and cosmetic outcome in women undergoing 5-fraction S-PBI. <h3>Materials/Methods</h3> Women undergoing S-PBI for invasive carcinoma and/or carcinoma in situ were prospectively enrolled. S-PBI was delivered with a robotic radiosurgery system with a dose of 30 Gy in 5 fractions. Simultaneously, women who were not a candidate for PBI, but were undergoing whole breast irradiation (WBI) were also enrolled for comparison. Patient-reported and physician-assessed adverse events were noted. Breast fibrosis was measured with a tissue compliance meter. Cosmesis was assessed with automatic computer-based software, BCCT.core. <h3>Results</h3> In total, 204 patients (n = 103, S-PBI; n = 101, WBI) were included, of whom 197 (97%) and 133 (65%) completed a 12-month and 24-month evaluation, respectively. The amount of fibrosis in uninvolved quadrants decreased over time following S-PBI for 12 months. In contrast, this finding peaked at 6 months and further decreased at 12 months in the WBI group. The amount of fibrosis of uninvolved quadrants at 6 months was significantly lower in the S-PBI group than in the WBI group (<i>P = 0.002</i>), while that of involved quadrants or scar sites was not significantly different between groups. In the S-PBI group, patient-reported grade 3–4 events were 3% at 6 months and 0% at 12 months. Physician-assessed grade 3–4 events were 2% at 6 months and 0% at 12 months. Moreover, in the S-PBI group, most cosmetic outcomes were excellent or good (82%) at 24 months, and there was no significant cosmetic detriment from baseline (<i>P = 0.353</i>). <h3>Conclusion</h3> Patients who underwent S-PBI presented with less fibrosis affecting their uninvolved breast quadrants than those who underwent WBI. Patients showed minimal toxicity with no detrimental effect on cosmesis after S-PBI. Longer-term follow-up is ongoing and necessary.

Feasibility Study of Removable Fiducial Marker Implantation with the Intelligent Navigation Bronchoscopy Technology in Robotic Radiosurgery System Tracking

<h3>Purpose/Objective(s)</h3> To investigate the feasibility of removable fiducial marker implantation with the intelligent navigation bronchoscopy technology in a frameless robotic radiosurgery system tracking. <h3>Materials/Methods</h3> CT scans of an inflatable anti-corruption pig lung were acquired, and two simulated tumor lesion sites were designed in the left and right lung lobes by intelligent navigation software, respectively. According to the principle of fiducial marker implantation, 24 removable fiducial markers were implanted around each simulated tumor lesion via bronchus after intelligent guiding. Simulating the end-expiratory state, the pig lung was scanned again to obtain CT images of the implanted removable fiducial markers and the number of successfully implanted fiducial markers was recorded. Six deliverable treatment plans were designed using the planning system, and then the pig lung plans were delivered based on the simulated respiratory movements. After the treatment, the implanted removable fiducial markers were retrieved through bronchoscopy, and the number of successful retrievals was recorded. The rigid body error and translation error were extracted and analyzed from the log file. <h3>Results</h3> No removed fiducial markers slipped and fell off during the experiment. 24 removable fiducial markers were successfully implanted under bronchoscopic intelligent magnetic navigation guidance, with a 100% implantation success rate (24/24) and 100% removable success rate (24/24). The fiducial marker tracking rate was 83.33% (20/24), with 4 fiducial markers being too far away from the simulated tumor location to be used during the tracking process. The data from the log file displayed that the mean rigid body error for 6 groups was 1.45 mm, the mean translation error was 1.78 mm. <h3>Conclusion</h3> The technology of bronchoscopy intelligent navigation and implantation of removable fiducial marker is feasible, and the tracking accuracy of the frameless robotic radiosurgery system can meet the clinical requirements, which has a good clinical application and teaching application prospect.

Stratified Assessment of a Commercial Deep Learning Algorithm for Automated Detection and Contouring of Metastatic Brain Tumors in Stereotactic Radiosurgery

