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\title{I am James F. Dempsey, Ph.D., Nucl. Chem., developer of new weapons to
fight cancer. My team solved ``impossible'' problems for treating cancer
with radiation - while clearly seeing inside the patient - with a linear
accelerator inside an MRI scanner, AMA!}



\author[1]{James_Dempsey }%
\author[1]{r/Science AMAs}%
\affil[1]{Affiliation not available}%


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  \date{April 24, 2026}


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\begin{abstract}
The radiation treatment field has invested a lot of research into making
better dose distributions and delivering accurately to patients. Many
advances have been made in tracking breathing motion, surgically
implanting marker or gels in the body, placing balloons in orifices to
immobilize tissues, using X-Ray flat-panels detectors to find markers or
make ``cone-beam'' CTs. However, all of these approaches still do not
see the actual organs and tumor in real time as they move in the body
during therapy. I founded ViewRay to solve this problem. MRI scanners
provide the best soft tissue visual clarity of patients organs but they
are not compatible with radiotherapy accelerators. People spent decades
unsuccessfully trying to combine an MRI and a Radiation beam into a
single, effective medically usefully device available to treat patients.
In a sense, the MRI scanner and the accelerate do not like each other.
The magnetic field generated by the MRI scanner can prevent the
accelerator from operating and the accelerator uses radar technology and
makes radiofrequency noise that can prevent the MRI from scanning clear
images. So, we took a superconducting MRI and we split it in half
opening it up, leaving the imaging volume floating in the middle where
we could shoot in radiation beams while scanning. We created magnetic
sleeves that could create voids in the magnetic field to protect the
accelerator. Then we borrowed ideas from stealth aircraft to absorb the
radiofrequency noise and eliminate it. Finally, we developed advanced
software to compute and optimize dose, as well as, track tissues with
real-time MRI video . This allows us to optimize, reshape, and track
moving tissues so we do not miss, which is important to eradicate the
tumor and spare healthy tissues. What we call the MRIdian\selectlanguage{ngerman}® Linac system
was FDA cleared in February of 2017. The MRIdian® an earlier generation
system has been treating patients for over 3.5 years and data published
at ASTRO 2017 showed significant early results in treating pancreatic
cancer, known to be one of the most difficult cancers to effectively
treat.
http://www.viewray.com/press-releases/early-clinical-data-suggests-prolonged-median-survival-pancreatic-cancer
I'll be back at 1 pm ET to answer your questions, Ask Me Anything. EDIT:
Thank you /r/science mods and all the redditors that asked very good
questions about MR image-guided RT. We'll check back later to see if
there's any late questions.%
\end{abstract}\selectlanguage{ngerman}%



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