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 Table of Contents  
REVIEW ARTICLE
Year : 2015  |  Volume : 6  |  Issue : 2  |  Page : 106-115

CyberKnife® : The cutting edge technology in precision surgery


1 Department of Oral Medicine and Radiology, Rama Dental College Hospital and Research Centre, Kanpur, Uttar Pradesh, India
2 Department of Dental Surgery, Ranchi Institute of Neuro-Psychiatry and Allied Sciences, Ranchi, Jharkhand, India
3 Department of Oral Medicine and Radiology, Rishiraj College of Dental Sciences and Research Centre, Bhopal, Madhya Pradesh, India
4 Department of Oral and Maxillofacial Surgery, Rama Dental College Hospital and Research Centre, Kanpur, Uttar Pradesh, India

Date of Web Publication20-Apr-2015

Correspondence Address:
Rahul Srivastava
783/4 W-1, Saket Nagar, Juhi-2, Kanpur - 208 014, Uttar Pradesh
India
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DOI: 10.4103/0976-433X.155469

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  Abstract 

Radiation therapy (RT) is an important part of treatment for cancer patients. Stereotactic radiosurgery is a type of RT that uses narrow beams of radiation coming from different angles to very precisely deliver radiation to a tumor while sparing the surrounding normal tissue. Traditional radiosurgery systems have limited mobility. They generally require the use of rigid frames attached to a patient's skull to effectively target a tumor. CyberKnife® (Accuracy, Inc., Sunnyvale, CA, USA) is a revolutionary radiosurgical device that uses a combination of robotics and sophisticated image-guidance technology. CyberKnife® is noninvasive alternative to surgery where high dose radiation beams can be given from any angle by precisely concentrating on the tumor while causing minimum damage to the nearby healthy tissue. The purpose of this article is to review the CyberKnife® robotic radiosurgery as an ideal option for treatment when there would be instances where a tumor cannot be operated completely due to locality of the tumor close to critical structures or tumor may only be partially excised.

Keywords: Cancer, CyberKnife® , radiation, robotics


How to cite this article:
Srivastava R, Jyoti B, Gupta M, Singh N. CyberKnife® : The cutting edge technology in precision surgery. SRM J Res Dent Sci 2015;6:106-15

How to cite this URL:
Srivastava R, Jyoti B, Gupta M, Singh N. CyberKnife® : The cutting edge technology in precision surgery. SRM J Res Dent Sci [serial online] 2015 [cited 2020 Aug 10];6:106-15. Available from: http://www.srmjrds.in/text.asp?2015/6/2/106/155469


  Introduction Top


In the 1950's, Professor Lars Leksell of the Karolinska Institute in Sweden coined the term stereotactic radiosurgery to define a neuro-surgical procedure that combined precision targeting with a large number of cross-fired beams of ionizing radiation. [1]

The word stereotactic is derived from the Greek word στερεoς (stereo), which translates to "solid" and the Greek word ταkτikή (taxis), a Greek military term, meaning "arrangement or order" or "tactic." The modern medical definition of stereotactic is the utilization of a surgical technique for precisely directing an instrument or beam of radiation in three planes using ordinance systems provided by medical imaging to reach a specific locus in the body. Today, the delivery of radiation is considered stereotactic only if it uses advanced imaging techniques and state-of-the-art treatment and image-guidance technologies to precisely deliver radiation to the intended target in either a single-stereotactic radio surgery (SRS) or a few (up to 5) treatments stereotactic body radiotherapy (SBRT). SRS and SBRT are used in the treatment of many types of benign and malignant tumors, as well as other pathologies. Dr. Lars Leksell developed the concept using many radiation beams that were focused on a target with a three-dimensional coordinate system and rigid skull fixation by means of a metal frame fixed to the skull with screws. High dose radiation was produced by this technique while controlling for patient movement to sub-millimeter precision. [2]

In 1972 the Gamma Knife radiosurgery system was developed on the basis of same concept, using the aforementioned frame fixed to the skull for exact stereotaxy and intracranial targets, typically defined by computed tomography (CT) or magnetic resonance imaging (MRI) that are localized by utilizing a three-dimensional coordinate system. [3],[4]

The Gamma Knife unit is still one of the leading stereotactic systems in the world, but it requires stereotactic frames for accurate beam targeting. Such skeletal fixation causes enough pain to preclude flexible treatment fractionation. Even more importantly, stereotactic frames only permit precise targeting of the treatment beam within or very close to the brain. The current radiosurgical instruments are isocentric-based, constraining all beams to converge on a common point. This design restricts more flexible and conformal treatment planning. Because of intrinsic limitations of current stereotactic radiosurgical devices, the image-guided robotic radiosurgery was developed, and these principles are embodied in the CyberKnife® System (Accuray, Inc., Sunnyvale, CA, USA).

