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370
J. L. Chin et al.
with urinary retention requiring re- catheterization
at 1 week post-procedure. He was able to reinitiate spontaneous voiding but had signicant hesitancy and persistent perineal discomfort.
Cystoscopy reviewed no urethral or bladder outlet obstruction but two epithelial-lined cavities,
emanating from either side of the prostatic urethra (Fig.30.13). Pelvic MRI conrmed the presence of a prostatic urethral cavity, which had
essentially replaced the entire prostate
(Fig. 30.14a–d). Urinary function slowly
improved, and the pelvic pain dissipated over a
few months. Evidently, the prostate tissue had
involuted almost completely, except for the capsule, and the resultant prostatic fossa became
lled with urine, acting and clinically behaving
essentially as a large urethral diverticulum underlying the residual prostatic urethral mucosa.
Fig. 30.13 Visualized
ostium of the prostatic
urethral cavity lateral to
the bladder neck with
overlying bands of
preserved prostatic
urethral mucosa. The
ostium extends into a
prostatic fossa cavity
that crosses the midline,
essentially replacing the
location of both lateral
lobes of the prostate
In a few selected patients after TULSA with
persistent bothersome voiding hesitancy and
weak ow after TULSA without improvement
after a few months, transurethral resection (TUR)
of residual bands of urethral tissue and bladder
neck to connect the bladder with the urethral cavity appears to signicantly improve voiding
parameters and lower urinary tract symptoms. For
example, one patient’s noninvasive uroow
parameters went from voided volume 96 ml,
Qmax 4.1 ml/s, Qavrg 1.6 ml/s, post-void residual
77ml (pre-TUR) to voided volume 267 ml, Qmax
22.1 ml/s, Qavrg 13.6 ml/s, post-void residual
12 ml (post-TUR). However, caution must be
taken during TUR given anatomic changes after
TULSA ablation, loss of landmarks by the apex,
and close proximity to the external urinary sphincter that could compromise urinary continence.
a
Fig. 30.14 (a–c) Post-TULSA T2 sagittal images,
depicting prostatic cavity lled with urine: (a) left lobe;
(b) near mid-line, (c) right lobe, (d) post-TULSA T2
b
c
transverse image, showing the entire prostate essentially
uid-lled (with urine)
d
30 Role ofTransurethral Ultrasound Ablation (TULSA) inProstate Cancer Focal Therapy
371
Follow-Up Routine Post-Focal TULSA
Follow-up after TULSA focuses on cancer surveillance and symptom assessment and management. Patients are typically discharged after the
procedure with a urethral catheter. A postoperative void trial is performed between postoperative
days 7 and 14. Timing of the postoperative void
trial may depend on the extent of ablation, the
degree of swelling during the procedure, or the
presence of existing LUTS.Patients will usually
be seen every 3 months after TULSA, where their
PSA will be checked, and their urinary and erectile function will be evaluated. The TULSA-Pro
questionnaire allows clinicians to systematically
assess patients’ lower urinary tract symptoms,
quality of life, continence, erections, and ejaculatory function in a standardized fashion. These
questionnaires should be completed at each clinic
visit to allow for continuity of symptom assessment and comparison to baseline. PSA should be
checked at each visit every 3 months. Concerning
PSA, kinetics may prompt repeat imaging or
biopsy sooner than 1 year. At 1 year, patients will
undergo repeat prostate MRI to assess for any
concerning lesions. Clinicians should note the
characteristics of the ablation site, assess for new
PIRADS lesions (and evaluate if these are in or
out of the prior ablation eld), and assess the
change in prostate volume. Patients will also
undergo a systematic and targeted prostate biopsy
at 1-year post-TULSA.Targeted sites include the
prior ablation zone and any new or concerning
lesions on MRI. Because most prostate glands
will decrease in size after TULSA, our recommendation is to obtain one core per 4 cc of residual prostatic tissue to account for changes in
prostate volume.
amount of energy delivered to a specic slice of
tissue is precisely and instantaneously determined by the tissue temperature achieved during
the procedure. It integrates quantitative imagebased planning, monitoring, and treatment control with transurethral delivery of therapeutic
ultrasound via ten independently controlled
transducers to ablate prostate tissue through thermal coagulation. The treatment is tailored to
patient-specic anatomy and pathology by delineating the treatment boundaries, rotational excursion, and controlling activation/deactivation of
the individual transducers in real-time. With the
unique design whereby ablative energy emanates
from within the urethra, treatment-related morbidity is theoretically ameliorated due to the
reduced exposure of ablative energy to vulnerable structures such as the neurovascular bundles
and rectal wall.
