Hello, and welcome to the Physics World weekly
podcast.
This episode features the medical physicist,
inventor,
and entrepreneur,
Brian Pogue, who is in conversation
with Physics World's Tammy Freeman.
They explore some of the crucial roles that
optical technologies
play in medicine.
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Here is that conversation with Brian Pogue.
It was recorded in association
with the journal
Physics in Medicine and Biology,
which celebrates its seventieth
anniversary
this year.
Optical technologies underlie many of today's routine medical
procedures,
from microscopic imaging of cells and tissues to
clinical applications
such as endoscopy,
ophthalmology,
blood oxygen monitoring, fluorescence guided surgery, and and
many more.
And the field of optics is also converging
with the world of medical physics,
enabling exciting new techniques for guidance, dosimetry, and
in vivo verification
of radio
radiation therapy cancer treatments.
I'm speaking today with Brian Pogue,
professor of biomedical engineering at Dartmouth College and
cofounder of several startups developing optics based systems
for medicine.
Welcome to the podcast, Brian.
Well, thank you. It's a pleasure to be
here.
So can you tell us a little about
your background? How did your interest in optics
and medicine
first begin?
Sure. Yeah. Well, you know, I was trained
as a physicist, and I wound up doing
a master's in laser
isotope separation. So I've learned a lot about
lasers and optics,
but then specifically pivoted into a PhD in
medical physics. And so that's where I sort
of blended my two
interests in optics as well as medicine,
which is, you know, at the time was
a little bit of an unusual mix, but
this
advisers I had were experts in the field,
and it was incredible opportunity. So I really,
have enjoyed it and continued,
through my postdoctoral
training
and today to to work at both medical
physics and biomedical optics at the same time.
Excellent. So, could you maybe give us a
brief introduction to some of the more general
applications of optics in medicine?
Sure. Yeah. I mean, I you know, I
routinely
remind my
radiology and radiation oncology and other folks in
who work in medical physics that optics is
actually an enormous field. It's much, much larger
than the field of radiation and medicine.
You know, if you think about surgical
intervention, pretty much all tools
use optics. If you if you even think
about a family physician, pretty much
most of the tools they use are optics
based, either just looking in your ear, in
your throat, in your eye,
looking in,
cat body cavities,
or
blood spectroscopy,
pulse oximetry,
and, pretty much all vision technology
to work in the to image the back
of the eye, the retina, the cornea.
These are all optical tools.
Laser surgery, an enormous field.
Most people don't realize, but dermatologists
are probably the biggest user of lasers
in the world because they have a vast
array of laser systems to to treat skin
conditions.
So it's just
through to all of medicine, really, optics has
a I I routinely say I I'm pretty
sure this is true that it's the largest
single technology sector
in medicine today is biomedical optics.
Yeah. Yeah. I guess people sort of like
you say, it's not immediately obvious,
but actually, yes, it's it's used in all
sorts of things. So, I mean, what main
advantages of using light for clinical applications such
as diagnostic tests?
Yeah. So the the, you know, the main
applications are, hey. It's not dangerous.
And so,
it's
used in, what I call point of care
technologies where the physician and the patient are
in the same room together. That's point of
care, and they're doing some procedure.
More often than not, that's an optical device,
either taking a measurement or doing a treatment
with a laser or an optical system.
So point of care is one area. The
other one is molecular diagnostics.
You know, most
molecular diagnostics
use optical wavelengths
to do spectroscopy
to take those measurements, either Raman or,
scatter or,
fluorescence
diagnostics.
So molecular features,
point of care technology,
and just the,
usability too. The fiber op the fact that
you can use fiber optics for delivery
or recovery,
means that you can do endoscopy or minimally
invasive procedures.
And so, again,
you know, has transformed medicine. Let's face it.
It's transformed medicine completely
by its ability to get information in or
out of the body through fiber optics.
Okay. And then
looking
specifically now at optics within medical physics, particularly
radiation therapy,
what are some of the uses of lights
in this field?
Yeah. So, again, I think it's,
not widely appreciated, but
most detector systems
in their core,
they're either the detected signal is electrical
or optical
or both.
But, you know, specs and PET systems all
use scintillation,
to turn x, gamma ray into an optical
signal. And so there's optical detectors at the
back end of most nuclear medicine devices,
often previously photomultiplier
tubes, but now more and more solid state,
silicon
devices.