The CyberKnife® System was invented by John R. Adler, a Stanford University Professor of Neurosurgery and Radiation Oncology, and Peter and Russell Schonberg of Schonberg Research Corporation.

Unlike most linac-based systems, the CyberKnife® was designed specifically to deliver stereotactic radiosurgery, and it overcame the main limitations of conventional linear accelerators by allowing:

  • The ability to continually track, detect, and correct for tumor and patient movement even during the treatment.
  • A significant expansion of treatment configurations utilizing so-called intelligent robotics. [1],[2]


The CyberKnife® is a frameless robotic radiosurgery system that has been utilized by clinicians around the world to treat intracranial and extracranial tumors. [5]

The CyberKnife® Robotic Radiosurgery System was cleared by the US Food and Drug Administration (FDA) in 1999 to treat tumors in the head and base of the skull. Despite its name, the CyberKnife® System is not a surgical procedure. In fact, there is no cutting involved. Instead, the CyberKnife® System delivers high doses of pin-point radiation directly to head and neck cancers.

The treatment of healthy tissue that surrounds the tumor leads to more side effects. With the sub-millimeter accuracy of the Cyberknife® , patients have experienced limited to no side effects with limited to no downtime, even on the days of treatment, returning immediately to normal activities. In addition, the Cyberknife® treatments are short and painless, completed in 1-5 treatments, one per day. While standard radiotherapy irradiates both normal and cancerous tissues, (5-20 mm accuracy), CyberKnife® delivers an ablative dose to the tumor with sub-millimeter accuracy and minimal exposure of normal tissue. As a result, CyberKnife® can treat inoperable patients, shrink tumors for fewer radical resections, destroy radio-resistant tumors and treat patients previously treated with radiation. [6]


  Cyberknife® System Top


The CyberKnife® System is basically composed of a radiation delivery device, called a linear accelerator (or Linac), which is mounted on a robotic arm. The flexibility of the robotic arm enables the CyberKnife® System to deliver radiation to tumors anywhere in the body, including the brain, head and neck, spine, lung, prostate, liver, pancreas, breast and other soft tissues [Figure 1]. The CyberKnife® System also utilizes sophisticated software and advanced imaging to track tumor and patient movement and adjust the beams of high-dose radiation to ensure treatment is delivered with a high degree of accuracy. Because of this exceptional tracking ability, the CyberKnife® System eliminates the need for patients to have stabilizing frames bolted to their head or limit their breathing during treatment to minimize movement of the tumor. [7]
Figure 1: CyberKnife® robotic radiosurgery system

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CyberKnife® treatment system is consisting of two following elements:

  • Radiation produced from a small linear particle accelerator is on a robotic arm, which allows megavoltage X-rays to be directed at any part of the body from nearly any direction;
  • Real-time images of the target are tracked with a frameless system.


These two essential features set CyberKnife apart from other stereotactic modalities.

Robotic-mounted linear accelerator

CyberKnife® System's robotic maneuverability allows physician to deliver a highly individualized treatment. With a linear accelerator mounted on a flexible robotic arm, the CyberKnife clinician can select from thousands of different angles from which to deliver radiation treatments.

The radiation of CyberKnife® comes from a robotic arm mounted on a general-purpose industrial robot. This robotic mounting allows near-complete freedom to direct radiation to the target from nearly any direction, in effect providing over 1,200 radiation shooting angles [Figure 2].
Figure 2: With over 1200 possible beam positions, the CyberKnife®

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The robotic mounting allows very fast repositioning without the need to move the patient, unlike current conventional radiotherapy with linac-based gantry configurations.

In addition, robotic technology allows for the real-time correction of patient and target motion.

Real-time image-guidance with target tracking allows for a frameless delivery system

The CyberKnife System uses imaging software to track and continually adjust treatment for any movement of the patient or tumor.