Early clinical trial data in North America and
Europe on whole-gland ablation have now been
supplemented by “real-life” clinical experience
globally, showing good oncologic efcacy and
functional outcomes. Treatment-related adverse
events have been Clavien-Dindo Grades I and II,
with rare exceptions. While the early experience
was primarily derived from whole-gland ablation
on low- to intermediate-risk patients, there is
mounting experience supporting wider applicability of the TULSA technology, e.g., in
intermediate- risk patients, patients with benign
prostatic hyperplasia concurrent cancer, and
post-radiation salvage situations. The technology
allows precise target-boundary planning and
energy delivery, thus rendering it a useful tool for
“lesion-directed” and “focal” treatment both in
the primary and salvage settings. TULSA is an
important addition to the arsenal of ablative
modalities for “focal therapy.”
Summary
TULSA is a novel minimally invasive ablative
modality for prostate cancer, which employs a
closed-loop control system with real-time thermal mapping to deliver precise cytocidal ultrasound energy via a transurethral route. The
References
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2020;22:79–87.
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Transurethral Vapor Ablation
inProstate Cancer
JamieS.Pak, ChristopherM.Dixon,
andSamirS.Taneja
31
The Science ofWater Vapor
Ablation
Transurethral water vapor ablation (Vanquish™
System) involves the delivery of stored thermal
energy in the form of water (or steam) to targeted
areas of the prostate. The vapor disperses quickly
and uniformly through the interstitial space, disrupting cell membranes without an obligatory
thermal gradient while respecting the boundaries
and zonal anatomy of the prostate. Using the convective properties of vapor, this therapy releases
large amounts of stored thermal energy (540 cal/g
H2O) as the vapor contacts tissue and condenses
back to water [1, 2]. To understand the underlying
mechanism of water vapor ablation, one must
have a basic knowledge of the convective heat
transfer method and the thermodynamic principles of water, which will be briey reviewed here.
Convection describes the transmission of
thermal energy by the movement of uid in the
form of gas and/or liquid. This form of heat
J. S. Pak (*) · S. S. Taneja
Division of Urologic Oncology, Department of
Urology, NYU Langone Health, New York, NY, USA
e-mail: jamie.pak@nyulangone.org; samir.taneja@
nyulangone.org
C. M. Dixon
Bon Secours Urology, WMC Health Good Samaritan
Hospital, Suffern, NY, USA
Francis Medical Inc., Maple Grove, MN, USA
transfer has distinct advantages for the ablation
of prostate tissue compared to the other methods
of conduction and radiation. The rate of convective heat transfer per unit area (q ) is a function of
the convective heat coefcient (h) and the difference in temperature between the surface (Ts) and
the uid (T∞): q = h(Ts − T∞). The efciency of
heat transfer by this method varies widely
depending on the convective heat coefcient (h)
of the medium. Table 31.1 lists convective heat
coefcient values that are applicable for this
review.
There are three main mechanisms of convective heat transfer such as free convection, forced
convection, and phase change convection. Free
convection is the movement of uid occurring
only from density changes due to differences in
temperature. An example of free convection is a
radiator, which places warm air at the top and
draws in cooler air at the bottom. Forced convection is similar to free convection but with an addi-
Table 31.1 Typical values of convective heat coefcients (h). Courtesy of Francis Medical
Process h(W/m2∗K)
Free convection
Gases
Liquids
Forced convection
Gases
Liquids
Phase change convection
(boiling or condensation)
2–25
50–1000
25–250
100–20,000
2500–100,000
© The Author(s), under exclusive license to Springer Nature Switzerland AG 2024
T. J. Polascik et al. (eds.), Imaging and Focal Therapy of Early Prostate Cancer,
https://doi.org/10.1007/978-3-031-66754-1_31
373
374
Fig. 31.1 The relative
energy of water at
different temperatures.
