eCAM Advance Access published online on September 13, 2007
eCAM, doi:10.1093/ecam/nem085
© 2007 The Author(s).
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.0/uk/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Blinding Techniques in Randomized Controlled Trials of Laser Therapy: An Overview and Possible Solution
Ian Relf1,
Roberta Chow2 and
Marie Pirotta1
1Department of General Practice, University of Melbourne, 200 Berkeley Street Carlton 3053, Victoria, and 2Private Medical Practice, NSW, Australia
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Abstract
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Low-level laser therapy has evidence accumulating about its
effectiveness in a variety of medical conditions. We reviewed
51 double blind randomized controlled trials (RCTs) of laser
treatment. Analysis revealed 58% of trials showed benefit of
laser over placebo. However, less than 5% of the trials had
addressed beam disguise or allocation concealment in the laser
machines used. Many of the trials used blinding methods that
rely on staff cooperation and are therefore open to interference
or bias. This indicates significant deficiencies in laser trial
methodology. We report the development and preliminary testing
of a novel laser machine that can blind both patient and operator
to treatment allocation without staff participation. The new
laser machine combines sealed preset and non-bypassable randomization
codes, decoy lights and sound, and a conical perspex tip to
overcome laser diode glow detection.
Keywords: low-level laser therapy – allocation concealment – treatment blinding
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Introduction
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Low-level laser therapy in various therapeutic forms is widely
used as a medical treatment modality. In general, low-level
laser machines deliver laser beams in the 0.1–200 mW power
range from the end of a hand held probe, and only require a
small battery/charger/timer unit for normal operation: similar
to the modified machine photographed in
Figs 1A and B. In Australia,
one in five general practitioners use acupuncture in their medical
practice, including the use of laser on acupuncture points (
1).
Laser use has been included alongside needle acupuncture in
post-graduate physician training in medical acupuncture for
more than 15 years, and is reimbursed as a treatment modality
by the Australian Health Insurance Commission.
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Figure 1. (A) DBL Laser machine in operation for a placebo treatment. Demonstration of laser probe applied to left hand whilst machine is activated. The dummy red light is visible on the skin and is shining out of the end of the probe. The probe is activated by pressing the tiny button visible on the central part of the probe. In this instance, the machine is in full operation, however the invisible infrared laser is switched off as would be the situation for a placebo treatment. The machine activation light on the laser front panel can be seen at the top left of the photograph. Aspect; DBL Laser machine is in the background sitting on carry case. (B) Front panel DBL laser machine. Four-digit patient entry code switch sited in upper right of panel. Indicator lights for machine operation in upper left. Laser probe (white) cord inserted into bottom right panel. Timer switch - central. Manual key lock and power on/off toggle in lower left of panel. Aspect; DBL Laser machine sitting on steel carry case.
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Laser treatment approaches include: laser on acupuncture points
(
2), laser therapy for direct treatment of joint pain (
3) and
the non-contact laser irradiation technique to facilitate skin
and wound healing (
4). Although the use of laser on acupuncture
points is not yet a proven substitute for needles, it does have
demonstrated effectiveness in a limited range of acupuncture
responsive conditions (
5). A small number of randomized controlled
trials (RCTs) have demonstrated significant benefits including
treatment of; neck pain, (
6–9) low back pain, (
10) chronic
tension headache, (
11) fibromyalgia, (
12) enuresis, (
5) and
post-operative vomiting (
2).
The advantages of low-level laser over needles include: ease of application, usage in anatomically dangerous areas, and use in needle-phobic patients including children. It is low cost, non-invasive and safe. (13) General advantages of laser use in RCTs include: (i) Laser light is invisible above 770 nm and can be switched off or on without visual recognition by the patient or operator. (ii) Low-level laser has been shown to have a negligible sensory stimulus, i.e. patients have difficulty discerning whether they have received real treatment.
