Sunday, December 22, 2019


Co-written by: Dr. Jesse A. Stoff  & Dr. Robert L. Bard | The NY Cancer Resource Alliance
Source Interview: Michael Repka, MD, with the Perlmutter Cancer Center at NYU Winthrop Hospital
Additional material provided by: Accuray Inc.

Since the advent of radiation therapy (and the invention of the x-ray) over a century ago, the noninvasive treatment approach of radiotherapy continues to be recognized as one of the most forward-thinking technologies in the pursuit of targeting cancer tumors. The CyberKnife® Robotic RadioSurgery System represents the latest performance innovation in this modality for treating benign and malignant tumors as well as other chronic disorders.   

To review the CyberKnife technology, we approached the Perlmutter Cancer Center at NYU Winthrop Hospital—the top radiotherapy and CyberKnife cancer treatment center in the country. Michael C. Repka, MD, a radiation oncologist there, shared his extensive insight and firsthand experience about CyberKnife technology including its performance and patient benefits.

The CyberKnife® system combines three different technological advances. The first is x-ray based or photon based radiation, the standard form—and vast majority—of medically induced radiation. This is delivered by a linear accelerator, a device that generates high energy x-rays that are far higher in intensity than a CT scan or a conventional x-ray. The CyberKnife combines a miniaturized linear accelerator (rather than the typical oversized linear device), to allow room for a second technological advance—the integration of a robotic arm, known as a manipulator. The third advance is equipping CyberKnife with an interactive image-guidance system that acquires stereoscopic kV images during treatment. 

The integration of these systems was designed to promote hyper-accuracy in treatment by allowing the robotic arm to direct radiation beams from many different angles – angles that are not typically accessible via a normal and more static radiation machine. Meanwhile, another advantage to CyberKnife over other radiation devices is that it can track all activities during treatment in real time—including the slightest motions such as a patient’s breathing— automatically adjusting the radiation targeting accordingly.

The CyberKnife system was initially developed by Stanford professor of neurosurgery John Adler and the Schonberg Research Corp. to treat intracranial tumors, with the first patients treated in 1999. It is developed for widespread medical use by Accuray Incorporated and has produced over six evolutions since its original design—including the CyberKnife® M6 System, which is the latest addition to the CyberKnife product family and was released in 2012. Accuray states that this system is “widely used to treat conditions in the brain, spanning benign and malignant primary tumors, brain metastases, trigeminal neuralgia, acoustic neuromas and arteriovenous malformations (AVMs). CyberKnife radiosurgery is even used to treat complicated neurosurgical cases, while sparing important functions, such as hearing and vision.” [1]

According to Dr. Repka, “CyberKnife is a unique and exciting tool in the treatment of cancer, delivering targeted radiation therapy with extreme precision that allows for large doses of radiation over a single or small number of sessions. This can be very beneficial for patients, such as those with prostate cancer, making the treatment not just shorter and more convenient, but in many cases decreasing associated side effects as well.” Though CyberKnife technology has been widely associated with NYU Winthrop, there are many different health centers nationwide that have access to this innovation. Dr. Repka underwent training at Georgetown University Hospital—one of a number of facilities treating patients with CyberKnife, but the Perlmutter Cancer Center at NYU Winthrop, which has locations in New York City and on Long Island, has performed more CyberKnife treatments to treat prostate cancer than any other facility in the U.S. 

By the time the CyberKnife was perfected and cleared by the FDA, it was recognized for treating tumors anywhere in the body, and the evolution of CyberKnife has continued to allow for an increasing range of applications over its prior prototypes. A similar but different form of radiation technology, called the Gamma Knife, is another successful industry innovation but mainly targets tumors in the brain. 

