Introduction
Gastric endoscopic submucosal dissection (ESD) has become increasingly popular worldwide
as a less invasive curative treatment for early gastric cancer. However, it requires
technical proficiency mainly due to the distinctive shape of the tract and diverse
locations of lesions [1]
[2]
[3]. This technique requires a strategy that includes keeping an adequate scope position,
control of devices, and the amount of air in the stomach for each location.
Generally, animal (extracted) digestive tracts or live animals are used for ESD training
[4]
[5]. However, it is difficult to simulate actual gastric ESD locations during such training,
and it also raises several issues, including ethics, cost, and infection. Also, when
novice operators perform ESD, they receive training on the job based on their abilities
[6] and their training level, which gradually increases by transitioning from performing
ESD on known, easy locations, such as the antrum, to difficult locations, such as
the upper or middle portion of the greater curvature [7]
[8]. However, it is difficult to prepare cases based on an operator’s abilities to meet
the demand.
Therefore, we developed a new gastric ESD training model that can accurately simulate
the locations of the human stomach using non-animal subjects and assessed the reproducibility
of each location of the training model.
Methods
Development and set-up of the new gastric ESD training model
We developed a new gastric ESD training model that comprises a rectangular simulated
mucous membrane sheet made of konjac flour ([Fig. 1a]) and a setting frame ([Fig. 1b]). The mucosal sheet consists of three layers of different hardness, strength, and
density, which simulate the mucosal, submucosal, and muscular layers. ([Fig. 1a]). The development of this model (G-Master) was a joint research project between
KOTOBUKI Medical Limited and the National Cancer Center Hospital East. The steps to
set up this model are as follows: the seat was fixed at four points; the seat position
was set with a two-axis gimbal structure; the position of the cardia was determined
in the XYZ direction, and the angle was also determined ([Video 1]). The mucosal tension regulator, reproducing the change in air volume in the stomach
during ESD, adjusted for the tension in the model on demand. The mucosal tension regulator
can tension or loosen the simulated mucosal sheet. A spatula that imitates the greater
curvature of the stomach was set up because the hard part of the scope was supported
by the greater curvature of the stomach in areas far from the cardia, such as parts
of middle and lower portions. This model can be set up in 11 different locations by
setting nine adjuster parts ([Fig. 1b]). The 11 locations consist of four circumferential locations (anterior wall, posterior
wall, lesser curvature, and greater curvature) and three locations (upper, middle,
and lower), except for the greater curvature of the lower portion, which was difficult
to reproduce ([Fig. 2]). Each location can be set up in about 5 minutes.
Fig. 1 a The plant-origin mucous membrane sheet was made out of konjac flour. The mucous membrane
sheet is composed of three layers: the mucosal layer (thickness: 0.5–1.0 mm), the
submucosal layer (thickness: 0.5–1.0 mm), and the muscular layer (thickness: 1.0–2.0 mm).
The composition of the konjac flour was changed for each layer to simulate the strength
and properties of the actual gastric mucosa. b The model consists of an esophagus-like tube, a seat position with a two-axis gimbal
structure, a cardia-like section with adjustable position and angle in the XYZ direction,
a spatula that imitates the greater curvature of the stomach, and a mucosal tension
regulator that can reproduce the change in air volume in the stomach during ESD and
adjust the tension on demand. The model can be set to various locations with nine
adjustment parts. c A specialized liquid is injected into the submucosal layer. Its components are polysaccharide
(0.1–10 %), sucrose (0.1–10 %), mineral salt (0.1–10 %), and dye (minute quantities).
Video 1 Setting of the location that reproduces the lesser curvature of the middle portion
based on this model.
Fig. 2 Set-up of 11 locations in G-Master. The first row is the upper portion, from left
a lesser curvature, b greater curvature, c anterior wall, d posterior wall. The second row is the middle portion, from left e lesser curvature, f greater curvature, g anterior wall, h posterior wall. The third row is the lower portion, from left i lesser curvature (gastric angle), j anterior wall, and k posterior wall.
Evaluation method
Eight ESD experts who were not involved in the development of this training model
used the model for ESD in three to five locations per person, and each location was
performed by three experts. ESD expert criteria was performing > 100 upper gastrointestinal
ESD cases.
ESD was performed using a single-channel upper gastrointestinal endoscope (GIF Q260J;
Olympus, Tokyo, Japan) with an electrosurgical unit (VIO-3 and VIO-300; ERBE, Tubingen,
Germany) and an electrosurgical knife (Dual knife KD-650 L / IT knife-2 KD-611L; Olympus,
Tokyo, Japan). IT knife-2 was the main knife used and traction devices as the clip
with thread were not used. A marking of a 20-mm regular circle that mimicked the lesion
on the seat was placed using an electrosurgical knife. A specialized liquid ([Fig. 1c]) (VTT-INJ; KOTOBUKI Medical, Inc.) was injected into the submucosal layer, and mucosal
circumferential incision and trimming, and submucosal dissection were performed using
an electrosurgical knife ([Video 2]).