The suitability for trial use has been tested in three double blind RCTs: a small trial by Irvine et al. (14) and two larger trials by Chow (N = 90) (15) and Brosseau et al. (N = 88) (16) have shown that neither the patient nor operator can discern whether they are using a laser or placebo treatment. Therefore when a laser machine is used correctly it offers a useful way to ensure blinding and treatment allocation where difficulties exist with adequate placebos in needle trials (17).
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Research Methods and Laser Trials
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The most important determinants of well-conducted RCTs are adequacy
of allocation concealment and blinding procedures. Allocation
concealment refers to a process whereby an unbiased allocation
sequence is implemented in a secure manner that prevents foreknowledge
by either the clinician, researcher or trial participant (
18).
Generally, allocation concealment appears to be an important
indicator of RCT quality, as an analysis of RCTs found that
those trials that do not detail an adequate process for allocation
concealment show a 40% increased likelihood of having positive
results (
19). Therefore, the design of laser machines and processes
to ensure allocation concealment and double blinding may be
critical to unbiased trial outcomes.
Laser machines delivering visible red light (e.g. using 630 nm laser diodes) are not suitable for double-blind trials because both the patient and operator can see when the laser is switched on. Even invisible lasers have problems in RCTs as the laser diode itself glows when in use. The diode glow can still be seen in the end of the probe whether or not the resultant beam is visible. This leaves open the possibility that participants could gain foreknowledge of treatment allocation and bias the results. This article reviews the methods of allocation concealment and blinding used in published laser RCTs. We then report the features of a novel laser machine that can blind both patient and operator without the involvement of extra clinical staff, and the results of a small study to test this capacity.
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Methods and Results of Literature Review
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A literature review was performed with systematic searches of
Medline, Embase, Pubmed, Amed, Cinahl, Ciscom and Cochrane databases.
Fifty-one trials of low-level laser therapy were found that
were double blind clinical RCTs (
Tables 1–4
).
Analysis of the 51 RCTs showed 30 positive and 21 negative laser
trials. However, laser beam detection or machine randomization
had only been modified in less than 5% of these trials. (
Table 1)
The laser machine described by Toya (
6) did address the problem
of allocation concealment: a computer was used to turn the laser
beam on/off using randomized numbers that were unknown to the
operator. This is the only trial using a machine with in-built
randomization. The second trial by Krasheninnikoff
et al. (
20)
used a beam filter to preset the laser off or on. However, none
of the reviewed trials use a reliable method that addresses
the problems of laser diode glow, blinding and allocation concealment
in a single laser machine.
The remaining 49 trials (Tables 2–4
) used less rigorous methodology for adequate allocation concealment or blinding: 27 trials used identical laser probes or identical laser machines; 17 used on/off switches; eight miscellaneous trials used opaque goggles or other blinding methods. The explanation of blinding was inadequate in eight trials, nine trials required patient cooperation, and the operator was not blinded in three of the trials. All trials required some degree of staff and/or patient cooperation to conceal treatment allocation and blinding on the day that the patient was being treated, allowing the possibility of bias.
These results demonstrate a need for a laser machine that can properly blind the operator and trial participants, ensuring concealment of treatment allocation. We now describe the features of a recently developed laser machine that combines these aims and report a small study to test these properties.
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Novel Laser Machine for RCTs (Figs 1A and B, 2)
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A laser machine suitable for use in RCTs should have the following
attributes:
- An invisible laser beam.
- Disguised laser diode glow.
- Ability to preset randomized number sets and seal them into the machine.
- Security of internal structures to prevent tampering.
We have developed a new laser machine that is similar in appearance
and function to a normal low-level laser machine i.e. it has
a typically sized hand held laser probe connected to a power
source. It also has a timer, sound emitter (beep) and key lock
as is normally required by law for laser devices. Added to this
are disguises to overcome the ability of operators or patients
to see the laser diode glow. These are as follows:
- A red decoy light: A biologically inactive (63), red, non-coherent non-laser light at <0.1 mW, is installed beneath the Perspex cone, next to the diode inside the end of the probe. (Fig. 1A) This red light acts as a decoy light and overshadows the small incandescent glow from the diode. This level of red light is below threshold for measurable clinical effects (45,59).
