Practical Laser Phototherapy: How, and how often, should I treat?

Peter A. Jenkins, MBA

The design of a laser therapy regimen for any injury or ailment should be approached from the perspective of the desired clinical outcome at the end of a course of treatments and, more specifically, the outcome of each individual treatment session:  The latter will largely determine the appropriate selection of each of the various treatment parameters, e.g., power density, irradiation time, treatment technique, etc.; and, the former will largely determine the frequency of treatments - although this is also influenced by the progress of the patient toward the desired outcome - and will take into account the effects of the various mechanisms of action and the condition of the tissues that are to be irradiated.

Let’s take, for example, an acute musculoskeletal injury, indicated by pain and inflammation due to soft tissue damage. The primary desired outcome of the initial stage of treatment is pain attenuation, and one quite effective mechanism involves an inhibitory ‘nerve block’ effect. For chronic pain, it has been shown that treatment should be repeated every two days because the effect lasts for about 48 hours.

For acute pain, however, one could treat even more frequently – even multiple times per day – although it should be noted that the underlying injured tissue within the irradiated area might be over-treated by this regimen if it were to be maintained beyond the first few days post-injury. Once the pain is at a bearable level, usually after 2-3 days, treatment frequency can be reduced to daily, as the primary desired outcome during this period is now the reduction of inflammation and its related pain.

As soon as the inflammation is under control, healing of the injured tissues can begin. The cells of injured tissue are more sensitive to exposure to light than are the cells of intact tissue, and so irradiation that is repeated too frequently can lead to an accumulation of effects in the local tissues and, therefore, an over-stimulation that subsequently leads to bio-inhibition (per the oft-referred Arndt-Shultz curve).

The dose should be reduced by approximately 30% at this point, and I would further suggest that the frequency of treatment should also be reduced, perhaps initially to once every 2-3 days for a week or two, then every 3-4 days for another week or two, and then once a week throughout rehabilitation.

If the patient suffers a flare-up in symptomatic pain and/or inflammation in the injured area as they progress through their rehabilitation and return to full function, as is often the case when someone over-exerts themselves during their rehab exercises, treatment frequency can be temporarily increased as the condition can again be considered acute – albeit usually at a lesser severity than the original injury.

It should be noted that what I have presented as distinct steps in the treatment process, e.g., pain attenuation -> inflammation reduction -> tissue healing, will actually produce a continuum of activity.

Continuing our example, with acute injuries there is often an increase in blood/fluid perfusion to the affected area, and blood is a major absorber of light within the range of wavelengths we use for laser therapy. While delivering higher, inhibitory levels of irradiation at the tissue surface to affect pain attenuation through the temporary inhibition of axonal transport, we are, due to the increased absorption of energy throughout the intervening tissues, consequently also delivering a lower level of irradiation that is more appropriate for affecting biostimulation, to the damaged deeper-lying tissues.

Thus, during the initial period of treatment targeted toward maximising pain attenuation, there will also be some effect upon inflammation. And, as inflammation resolves, healing will begin even before this becomes the primary targeted outcome of treatment.

As this is obviously an imprecise process, the outcome of each treatment session and the patient’s overall progress should be continuously monitored and the treatment plan adjusted accordingly.

Another important factor in the practical application of laser therapy is treatment technique. There are two basic application techniques – contact and non-contact – and a number of variations of each. For example, you could use a non-contact scanning technique, in which the laser beam is kept moving over the treatment area, or a non-contact stationary technique, in which the beam is held steady over one particular site. Then there’s stationary contact, contact with pressure, contact with pressure and movement, and so on.

There are a number of considerations to make when deciding which technique to use. The stationary contact with pressure technique is, for example, indicated when the treatment target is at depth in the tissue.

When using the stationary contact-with-pressure technique the maximum effective penetration depth is essentially deterimined by the wavelength & amount of pressure applied. At that depth, the intensity of the laser beam is significantly reduced, compared to that delivered at the tissue surface, due to absorption and scattering of the beam in the tissue that lies between the laser source and the target tissue, so the rate of energy delivery at the maximum penetration depth is significantly slower than in the tissues closer to the source. Therefore, to deliver a given amount of energy (power x time) at that maximum penetration depth, you must increase the irradiation time accordingly.