The CyberKnife® continually detects, tracks, and corrects for tumor motion throughout treatment, and there are several options to accomplish following objectives:

  • Taking X-rays periodically during treatment of bony anatomy.
  • Using metal markers placed within the body.
  • As exemplified by lung cancer, using differences in soft tissue densities.


Tracking is accomplished by light-emitting optical fibers mounted on the patient and tracked using a Charge couple device camera (Accuray Inc. 1310 Chesapeake Terrace, Sunnyvale, CA, United States). The tracking system is utilized primarily for lung, liver, pancreatic and other tumors that move significantly because of respiratory motion.

The CyberKnife® depends on a co-registration of digitally reconstructed radiographs (DRRs) that are generated from CT images and X-ray projections that are captured during the treatment session. Changes in target position are relayed to the robotic arm, which adjusts pointing of the treatment beam. The robotic arm moves through a sequence of positions (nodes). At each node, a pair of images is obtained, the patient position is determined, and adjustments are made. [1],[2],[5],[7]

When is CyberKnife a suitable treatment option?

Radiation therapy (RT), surgery or chemotherapy are some of the traditional therapies that are used in combination with Cyberknife stereotactic radiosurgery. Following are the circumstances that require Cyberknife system:

  • Where RT can be an option instead of open surgery, and then CyberKnife delivers high doses of radiation to tumors with extreme accuracy.
  • Inoperable or surgically complex tumors, or who may be looking for a nonsurgical option.
  • Recurrence of a tumor close to a significant structure like the spine that previously received maximum dose of radiation.
  • When surgery is not able to remove the entire diseased tissue.
  • When tumor is located near to a significant structure like optic nerves where performing a traditional surgery can increase the risk of damage to these structures.
  • When a surgical procedure is difficult to perform. [8]


Procedure of treatment

The CyberKnife® treatment process generally requires six simple steps from start to finish.

Evaluation of patient

After the proper and definitive diagnosis, contact a CyberKnife center. Though it may vary based on specific treatment, there should be a team of clinicians, including a radiation oncologist, surgeon, medical physicist, radiation technician and nurse coordinator.

Fiducial placement

Depending on the type and location of the tumor, team may recommend the placement of fiducials - that are small gold markers inserted near the tumor - to help identify the exact location of the tumor during treatment. Not all treatments require fiducial markers. The determination will be made based on the density, size and location of the tumor, e.g., fiducial marker placement into lung lesions is associated with a high risk of pneumothorax and a risk of fiducial migration.

Imaging

Prior to treatment, an MRI and a CT or CT/positron emission tomography scan is taken to determine the size, shape and location of the tumor.

Treatment planning

Using images from a CT scan, the data are digitally transferred to the CyberKnife® System's treatment planning workstation, where a qualified physician identifies the tumor to be targeted and the surrounding vital structures to be avoided. This plan is designed to match the desired radiation dose to the tumor location and limit radiation exposure to the surrounding healthy tissue.

Treatment

Once the treatment plan is developed, the Cyberknife® treatment can be started. At the CyberKnife center, patient will be comfortably positioned on the treatment table. Then the CyberKnife® System's computer-controlled robot will carefully move around the patient to deliver radiation at various locations as prescribed by patient's treatment plan. At the same time, the CyberKnife® System is taking continual X-ray images that will provide real-time information about the location of the tumor and enable the system to dynamically track and correct for any movement of the tumor. Depending on the type and location of the tumor, a patient can expect to undergo between one and five treatment sessions.


  Tumor-Tracking Facilities Top


There are following different tumor-tracking facilities in CyberKnife treatment. These tracking methods are used in different types of sites and with various natures of the organ to be treated.

Six-dimensional skull tracking

This method can be used for intracranial targets as well as head and neck targets that are considered to be fixed relative to the skull. Image registration is performed using high contrast bone information contained within the entire field of view. Each two-dimensional registration is performed in multiple stages, using two image similarity measures and several search methods. The resulting two-dimensional transformations for each orthogonal projection are combined and back projected to determine the three-dimensional rigid transformation that aligns the position and orientation of the skull in the treatment planning CT image with the treatment delivery coordinate system.

X sight® spine tracking

This method can be used for targets located anywhere in the spine, or targets located near the spine and considered to be fixed relative to it.

