Short Scientific Communication—Endocrine Surgery
Comparison of Laser Ablation Using
Multidirectional and Forward-Firing Fiber
in Human Thyroid Gland: Experimental
Study
Otolaryngology–
Head and Neck Surgery
149(5) 689–691
Ó American Academy of
Otolaryngology—Head and Neck
Surgery Foundation 2013
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DOI: 10.1177/0194599813499895
http://otojournal.org
Ho Yong Park, MD1, Hyang Hee Choi, MD1, Jung Ju Lee, MD1,
Seung Ook Hwang, MD1, Jin Hyang Jung, MD1, Ik-Bu Sohn, PhD2,
Ho Lee, PhD3, and Wan Wook Kim, MD1
Sponsorships or competing interests that may be relevant to content are disclosed at the end of this article.
Abstract
The aim of this study is to evaluate the differences between
forward-firing and multidirectional lasers and to evaluate the
effects of exposure times and power on laser ablation of
thyroid tissue. This is an experimental, ex vivo study. The
experiments were conducted on 3 thyroid glands using 2
power levels (3 and 5 W) and exposure times (3 and 5 minutes) with forward-firing and multidirectional lasers. The
length and width of the demarcated zone were measured to
assess the size of thermal effect. NADPH staining was performed to determine tissue viability. Thermal transformation
caused by the forward-firing laser produced oval necrotic
zones, whereas thermal transformation caused by the
multidirectional-firing laser produced clear round necrotic
zones, which clearly demarcated in both hematoxylin and
eosin staining and NADH staining.
Keywords
forward-firing fiber, laser ablation, multidirectional fiber,
thyroid gland
Received January 8, 2013; revised July 1, 2013; accepted July 11, 2013.
M
ost thyroid cancers are papillary thyroid cancer,
which have been associated with excellent prognoses. However, surgery may be risky for patients
for whom general anesthesia is not viable due to old age or
a severe underlying disease. Accordingly, nonsurgical therapy such as cryoablation, radiofrequency ablation, ethanol
injection, and laser ablation have been introduced.1-3 A previous study has suggested that laser-based procedures are
effective in treating large benign thyroid nodules by a significant volume reduction (40%~80%).4 Downsides of laser
have so far been that forward-firing lasers are less effective
at removing round tumors. Thyroid glands are located
adjacent to the major structures, meaning complications due
to the thermal effect can have more devastating consequences. In this respect, our group has developed a multidirectional laser fiber that produces circumferential thermal
effects and makes up for the downfalls of the forward-firing
laser. The aim of this study is to evaluate the differences
between forward-firing and multidirectional lasers and to
evaluate the effects of exposure times and power on laser
ablation of thyroid tissue using a multidirectional laser fiber
developed by our group.
Materials and Methods
This study was approved by Kyungpook National University
Hospital Institutional Review Board. Specimens were normal
human thyroid glands, and the experiment was performed ex
vivo with 3 cases under each condition. A forward-firing
system (600 mm-wide, 980-nm wavelength laser beam) using
a conventional optical fiber tip and a multidirectional firing
system with a conical distal tip of the fiber were prepared
(Figure 1).
However, irradiation at power levels .7.5 W and exposure times .10 minutes resulted in extensive necrosis and
carbonization. Accordingly, our group limited the settings to
2 power levels (3 and 5 W) and two exposure times (3 and
5 minutes). Following laser ablation, the length and width
of the demarcated zone were measured by a pathologist to
assess the size of the thermal effect on the tissue. Lastly,
NADPH staining was performed through enzyme assessment of irreversible cell damage. With the forward-firing
laser, the total volume of the necrosis was derived based on
1
Department of Surgery, School of Medicine, Kyungpook National
University, Daegu, Korea
2
Advanced Photonics Research Institute (APRI), Gwangju Institute of
Science and Technology (GIST), Gwangju, Korea
3
School of Mechanical Engineering, Kyungpook National University, Daegu,
Korea
Corresponding Author:
Wan Wook Kim, MD, Department of Surgery, Kyungpook National
University, 807 Hogukno, Buk-gu, Daegu, 702-120, Korea.
Email: kww1324@naver.com
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690
Otolaryngology–Head and Neck Surgery 149(5)
Figure 2. Histopathological findings of the ex vivo impact the (a)
forward-firing laser fiber system and the (b) multidirectional-firing
laser fiber system had on normal thyroid tissue.