Radiation detectors in general,
Again, the once the radiation is
converted to something, it's usually an electrical or
an optical signal.
And so,
a lot of,
personal radiation monitors like film badges,
thermoluminescent
detectors,
optical sent
to, optical,
OSLDs
are are,
optical in their nature.
So, you know, optics has a major role.
And then even just very simple things like
positioning of patients in the room. You know,
we use
laser lines
to align patients,
to millimeter level precision when they sit on
a CT scanner or an MRI or a
radiation therapy device. So,
optical systems are used for patient alignment.
And then more and more,
we are using optical systems for alignment where
there's some kind of a surface scanning technology
where the body entire body is,
scanned
with, stereo vision or with, speckle patterns
to,
verify the position of the patient in the
treatment device or the imaging device.
Okay.
And,
is it used within
dosimetry
in radiotherapy?
Yeah. So so in dosimetry,
again,
scintillators
are probably the most one of the most
ubiquitous.
Ionization chambers are most commonly used as reference
dosimeters,
but to do basic
measurements that are undistorted
by,
radiation fields or magnetic fields, scintillators are very
commonly used.
Film
is also commonly used in a lot of
the probably one of the oldest optical detectors
that exists. Is film
still, routinely used for surface dosimetry,
and then it gets read out.
The types of film we use today are
different than the old types that needed development,
but it's still an optical readout
of,
radiation dose.
And then, you know, in the last couple
of decades, people have developed these gel dosimeters
that are three-dimensional. It's sort of like a
three-dimensional film
that,
is exposed to radiation and then turns color
or turn either absorption or fluorescence,
and that can be read out optically to
get a three-dimensional
image
of radiation delivery.
So, you know, all the way from point
detectors
to surface dose to three-dimensional
dose,
optical devices are used throughout radiation therapy.
And
then
one really interesting development is, harnessing Cherenkov light
to image radiation.
So, first of all, can you just explain
what Cherenkov light is?
Sure. Yeah. So Cherenkov light is,
this,
a funny little light signal
that comes off when ionizing radiation is incident
in any material.
And we
almost everybody routinely
thinks of
when you think of radiation, you think of
a blue glow. And in fact, that blue
glow
is Cerenkov light. So we implicitly most of
us
know of radiation
in Cerenkov light already,
and it's because we've seen pictures of used
nuclear fuel bundles in water where there's a
blue glow happening,
or, there's pictures in the public media about
radiation and,
you know, this blue glow is sort of
used to illustrate
the presence of radiation. But in fact, it's
real.
It's it comes from soft
collisions of high energy electrons with matter, and,
the electromagnetic
torque, if you will, of the medium emits
this blue light as the electrons,
collide. And and so it's a direct measurement
of radiation
dose in any material.
Okay. So when this happens within tissue in
a in a body, how can this light
be used in radiotherapy
for,
measuring dose?
Yeah. So, you it's possible to image. It's
very low. You know, if you if you
were actually standing in the room,
you wouldn't be able to see Crenkov light
unless you turned the room lights off. And
it was pitch black and the radiation beam
is hitting the patient. You actually could see
the blue glow. You could see Cerenkov light
coming off them. Patients for years have,
commented on the fact that when their eyes
are closed and there's radiation to their head,
that they can see blue light in their
eye, and that's a Cherenkov light, we believe.
And so it is
possible to image it. It's but it's very,
very low. And so to do it,
so we developed
systems back in the,
2012, 2014
time frame
to image this, and they have to be,
especially time gated
to linear accelerator pulses. And so that is
the unique
aspects that allows it to be detectable as
you have to time gate your acquisition
to the, delivery of the radiation.
But it's it it comes off of everything
that gets irradiated
at some level.
It's just a really small light
signal. And and can you use, like, the
sort of the level of this signal to
indicate the dose that's been delivered? Is is
one proportional to the other?
That's right. So the the emission of Cherenkov
light is directly proportional
to the dose.
It could you know, the signal can be
distorted by the object that it's coming out
from, but the production of Cherenkov is directly
proportional to the radiation dose. So
if you collect it properly,
it can be a direct indicator of dose
delivery.
Okay.
So, I mean, you are cofounder and president
of a a Dartmouth spin off company called
Dose Optics,
which is commercializing this drink of imaging technology.
So can you tell us about the company's
BeamSight product?
