How to Report Low-Level Laser Therapy (LLLT)/Photomedicine Dose and Beam Parameters in Clinical and Laboratory Studies

Abstract

Background: Dose and beam parameters are critical for successful laser, LED, and other light therapy treatments; however, in our experience, researchers frequently make critical errors and omissions when submitting papers for publication. Journals frequently publish studies with missing data, mathematical errors, and no reported verification of beam parameters. This makes reproducibility impossible, and further confounds an already complex subject. Objective: This article is intended to be a reference document for non-physicist researchers conducting low-level laser therapy (LLLT) laboratory studies and clinical trials to help them design and report the beam and dose aspects of their trials. Recommendations: It provides a checklist to help LLLT researchers understand and report all the necessary parameters for a repeatable scientific study. It includes the eight most important beam parameters to report, which are: wavelength, power, irradiation time, beam area at the skin or culture surface (this is not necessarily the same as the aperture size), pulse parameters, anatomical location, number of treatments, and interval between treatments. The three commonly used dose parameters are time, energy, and energy density. In addition, more thorough reporting would include coherence, application technique (contact, projection, scanning, pressure), beam profile, and spectral width, as these may also be considered important. Beam power often decreases as the device warms up and as the device ages; therefore, this should be checked routinely during an experiment/trial. Measurements of beam area and beam power require special instruments and trained technicians to operate them. Power measurements should be taken before, after, and at frequent intervals during research trials. Conclusion: Reviewers should insist that the minimum eight most important beam parameters are included, and authors should take care to measure and record these accurately before, during, and after an experiment or clinical trial.

Introduction

A s reviewers for this and other journals, and as earnest consumers of the broader body of low-level laser therapy (LLLT) literature, we see many apparently high-quality articles in which most of the methods and materials are explained in great detail; however, despite these being studies on the effects of light, they often lack necessary beam and dose information. Several reviews of LLLT have been published in recent years and many have commented on the absence of essential beam parameters and/or dose information.^1

–6 Of 22 articles reviewed by Fulop et al.,² 19 were missing either wavelength, power, or power density information.

Much has already been written about beam measurement, dose calculation, and the reporting of parameters,^7

–11 but no guidelines have been imposed on reviewers or authors setting out the minimum standards for reporting beam parameters and dose. There is also no consensus among manufacturers in the way they measure and present the specifications of their devices, thus further complicating the issue.

Without some standardization in beam measurement, dose calculation, and the reporting of these parameters, advancing the field of LLLT/photomedicine will be more difficult, as studies will not be reproducible, and outcomes in clinical research and practice will not be consistent.

To establish the importance for the standardized reporting of beam parameters and dose, we will first define the problems caused by incomplete reporting, which is the loss of information, and why we think this has happened.

Reciprocity

It seems that many researchers, practitioners, and manufacturers believe that wavelength and energy (Joules) or energy density (J/cm²) are all that is necessary in order to replicate a successful treatment, and that it does not matter what the original power, power density (irradiance), and time parameters were. They will substitute a laser/LED of the same wavelength, and then vary the power or exposure time until the same energy is delivered. This is a very common but fundamental mistake.

The belief may have arisen from the Bunsen–Roscoe law of reciprocity (also known as the third law of photobiology, and the reciprocity rule), which asserts that the effects of irradiation will be independent of irradiance and exposure time as long as radiant exposure is maintained.^12,13 This rule has subsequently been disproven in general photobiology, photography, and LLLT/photomedicine.

Lanzafame et al.¹⁴ showed that LED radiation at 660 nm on their murine pressure ulcer model, when applied with increasing power density (irradiance) and decreasing irradiation time, produced very different effects, despite keeping energy density (fluence, J/cm²) constant.

Lopes et al.¹⁵ compared two 660-nm lasers on a hamster model for oral mucositis. One was 32.8 mW and applied for 16 sec, the other was 92.6 mW and applied for 9 sec, each delivering 2.78 J of energy per treatment. The 32.8 mW laser reduced inflammation, whereas the 92.6 mW laser actually increased the inflammation.

Oron et al.¹⁶ compared 810 nm on rat infarcted heart at 2.5, 5, and 20 mW/cm² with a total of 0.3 J/cm² applied for each, but only the 5 mW/cm² groups showed a marked reduction in scar tissue.

