Page 62 - Veterinary Laser Therapy in Small Animal Practice

48 Veterinary Laser Therapy in Small Animal Practice

interaction. With infrared light, since scatter is the exactly perpendicular to the surface at all times. So if
primary interaction, it is more appropriate to talk about you were to treat an exact area of 500 cm – i.e. the very
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the energy that passes through a given cross-sectional edge of the visible light you see on the surface of the
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area, rather than a given volume. patient is exactly 500 cm – you are actually treating an
So now we have to revisit those two critical values additional 20% around the edges of your treatment area
and add some spatial dimensionality to them in order to (Fig. 6.6). BUT that extra 20% is virtually all subdermal
be useful. We started with energy and power. Now we treatment. So when treating the fringes of a wound,
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move to energy density, better known as dose (J/cm ) make sure you cover (with your visible aiming beam)
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and irradiance (W/cm ), or what is more commonly an extra 2–5 cm along the periphery, and then you will

referred to (especially in this book) as power density. get the benefit of this additional 20% beyond that.
6.4 How this adds up to dose That extra 20% is welcome, since there is no
disadvantage from treating healthy tissue (except for
Talking about the number of joules of energy you deliv- the usual contraindications). Having said this, 20%
ered in a therapy session is a little like talking about of a 1–5 cm spot is a small area, so
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how much water came out of the hose as you water don’t think that treating a few points in
your garden. Is 20 liters a lot of water? If you poured an area is the same as spreading a full
it all into a single flower pot, then yes. If you watered dose over every square centimeter of it.

your whole lawn, then absolutely not. The same goes Unless you are treating trigger points or acupuncture
with light. points, your aim is to cover the whole area.
If you deliver 100 J of energy to an entire hip, you’re

not going to get much of a therapeutic effect. The hip of

a medium-sized dog spans something like 500 cm and The following chapters will give you specific recom-

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so this 100 J divided by 500 cm yields an average dose mendations for a variety of treatable pathologies and

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of 0.2 J/cm . If you gave that same 100 J to an affected anatomies, but these basics of measurement set the
paw that spans only 50 cm , then you would have given stage. Almost.
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an average dose of 2 J/cm . Now we’re talking.
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However, there is still the lateral spread of light, even 6.5 Interpreting dose in vitro vs. in vivo
if you are diligent enough to keep the treatment head

The simple calculation above is just that: simplified. It
gives the average dose delivered to the SURFACE of the
patient. We’ve just spent many pages talking about how
complex the light transport and penetration situation is.
And if you are talking about treating wounds, the sim-

plified calculation in the last section is pretty much the
whole story. But the majority of what you’ll be treating

won’t be superficial; it will live within the soft tissue and
bones and joints of animals ranging from 2 to over 50 kg.
This is important to keep in mind as you continue to

read through the rest of this book, especially as we cite
dose values from publications.
Virtually all of the empirical investigations that
attempt to narrow the optimal treatment parameters

Figure 6.6 Treatment boundaries for an example wound. have been performed in vitro. These studies have the
The blue area represents the boundaries of the actual wound. advantage that the majority of the parameters can be
The purple encompasses the recommended treatment area easily measured and well controlled, and many of the
(the amount to cover when aiming your beam). The red results of these experiments have indeed shown an
approximates the area through which you actually deliver a optimal dose region for biostimulation above which very
subdermal treatment dose. little clinical benefit results. There are, however, inherent

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