Historically, any tumor that is to be treated with CyberKnife requires the placement of a marker, called a fiducial— a tiny piece of gold implanted directly into the tumor. This gold fiducial is a small, seed-sized marker used to aid the CyberKnife in visibly tracking and locking on to the tumor’s exact location in real time. This marker is able to account for any movement of the tumor during the actual delivery of the treatment. Not all cancers require this marker. In cases of tumors in areas like the spine or in the brain, for example, the CyberKnife can use the bony anatomy of the skull or the vertebral bodies as marker references or surrogates, so the CyberKnife can be very precise in treatment delivery.

As with all innovations and their paths of evolution, the success of the CyberKnife system has a direct connection with its users’ feedback and systemic challenges. In response, a significant new upgrade is in the delivery of the radiation beam using a multileaf collimator, little finger-like leaflets that can adjust the beam into different shapes. By using this multileaf collimator, the CyberKnife raises its level of control in the delivery of big doses of radiation to a very targeted area. This recent improvement reduces the treatment time significantly compared to treatment in the past. 

As with any treatment protocol, results of the CyberKnife depend on each individual patient, their situation and the specific type of cancer. As an example, with brain tumors, treatment is often done in a single setting—essentially like a single Space Invaders zap. Meanwhile, other cases necessitate spreading the treatment out over a few days or a week, in order to be more effective.

Radiation is geo-targeted and very specific, so the effects are only in the area being treated—as opposed to chemotherapy that goes everywhere in the body through the bloodstream. Radiation side effects are on a case-by-case basis, and many patients may experience mild side effects or no side effects at all.  

With prostate cancer, for example, side effects tend to be mild and are very similar to those experienced with conventional radiation therapy, such as a mild increase in urinary urgency, some occasional burning during urination, etc. These common side effects typically do not occur until a near the end of treatment and gradually go away within a few weeks of treatment. There are always some low risks of long-term toxicity from any prostate-directed radiation, but the precise treatment delivered by CyberKnife allows physicians to mitigate those risks substantially.

According to Dr. Repka, CyberKnife and radiation therapy do not replace chemotherapy but are valued additions to the therapeutic arsenal for treating cancer patients. “When I think about oncology, I think of the traditional three pillars: surgeons or SURGICAL ONCOLOGY, chemotherapy doctors or MEDICAL ONCOLOGY, and then radiation doctors or RADIATION ONCOLOGY—each playing a separate but oftentimes complementary role. As every cancer is different, the cancer’s response to treatments—radiation or chemotherapy or surgery—also varies. . . . I think the most important thing is maximizing the number of tools available for each patient’s unique case, to not only treat their cancer, but minimize their side effects.”


Radiation therapy (or radiotherapy) is a cancer treatment that uses high doses of radiation to kill cancer cells and shrink tumors. At high doses, radiation therapy kills cancer cells or slows their growth by damaging their DNA. Cancer cells whose DNA is damaged beyond repair stop dividing or die. When the damaged cells die, they are broken down and are removed by the body. (see: NIH Link)

There are a variety of options on the market for radiation therapy.  Each device targets tumors and performs the treatment tasks differently.

• CYBERKNIFE: Delivers high energy x-ray based or photon based radiation by an image-guided miniature linear accelerator mounted on a robotic arm. Available for use on cancer tumors in ANY part of the body.

• CONVENTIONAL, EXTERNAL BEAM RADIATION THERAPY (EBRT): Conventional EBRT is typically delivered by means of a four-field technique—designed to include the prostate, the seminal vesicles, and the regional lymphatic vessels. Conventional radiotherapy includes irradiation of large volumes of tissue, including the skin, small bowel, bladder, large bowel, pelvic bones, and additional areas of soft tissue

• STEREOTACTIC BODY RADIATION THERAPY (SBRT): SBRT it deals with tumors outside of the CNS and involves the delivery of a single high dose radiation treatment or up to 5 fractionated radiation treatments to the outside area of the tumor and into the surrounding normal tissue. (more)

• PROTON THERAPY: Uses proton beams (positively charged particle) rather than x-rays to treat cancer 

• GAMMA KNIFE: Targets only brain or cervical spine tumors with one high-dose treatment. Gamma Knife delivers 192 precisely focused beams of gamma radiation to small targets inside the brain. 