Courtesy of Francis
Medical
Table 31.2 Temperature and tissue effects of ablation [4]
Temperature (°C) Effect visible Delayed Mechanism
34–44 None Edema Vasodilatation and inammation
44–50 None Necrosis Disruption of cell metabolism
50–60 Blanching Sloughing Collagen denaturization
80–100 Shrinkage Sloughing Desiccation
a
100
100-200 Steam ‘popping’ Ulcerization Vaporization
>200 Carbonization cratering Larger ulcer Combustion of tissue, hydrocarbons
a
Due to water vapor exposure
Blanching Sloughing Cell membrane denaturation
J. S. Pak et al.
tional mechanism to force movement, such as a
fan blowing across a radiator to increase the transmission of heat. As shown in Table31.1, the largest convective heat coefcient is with phase
change convection, or the transfer of heat resulting from the release/absorbance of energy from a
phase change at a constant temperature. This is
the mechanism utilized by water vapor ablation to
deliver the large amount of thermal energy stored
within the vapor molecules as kinetic energy [3].
Figure 31.1 illustrates the signicant increase
in relative energy of water in the phase change
from liquid to vapor, which is available for
release upon condensation. For heat transfer in
general, the rate of energy transfer (Q) is a function of the mass of the object (m), the specic
heat (Cp), and the change in temperature (ΔT): Q
= mCpΔT. Therefore, to heat 1kg of water from
20 to 100 °C, for example, this would require
1kg × 4.18 kJ/kg K × (100 °C − 20 °C) = 334.4
kJ.Then, to convert the water to vapor, the energy
required is referred to as the heat of vaporization
and equals the change in specic energy of water.
For the same 1kg of water, the required energy to
create vapor equals: Q = m × (uf − ug) = 1kg ×
(2506.5 kJ/kg − 418.91 kJ/kg) = 2087.6 kJ,
where uf and ug equals the specic internal energy
of water in vapor and liquid forms, respectively.
In this example, the energy to boil water at a constant temperature is more than six times the
energy needed to raise the water to boil. When
the vapor is condensed back to liquid, such as on
the surface of the prostate tissue, this large
amount of stored energy is released at a constant
temperature and transmitted to the cellular membranes, causing immediate disruption of the
membranes and ultimately cell death.
The goal of thermal therapies is to cause an
area of focused tissue necrosis by causing a rise
in temperature. In Table31.2, the resultant tissue
effects of thermal therapies at different temperatures are listed. This illustrates the efcacy and
safety of water vapor ablation as the temperature
is held constant at the condensation temperature
31 Transurethral Vapor Ablation inProstate Cancer
of 100 °C, which leads to cell membrane denaturation without carbonization or burning of the tissue. By contrast, other minimally invasive
delivery systems, such as microwave, interstitial
laser, focused ultrasound (HIFU), cryoablation,
and radiofrequency ablation utilize conduction,
which requires longer treatment time and substantial energy deposition to produce tissue
destruction with a required temperature gradient
[1]. Water vapor is injected under slight pressure
to propel it into the interstitial space of the prostate, and the volume contraction that occurs with
condensation to about one-thousandth of the volume in liquid form subsequently removes this
pressure. In addition, as vapor is relatively mobile
in the interstitial spaces of the prostate, the diffusivity of heat to the tissue is increased while
minimizing the effects of conductive heat
transfer.
The convective mechanism of Vanquish™
technology has been demonstrated to produce
ablation that is both conned by anatomic tissue
boundaries and controlled to a reliable radial
extension in unencumbered space. Inhibition of
vapor movement by tissue membranes of the
prostate “capsule” (surgical capsule) and zonal
boundaries allows focused treatment of regions
of interest with minimal collateral damage to surrounding structures and other zones of the prostate [3]. Even in unencumbered space, the
pressure equilibrium of vapor is reached at the
interface of interstitial uid, which produces a
reliable ablation size.
A technical report of vapor ablation in surrogate tissue models of fresh beef liver demonstrated an average radial extension of 9–10mm
from the device emitter holes. This controlled
degree of ablation additionally allows precise
focal treatment of prostate tissue (Fig. 31.2).