<h3>Purpose/Objective(s)</h3> Artificial intelligence-based tools can be leveraged to improve detection and segmentation of brain metastases for stereotactic radiosurgery (SRS). This study explores a deep learning algorithm with recent FDA clearance to assist in brain tumor contouring. In this study, we aimed to assess the performance of this tool by various demographic and clinical characteristics among patients with brain metastases treated with SRS. <h3>Materials/Methods</h3> We randomly selected 100 patients with brain metastases who underwent initial SRS on a frameless robotic radiosurgery system from 2017 to 2020 at a single institution. Cases with resection cavities were excluded from the analysis. Computed tomography (CT) and axial T1-weighted post-contrast magnetic resonance (MR) image data were extracted for each patient and uploaded to VBrain. A brain metastasis was considered "detected" when the VBrain "predicted" contours overlapped with the corresponding physician contours ("ground-truth" contours). We evaluated performance of VBrain against ground-truth contours using the following metrics: lesion-wise Dice similarity coefficient (DSC), lesion-wise average Hausdorff distance (AVD), false positive count (FP), and lesion-wise sensitivity (%). Wilcoxon rank-sum tests were performed to assess the relationships between patient characteristics including sex, race, primary histology, age, and size and number of brain metastases, and performance metrics such as DSC, AVD, FP, and sensitivity. <h3>Results</h3> We analyzed 100 patients with 422 intact brain metastases treated with SRS. Our cohort consisted of patients with a median number of 2 brain metastases (range: 1 to 47), median age of 79 (range: 19 to 91), and 50% male and 50% female patients. The primary site breakdown was 56% lung, 10% melanoma, 9% breast, 8% gynecological, 5% gastrointestinal, 2% prostate, and 5% other, while the race breakdown was 60% White, 18% Asian, 3% Black/African American, 2% Native Hawaiian or other Pacific Islander, and 17% other/unknown/not reported. The median tumor size was 0.118 c.c. (range: 0.003-28.838 c.c.). We found mean lesion-wise DSC to be 0.714, mean lesion-wise AVD to be 8.44% of lesion size (0.796 mm), mean FP count to be 0.17 tumors per case, and lesion-wise sensitivity to be 83.65% for all lesions. Moreover, mean sensitivity was found to be 98%, 91.93%, and 79.87% for lesions with diameter equal to and greater than 10 mm, 5 mm, and 3 mm, respectively. No other significant differences in performance metrics were observed across demographic or clinical characteristic groups. <h3>Conclusion</h3> A commercial deep learning algorithm showed promising results in segmenting brain metastases, with 98% sensitivity for metastases with diameters of 1 cm or higher. Performance declined for smaller lesions. As advances in imaging and radiosurgery enable the detection and treatment of smaller brain metastases, future work is ongoing to develop and improve these tools to assist in radiosurgical treatment planning.

Real-World Dose Delivery Accuracy of Prostate SBRT with Tomotherapy Based Target Tracking

<h3>Purpose/Objective(s)</h3> The frameless robotic radiosurgery system target tracking system was recently adapted to Tomotherapy. While a previous dosimetric study has demonstrated comparable prostate SBRT plans between the two systems, we report here our real-world dose delivery accuracy of synchronization technology motion compensation for prostate SBRT and the initial clinical outcomes. <h3>Materials/Methods</h3> Patients undergo insertion of 3 fiducials and hydrogel before planning CT and MRI. Prostate and proximal seminal vesicles were included in the CTV. A PTV margin of 3 to 5 mm was utilized. Prescription was 40 Gy in 5 fractions. Patient motion files were analyzed and the maximum shift and gradient in each direction calculated to allow for motions to be categorized. Eight patients were enrolled in the TPS which uses daily imaging to deform VOI's and accumulate delivered doses based on organ volume and position changes. <h3>Results</h3> 14 patients with Gleason 6/7 prostate cancer were included with median prostate volume of 32.3 cm³ (17.7 - 99.6 cm³). Patient motion files showed 20 deliveries had motions <2 mm, 26 with slow position changes ≥ 2 mm. 10 deliveries had rapid position changes <5 mm and 14 had rapid changes ≥5 mm. For most OARs delivered D_max was within 2% of the planned dose. Larger differences were found for OARs located superiorly or inferiorly to the target, due to the rapid dose fall off in this direction. Large reductions in the D_max and D50 to the bladder and sigmoid are seen in patients who were asked to increase their bladder fill to reduce bowel dose. Mean dose to the CTV and PTV was found to agree to within 1.5% and 2.0% respectively. From 12 patients with median follow up time of 1 month (1 – 9 months), 3 reported grade 1 GU toxicities. 2 patients reported grade 1 GI toxicities and grade 1 fatigue. <h3>Conclusion</h3> The range of motions measured highlight the need for compensation techniques for precise dose deposition with Tomotherapy. Daily OAR variations resulted in dose delivery accuracy within 2% of planned dose.