Figure 1. (a) The forward-firing fiber tip optical image, bullet-like
oval patterned beam image (b) multifiring fiber tip optical image,
beam divergence optical image.
the ellipsoid volume formula, where a is length and b is
width:
pab2
:
V5
6
With the multidirectional-firing laser, the total volume of
the necrosis was derived using the spherical volume
formula:
4
V 5 pr3 :
3
Results
Thermal transformation caused by the forward-firing laser
produced oval necrotic zones, whereas thermal transformation caused by the multidirectional-firing laser produced
clear round necrotic zones. In both cases, thermal transformation produced 3 visibly distinct zones: carbonization
zone (zone 1, necrosis due to direct laser exposure) and coagulation zone (zone 2, thermal transformation [damage] surrounding the necrotic cavity). Zones 1, 2, and 3 were
clearly demarcated in both hematoxylin and eosin staining
and NADH staining (Figure 2). It was also possible to
observe that cells in zone 1 were completely destroyed due
to carbonization, and cells in zone 2 were clearly dead in
comparison to cells in zone 3.
The means of these results confirm an increase in the
lesion width with an increase in power and exposure time
(Figure 3a). The length of the lesions also increased with
an increase in power and exposure time but not to the same
degree (Figure 3b).
With the multidirectional-firing laser fiber system, the
parameters of the lesion did not change greatly with the
increase in power and exposure time, which can be
attributed to the fact that the multidirectional-firing laser
fiber system’s tip is at an angle as to direct the laser sideways. Comparison of the aspect ratios (width/length) of
thyroid tissue zones reveals that the aspect ratio of the carbonized zones produced by the multidirectional-firing laser
and forward-firing laser is 0.6 and 0.4, respectively; the
multidirectional laser is closer to 1, which in turn indicates
thermal transformation that is rounder in shape.
Discussion
Nonsurgical methods of treating thyroid nodules are technically feasible under local anesthesia; require minimal surgical access, resulting in little scarring and superior aesthetic
results; and reduce major surgical complications.4 Sung et al2
concluded that percutaneous ethanol injection has proven to
be particularly effective at treating cystic nodules but has
little effect on solid nodules. Papini et al3 suggested that laser
ablation was a good effective option for treating benign solid
thyroid nodules. However, most conventional laser fibers are
capable of unidirectional firing only. This means it is difficult
to irradiate the entire lesion evenly and to estimate the extent
and size of the necrosis, and multiple needle punctures are
needed for ablation of a large-sized nodule.5 Forward laser
ablation in the thyroid gland made it easy to damage surrounding major structures.
In this study, our group was able to confirm that with the
forward-firing laser, the size of thermal degradation and
necrotic tissue increased along with an increase in power
levels and exposure times in a bullet-like oval pattern. With
the multidirectional laser, on the other hand, the thermal
transformation pattern grew in size and became more spherical, indicating that use of this multidirectional laser fiber
in clinical applications can enable accurate estimation of the
volume of the thermal transformation zone and that it is
possible to develop standard indices for various power
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Park et al
691
Figure 3. Widths (a) and lengths (b) of cavity regions versus combination of conditions applied for the forward-firing fiber and multidirection-firing fiber.
levels and exposure time combinations by measuring the
degrees of coagulation and necrosis. Furthermore, development
of said standard indices will make it possible to completely
ablate the tumor without special monitoring, with little complications due to collateral thermal damage, and it will allow the
surgeon to estimate the volume and achieve precise coagulation necrosis. We plan future studies to evaluate the effect of
ex vivo laser ablation on thyroid benign nodules and cancer
with multidirectional laser after thyroidectomy.
Conclusion
The forward-firing laser produced an oval-shaped thermal
transformation pattern, and the multidirectional laser produced a nearly spherical one on human thyroid tissue.
Author Contributions
Ho Yong Park, wrote article; Hyang Hee Choi, collected data;
Jung Ju Lee, collected data; Seung Ook Hwang, analyzed data;
Jin Hyang Jung, analyzed data; Ik-Bu Sohn, designed study,
revised article; Ho Lee, designed study, revised article; Wan Wook
Kim, designed study, revised article.
Disclosures
Funding source: This research was supported by the Bio &
Medical Technology Development Program of the National
Research Foundation (NRF) funded by the Korean government
(MEST; No. 2012-0006062).
References
1. Kim YS, Rhim H, Tae K, Park DW, Kim ST. Radiofrequency
ablation of benign cold thyroid nodules: Initial clinical experience. Thyroid. 2006;16:361-367.
2. Sung JY, Baek JH, Kim YS, et al. One-step ethanol ablation of
viscous cystic thyroid nodules. AJR Am J Roentgenol. 2008;
191:1730-1733.
3. Papini E, Guglielmi R, Bizzarri G, et al. Treatment of benign
cold thyroid nodules: a randomized clinical trial of percutaneous laser ablation versus levothyroxine therapy or follow-up.
Thyroid. 2007;17:229-235.
4. Amabile G, Rotondi M, Pirali B, et al. Interstitial laser photocoagulation for benign thyroid nodules: time to treat large
nodules. Lasers Surg Med. 2011;43:797-803.
5. Amabile G, Rotondi M, Pirali B, et al. Interstitial laser photocoagulation for benign thyroid nodules: time to treat large
nodules. Lasers Surg Med. 2011;43:797-803.
Competing interests: None.
Sponsorships: None.
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