Holding a laser aperture with a convex lens in contact with the tissue will maximise the amount of light that enters the tissue by reducing reflection and backscatter. Applying pressure will compress the tissue change its optical properties, reducing lateral scattering and forcing blood from the tissue directly under the aperture, and it will reduce the distance from the laser aperture to the target of treatment.  Combined, these effects serve to reduce the amount of additional time one must spend treating deeper tissues.

Whilst treating in the contact-with-pressure technique you could also make small circular ‘massaging’ movements with the probe tip, thus providing mechanical stimulation to the tissue to help e.g. break up adhesions or stimulate circulation.

When treating open wounds or mucosa a non-contact technique is often necessary to prevent cross-contamination.  This technique is potentially beneficial, too, in terms of reducing the intensity of the beam when using higher-powered laser probes for such indications. This is due to the loss of light from reflection and backscatter, which Al-Watban has shown to be between 50-85% of the incident beam from bare skin.

When treating deeper-tissues, however, a non-contact method of application confers no benefit and, regardless of the power or wavelength of the laser, reduces its ability to achieve any appreciable depth of effective penetration. And, if irradiating over hair, such as in veterinary applications, the amount of light lost – and, therefore, no longer available to any therapeutic effect – can be up to 100%.

As we can see, the non-contact scanning technique, as must be employed when using e.g. high-powered therapeutic lasers to prevent discomfort or burning, is very inefficient. And, with specific regard to the performance of laser therapy itself, constantly moving probe makes it impossible to accurately determine or control the amount of energy that is actually delivered to the target tissue.

The target tissue is, in the majority of cases, the specific location of the pathology itself. Bjordal showed that for tennis elbow, for example, treating two or three appropriate anatomical points at a few Joules per point with a low-powered laser was more effective than simply bathing the whole area with light. For tennis elbow these anatomical targets are quite superficial and accessible to a scanned beam, yet the treatment of individual points was more effective, which shows that accuracy of delivery is an important factor in determining efficacy.

Holding the probe stationary and in contact with the skin directly over the pathology for the appropriate amount of time, and applying pressure when the pathology is deep-seated, then moving to another point and repeating the exposure, is the only way to accurately and precisely deliver the correct amount of light to the target tissue. Treating individual points also means you’re not wasting time and money treating areas that don’t contribute to the overall outcome.

So, in summary, the main considerations at each treatment session are:

  • Is the injury/condition acute, sub-acute or chronic?
  • What symptoms/indications am I addressing in this treatment session?
  • What is the depth of the injured (target) tissue?
  • What is the desired outcome of this particular treatment session?
  • How large is the area I need to irradiate?
  • What other factors must I consider (anatomical location, hair/skin color, tissue condition, etc.)?

Some other things to keep in mind are:

  1. Not targeting the pathology and under-treating are two of the most prevalent causes of nil/poor outcomes in laser therapy;
  2. In vivo, the energy actually available to the tissue to elicit photobiological effects can be significantly less than what leaves the laser source;
  3. Irradiation time and intensity is more important than the actual dose when determining outcomes; and,
  4. Reciprocity (the Bunsen-Roscoe Law of Photochemistry, which effectively states that you can double the power and halve the time and still get the same outcome) in LPT does not hold true over large variations of power and time.

As you can see there are a lot of factors for which we must account in order to optimise the clinical benefits of laser phototherapy. For this very reason, I strongly advise against the use of ‘cookie-cutter’ protocols, whether they are pre-programmed into a laser device or provided in written form. Firstly, they rarely provide the flexibility you, as the practitioner, need to change the parameters of each treatment session to maximise the benefit to each patient. And, secondly, by relying upon the arbitrary decisions of others in deciding how to treat each named condition you do not develop the knowledge or skills necessary to make these changes or to treat any non-standard cases that may present.

Further, one must not get fooled into believing the marketing hype about high-power laser therapy, which often relies upon false claims of faster treatment times, or of mitigating the risk of under-treating. While it is true that under-treating can be affected by using insufficient light intensity to obtain and sustain an effect, it can also easily be affected by using a high power beam to deliver a lot of light quickly, but for insufficient time actually over the pathological target because the beam must be kept moving across a large area of both healthy and pathological tissue, or because it’s being absorbed in hair or fur before it can reach living tissue.

A final note to remember, is that even a perfectly-structured protocol and ideal treatment technique will not produce optimal results, or, necessarily, any results at all, if the irradiation parameters are inappropriate: Whether too little light or too much, or too little time or too much, all will lead to less-than-optimal outcomes.