Reproducibility

A further impact of the acceptance of reciprocity is the incomplete reporting of parameters in the literature: If one only needs to know the radiant exposure, why record the other parameters?

To understand the extent of the problem, one must only look at the numerous instances in literature reviews in which key parameters are stated as being “not reported” or “unavailable”.

According to Landauer's Principle, information is lost whenever the inputs to a calculation are lost. This can be likened to the increase in entropy in physical systems, in that it is an irreversible condition, that is, once lost, information cannot be reconstructed.

Therefore if, for example, one calculates and reports the radiant exposure but does not similarly report the radiant power, irradiated area, and exposure time, the total amount of information available to future researchers and practitioners is reduced to one number which, in isolation, does not hold much value.

Over the years, many articles have been published, and protocols developed, which present only one or two parameters at best, such as the dose (Joules or J/cm²) and wavelength. Unfortunately, the resulting lack of information about other as, if not more, important parameters means that many hours of tedious work by numerous researchers has added virtually nothing to the body of knowledge.

Standardizing the Reporting of Parameters

Having reconfirmed the need for the accurate, complete reporting of a comprehensive range of technical and treatment parameters, herein we now propose a standardized tabular format (Tables 1 –3) for presenting this information, and suggest accompanying procedures for this and other Journals to follow to ensure compliance by authors.

Table 1.

Device Information

^*Manufacturer
^*Model Identifier
Year Produced
^*Number of Emitters
^*Emitter Type¹
^*Spatial Distribution of Emitters²
^*Beam Delivery System³

e.g., InGaAlP LED, GaAlAs LASER, KTP LASER

e.g., Four emitters spaced 2 cm apart in a square pattern.

e.g., Fiberoptic, free air/scanned, hand-held probe.

Note: Essential details are marked with an asterisk (^*), but it is recommended that all known parameters be provided.

Table 2.

Irradiation Parameters

Parameter [unit]	value	Measurement method or information source
^*Center wavelength [nm]
^*Spectral bandwidth [nm]
^*Operating mode¹
^*Frequency [Hz]
^*Pulse on duration [sec]
^*Pulse off duration [sec] or duty cycle [%]
Energy per pulse [J]
^*Peak radiant power [mW]
^*Average radiant power [mW]
Polarization²
Aperture diameter [cm]
Irradiance at aperture [mW/cm²]
Beam divergence [rad or deg]³
Beam shape⁴
^*Beam profile⁵

e.g., Continuous wave (CW), switched CW, pulsed, Q-switched.

e.g., Yes, no, linear.

e.g., 9° x 27° full width half-maximum (FWHM) for an elliptical source, or, e.g., 0.44 rad (1/e² half-angle) for a Gaussian source.

e.g., Circular, elliptical.

e.g., Gaussian, Top Hat (essential for in vitro culture studies).

Note: Essential details are marked with an asterisk (^*), but it is recommended that all known parameters be provided.

Table 3.

Treatment Parameters

Parameter (unit)	Value	Additional notes
^*Beam spot size at target [cm²]
^*Irradiance at target [mW/cm²]
^*Exposure duration [sec]
^*Radiant exposure [J/cm²]
^*Radiant energy [J]
^*Number of points irradiated
^*Area irradiated [cm²]
^*Application technique¹
^*Number and frequency of treatment sessions²
^*Total radiant energy [J]³

e.g., Skin contact, contact with pressure, interstitial fiberoptic.

e.g., 12 treatments total, delivered one every other day over 24 days.

The total accumulated energy delivered per session and over all sessions.

Note: Essential details are marked with an asterisk (^*), but it is recommended that all known parameters be provided.

It is not uncommon to find discrepancies between the specifications provided by a manufacturer and the actual performance of any given device.¹¹ Therefore, in order to maximize their value, it is also useful – and, we would argue, necessary – to know whether the parameters as reported were:

1. Sourced from the equipment manufacturer's specifications (in which case tolerances should be included, e.g., 830 ± 5 nm);

2. Measured by the manufacturer and/or researcher (in which case a description of the test equipment, its calibration status, and the test method used should be included); or,

3. Independently measured and/or verified (in which case details of the test agency and/or a copy of the test results should be provided).

