Comparison of Ray Tracing and Monte Carlo Calculation Algorithms for Spine Lesions Treated With CyberKnife.

Purpose: This study attempts to evaluate Ray Tracing (RT) and Monte Carlo (MC) algorithms for CyberKnife treatments of spine lesions and determine whether the MC algorithm is necessary for all spine treatment and compare the RT algorithm and MC algorithm at various spine lesion sites. Methods: The CyberKnife is used for stereotactic body radiotherapy for lesions in the cervical spine (30), thoracic spine (50), lumbar spine (30), and sacral spine (15). Dose was calculated using RT and MC algorithms for patients planned with the same beam angles and monitor units. Dose-volume histograms of the target and selected critical structures are evaluated. Results: The average target coverage of prescribed dose with MC algorithms was 94.80%, 88.47%, 92.52%, and 93.41%, respectively, in cervical, thoracic, lumbar, and sacral spine. For the thoracic spine, the RT algorithm significantly overestimates the percentage volume of the target covered by the prescribed dose, as well as overestimates doses to organs at risk in most cases, including lung, spinal cord, and esophagus. For cervical, lumbar, and sacral spine, the differences of the target coverage of prescription dose were generally less than 3% between the RT and MC algorithms. The differences of doses to organs at risk varied with lesion sites and surrounding organs. Conclusions: In the thoracic spine lesions with beams through air cavities, RT algorithm should be limited and verified with MC algorithm, but the RT algorithm is adequate for treatment of cervical, lumbar, and sacral spine lesions without or with a small amount of beams passing through the lungs.

Assessment of Delivery Quality Assurance for Stereotactic Radiosurgery With Cyberknife.

PURPOSE: The purpose of this study is to establish and assess a practical delivery quality assurance method for stereotactic radiosurgery with Cyberknife by analyzing the geometric and dosimetric accuracies obtained using a PTW31016 PinPoint ionization chamber and EBT3 films. Moreover, this study also explores the relationship between the parameters of plan complexity, target volume, and deliverability parameters and provides a valuable reference for improving plan optimization and validation. METHODS: One hundred fifty cases of delivery quality assurance plans were performed on Cyberknife to assess point dose and planar dose distribution, respectively, using a PTW31016 PinPoint ionization chamber and Gafchromic EBT3 films. The measured chamber doses were compared with the planned mean doses in the sensitive volume of the chamber, and the measured planar doses were compared with the calculated dose distribution using gamma index analysis. The gamma passing rates were evaluated using the criteria of 3%/1 mm and 2%/2 mm. The statistical significance of the correlations between the complexity metrics, target volume, and the gamma passing rate were analyzed using Spearman's rank correlation coefficient. RESULTS: For point dose comparison, the averaged dose differences (± standard deviations) were 1.6 ± 0.73% for all the cases. For planar dose distribution, the mean gamma passing rate for 3%/1 mm, and 2%/2 mm evaluation criteria were 94.26% ± 1.89%, and 93.86% ± 2.16%, respectively. The gamma passing rates were higher than 90% for all the delivery quality assurance plans with the criteria of 3%/1 mm and 2%/2 mm. The difference in point dose was lowly correlated with volume of PTV, number of beams, and treatment time for 150 DQA plans, and highly correlated with volume of PTV for 18 DQA plans of small target. DQA gamma passing rate (2%/2 mm) was a moderate significant correlation for the number of nodes, number of beams and treatment time, and a low correlation with MU. CONCLUSION: PTW31016 PinPoint ionization chamber and EBT3 film can be used for routine Cyberknife delivery quality assurance. The point dose difference should be within 3%. The gamma passing rate should be higher than 90% for the criteria of 3%/1 mm and 2%/2 mm. In addition, the plan complexity and PTV volume were found to have some influence on the plan deliverability.

Early response assessment after CyberKnife stereotactic radiosurgery for symptomatic vertebral hemangioma by quantitative parameters from dynamic contrast-enhanced MRI.