Long-term toxicity of radiosurgery for ablation of ventricular tachycardia

Abstract Introduction There is a rising interest in using radiosurgery to modify arrhythmogenic substrate in patients with recurrent VT. However, data on the safety are still inadequate. Purpose This is update of toxicity evaluation based on the compilation from our case series, NIRA-VT and STAR-VT. Methods Between 2014 and March 2021, 36 patients (33 male, 3 females; mean age 66±10 years) with structural heart disease (ischemic cardiopathy, dilated cardiopathy or fibroma associated scar) from two electrophysiology centers in the Czech Republic (Trinec, Prague) underwent radiosurgery for recurrent VT. Radiosurgery was performed after at least one failed catheter ablation for VT. The critical part of the VT substrate was identified by electroanatomic mapping using a combination of voltage mapping, pace mapping, and activation mapping; and it was marked on a contrast-enhanced computer tomography study as a CTV. In NIRA-VT trial, CTV included scar based on PET/CT evaluation. Radiosurgery system with real-time motion tracking using the tip of the electrode of an indwelling defibrillator as a fiducial marker was used. A total radiation dose of 25 Gy was delivered to the ablation target in a single session during free breathing. Radiation-induced toxicity was evaluated according to the Common Terminology Criteria for Adverse Events (CTCAE) version 4.0. Only patients with follow up longer than 6 months were included in long term radiation related side effects evaluation. Results The mean CTV and PTV were 26±11 ml and 41±22 ml respectively. No patient exhibited acute (up to 3 months) elevation of troponin, pericardial effusion, or a decrease in left ventricular ejection fraction from baseline. Four patients developed acute mild nausea, which waned after antiemetic drugs. Long-term radiation related side effects were evaluated in 19 patients. Two patients (11%) presented radiological signs of lung fibrosis in small area in close distance from PTV. There was no significant decrease in left ventricular ejection fraction during follow up. Six patients (33%) gradually developed significant progression of known mitral regurgitation after SBRT, two (11%) of them had to undergo mitral valve replacement (grade 4 toxicity). Two cases of esophagitis (12%) were seen with one radiation toxicity related death (grade 5 toxicity) due to the unresectable esophagi-pericardial fistula (6%). Conclusions Our data indicate the feasibility of radiosurgery, majority of patients presented no/mild radiation related toxicity and decrease of VT burden. However, we have seen three cases of grade 4,5 toxicity. To further investigate long-term safety and efficacy of radiosuergery for VT, enrolling into a randomized prospective study is in progress. Funding Acknowledgement Type of funding sources: Public grant(s) – EU funding. Main funding source(s): European Union's Horizon 2020

Technical note: Absolute dose measurements of a vault-free radiosurgery system.

Methods for accurate absolute dose (AD) calibration are essential for the proper functioning of radiotherapy treatment machines. Many systems do not conform to TG-51 calibration standards, and modifications are required. TG-21 calibration is also a viable methodology for these situations with the appropriate setup, equipment, and factors. It has been shown that both these methods result in minimal errors. A similar approach has been taken in calibrating the dose for a recent vault-free radiosurgery system. To evaluate modified TG-21 and TG-51 protocols for AD calibrations of the ZAP-X radiosurgery system using ion chambers, film, and thermoluminescent dosimeters (TLDs). The current treatment planning system for ZAP-X requires AD calibration at dmax (7mm) and 450mm source-to-axis distance. Both and Nx [R/C] calibration coefficients were provided by an accredited dosimetry calibration laboratory for a physikalisch technische werkstatten (PTW) 31010 chamber (0.125 cc). The vendor provides an f-bracket that can be mounted on the collimator. Various phantoms can then be attached to the f-bracket. A custom acrylic phantom was designed based on recommendations from TG-21 and technical report series-398 that places the chamber at 500mm from the source with a depth of 44-mm acrylic and 456-mm SSD. Nx along with other TG-21 parameters was used to calculate the AD. Measurements using a PTW MP3-XS water tank and the same chamber were used to calculate AD using and TG-51 factors. Dose verification was performed using Gafchromic film and 3rd party TLDs. Measurements from TG-51, TG-21 (utilizing the custom acrylic phantom), film, and TLDs agreed to within±2%. A modified TG-51 AD calculation in water is preferred but may not be practical due to the difficulty in tank setup. The TG-21 modified protocol using a custom acrylic phantom is an accurate alternative option for dose calibration. Both of these methods are within acceptable agreement and provide confidence in the system's AD calibration.

Comparison of survival outcomes after CyberKnife® radiotherapy in Taiwan using preapproved insurance-based reimbursement versus out-of-pocket expenditure.

