Clinical Associate Professor, Radiation Oncology - Radiation Physics
Cyberknife treatment planning and other Cyberknife related research.
There are 2 Cyberknife units at Stanford University. The robot of 1 Cyberknife is positioned on the patient's right, whereas the second is on the patient's left. The present study examines whether there is any difference in dosimetry when we are treating patients with trigeminal neuralgia when the target is on the right side or the left side of the patient. In addition, we also study whether Monte Carlo dose calculation has any effect on the dosimetry. We concluded that the clinical and dosimetric outcomes of CyberKnife treatment for trigeminal neuralgia are independent of the robot position. Monte Carlo calculation algorithm may be useful in deriving the dose necessary for trigeminal neuralgia treatments.
View details for DOI 10.1016/j.meddos.2010.12.012
View details for Web of Science ID 000301035000009
View details for PubMedID 21723113
The Cyberknife is an image-guided radiosurgical system. It uses a compact X-band 6-MV linear accelerator mounted on a robotic arm to deliver radiosurgical doses. While routine quality assurance (QA) is essential for any radiosurgery system, QA plays an even more vital role for the Cyberknife system, due to the complexity of the system and the wide range of applications. This paper presents a technique for performing quality assurance using thermoluminescence detectors (TLDs) and Gafchromic films that is intended to be specific for the Cyberknife. However, with minor modification, the proposed method can also be used for QA of other radiosurgery systems. Our initial QA procedure for the CyberKnife utilized a 30 x 30 x 11-cm solid water phantom containing a planar array of slots for 1x 1 x 1-mm TLDs on a 2-mm grid. With the objective of significantly simplifying CyberKnife QA, a new procedure for verification was developed, which uses much fewer TLDs than the prior solid water phantom technique. This new method requires only that the system target dose to the center of a cluster of 7 TLDs. In a prior study with Gafchromic films, conducted at 3 different Cyberknife facilities, the mean clinically relevant error was demonstrated to be 0.7 mm. A similar Gafchromic film analysis replicated these error measurements as part of the present investigation. It cannot be emphasized enough the importance of implementing routine QA to verify the accuracy of any radiosurgery system. Our quality assurance procedure tests the treatment planning system, as well as the entire treatment delivery including the image targeting system and the robot system. Either TLDs or Gafchromic films may be used for QA test of a radiosurgery system. Using both methods for measurement has the advantage independently verifying the accuracy of the system. This approach, which is routinely in used at our institution, has repeatedly confirmed the submillimeter targeting accuracy of our Cyberknife.
View details for DOI 10.1016/j.meddos.2007.04.009
View details for Web of Science ID 000253610200006
View details for PubMedID 18262121
New technology has enabled the increasing use of radiosurgery to ablate spinal lesions. The first generation of the CyberKnife (Accuray, Inc., Sunnyvale, CA) image-guided radiosurgery system required implanted radiopaque markers (fiducials) to localize spinal targets. A recently developed and now commercially available spine tracking technology called Xsight (Accuray, Inc.) tracks skeletal structures and eliminates the need for implanted fiducials. The Xsight system localizes spinal targets by direct reference to the adjacent vertebral elements. This study sought to measure the accuracy of Xsight spine tracking and provide a qualitative assessment of overall system performance.Total system error, which is defined as the distance between the centroids of the planned and delivered dose distributions and represents all possible treatment planning and delivery errors, was measured using a realistic, anthropomorphic head-and-neck phantom. The Xsight tracking system error component of total system error was also computed by retrospectively analyzing image data obtained from eleven patients with a total of 44 implanted fiducials who underwent CyberKnife spinal radiosurgery.The total system error of the Xsight targeting technology was measured to be 0.61 mm. The tracking system error component was found to be 0.49 mm.The Xsight spine tracking system is practically important because it is accurate and eliminates the use of implanted fiducials. Experience has shown this technology to be robust under a wide range of clinical circumstances.
View details for PubMedID 17297377
The purpose of this study was to report initial results of a phase I study using single-fraction stereotactic radiotherapy (RT) in patients with inoperable lung tumors.Eligible patients included those with inoperable T1-2N0 non-small cell lung cancer (NSCLC) or solitary lung metastases. Treatments were delivered by means of the CyberKnife. All patients underwent computed tomography-guided metallic fiducial placement in the tumor for image-guided targeting. Nine to 20 patients were treated per dose cohort starting at 15 Gy/fraction followed by dose escalation of 5 to 10 Gy to a maximal dose of 30 Gy/fraction. A minimal 3-month period was required between each dose level to monitor toxicity.Thirty-two patients (21 NSCLC and 11 metastatic tumors) were enrolled. At 25 Gy, pulmonary toxicity was noted in patients with prior pulmonary RT and treatment volumes greater than 50 cc; therefore, dose escalation to 30 Gy was applied only to unirradiated patients and treatment volume less than 50 cc. Ten patients received doses less than 20 Gy, 20 received 25 Gy, and two received 30 Gy. RT-related complications were noted for doses greater than 25 Gy and included four cases of grade 2 to 3 pneumonitis, one pleural effusion, and three possible treatment-related deaths. The 1-year freedom from local progression was 91% for dose greater than 20 Gy and 54% for dose less than 20 Gy in NSCLC (p = 0.03). NSCLC patients had significantly better freedom from relapse (p = 0.003) and borderline higher survival than those with metastatic tumors (p = 0.07).Single-fraction stereotactic RT is feasible for selected patients with lung tumors. For those with prior thoracic RT, 25 Gy may be too toxic. Higher dose was associated with improved local control. Longer follow-up is necessary to determine the treatment efficacy and toxicity.
View details for Web of Science ID 000241649300008
View details for PubMedID 17409963