Our Physicians

CyberKnife treatments are an example of the efficacy of medical collaboration. The Denver radiation oncologist is the primary physician involved with the treatment. However, for the majority of the cases treated, a collaborating specialist will assist in the development of the treatment plan for his/her patient’s case. Below are some of the specialists who we most often work with.

Denver Radiation Oncologist:

Gregg A. Dickerson, M.D.

Gregg A. Dickerson, M.D., is the medical director and specialist in CyberKnife Robotic Radiosurgery at Anova Cancer Care.

Dr. Dickerson graduated from the Indiana University School of Medicine and completed his residency in radiation oncology at the Thomas Jefferson University Hospital where he served his final year as Chief Resident and Fellow of the American Cancer Society.

He was Director of Radiation Oncology at Indiana University Health Ball Memorial Hospital and President of East Central Indiana Radiation Oncology. He was also President of the Indiana and Mississippi Radiological Societies. Dr. Dickerson has served as an Assistant Clinical Professor of Radiation Oncology at Indiana University School of Medicine, a Clinical Assistant Professor of Radiation Oncology at St. Louis University School of Medicine, and currently serves as a Professor of Clinical Medicine at Rocky Vista University School of Medicine.

Dr. Dickerson is a Fellow of the American College of Radiology and a Fellow of the American College of Radiation Oncology. He is a past member of the Economics Committee of the American College of Radiology. He served as a flight surgeon in the U.S. Air Force/Air National Guard for almost 10 years and reached the rank of Major. He has over eight years of CyberKnife experience, and prior to Anova Cancer Care, founded the 12th CyberKnife center in the country in Jackson, Miss.

His Denver-area hospital affiliations include Presbyterian/St. Luke’s Medical Center, Swedish Medical Center and Sky Ridge Medical Center. Additionally, Dr. Dickerson serves on the board of directors for the CyberKnife Coalition and the Registry for Prostate Cancer Radiosurgery clinical trial. He is also the Colorado Medicare Contractor Advisory Committee representative for radiation oncology

Dr. Dickerson is a member of the following organizations: CyberKnife Society; American Society of Therapeutic Radiologists and Oncologists; American College of Radiology; American College of Radiation Oncology; and Colorado Radiological Society.

In his personal time, Dr. Dickerson loves mountain biking, hiking, fly fishing and just spending time in the mountains. He is married 30 years with three great children, all in college.


We work with any and all urologists in the Denver area. If you need a urologist, below is a list of recommended urologists that we work with:

Dr. James Fagelson, M.D., Urologist
Urology Associates

Dr. Fagelson completed his undergraduate training at the University of California, San Diego in 1989 where he graduated magna cum laude with a degree in biochemistry and cell biology. He was elected to the Phi Beta Kappa honor society. He received his medical degree from the University of Texas Southwestern Medical School in Dallas, Texas where he was elected to the Alpha Omega Alpha honor society.

Dr. Fagelson completed two years of general surgical training followed by a four-year urology residency at the University of Texas Southwestern Medical Center. He was chief urology resident from 1999-2000.

Dr. Fagelson joined Urology Associates, P.C. in 2000. He is board certified and a fellow of the American College of Surgeons. He is committed to minimally invasive treatments for all urologic diseases. He has specific expertise in prostate disease including enlarged prostate (BPH) and prostate cancer. He has extensive experience with LASER surgery as well as microwave thermotherapy (TUMT) for enlarged prostate problems. Dr. Fagelson incorporates daVinci robotic prostatectomy and prostate radiation seeds in the comprehensive management of prostate cancer. He has extensive experience in the management of kidney cancer with minimally invasive surgery (laparoscopy). Finally, he has interest and expertise in the comprehensive management of kidney stones including surgery and prevention.

Dr. Fagelson’s goal is that you are treated in a compassionate manner and that you understand all aspects of your diagnosis and treatment.


J. Adair Prall, M.D.

Board certified by the American Board of Neurological Surgery in 2001, J. Adair Prall, M.D., is a leader in his field with more than 19 years of neurosurgical experience. His neurosurgical expertise includes complex cervical surgery and neuro-oncology, with training under Dr. Glenn Kindt and Dr. Kevin Lilihei at the University of Colorado Health Sciences Center, as well as trigeminal neuralgia, for which he trained with Dr. John Tew at the University of Cincinnati, and Dr. Robert Breeze at the University of Colorado Health Sciences Center.

Dr. Prall earned his Bachelor’s degree from Princeton University in 1986 and his medical degree from The University of Cincinnati in 1991. Prior to joining South Denver Neurosurgery in 2004, Dr. Prall practiced at Intermountain Neurosurgery and Neuroscience, with an appointment as a clinical professor in the Department of Neurosurgery at the University of Colorado Health Sciences Center. He now serves as Director of Neurosurgery at Littleton Adventist Hospital.

David VanSickle, M.D.

Neurological Surgery
Bio coming sooon.

Sean Markey, M.D.

Neurosurgical and Spine Specialist
Dr. Sean Markey is board certified by the American Board of Neurological Surgery. He earned his medical degree in 1997 from the University of Colorado Health Sciences Center, where he also completed his surgical internship and neurosurgery residency. Dr. Markey has served as the director of neurosurgery at Littleton Adventist Hospital and currently serves as the director of neurosurgery at Parker Adventist Hospital. He also serves as faculty for a number of medical device companies, which includes ongoing work in the development of new spinal surgery techniques. He has been listed in “5280: Denver’s Mile-High Magazine” as one of the city’s top doctors for his work with brain and spine disorders. Dr. Markey currently serves as the Neurosurgical Consultant to the Denver Broncos.

Bradley Duhon, M.D.

Dr. Duhon completed his undergraduate and medical degrees in Texas, before moving to Salt Lake City, UT for residency. Dr. Duhon joined a private practice neurosurgery group specializing in degenerative spine, minimally invasive spine, and deformity surgery in Tyler, Texas. Dr. Duhon’s career interests include degenerative spine surgery, minimally invasive techniques, neurosurgical oncology, spine and cranial trauma.


Robert Benkert, M.D.

Dr. Benkert is board certified by the American Board of Internal Medicine and Pulmonary Medicine. He earned his medical doctorate from the University of Cincinnati College of Medicine in 1980 and has been practicing as a Pulmonologist in Colorado since 1994. His practice consists of all aspects of Pulmonary Disease. Dr. Benkert is very dedicated to his patients and finding the right treatment for them. “I have a passion to help people with lung tumors, even inoperable patients. Anova Cancer Care helps me pursue that passion.”

Neurotology and Skull Base Surgeons

Daniel Zeitler, M.D.

Dr. Daniel Zeitler graduated Magna Cum Laude from Northwestern University and completed his medical education at New York University School of Medicine in 2004 where he graduated with honors. Dr. Zeitler went on to complete his internship and residency in Otolaryngology/Head and Neck Surgery at New York University in 2009 and subsequently completed a two-year fellowship in Otology/Neurotology & Skull Base Surgery at the University of Miami before joining Denver Ear Associates in 2011. Dr. Zeitler is board certified in Otolaryngology and has received subspecialty certification in Neurotology (i.e. surgery of the ear and skull base). Dr. Zeitler is a member of the American Academy of Otolaryngology and the American Neurotology Society, and currently serves as a member on the Otology/Neurotology Education Committee within the Academy.

Among Dr. Zeitler’s many clinical interests is his passion for the treatment of both benign and malignant tumors of the ear, temporal bone, and skull base, and he has written numerous articles and given multiple national and international lectures on the use of Cyberknife stereotactic radiation in the treatment of these diseases.


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