Sure. Yeah. So we,
as I said, we
developed the techniques of how to optimize
collection of Cherenkov light and radiotherapy
back in about 2012 to 2014,
and we, developed patents around that as as
every technology person should do,
and then realized there was an opportunity there
to spin off this as a as a
unique dosimetry technology for radiation therapy.
So this was really exciting for us because
we had invented it in our lab and
realized that there really should be a product
here.
And so
myself with
a a couple of other people from Dartmouth,
spun out a company. And we were very
lucky to get a pilot a series of
pilot grants from the,
NIH, National Institute of Health
to kick off the company.
And we,
embarked for the next few years on sort
of perfecting the product. And so we now
it's gonna I'll call BeamSight,
and it's really it's a camera system
that's very sensitive,
has a intensifier
built into it to,
both time gate the acquisition
and amplify
the intensity.
Time gating is critical because the room is
well lit, so we didn't. We knew we
didn't wanna we couldn't ask
the therapy people to turn the room lights
off. So we have to capture this Trinkoff
light signal that's really tiny
in a massive ambient room background light.
And so
the key is time gating,
and temporal sequencing of that,
and then,
pretty massive amount of image processing and signal
processing on the back end. So these cameras,
as most high end cameras are,
they have a what's called a field programmable
gate array. It's like a little programmable computer
on board on the back end of the
camera,
and that does a a quite a bit
of image processing,
to make the image usable.
And so,
it's quite striking because the patients in the
room,
they're getting radiation therapy treatment.
They are, I would say, unaware that there's
this light signal coming off of them, but
the camera picks it up, locks into it,
rejects,
you know, 99.99%
of the background room light
and,
displays an image of that Cherenkov
light coming off of their tissue.
And and then this is used
and displayed at the therapy console so the
radiation therapy team can actually see what's happening.
And it and it's,
developed so it can image at 30 frames
per second. So it's real time video,
and and they can see the radiation treatment
as it happens. And so,
you know, most radiation treatments are just fine,
perfect, you know,
but that patients have to come in every
single day for thirty days in a row
and get millimeter level
accuracy in their delivery.
And so this camera system allows them to
actually just see
what's happening each day and and and help
verify
that the treatment is truly accurate. And, you
know, I mean, let's face it. They're not
all treatments are perfectly accurate, and so this
camera can pick up little,
incidents and help the therapy team, fix it
when it does happen.
Okay. So and is this in a routine
clinical use yet?
Yeah. So we,
the company
developed it as BeamSight.
It got picked up,
and is distributed by a British company called
Vision RT,
and they market it as DOSRT.
It is now,
in worldwide sales as of 2025,
and I think the number is it's installed
or being installed in over 40 cancer centers
today.
Oh, wow. That's that's impressive.
Yeah.
So, I mean, what's next in the pipeline
for Cherenkov Imaging?
Are there other things you can do with
this
technique? Yeah. So, I mean, I think we're
in a a deployment phase where, you know,
it's there were a couple early adopter academic
medical centers that picked it up and used
it, but we're really now in a phase
where regular
cancer therapy clinics are installing it, using it,
and,
they're using it in everyday radiotherapy. So that
pay you know, every single day when a
patient's getting treated, they can see it. And,
we actually have a consortium of users now,
and they sure sort of share stories and
tips on how to use the technology and
make sure that,
they use it to effectively make their
therapy as safe as possible.
So we're in this kind of phase where
there's a a growing
slate of adopters, and those adopters
are sharing
use cases with each other.
We are
doing a couple different studies. You know, we're
actually
doing a study at Dartmouth now on contralateral
breast dose. So, you know, the biggest use
of radiation therapy is in breast cancer.
And so women who get lumpectomy for
a a cancer
in the breast go on to radiation almost
always.
And the design of that radiation therapy is
to treat the diseased breast, but do not
treat the normal breast on the contralateral
side. And but, you know, sometimes the alignment
isn't as good as it should be, and
and there can be dosed to the contralateral
breast. And so we're doing a study now
to minimize that to or to well, a
a, to identify when it happens,
and then the second step will be to
develop techniques to minimize that and using Cherenkov
as a tool. Again,
you know, the the benefit of Cherenkov is
that prior to its invention,
radiation therapy is completely invisible. So
the patient gets lined up on the
patient treatment couch,
and everybody walks out of the room, and
the patient's lying there by themselves.
Radiation therapy device is doing the treatments to
them,
and there's a video camera, you know, in
displaying the patient,
view to the therapy team, but they're outside
the room, you know, a few
meters away.