Water vapor dose is expressed as calories per second. The lesion size can be varied in size depending on the amount of calories per second delivered.
Vapor treatment inside prostatic parenchyma produces a relatively large ablation volume (>2cm
diameter) in a very short period of time. This is
due to a convective mass movement of vapor with
a concomitant isothermal condensation. On the
capsule wall, however, heat is transferred via con-
375
Fig. 31.2 Region of ablation. Courtesy of Francis
Medical
densation convection to the inside surface, but is
limited by the slower, time- based thermal conduction or diffusion rate into the capsule wall. The
thermal diffusion distance producing ablation has
been experimentally modeled to approximate
0.5mm when the standard thermal dose (22 cal/s)
and treatment time of 10 s was used. Obviously,
the thermal diffusion distance into the capsule
wall increases if additional treatments are added
in the same location.
The Device andEnergy Delivery
System
The Vanquish™ device has been through several
iterations, the rst being the Rezum device,
which received FDA 510(k) designation in 2015
and 510(k) clearance for relieving symptoms,
obstruction, and prostate tissue reduction for
benign prostatic hyperplasia (BPH). As depicted
in Fig.31.3, the Rezum delivery device is a single
piece that is rotated with the wrist. This was modied into two pieces for the Poseidon (VAPOR 1)
device, consisting of a rotating cartridge which
inserted into a separate handpiece. The needle
length was also upgraded from a xed 1cm in
Rezum to a variable length, which could be
advanced or retracted at 1-mm increments up to
2.5 cm in Poseidon, which allows treatment of
376
J. S. Pak et al.
Fig. 31.3 The evolution of the delivery device. (1)
Rezum device. (2) Poseidon VAPOR 1 device. (3 and 4)
Vanquish VAPOR 2 device with delivery device that
the transition zone and the peripheral zone under
ultrasound guidance. In addition, the power supply was increased from 124 W radiofrequency
with Rezum to 500 W radiofrequency with
Poseidon.
The latest iteration is the Vanquish™ (VAPOR
2) device (Figs.31.3 and 31.4), which is a single
piece with a lumen for a 30-degree, 4 mm, 30cm
cystoscope lens. This piece attaches to a stabilizer with a separate controller to adjust the orientation and movement of the delivery device. The
needle length remains adjustable up to 2.5cm to
enable treatment of the peripheral, central, and
transition zones as needed, with improved needle
tracking to personalize treatment to the patient’s
size and anatomy. The power supply was changed
to a 500-W DC vapor coil for vapor production,
with various settings of the power generator (e.g.,
power, ow, and time used to determine the levels of energy delivered) based on the treatment
approach and the nature of cancerous tissue.
Additional features that were added include an
electromagnetic Needle Guidance System
attaches to a stabilizer with separate controller and needle
extended. Courtesy of Francis Medical
(NGS), Biocap tissue sensing that recognizes the
proximity of the treatment needle tip to the prostate capsule, and automated periprostatic cooling
when needed.
The current Vanquish™ system consists of
multiple components (Fig. 31.5). The stabilizer
system attaches to surgical bed rails and allows a
full range of motion to manipulate both the transrectal ultrasound (TRUS) probe and the delivery
device. The TRUS cradle allows large and ne
movements to position and stabilize the TRUS
probe during the procedure. With the addition of
a separate controller, vapor treatments can be
controlled in a hands-free manner; the controller
also allows advancement and retraction of the
needle, initiation of vapor treatment, views on the
monitor, and the perineal and urethral saline
ushes. These functions are also performed on
the touchscreen display of the generator, which
provides power to the delivery device and displays the NGS (Fig. 31.6). NGS is the needle
tracking system that aids the operating physician
in needle visualization and positioning during the
31 Transurethral Vapor Ablation inProstate Cancer
Fig. 31.4 (5) Std and PZ needle emitter hole conguration. (6) Vanquish system controller. Courtesy of Francis Medical
377
Fig. 31.5 Current Vanquish procedure equipment overview. Courtesy of Francis Medical
procedure. An example treatment view is displayed on the generator monitor in Fig.31.7.