For spine tracking, however, image processing filters are applied to enhance the skeletal structures in both the DRR and the treatment X-ray images. This improves estimation of local displacements for these structures. Optionally, the DRRs can be generated by restricting attenuation to voxels within a region surrounding the spine such that the DRRs represent only spine anatomy and do not include image artifacts from tissue motion or from nonspinal bony anatomy such as the rib cage. Registration is performed in a region of interest (ROI) that generally includes the vertebra of interest plus the two adjacent vertebrae. The local displacement vector that aligns a point in the DRR image with the corresponding point in the X-ray image is estimated at each node point in a grid laid over the ROI. A small region or block surrounding the node point in the DRR image is compared with regions in the X-ray image. Block matching, which is essentially the estimation of local displacements of the skeletal structure, is performed in a multi-resolution approach to increase efficiency and robustness. The position (translation) and orientation (rotation) of the skeletal anatomy, and thus the target, is computed from the resulting local displacement fields between the X-ray image and the DRR image.

Xsight lung tracking

This method can be used to track tumors located within the lung without the use of implanted fiducial markers. Xsight lung tracking begins with global patient alignment, including both position and orientation, using the region of the spine nearest the lung tumor. Global alignment happens only once, at the beginning of treatment. After the patient is globally aligned, the treatment couch moves the patient from the spine alignment center to the tumor treatment center (these are defined during treatment planning). After this movement, the tumor will be close to the reference position around which it will move during breathing. Direct tumor tracking is performed by image registration of the tumor region in the DRRs to the corresponding region in the treatment X-ray images. Specifically, the image intensity pattern of the tumor region in the DRR is matched to the most similar region in the X-ray image. A matching window for the tumor is defined based on the tumor silhouette in each projection. The registration process is conducted separately for each projection, resulting in two-dimensional translations for each projection; the three-dimensional tumor translation is determined by back projection of the two-dimensional translations. This requires that the image intensity pattern of the tumor is distinguishable from other objects in the image, which requires the tumor to have sufficient contrast relative to the surrounding region.

Fiducial marker tracking

This method can be used for soft tissue targets that are not fixed relative to the skull or spine (e.g., prostate, pancreas, liver), including lung tumors for which the Xsight lung tracking method is unsuitable. Radiopaque fiducial markers are implanted in or adjacent to the lesion being treated to provide an internal frame of reference. Cylindrical gold seeds are often used, with dimensions of 0.8-1.2 mm in diameter and 3-6 mm in length. Fiducial markers are often implanted percutaneously under image-guidance. Implantation in the lung can also be performed bronchoscopically. Between three and five fiducial markers are typically implanted, and in most instances the treatment planning CT scan is acquired a week or more after implantation to allow the fiducial marker positions to stabilize. Fiducial markers are identified in the planning CT scan and, therefore, their positions are known in the DRR images. Image registration is based on alignment of these known DRR positions with the marker locations extracted from the treatment X-ray images.

Synchrony respiratory motion tracking system

The Synchrony Respiratory Tracking System provides real-time tracking for tumors that move with respiration. Alignment of each treatment beam with the moving target is maintained by moving the beam dynamically during treatment, achieving a 100% duty cycle while the patient breathes normally throughout treatment without the need for breath-holding. The primary system concept is a correlation between tumor position and external marker position. To minimize radiographic imaging exposure, episodic imaging is combined with continuous measurement of an external breathing signal. At the start of treatment, the tumor position is determined at multiple discrete time points by acquiring orthogonal X-ray images and using either the fiducial marker or Xsight lung tracking methods. A linear, quadratic, or constrained fourth order polynomial correlation model is generated by fitting the tumor positions at different phases of the breathing cycle to the simultaneous external marker positions. To ensure that the full motion range within the breathing cycle is evenly sampled, the X-ray imaging system can be automatically triggered based on the external breathing signal. An important feature of this method is its ability to fit different models to the inhalation and exhalation phases. During treatment, the internal tumor position is estimated from the external marker positions using the correlation model, and this information is used to move the linear accelerator dynamically with the target. [9]

Recovery

Most CyberKnife® patients do not experience side effects. Depending on the type of treatment patient receive, the side effects will vary. Patients that do experience side effects are typically mild and considered acute and do not require intervention. Patients should speak to their doctor and discuss what side effects may occur and learn about potential risks. [7]


  How Cyberknife® is Different from Other Systems Top


Although Radiosurgery has been used for over 30 years to treat both cancerous and benign tumors and growths, CyberKnife is a very new concept and different than its counterparts. Radiosurgery does not remove the tumors; rather it uses high doses of radiation to destroy the tumor cells and stop the growth of active cells. Multiple beams of radiation produced by a linear accelerator are directed at the abnormal growth within the body.