Video 2 ESD was performed on the location that reproduced the gastric angle based on this
model.
The following parameters were recorded: 1) ESD procedure time; 2) complete resection;
and 3) perforation. To evaluate the technical difficulty level of each location, we
calculated the ESD procedure speed. The ESD procedure speed was evaluated using the
total procedure speed (from the beginning of local injection to specimen resection)
and the dissection speed (from the end of the full circumferential incision to specimen
resection). The ESD procedure speed (mm2/min) was calculated using the area of the resected specimen (mm2) per unit procedure time (min). The area of the resected specimen was calculated
using the following formula: major axis (mm)/2 × minor axis (mm)/2 × 3.14. Complete
resection was defined as one-piece resection with no incision within the specimen.
Perforation was defined as a hole in the sheet that penetrated the muscular layer.
The diameter of the virtual lesion was standardized as a 20-mm regular circle. Quantitative
data was expressed as median and range.
A questionnaire was distributed after each ESD. Using a six-point scale, participants
subjectively scored the following: 1) similarity of locations; 2) similarity of mucosal
tension changes due to adjustment of the amount of air in the stomach, and 3) similarity
of simulated mucosal sheet. The similarity of locations was evaluated based on the
following scoring points: 1) similarity to the actual location; and 2) feeling of
the scope’s movement. The similarity of simulated mucosal sheet was evaluated for:
1) protruding after local injection; 2) feel of mucosal incision; and 3) feel of submucosal
dissection. A score of < 2 points was considered a low rating, 2 to 4 points was a
medium rating, and > 4 points, high rating. The rating for each location was defined
as the mean of the three experts' scores.
Results
All 33 mimicked lesions were resected completely without perforations. The mucosal
tension was changed at least once during all ESDs. The overall median (range) total
procedure speed/dissection speed was 31 (22–45)/51 (31–79) mm2/min ([Table 1]). The ESD procedure speed was slower at the following locations compared with the
overall median speed: on the greater curvature side of the upper (25 (24–29)/44 (31–48)
mm2/min) and middle (23 (22–38)/37 (34–38) mm2/min) portions, and on the anterior (28 (26–31)/44 (42–46) mm2/min) and posterior (26 (23–27)/40 (38–41) mm2/min) walls of the lower portion ([Table 2]).
Table 1
Endoscopic submucosal dissection procedure data
|
Total (n = 33)
|
|
ESD procedure speed, median (range), min/cm2
|
|
|
31 (22–45)
|
|
|
51 (31–79)
|
|
ESD procedure time, median (range), min
|
|
|
19 (14–31)
|
|
|
11 (7–19)
|
|
Areas of resected specimen, median (range), cm2
|
589 (415–687)
|
|
Complete resection, n (%)
|
33 (100)
|
|
Perforation, n (%)
|
0 (0)
|
|
ESD endoscopic submucosal dissection
|
|
Table 2
ESD procedure speed for each location
|
|
Total procedure speed,
median (range), min/cm2
|
Dissection speed,
median (range), min/cm2
|
|
Upper portion
|
Lesser curvature
|
32 (25–40)
|
51 (47–57)
|
|
Greater curvature
|
25 (24–29)
|
44 (31–48)
|
|
Anterior wall
|
32 (31–40)
|
67 (57–79)
|
|
Posterior wall
|
33 (31–44)
|
65 (55–77)
|
|
Middle portion
|
Lesser curvature
|
34 (33–36)
|
66 (62–73)
|
|
Greater curvature
|
23 (22–38)
|
37 (34–38)
|
|
Anterior wall
|
36 (32–45)
|
63 (51–79)
|
|
Posterior wall
|
31 (24–34)
|
57 (44–68)
|
|
Lower portion
|
Lesser curvature
|
44 (27–44)
|
66 (42–76)
|
|
Anterior wall
|
28 (26–31)
|
44 (42–46)
|
|
Posterior wall
|
26 (23–27)
|
40 (38–41)
|
In the questionnaire, the mean score for all locations was high, with 4 points or
more in the similarity of locations and 4.5 points in the similarity of mucosal tension
changes. By location, similarity of locations generally had high ratings, with > 4
points, but only the lower anterior and posterior walls had medium ratings with 3
to 4 points ([Fig. 3]). All locations’ similarity of mucosal tension changes had high ratings, with > 4
points ([Fig. 4]). In the similarity of simulated mucosa, the mean score for all the locations was
high, with four points in all of the categories.
Fig. 3 The questionnaire responses as scored on a six-point scale. The similarity of locations
was evaluated based on similarity to the actual location and feeling the scope’s movement.
The mean score of similarity of locations for all locations was ≥ 4. By locations,
similarity of locations of lower anterior and posterior walls were 3 to 4 points,
and all other locations were ≥4 points.
Fig. 4 Questionnaire responses as scored on a six-point scale. The mean score of similarity
of mucosal tension changes for all locations was 4.5 points. By locations, the similarity
of mucosal tension changes of all locations was ≥ 4 points
Discussion
To date, there has been no training model in which ESD of various stomach locations
can be reproduced. We developed a new gastric ESD training model that consists of
a simulated mucous membrane sheet and a setting frame. This study showed that the
new gastric ESD training model reproduced most of the real gastric ESD locations in
the questionnaire, and the ESD procedure speed for each location was associated with
the difficulty level in the real gastric ESD.