Background:With technological advances, radiotherapy has progressed from simple irradiation to robotic arm-based stereotactic radiosurgery systems (SRS, in this case, CyberKnife®). This equipment is high-priced and might be cost-effective or not. The National Health Insurance (NHI) in Taiwan has a premedical claims review process for approving CyberKnife® treatment; however, patients might have to pay for the procedure themselves if the NHI rejects the practice. Under the high treatment cost and such an insurance system, a sketch of patients treated by these high-cost machines and whether the prereview of insurance for reimbursement is reasonable without hindering the patient’s right to undergo treatment should be investigated. In this study, the patients of CyberKnife® radiotherapy in our institute were investigated as an example for this purpose.Methods:Patients who underwent CyberKnife® radiotherapy in our department were investigated retrospectively. Their demographic characteristics, disease patterns, and treatment sites were analyzed. Survivals were compared according to clinical features, and treatment expenses were reimbursed after prereview or out-of-pocket.Results:From October 19, 2014, to January 30, 2018, there were 331 patients included in this study, 205 (55.3%) of whom underwent CyberKnife® radiotherapy at their own expense, while 166 (44.7%) had their expenses approved for reimbursement after prereview by NHI. Most patients were treated for metastatic tumors (37.5%), and the brain was the most frequent treatment site (46.1%). The 1-year overall survival was 67.1%, and the 2-year overall survival was 56.3% after CyberKinfe® radiotherapy. The best survival rate (96.8% at 1 year) was for patients with brain tumors. In patient’s characteristics, A better Eastern Cooperative Oncology Group (ECOG) performance status, treatment for primary tumors, and outpatient treatment were independent factors for superior survival after CyberKnife® radiotherapy. The survivals for patients whose treatment expenses were approved for reimbursement after prereview by NHI were also better than out-of-pocket.Conclusions:Besides the patients’ characteristics, the treatment expense could be approved or rejected for reimbursement by the NHI prereview was an independent factor for survival in CyberKnife® radiotherapy. Prereview to reimburse expensive treatment is not an unreasonable requirement.

Effectiveness of Porous Glass Membrane Pumping Emulsification Device in Transarterial Chemoembolization for Solitary Hepatocellular Carcinoma.

A porous glass membrane-pumping emulsification device (GMD) enables the formation of a high-percentage water-in-oil emulsion with homogeneous and stable droplets. Although GMD is expected to improve the locoregional therapeutic effects of transarterial chemoembolization (TACE) in hepatocellular carcinoma (HCC), its effectiveness in the management of solitary HCC remains unclear. Patients treated for solitary HCCs (<5 cm) were retrospectively reviewed. A total of 46 patients who could not undergo liver resection and were unsuitable for radiofrequency ablation were included in this study. Among these, 22 patients underwent TACE using a GMD (GMD-TACE group) and 24 underwent stereotactic body radiotherapy (SBRT) using a robotic radiosurgery system (SBRT group). Local control rates were compared between the two groups. The median HCC tumour size was 24 mm (range=12-50 mm) and 22 mm (range=8-39 mm) in the GMD-TACE and SBRT groups, respectively; however, the difference between the groups was not significant. Age, liver function test results, or Child-Pugh scores were not significantly different between the two groups. The rate of local control at 6 months after treatment was 100% in both groups. Although the 1-year local control rate was higher in the SBRT group (92.3%) than in the GMD-TACE group (81.8%), there was no significant difference in the log-rank test (p=0.654). No major treatment-related complications occurred in either group during the observation period. TACE with GMD could be considered an effective treatment option for the management of solitary HCC.

Technical feasibility of online adaptive stereotactic treatments in the abdomen on a robotic radiosurgery system.

Stereotactic body radiotherapy (SBRT) has been proven to be beneficial for several disease sites in the (lower) abdomen. However, the quality of the treatment plan, based on a single planning computed tomography (CT), can be compromised due to large inter-fraction motion of the target and organs at risk (OARs) in this anatomical region. The aim of this study was to investigate the feasibility of online adaptive SBRT treatments on a robotic radiosurgery system and to record estimated total treatment times. For two disease sites, locally advanced pancreatic cancer (LAPC) and oligometastatic lymph nodes, four patients with repeat CTs were included in the feasibility study. Quick treatment plan templates were generated based on the planning CT and validated by running them on the plan and fraction CTs. For two cases a dummy run was performed and the individual steps were timed. Dose delivery was the largest contributor to the total treatment time, followed by contour adaptation. Running the quick plan templates resulted in plans similar to unrestricted plans, obeying the OAR constraints. The dummy runs showed that online adaptive treatments were completed in 64 to 83min respectively for oligometastases and LAPC, comparable to other clinically available solutions. This study showed the feasibility of online re-planning for two challenging disease sites within a clinically acceptable time frame on a robotic radiosurgery system, making use of commercially available elements that are not integrated by the vendor.