Various radiosurgery systems are available; the most widely used being the Gamma Knife and modified linear accelerators. CyberKnife's distinction advantage over the other options is its precision, which enables physicians to maximize the amount of radiation that reaches the tumor or abnormal growth while minimizing exposure to healthy tissue and organs. [10]

The M6 series will be the first CyberKnife system to have the InCise multileaf collimator (Accuray Inc. 1310 Chesapeake Terrace, Sunnyvale, CA, United States), a device made up of individual leaves that can move independently in and out of the radiation beam to modulate its intensity and shape. This new technology will greatly expand the selection of patients eligible for CyberKnife treatment to include those with larger or more irregular shapes, while also perhaps decreasing treatment times from an average of 30-45 min to approximately 15-20 min. [2]


  Cyberknife® Versus Gamma Knife Top


The Gamma Knife and CyberKnife are two different technologies used to deliver stereotactic radiosurgery, a type of treatment that uses precise beams of radiation to destroy tumors of the brain, head, and neck, and to treat other neurological disorders.

Gamma Knife treatment delivered during one session with radiologic accuracy better than 0.3 mm. Gamma Knife treatment uses stereotactic head frame for rigid immobilization to the outer skull. It also provides exact magnetic resonance and CT correlation from planning to treatment delivery in three-dimensional. Gamma Knife is used exclusively for noninvasive brain surgery, focusing 192 beams of gamma radiation directly upon a tiny targeted area and thus sparing the healthy surrounding brain tissue.

CyberKnife requires single or multiple treatments, possibly over a period of days. CyberKnife has 1 mm accuracy and dose outside the target area is 2-6 times greater than with Gamma Knife. CyberKnife has sub-millimeter accuracy in tracking tumor position. If sub-millimeter accuracy is not achieved, it gives warning and stops the treatment. CyberKnife treatment uses nonrigid immobilization using a thermoplastic face mask that is shrink-wrapped to the table during treatment. It uses a single-source linear accelerator not exclusive to brain surgery. Treatment target is confirmed once every 10 s. [11],[12]

There are several ways of performing stereotactic radiosurgery. Some types of stereotactic radiosurgery methods require a rigid, invasive metal head frame that is screwed into the skull to hold the head in place during treatment [Figure 3]. However, such frame-based systems have various limitations, these limitations are:

  • Restricting treatments of 1 large radiation dose.
  • Limiting the possible angles that radiation could be delivered.
  • Causing considerable discomfort for the patient.
  • Limiting treatments to the brain.
Figure 3: No requirement of immobilization with a metal frame screwed directly into a patient's skull

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In contrast to the standard frame-based radiosurgical instruments, the CyberKnife® robotic radiosurgery system combines three features unique to any other system:

  • Image-guidance.
  • Intelligent tracking of the tumor.
  • Robotic delivery system. [6]



  Cyberknife versus conventional radiation therapy Top


Radiation therapy has been used from a long time for treating malignant and benign tumors. CyberKnife is altogether a new and latest concept that is very different from other treatment methods. The major benefit of Cyberknife as compared to other treatment options is its accurate precision that helps in maximizing the quantity of radiation. This radiation reaches to the abnormal growth or tumor that minimizes the damage to healthy organs and tissues. The comparison between cyberKnife, Gamma Knife and conventional RT are summarized in [Table 1]. [6],[8]
Table 1: The comparison between cyber knife, gamma knife and conventional radiation therapy

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Conventional RT requires the administration of a broad beam of low dose radiation from only a few directions, thus limiting how closely the tumor can be covered with radiation. In order to prevent the normal surrounding tissues from receiving too much daily radiation, many low doses of radiation must be administered over a longer period. Conventional RT requires 30-45 treatments over a period of 6-8 weeks - each lasting 15-30 min in duration as well as has various side effects.