- Conical perspex cone tip: A conical perspex cone tip has been added to cause partial internal reflection of both the dummy red light and the laser diode glow; thereby ‘blending’ the two light sources and making direct visual detection of the diode glow impossible. After fitting the conical perspex tip to the laser probe, the laser diode strength has been reset to an exit power of 10 mW as per the machine's original specification.
- Allocation concealment is ensured using a randomization keypad: The randomization schedule is generated and held by an independent researcher. This schedule is then built and sealed into each machine at manufacture. This preset schedule number is a code that allocates patients into treatment or placebo groups. Therefore, each participant will be allocated without the knowledge of the participant or treating doctor/operator. Each participant is allocated by entering their particular patient code number into the keypad on the front of the laser machine. (Fig. 1B) As mistakes can occur with the keypad number entry, the patients are asked to check their keypad number with the operator before each treatment.
- Decoys: When the machine is activated for treatment, it makes an audible beep and the console lights turn on; indicating to the patient that the machine is switched on. These decoys are in operation whether or not the real laser beam is activated. (Fig. 1B)
- Non-bypass system: the four-digit patient code switch cannot be bypassed. It is impossible for the treatment group allocation to be altered after being preset and sealed in manufacture.
- Equipment testing: the preset randomization schedule can be checked by an independent researcher prior to the commencement of the trial.
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Method of Laser Machine Testing
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To test our novel machine in its capacity to ensure allocation
concealment and blinding, a sample of 20 doctors was asked to
participate in a double blind test. The group was an opportunistic
sample of doctors who practiced medical acupuncture and presented
for a discussion group on medical acupuncture treatment in chronic
pain. All of them were familiar with the usage and risks of
low-power lasers and consented to participate. There were no
refusals. They knew there were deliberate disguises in place
i.e. the decoy red light and perspex cone. Participants were
asked to examine the laser machine and activate the laser whilst
switched between two-unknown preset positions that switched
the real laser beam off and on. The participants were asked
to determine whether they could see the laser diode operating
through the perspex cone. The possible responses: either ‘on’,
‘off’ or ‘cannot tell’, were recorded.
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Results and Discussion of Laser Machine Testing
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In this preliminary study, none of the 20 laser familiar participants
could see the operation of the laser diode. This is supportive
evidence that the laser diode disguise is effective and overcomes
this important problem in double blinding laser trials. The
preset concealed randomization-coding system also worked effectively.
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Conclusions
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Analysis of 51 double blind RCTs of laser treatment revealed
58% showed benefit of laser over placebo. However, less than
5% of the trials had addressed beam disguise or allocation concealment
in the laser machines used. This indicates significant deficiencies
in laser trial methodology. A new laser machine has been developed
that can blind both patient and operator to treatment allocation
without staff participation. Preliminary testing has verified
that the laser machine diode operation could not be detected,
and the preset sealed randomization-coding system was effective.
We consider this machine could be a useful tool in conducting
double blind RCTs, however a larger clinical study should be
undertaken before it can be fully validated as a trial instrument.
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Footnotes |
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For reprints and all correspondence: Dr Ian Relf, Department of General Practice, University of Melbourne, 200 Berkeley Street Carlton 3053, Victoria, Australia. Tel: 61 3 8344 7276; E-mail:
i.relf{at}unimelb.edu.au
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Acknowledgments
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We would like to thank Dr Alan Harvey who built the DBL Trial
Laser machine with assistance from the Royal Melbourne Institute
of Technology and Acupak Pty. Ltd. Melbourne, Australia.
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Received April 1, 2006; accepted March 9, 2007
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Abstract
Introduction