And and nobody can see the treatment, you
know, because the X rays aren't visible. So
the TranKov allows the team to just very
simply intuitively
see the treatment.
And that, I think, is the main benefit
is,
you know, safety,
really needs to be simple.
If the safety tools you're using
are complicated,
it means there's lots of room for human
error. You know? So I think the the
value of Chernkoff
is that it makes safety simple,
and very visual and intuitive.
And, I think that will be the the
lasting power of it as a technology.
And I guess this light is just it's
generated within the patient. You're not doing anything
extra other than detecting it. It's sort of
there for you to use already.
That's right. It's it's always there. It just
needs a camera system to pick it up
and display it, and every every patient who
gets radiation therapy could benefit from it just
to verify that the treatment was accurate.
And and, again, the the important piece of
this is patients come in for many days
in a row, typically thirty days in a
row. So, you know, if if you make
one
small positioning error, you you can fix it
for the other 29.
And that's the key is is the tool
because positioning is so
is supposed to be so high precision,
we need tools to verify that high precision,
and then it's gotta be done every single
day for thirty days in a row. So,
that is where why it's so important to
have a intuitive and easily used tool
like Cherenkov Imaging.
Excellent.
And then
shifting focus now, you you've also cofounded
another company called Hypoxia Surgical,
and this company is developing an imaging system
to visualize oxygen levels in tissue in real
time.
So could you explain how this technology works?
Sure. Yeah. So I I, you know, so
I I'm an optics person in general, not
really necessarily
married to one
therapy. I I work in surgical guidance technologies
as well,
and and there's a whole field of what
is sometimes referred to as molecular guided surgery,
where you wanna give the surgeon
a view of what they're cutting or doing
based on the molecular signatures of the tissue.
And and that's really what this technology is
is,
we have, developed a, again, a time gated
technique
to image a light signal
that comes out of tissue
that is
amplified when there's no oxygen. So it's high
when the tissue is hypoxic or no oxygen
in it,
this special light signal comes out. And we
we induce,
where we amplify that light signal by giving
the the patients
a metabolic
drug called aminolubalinic
acid. It's a very, commonly used agent,
for a number of diagnostic and therapeutic conditions.
So it's in wide human use.
The cameras that we have developed,
again, pick up when
a signal from the tissue when it's hypoxic.
And, you know, oxygen is ubiquitous in living
organisms and tissue. Right? So when there's a
lack of oxygen, that's a a disease state.
And so tumors
or peripheral vascular disease
or,
compromised lymphatics,
have hypoxia.
And so that's where
this imaging tool,
could have, its potential. So we're in early
stage of this company,
Hypoxia Surgical.
The camera systems developed
were exploring a couple different sort of medical
use cases of it.
But we know
that the lack of oxygen is indicative of
damage or disease.
And so there's we're pretty confident that it
will have
its role in medicine.
It's just,
determining which one it is. And right now,
we're looking at surgical guidance for,
cancer or lymph nodes
as one of the more compelling
application areas for it. Yeah. But is there
a way it could be used in radiotherapy
as well? Because, obviously, hypoxia
is a big important part of such treatments.
Yeah. Great question. So oxygen is a is
a very important molecule in radiation therapy. It
increases the effect of radiation by close to
a factor of three.
So the lack of oxygen would increase would
would indicate that radiation therapy would not be
very as effective. And so we are exploring
that use in,
radiotherapy
as a adjuvant tool as well.
And this is more in early stage investigation,
you know, studies in animals right now.
But, for sure, we we can use it
to,
see when radiotherapy will be less effective.
And then there's this,
ultra high dose rate radiotherapy that actually consumes
oxygen very rapidly,
and so we're using the hypoxia surgical cameras
to image that as well.
So it's been a great tool.
You know, figuring out its use case in
radiotherapy will take a little bit of time,
but we're certainly working on that right now.
Excellent.
So
many of these developments
would have been published in the journal Physics
in Medicine and Biology,
which is celebrating its seventieth anniversary this year.
So so with that in mind, I wonder
if you could give us an example of
some exciting research that you or your team
has has published in PMB.
Sure. Yeah. I mean, we've,
I've published
so many articles in PMB. It's actually hard
to choose,
which one exactly.
But, certainly,
the use of,
oxygen imaging and flash radiotherapy
has been a big one. And, we recently
published a paper where we
looked at the oxygen consumption
in flash radiotherapy and,
how it can be a limitation
in, delivery.