CyberKnife Radiosurgery delivers radiation beams that can be targeted from virtually any direction with sub-millimeter accuracy while limiting the damage to surrounding healthy tissue. As a result, a higher and more effective dose of radiation can be delivered to the tumor in fewer treatment sessions, which increases patient convenience. Each treatment generally lasts between 1 and 3 h, and the treatment course is typically completed in one to five visits. CyberKnife treatment has fewer side effects when compared to conventional radiation techniques. [13]

Complications of stereotactic radio surgery

Adverse radiation effects due to SRS include focal edema and radionecrosis. These effects correspondingly intensify with the tumor volume and radiation dose and found more frequently in patients who received boost SRS concurrently with RT. Frequency of adverse radiation effects range between 0% and 40% in different series, albeit it's uncommonly more than 5%. These effects are usually completely reversible with anti-edema medications and rarely results in permanent neurological complications. Previous irradiation history should be considered particularly for lesions located in eloquent areas, and dose should be reduced. Aggressive irradiation might result in excessive edema and radionecrosis requiring additional procedures such as an emergent decompression or shunting (Smith et al., 2008). Radiation induced tumors is another potential complication of SRS. Several sporadic reports of GBM formation in the long term following high dose SRS are already present. However, long term follow-up is needed to assess this potential, incidence seems less than 1:100.000 for now (Berman et al., 2007; Salvati et al., 2003). [14]

Also in adjuvant RT and preoperative RT the radiation given is 40 Gy that too via split course hence use of CyberKnife has limitations in such cases.


  Indications Top


The CyberKnife® System has FDA clearance for treatment of tumors in any location of the body. CyberKnife® surgery is administered for both cancerous and benign tumors. All stages, from I until IV (metastases) can be treated. Following are some important lesions can be treated using CyberKnife® System:

  • Cancers involving the brain.
  • With the radiobiology of SRS proven to be successful, various clinical studies have been conducted to evaluate the efficacy of SRS for intracranial lesions.


The most commonly treated lesions with SRS include arteriovenous malformations (AVMs), vestibular schwannomas (VSs), acoustic schwannomas, meningiomas, gliomas and metastatic brain tumors. Recently, there have been studies showing strong evidence of the efficacy of SRS. University of Pittsburgh Medical Center (UPMC) reported a study including 829 patients with VS who were treated with SRS to dose of 12-13 Gy. The results showed a 10 years control rate as high as 97%. Studies performed evaluating SRS treatment of brain metastases either alone or in addition to whole brain irradiation have shown improved local control. A trial conducted by Radiation Therapy Oncology Group 9-58 randomized 333 patients with 1-3 brain metastases (<4 cm diameter) and Karnofsky performance status ≥70 to either whole brain radiation therapy (WBRT) alone versus WBRT followed by an SRS boost. The results demonstrated significant improvement in local control for all patients, in addition to improved survival rates for patients with a single brain metastasis with WBRT followed by an SRS boost. There were two studies conducted by UPMC evaluating treatment of meningiomas. The first study included 159 patients treated with a median margin dose of 13 Gy. The results showed tumor control rates at 5 and 10 years both to be 93.1%. The second trial included 168 patients with petroclival meningiomas. The 5 and 10 years survival rates were 91% and 86% respectively. [15],[16]

In general, most of the retrieved literatures reported that there are minimal side effects with the use of CyberKnife. In a study of 61 patients with glioma and glioblastoma treated with CyberKnife, only four patients (2.44%) showed symptomatic radiation necrosis (Sato, 2003 level 4). In another study on fifteen patients with intramedullary spinal cord AVMs, there was no evidence of further hemorrhage after CyberKnife treatment or neurological deterioration attributable to SRS (Sinclair, 2006 level 4). Yoshikawa et al. (2006) reported that in CyberKnife stereotactic radiotherapy for patients with malignant glioma, delayed radiation necrosis was seen in one glioblastoma patient and no other patient suffered acute or delayed neurological morbidity after CyberKnife therapy (Yoshikawa et al., 2006 level 4) [17] [Table 2].
Table 2: Level of evidence (adapted from CAHTA Spain)