The simulated mucosal sheet has three layers that simulate the mucosal, submucosal,
and muscular layers. The hardness, strength, and density of the three layers can vary
by changing the compounding materials and manufacturing conditions. To reproduce the
actual stomach wall, each layer is characterized by high density and high strength
in the mucosal layer; low density and loose structure in the submucosal layer; and
high hardness in the muscular layer. Separation of the layers allows for more realistic
reproduction of the mucosal incision and submucosal dissection procedures. Presence
of the muscle layer also allows ESD training to be performed with caution with respect
to muscle layer damage and perforation during submucosal dissection. This setting
frame enables ESD in various lesion sites in the stomach by adjusting the angle of
the seat position, distance between the cardia and the seat, angle of the cardia,
and a spatula that imitates the greater curvature of the stomach. Therefore, the feeling
of the scope's movement for each location is reproduced, and this makes it possible
to be used for training while considering ESD strategies for each location.
In this study, most locations were evaluated as similar to actual gastric ESD. Additionally,
the dissection speed was slower in the greater curvature of the upper and middle portions
than in other locations, which is in line with that of a previous report in actual
gastric ESD [8]. The lesions in the greater curvature of the upper and middle gastric portions in
the model is difficult to approach as well as actual gastric ESD. Also, the direction
of gravity on the lesion is similar to that of actual gastric ESD, which makes it
difficult for water to accumulate and getting into the submucosal layer. We considered
that this is the reason for the longer ESD procedure time. Thus, we considered that
this model could duplicate the actual gastric ESD in terms of the procedure speed
in each location. Sato et al. and Chen et al. have reported the feasibility of ESD
training models using non-animal subjects [9]
[10]. The model that uses non-animal subjects can be trained to be effective for ESD
in any facility equipped for endoscopy, without requiring endoscopic units specialized
for animal use. However, these models did not reproduce the various parts of the stomach.
In our model, each location was well reproduced, and the training can be performed
assuming the location with the specific strategy before the real gastric ESD.
Using the model, ESD in the anterior and posterior walls of the lower portion had
low reproducibility compared to other locations. The ESD procedure speed at these
two locations was slower than the overall speed. However, Konuma et al. reported that
ESD in the antrum is relatively easy to perform, and the dissection speed is faster
than in other locations [8]. In an isolated porcine model, Horii et al. reported that the reason for the difference
in reproducibility of actual ESD in the lower portion may be related to differences
in mucosal thickness and direction of gravity [11]. In line with previous reports, it was difficult to reproduce the gravity direction
of the lesion and thickness of the mucosal layer to simulate the ESD in the anterior
and posterior walls of the lower portion. In the future, we plan to increase the variety
of thickness of the mucosal layer and submucosal layer to create simulated mucosal
sheets suitable for each location.
To become an expert in ESD, it was recommended to start with gastric locations where
ESD is technically easy, followed by more difficult locations [12]
[13], and eventually transition to esophageal and colorectal ESD [14]
[15]. Despite the relatively high incidence of early-stage gastric cancer in Japan, novice
endoscopists are only able to perform gastric ESD of various locations in a few institutions
such as high-volume centers. In addition, gastric ESD is rare in the United States
and Europe; hence, there are few opportunities of training for beginners. Therefore,
endoscopists in these regions would need to perform more difficult ESD such as colorectal
and Barrett's on the job. The learning curve for ESD in these regions is different
from that for endoscopists in Japan, and it is considered that an endoscopist’s ESD
skills will not improve without more ESD experience [16]
[17]. Therefore, it is considered necessary to use training models, such as animal models,
for ESD training before starting ESD [18]. However, there are several issues associated with the use of animals in education.
Training based on the present model, which uses simulated plant-derived mucosa and
accurately reproduces the shape of the stomach, is considered to be very important.
Also, to improve the technique of a special technique, it is necessary to perform
it multiple times to establish muscle memory. Establishing muscle memory leads to
increased efficiency, reduced costs, and improved patient safety. Since this model
can reproduce the same site, repeated training is expected to acquire muscle memory
[19].
This study has some limitations. First, this was a single-center, small-group study.
However, all evaluations were conducted by experts. Second, the evaluation was subjective
and based on a questionnaire; therefore, we examined the ESD procedure speed of each
location to obtain an objective evaluation. Third, the change of the mucosal tension
in this model still only allows for changes in the longitudinal direction. Actual
ESD is thought to involve changes in both the longitudinal and lateral directions.
Fourth, this study focused on reproducibility and not on improving technical ESD skills.
The usefulness of this ESD model in improving ESD technical skills needs to be investigated
in the future.
Conclusions
In conclusion, the new gastric ESD training model appeared highly reproducible for
each stomach position and may serve as a promising device for training with respect
to assumed actual gastric ESD positions.