Once the treatment needle is deployed into the
region of interest, the Vanquish™ system transurethrally injects a controlled amount of sterile
water vapor generated within the handpiece and
through the needle placed within prostate tissue
Fig. 31.8. Saline ush during energy delivery
protects and preserves the urethra. To protect the
rectum from thermal damage, a saline needle
and/or thermocouple monitoring needle is placed
between the rectum and prostate.
378
Fig. 31.6 The needle guidance system. Courtesy of Francis Medical
J. S. Pak et al.
Fig. 31.7 Example treatment view of Vanquish system
monitor. The top left displays the treatment plan, which
includes MRI images of the target lesion and an overlying
clock face to guide treatment with prostate and target
lesion information. The bottom left is the cystoscopic/
endoscopic view, which displays the white treatment needle deployed into the prostate, and an overhead view specifying the distance from the target lesion to the tip of the
Delivery Device and to the prostate apex in the axial
plane. The top right displays the Status and Settings banner at the top, a live transverse or axial TRUS view, and
the BioCap data that senses tissue capacitance at the tip of
the vapor needle to recognize the proximity of the needle
to the prostate capsule. The bottom right displays the live
sagittal TRUS view and treatment data. Courtesy of
Francis Medical
31 Transurethral Vapor Ablation inProstate Cancer
Fig. 31.8 Cartoon of
treatment needle
deployed into peripheral
zone lesion with the
release of vapor.
Courtesy of Francis
Medical
379
Background Clinical Data forBPH
Approval
The rst report of in vivo treatment of human
prostate tissue with the Rezum device examined
triphenyl-tetrazolium chloride (TTC) stained
whole mounts and MRIs to assess the acute ablative characteristics of water vapor [5]. TTC marks
viable tissue with healthy metabolic enzymes in
bright red, while permanently damaged tissues
without metabolic enzymes will not take up the
stain and remain a natural tan color. All prostate
lobes that were treated demonstrated nonviable
tissue by TTC in the transition zone that correlated with the Rezum injection sites, with no
thermal effects observed outside of the prostate
on gross examination (Fig.31.9).
All MRIs at 1 week after treatment demonstrated gadolinium defects in the transition zones,
with no thermal effects seen in the peripheral
zones or the urethra (Fig. 31.10). Gadolinium
defects on MRI have been demonstrated to correlate with histologically proven necrosis in prior
studies [6].
A larger study of men with lower urinary tract
symptoms treated with the Rezum system and
imaged serially with MRI again demonstrated
thermal lesions corresponding to areas in addition
to a signicant reduction in the volumes of the
lesions and the whole prostate [2]. MRIs were
performed at 1 week, 1, 3, and 6 months after
treatment. For the cohort, the mean (range) volumes at 1 week to 6 months after treatment of the
whole prostate were 61.2 cm3 (20.4–133.2) to
43.5cm3 (16.0–116.6), of the transition zone were
36.3cm3 (9.1–87.8) to 22.5cm3 (6.6–79.3), and of
the gadolinium defect lesion volume were 8.2cm3
(0.5–24.0) to 0.4cm3 (0.0–3.7), respectively.
To assess the efcacy and safety of Rezum for
symptomatic BPH, a multicenter, randomized,
controlled study included 197 men (136 assigned
to Rezum treatment, 61 assigned to control mock
procedure) with an International Prostate
Symptom Score (IPSS) of 13 or greater, maximum ow rate of 15 ml/s or less, and prostate
size of 30–80 cc [7]. The primary endpoint was a
reduction in IPSS at 3 months, which was
achieved as IPSS was reduced by 50% in the
Rezum arm and by 20% in the control arm (p <
0.0001). Treatment with Rezum resulted in a signicant reduction in IPSS as early as 2 weeks,
with further reduction by 50% or more by 3
months, and sustained at 12 months. Other outcomes, including Qmax and Quality of Life
scores from IPSS and the BPH impact index were
signicantly improved with Rezum compared to
the control procedure, with differences sustained
through 12 months. In terms of safety, two
patients had serious adverse events adjudicated
as procedure-related, including de novo extended
urinary retention and nausea/vomiting due to
alprazolam requiring an overnight hospital stay
for observation. All other adverse effects were of
mild to moderate severity, with most resolving by
3 weeks. Based on these results, the Rezum
device received FDA clearance in 2015.