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  • Lung cancers.
  • Pancreatic cancers: Preoperative RT (involves 7 weekly doses of gemcitabine 400 mg/m 2 plus 30 Gy radiation in 10 fractions), Adjuvant RT (involves 40 Gy delivered via split course, with a 2-week break after 20 Gy. Patients received 5-fluourouracil (5-FU) chemotherapy during RT, followed by maintenance 5-FU chemotherapy for 2 years or until progression), intraoperative RT (20 Gy IORT following surgical resection), and hyperfractionated accelerated RT (1.5 Gy twice daily doses, separated by 6 h for 5 days a week-total dose of 45 Gy) are the various modalities in treatment of pancreatic carcinomas. [18],[19]
  • Metastatic liver cancers.
  • Cancers involving the spine.
  • Benign brain tumors.
  • Malformations of blood vessels within the brain.
  • Trigeminal neuralgia (TN).
  • Metastatic orbital tumors, orbital lymphomas and orbital inflammations (tumors or inflammations around the eye).
  • As a sole modality in early head and neck cancer, when surgery is not contemplated, and long duration of conventional radio therapy is time consuming.
  • Also used as a boost to Residual disease in locally advanced head and neck cancers.
  • Cancer of the Nasal Fossae, and inoperable otolaryngologic tumors involving critical structures may be the reason a tumor is considered unresectable or only marginally resectable.
  • With significantly less irradiation of surrounding tissues, CyberKnife® can even treat tumors untreatable or already treated with conventional radiotherapy. [10],[20]


Tsai et al. conducted a study in 2013 assessed the post treatment tumor control and auditory function of VS patients after CyberKnife (CK) and analyzed the possible prognostic factors of hearing loss. They studied 117 VS patients, with Gardner-Robertson (GR) classification grades I to IV, who underwent CK between 2006 and 2012. Data including radiosurgery treatment parameters, pre- and post-operative tumor size, and auditory function were collected and examined. They concluded that CK treatment provided an excellent tumor control rate and a comparable hearing preservation rate in VS patients. Patients with pretreatment GR II hearing levels, larger tumor volumes, smaller cochlear sizes, and higher prescribed cochlear doses may have poor hearing prognoses. [21]

Lazzara et al. conducted a study to assess the short-term efficacy of Cyberknife stereotactic radiosurgical treatment of TN. Totally, 17 consecutive patients with medically or surgically refractory unilateral TN were treated with Cyberknife radiosurgery. A radiosurgical rhizotomy was performed with the Cyberknife utilizing a single collimator to deliver an average maximum dose of 73.06 Gy (range: 72.91-73.73) to the target and they concluded that Cyberknife radiosurgery is a viable treatment alternative in patients with TN with competitive efficacy demonstrated in patients while minimizing adverse effects. [22]

Klingenstein et al. in 2012 evaluated radiographic therapy response, clinical out-come and adverse effects of CyberKnife radiosurgery in patients suffering from orbital metastases. Sixteen orbital metastases originating from different solid cancers in fourteen patients were treated by single fraction CyberKnife radiosurgery. Radiographic response and clinical out-come were evaluated. No serious adverse effects were reported in this series, CyberKnife therapy has proven to be of great value in the local management of orbital metastases. The CyberKnife system seems to be an effective and safe alternative to traditional radiotherapy in orbital metastases. [23]

Ashu et al. treated a case of nonsmall cell lung cancer with solitary adrenal metastasis with curative intent using SBRT with CyberKnife. He concluded that with the help of new technology like CyberKnife, patients with solitary metastasis can be treated with radical intent with limited toxicity and such therapy may contribute to improved survival in these patients. [24]

Recently, in June 2014, a 33-year-old lady presented with retroperitoneal fibromatosis-biliary obstruction. PET CT showed a small recurrent mass causing the obstruction. She was reirradiated with CyberKnife radio surgery at Apollo Specialty Hospital, Chennai. Follow-up PET CT showed regression in the size and activity of the mass. This patient benefited of this treatment modality without major surgery.

A 49-year-old man with known case of carcinoma colon postoperative, postchemo (in August 2013) was evaluated for back ache. He was operated upon for spondylolisthesis in November 2013. He had no relief of symptoms. A PET CT done in March 2014 showed an aortocaval mass. There was no lesion elsewhere in the body. He was treated with CyberKnife radio surgery. He started having pain relief during treatment and a substantial relief during follow-up. Two months follow-up PET scan revealed no lesion in the region treated with cyberknife radiosurgery.