The rationale for the chosen parameters and dosage, and patient/medical factors such as the presenting pathology, etiology, type of lesion (acute versus chronic condition), anatomical location, depth of the target tissue, skin pigmentation, and the overall condition of the patient are also important and must be reported,⁹ but fall outside the scope of the current article.

In order for a standardized method of information collection and presentation to be of value, its application must also become standard procedure. Therefore, we suggest presenting authors with a document containing the proposed tables and instructions for completing same, and requiring this to be completed and submitted before a manuscript is disseminated for review.

Conclusions

Reproducibility of research is a fundamental tenet of good science; therefore, any instance of incomplete reporting of parameters is bad science. Reproducibility requires accurate and complete reporting of technical and treatment parameters, as is applicable and appropriate in each case.

We propose a tabular format, in an attempt to provide a standardized method for presenting what can amount to a quite comprehensive set of parameters.

Such a format will not prevent other problems, such as calculation errors and typographical mistakes, but it will enable such errors to be easily and quickly identified during the review process and corrected before an article is published.

This rigor will significantly increase the information content of many published works and, therefore, enhance the value of those works in the overall body of knowledge pertaining to photomedicine and its underlying mechanisms and clinical applications.

References

Chow

R.T.

et al. 2009. Efficacy of low-level laser therapy in the management of neck pain: a systematic review and meta-analysis of randomised placebo or active-treatment controlled trials. Lancet., 374:1897–1908.

Fulop

A.M.

et al. 2010. A meta-analysis of the efficacy of laser phototherapy on pain relief. Clin. J. Pain, 26:729–736.

Tumilty

et al. 2010. Low level laser treatment of tendinopathy: a systematic review with meta-analysis. Photomed Laser Surg,., 28:3–16.

Bjordal

J.M.

et al. 2003. A systematic review of low level laser therapy with location-specific doses for pain from chronic joint disorders. Aust. J. Physiother., 49:107–116.

Chow

et al. 2011. Inhibitory effects of laser irradiation on peripheral Mammalian nerves and relevance to analgesic effects: a systematic review. Photomed. Laser Surg., 29:365–81.

Bjordal

J.M.

et al. 2008. A systematic review with procedural assessments and meta-analysis of low level laser therapy in lateral elbow tendinopathy (tennis elbow). BMC Musculoskelet. Disord., 9:75.

Stuck

B.E.

1993. Measuring and reporting physical parameters in laser biolnodulation research. Proc. SPIE, 1883:21(1993)doi:10.1117/12.148024.

Tunér

, Hode

2004. The Laser Therapy Handbook. Prima Books AB: Grängesberg, Sweden.

Enwemeka

C.S.

2008. Standard parameters in laser phototherapy. Photomed. Laser Surg., 26:411.

10.

Enwemeka

C.S.

2009. Intricacies of dose in laser phototherapy for tissue repair and pain relief. Photomed. Laser Surg., 27:387–393.

11.

Guirro

R.R.

, Weis

L.C.

2009. Radiant power determination of low-level laser therapy equipment and characterization of its clinical use procedures. Photomed. Laser Surg., 27:633–639.

12.

Nussbaum

E.L.

, Lilge

, Mazzulli

2003. Effects of low-level laser therapy (LLLT) of 810 nm upon in vitro growth of bacteria: relevance of irradiance and radiant exposure. J. Clin. Laser Med. Surg, 21:283–290.

13.

Bunsen

R.W.

, Roscoe

H.E.

1862. Photochemical researches - Part V. On the measurement of the chemical action of direct and diffuse sunlight. Proc. R. Soc. London, 12:7.

14.

Lanzafame

R.J.

et al. 2007. Reciprocity of exposure time and irradiance on energy density during photoradiation on wound healing in a murine pressure ulcer model. Lasers Surg. Med., 39:534–542.

15.

Lopes

N.N.

et al. 2009. Cyclooxygenase-2 and vascular endothelial growth factor expression in 5-fluorouracil-induced oral mucositis in hamsters: evaluation of two low-intensity laser protocols. Support. Care Cancer, 17:1409–1415.

16.

Oron

et al. 2001. Attenuation of infarct size in rats and dogs after myocardial infarction by low-energy laser irradiation. Lasers Surg. Med., 28:204–211.