In in the field of flash radiation therapy,
people are trying to figure out, what's going
on. Like, in flash radiotherapy, if you give
very high dose rate radiation,
you reduce the damage to normal tissue, but
you don't reduce the damage to tumor tissue.
So that's the mystery. Like, why nobody can
explain why that's true. Why do we reduce
damage to normal tissue but not tumors?
And so we're looking at the oxygen effect
and its role,
and that's what we published recently in,
PMB,
to try to explain that we we don't
have the
solution yet. It's like,
we're writing a mystery novel, but we don't
have the last chapter. You know?
But, certainly,
the pieces of the story
are that oxygen is involved,
and the consumption of oxygen
changes when you change the dose rate. And
so we think that's an important piece. We
think it's a we know it's a major
factor, but we we don't know the underlying
mechanism yet. And, hopefully, that'll be our next
paper once we discover the mystery of flash
and publish that in PMB as well. Excellent.
Yes. I want to keep an eye out
on,
I guess, what once the mystery is solved,
then maybe we'll see FLASH
radiotherapy
in you being used in the clinic perhaps.
It is. Yeah. There are clinical trials ongoing,
but like most things in medicine, you know,
you don't have to know the mechanism
to use it clinically. So it is being
explored clinically,
but I think it would most people would
agree it'd be more comforting if we sort
of had at least a really solid guess
about the underlying mechanism for how it works.
And so we wanna do both, really.
Exactly.
Okay. And then finally, looking into the future,
where do you see optics having the biggest
impact in impact in medical physics? So,
will the techniques that we discussed become increasingly
common perhaps for guiding and improving radiotherapy?
Or do you think perhaps there's another area
of medical physics in which optics could play
a a really important role?
Yeah. That's a great question. It's a question
I think about all the time because I
live in both of these worlds.
It's almost impossible for me to pick one
area, you know, but I I would just,
leave off perhaps by saying, you know,
the use of optics is much, much larger
than the use of radiation
in medicine. Right? And so the tools
for imaging
or diagnosing things with optics are incredible.
And so
the intersection
between radiation medicine
and optical diagnostics
or therapeutics is really wide open.
You know, we're looking at some,
we're looking at some areas now where optical
photosensitizers
can become radiation sensitizers.
You know, that's one really exciting area to
me. But even more broadly than that, just
the idea that optical,
diagnostics and treatments can be combined
with radiation
therapy or diagnostics or treatments. To me, that's
the intersection that is really fertile
and and really quite unexplored.
There's only a handful of researchers I know
working at that intersection space,
but it's huge because both fields are enormous.
You know, again, the optical devices are just
everywhere.
Radiation is incredibly powerful.
And and and often, they kill tissue in
a complimentary ways
or the diagnostic
measurements are complimentary.
You know? X rays are good at structure.
Optics is good at molecular signatures.
You know? So why not combine them to
get more detailed information?
That those those are the areas that excite
me the most and I think has
the enormous potential
for, future development.
Brilliant. Well, thank you very much for speaking
with us today.
Sure. Well, thank you, Tammy. It's been a
pleasure.
That was the medical physicist
Brian Pogue in conversation with Physics World's Tammy
Freeman.
It was recorded in association with the journal
Physics in Medicine and Biology,
which celebrates
its seventieth
anniversary this year.
I'm Hamish Johnston, and our producer is Fred
Iles.
The theme music for this podcast
is called one three seven, and it was
composed and performed
by the physicist
Philip Moriarty.
This episode
is supported by One Physics.
One Physics is The USA's
largest
outsourced medical physics provider,
trusted by over 4,000
clients.
We proudly deliver diagnostic and therapy physics services,
linear accelerator commissioning,
dosimetry
treatment planning, and radiation safety officer services
nationwide.
We are experts in medical physics services
and radiation safety and can support your organization,
whether you need annual physics testing to meet
regulatory guidelines
or are looking to implement a theranostics
program.
We are experts in all areas related to
physics and radiation safety.
With national scale and a local
relationship driven approach,
our best in class physicists
bring precision and personalized care to every facility
we serve.
In the world of medical physics,
precision
isn't optional.
It's everything.
One Physics,
your trusted partner in medical physics,
linear accelerator
commissioning,
and radiation safety.
Learn more about our approach
to radiation safety,
or schedule a personalized
consultation
at 1physics.com.