A 60-year-old man with hepatocellular carcinoma is presented. The patient was not keen for surgery and due to the proximity of the hepatic vein, RFA was also difficult, so it was decided to give radio surgery with CyberKnife to the residual lesion. After fiducial placement for real-time tracking of the lesion, a total dose of 40 Gy was delivered in 5 fractions. He underwent the treatment quite well with no difficulties. Follow-up after 2 months imaging showed a decrease in the size of the lesion with reduced activity of fludeoxyglucose uptake indicating good response to the treatment. [25]


  Advantages Top


CyberKnife treatment of cancer is an entirely new approach and offers many advantages over other methods. Unlike the 6-8 weeks of conventional RT treatment, treatment is typically completed over a week in 4-5 short outpatient treatment sessions and most patients continue with their normal daily activities throughout the treatment. After CyberKnife therapy, the short-term improvement in the quality of life is significant.

The advantages of this treatment are:

  • No requirement for anesthesia.
  • Painless treatment procedure.
  • Noninvasive.
  • No blood loss.
  • Immediate return to normal routine.
  • Completely frameless.
  • No hospitalization.
  • Minimal radiation exposure to healthy tissues and organs.
  • Even if tumors have received the maximum allowed dosage of radiation, they can still be treated.
  • The ability to give stronger, more accurate doses of radiation directly to the tumour means that the number of treatment doses can be shortened.
  • The risk of radiation damage to normal surrounding healthy tissues is minimized greatly.
  • Increased patient comfort due to the elimination of the invasive head frame. [10],[20]



  Cyberknife surgery cost in india Top


CyberKnife treatment costs will vary from patient to patient and between centers, but hospital, accommodation, and associated expenses are generally much lower than with conventional surgery. Cost of CyberKnife treatment will depend on geographical location as well as the type and location of the tumor being treated. Costs will also depend on the number of sessions necessary to treat the tumor. Patients in the United States can expect to pay between $50,000 to $100,000 for CyberKnife treatment, which may or may not include follow-up visits and hospitalization costs. Patients traveling to India save 60% to 80% (Rs. 500,000/$10,000-$11,000) of the cost than that offered in US and UK.

So far, more than 50,000 patients worldwide have been treated by the CyberKnife® System. CyberKnife® treatments abroad are a much cost effective option, and while the number of centers providing such treatments is few, they are of high quality and technologically advanced. [10] The Components of CyberKnife® radiosurgery that play a vital role in precise treatment out-comes are treatment planning and treatment delivery. The first step couples diagnostic imaging and localization techniques to ensure the accuracy of the planning. In this stage, imaging tools - most commonly MRI, CT, and angiography - are employed to evaluate the pathology and develop a treatment plan. In neuro-surgical cases, neurosurgeons identify critical structures and targets, while radiation oncologists specify radiation dosing and treatment parameters. For frame-based systems, the neurosurgeon also affixes the stereotactic head frame to the patient prior to imaging. The neurosurgeon is also essential for SRS treatment of a central nervous system condition outside the brain, such as a spinal cord tumor.

As SRS is used for extracranial applications, general surgeons, and cancer surgeons are beginning to play a significant role in treatment planning and delivery - in collaboration with the radiation oncologist. As with all radiation devices, a physicist is an essential partner in treatment planning and safety and quality assurance. New images are required on the day of treatment to account for any change in shape or size of the target from initial diagnostic scans and quality assurance.

The second component is a single, but complex step: Treatment delivery. Physicists create treatment plans with dose intensity modulation to shape radiation beams to the specific target, reducing collateral damage to surrounding tissue. [26]


  Conclusion Top


The CyberKnife is one of the most advanced forms of radiosurgery and a painless, noninvasive treatment that delivers high doses of precisely targeted radiation to destroy tumors or lesions within the body. It uses a robotic arm to deliver highly focused beams of radiation. The flexibility of the robotic arm makes it possible to treat areas of the body, such as the spine and spinal cord, which can't be treated by other radiosurgery techniques. CyberKnife is an option for deep seated, inoperable tumors/lesions those are relative radiosensitive, close to critical structures and in recurrent tumors after surgical excision.

 
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    Figures

  [Figure 1], [Figure 2], [Figure 3]
 
 
    Tables

  [Table 1], [Table 2]


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[Pubmed] | [DOI]



 

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