PURPOSE: The present study aimed to explore the value of DCE-MRI to evaluate the early efficacy of CyberKnife stereotactic radiosurgery in patients with symptomatic vertebral hemangioma (SVH). METHODS: A retrospective analysis of patients with spinal SVH who underwent CyberKnife stereotactic radiosurgery from January 2017 to August 2019 was performed. All patients underwent DCE-MRI before treatment and three months after treatment. The parameters included volume transfer constant (Ktrans), transfer rate constant (Kep), and extravascular extracellular space volume fraction (Ve). RESULTS: A total of 11 patients (11 lesions) were included. After treatment, six patients (54.5%) had a partial response, five patients (45.4%) had stable disease, and three patients (27.3%) presented with reossification. Ktrans and Kep decreased significantly in the third month after treatment (p = 0.003 and p = 0.026, respectively). ΔKtrans was -46.23% (range, -87.37 to -23.78%), and ΔKep was -36.18% (range, -85.62 to 94.40%). The change in Ve was not statistically significant (p = 0.213), and ΔVe was -28.01% (range, -58.24 to 54.76%). CONCLUSION: DCE-MRI parameters Ktrans and Kep change significantly after CyberKnife stereotactic radiosurgery for SVH. Thus, DCE-MRI may be of value in determining the early efficacy of CyberKnife stereotactic radiosurgery.

Assessment of Spinal Tumor Treatment Using Implanted 3D-Printed Vertebral Bodies with Robotic Stereotactic Radiotherapy.

To investigate the feasibility and early efficacy of 3D-printed vertebral body implantation combined with robotic radiosurgery in the treatment of spinal tumors. This study included 14 patients with spinal tumors from December 2017 to June 2018. Before surgery, all patients were subjected to CT scan and 3D data of the corresponding vertebral segments were collected. Titanium alloy formed 3D-printed vertebral body implantation and robotic stereotactic radiotherapy were performed because of the risk of postoperative residual, high risk of recovery, or recurrence after surgery. The main outcomes included the remission of symptoms, vertebral body stability, robotic stereotactic surgical precision, and local tumor control. All patients received complete and successful combination therapy, and all healed primarily without complications. The error of the coverage accuracy for robotic radiosurgery was less than 0.5 mm, and the error of the rotation angle was less than 0.5°. The therapeutic toxicity was limited (mainly in grades 1-2), and adverse events were uncommon. The evaluation of vertebral body stability and histocompatibility for all patients met the postoperative clinical requirements. For patients with post spinal injury, the pain symptoms were reduced or disappeared (93%), and nerve function was improved or even recovered after treatment (100%). During our follow-up period, most tumors were locally well controlled (93%). 3D- printed vertebral body implantation combined with robotic radiosurgery may offer a new treatment of spinal tumors. Chinese clinical trial registry: ChiCTR-ONN-17013946.

Robotic stereotactic irradiation and reirradiation for spinal metastases: safety and efficacy assessment.

BACKGROUND: Spine is the most common site of bone metastases in patients with cancer. Conventional external beam radiotherapy lacks precision to allow delivery of large fraction radiation but simultaneously limit the dose to spinal cord. The purpose of this study was to evaluate the safety and efficacy of CyberKnife(®) radiation therapy for spinal metastases. METHODS: Seventy-three lesions in 62 patients treated with CyberKnife radiotherapy from September 2006 to June 2010 for spinal metastases were retrospectively reviewed. Thirteen tumors in 12 patients had received prior radiation. Patients were followed clinically and radiographically for at least 12 months or until death. In all patients, the spinal cord and thecal sac were contoured for dose-volume constraints, and maximum doses to 0.1, 0.5, 1, 2, and 5-ml volumes were analyzed. RESULTS: Using the CyberKnife System, 20-48 Gy in one to five fractions for unirradiated patients, and 21-38 Gy in one to five fractions for the previously irradiatied patients, were delivered. Median 2-Gy normalized Biological Equvalent Dose (nBED) of unirradiated targets and irradiated targets were 49.6 Gy10/2 (range, 31.25-74.8 Gy10/2) and 46.9 Gy10/2 (range, 29.8-66 Gy10/2), respectively. With a median follow-up of 9.4 months (range, 2.5-45 months), twenty-nine patients (46.7%) were alive, whereas the others died of progressive disease. Fifty-six patients (93.3%) reported complete or partial reduction of pain after CyberKnife radiotherapy at one-month follow-up, 17 patients (28.3%) reported some degree of pain relief after first fraction of the treatment course. Two patients experienced local recurrence at fifth and ninth months post-radiotherapy. Median maximum nBED for spinal cord and thecal sac of naive targets were 68.6 Gy2/2 (range, 8.3-154.5 Gy2/2) and 83.5 Gy2/2 (range, 10.5-180.5 Gy2/2), respectively. Median maximum nBED for spinal cord and thecal sac for the re-irradiated targets were 58.6 Gy2/2 (range, 17.7-140 Gy2/2) and 70.5 Gy2/2 (range, 21.7-141.3 Gy2/2), respectively. No patient developed radiation related myelopathy during the follow-up period. CONCLUSION: Cyberknife radiotherapy is clinically effective and safe for spinal metastases, even in previously irradiated patients.