• RADIOIMMUNOTHERAPY: A type of systemic therapy using monoclonal antibodies to deliver low doses of radiation directly to the cancerous tumor while not affecting noncancerous cells. 

Radiation therapy does not kill cancer cells right away. It takes days or weeks of treatment before DNA is damaged enough for cancer cells to die. Then, cancer cells continue dying for weeks or months after radiation therapy ends.


Dr. Michael Repka is a radiation oncologist at the Perlmutter Cancer Center at NYU Winthrop Hospital in Mineola, New York, which is part of NYU Langone Health. He received his medical degree from Sidney Kimmel Medical College. Previously, he worked in a research laboratory studying the molecular genetics of cancer while pursuing the passion for the field of oncology. As a radiation oncologist at Perlmutter Cancer Center, Dr. Repka is involved in many aspects of cancer care—curative, adjuvant, and palliative. He has extensive training in all forms of radiation therapy, including external beam radiotherapy, brachytherapy, stereotactic body radiotherapy (SBRT), and stereotactic radiosurgery. NYU Winthrop Hospital is one of the foremost centers in the world for SBRT. Dr. Repka has published multiple peer-reviewed publications, including novel research, review articles, and book chapters. Also, he has presented research at annual meetings for the European Society for Radiation Oncology and the American Society for Radiation Oncology. Dr. Repka has no financial disclosures to report. 

JESSE STOFF, MD, HMD, FAAFP - Dr. Stoff is a highly credentialed medical expert specializing in cancer immunology and a publisher of current educational programs about prevention, wellness and medical texts about onco-immunology. As a senior clinical investigator for cancer treatment protocols, Dr. Stoff is dedicated to resolving the most challenging health issues of our time. He has spoken worldwide at some of the top medical conferences about his experiences and analyses on the study of human disease. His medical practice (INTEGRATIVE MEDICINE OF NY, Garden City, NY ( has been continually providing patients with the many comprehensive clinical options and modalities available- including "ONCO-IMMUNOLOGY,” the science of battling cancer cells and reversing pre-cancerous conditions through a complete prevention program that has earned him great success in this field.  For more information, visit:

ROBERT L. BARD, MD, PC, DABR, FASLMS - Dr. Bard is recognized for his specialized work in advanced cancer diagnostic imaging. He co-founded the 9/11 CancerScan program to bring additional diagnostic support to all first responders from Ground Zero. His main practice in midtown, NYC (Bard Diagnostic Imaging- uses the latest in digital imaging technology and has been also used to help guide biopsies and in many cases, even replicate much of the same reports of a clinical invasive biopsy. Imaging solutions such as high-powered sonograms, Power Doppler Histogram, sonofluoroscopy, 3D/4D image reconstruction and the Power Doppler Histogram  are safe, noninvasive, and do not use ionizing radiation. It is used as a complement to find anomalies and help diagnose the causes of pain, swelling and infection in the body’s internal organs while allowing the diagnostician the ability to zoom and ‘travel’ deep into the body for maximum exploration.

NYU Winthrop is the Long Island hospital base of NYU Langone Health System and is ranked by U.S. News & World Report as one of the top-10 New York metro-area hospitals. The hospital was founded in 1896 and is now a 591-bed medical academic center and ACS Level 1 Trauma Center. The hospital features more than 75 divisions of specialty care, offering comprehensive inpatient and outpatient programs and services to address every stage of life. NYU Winthrop also has a Research Institute that conducts robust research and studies that are helping to shape the future of medicine. The hospital, with ties to New York University, blends the progressive philosophy and advances of a teaching and research institution with a personal approach to patient care that is the cornerstone[buzzword] of the organization. The NYU Winthrop campus is also home to the new NYU Long Island School of Medicine—a tuition-free school with an accelerated three-year curriculum devoted exclusively to training primary care physicians.


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