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Chapter26:Cementoplasty and musculoskeletal interventions
Table 26.1 Comparison of mechanical properties between normal bone (femur), polymethylmethacrylate (PMMA), biocompatible calcium phosphate
(Norian SRS), and calcium hydroxyapatite (CAH)
Property Thighbone (femur) PMMA (bone cement) Norian SRS CAH
Density (g/cm3) 1.6–1.7 1.1–1.2 2.0–2.5 2.2–2.5
Young’s modulus (GPa) 10–15 1–3 20–30 10–20
Tensile strength (MPa) 90–130 30–70 5–7 10–20
Compressive strain (MPa) 130–200 80–120 20–30 100–250
Fracture strain (%) 1–3 0.1–0.3 0.1–1 0.5–1
Toughness (MPa m
Hardness (Vickers) 50–100 50–100 10–20 50–100
SRS = skeletal repair system.
reduced myocardial function, tract seeding, and failure to control pain ortumor.
Extraosseous cement leakage is common; however, in most
cases it is clinically insignicant, producing no symptoms or
sequelae. ese asymptomatic leakages have been reported with
all cementoplasty techniques depending on the material used,
the lesion location, and the operator’s experience.
cement leakage close to a nerve root, injection of cooled normal
saline can assist in preventing neuralgia.25 In case of radiculopathy, transforaminal inltrations with corticosteroids or systemic
steroid therapy can be used for pain reduction. Surgical decompression in case of leakage or seeding is rarely required.
1/2
) 1–2 1–3 0.06–0.14 0.5–2
e stiness of PMMA is greater than cancellous bone,
which explains some of the challenges experienced in vertebral
augmentation with concerns of increased incidence of subsequent fractures due to increased stress riser eects on the adjacent vertebrae.
PMMA is created through a polymerization reaction
20,25,26
In case of
with a monomer and the acrylic powder forming the acrylic
epoxy known as PMMA through an exothermic reaction
(Figure26.5). Modern cements are opacied with barium sulfate or tantalum powder to allow for enhanced visualization
(radiopacity) during uoroscopy.
By varying the ratio of monomer and polymer, the reaction time (set time) and viscosity can be varied. e current
Postprocedural care and follow-up
e patient remains at bed rest for the rst 1–4hours depending on the extent of treatment. In osteoporosis, the vast majority
are treated as outpatients, but in tumor treatment patients may
require overnight hospitalization if combined with ablation or
more invasive treatments. CT can assess implant position and
distribution post treatment. In general, however, these directions dier along local practice patterns. Procedure-related
pain is usually muscular in character and dierent from the
patient’s presenting complaint and can be treated with analgesics and non-steroidal anti-inammatory drugs for 2–3days.
Current bone cement properties and future directions
An ideal bone cement would have physical and structural
properties that are identical to cancellous bone, be non-toxic,
and have the ability to promote new bone induction and
ingrowth. PMMA has been the preferred cement for general
cement preparations have been signicantly improved over
the original cements, with greater opacity to visualize during
uoroscopy, higher viscosity reducing leakage, and longer set
(working) times to improve vertebral lling and potentially
improve height restoration.
PMMA undergoes polymerization via an exothermic reaction during injection into the vascular, cell-rich cancellous
bone. e free monomer is known to be toxic and these undesirable chemical properties explain the occasional hypotensive
response and subsequent granulation tissue reaction that occur
around the bolus aer injection and the absence of desired osteoinductive properties. Further, the cement bolus is permanent
and its density prevents signicant new bone ingrowth, but this
same property also prevents signicant tumor ingrowth and in
eect renders PMMA somewhat tumoricidal.
Despite these shortcomings, PMMA is still by far the most
common bone void ller utilized in vertebral augmentation
and other osteorestorative procedures. e quest for a more
homeopathic injectable construct continues.
orthopedic and spine procedures, vertebroplasty, vertebral
augmentation, sacroplasty, osteoplasty, and many restorative
dental procedures. PMMA has specic physical characteristics
that make it ideal for bone restoration. PMMA has excellent
axial load-bearing properties. is makes it well suited for vertebral augmentation, as this is the dominant force exerted on
the “axial” skeleton. It is important to also note that PMMA, by
itself, does not exhibit properties suited to withstanding shearing or bending forces and this impacts its utility as a stand-alone
augmentation strategy outside the spine. Table 26.1 outlines
the relative strengths ofPMMA.
Percutaneous sacroplasty, osteoplasty, and advance hybrid stabilization techniques
Metastatic disease is distributed to red marrow due to its
increased blood ow; therefore, apart from spine, metastases are commonly found in the pelvis, femur, humerus, and
skull. ese tumors can result in bone pain secondary to direct
tumor eects, but are also frequently the cause of instability
due to impending and completed pathologic fractures which
have devastating impact on the patient.
259
Section VIII:Musculoskeletal
A
O
+CH
•
O
Initiator
B
O
CH
2
CH
3
CC
2
MMA monomer
O
CH
3
C
•
O
OCH
3
CH
3
CH
OCH3+CO
2
CC
O
CH
2
O
OCH
3
CH
CO
•
O
3
OCH
C
3
OCH
O
CH
O
C
CO
2
CH
3
OCH
3
CH
n
3
CO
•
C
2
CH
3
Figure 26.5 Schematic illustration of PMMA’s polymerization process.
Figure 26.6 Multiple myeloma – lytic lesion in the iliac bone. (A) 3D CT coronal reconstruction illustrating vertebroplasty needles and cement within the lesion. (B) 3D
CT coronal reconstruction illustrating satisfactory filling of the lesion with polymer. (C) 3D CT axial reconstruction illustrating satisfactory filling of the lesion with polymer.
Denitive surgical resection is only oered in a highly
selected subset of patients. Factors that favor surgical interventions include good prognosis (greater than 1year), absence of
other metastases, likelihood of complete resection, patient’s overall health, and performance status. Unfortunately, the majority
of metastatic and a large percentage of primary tumors are not
amenable to surgical therapy. Further, surgical therapy requires a
necessary delay in chemotherapy and radiation for wound healing and results in immunologic suppression, where rapid tumor
growth can be observed. It is this constellation of factors that has
led to the growth and adoption of minimally invasive alternatives in stabilization of pelvis. Sacral lesions are common in multiple myeloma, and metastatic renal cell, breast, and lung cancer
routinely aect the pelvis (Figures 26.6 and 26.7).
e growing experience and body of literature supporting the ecacy of vertebral augmentation have naturally
led to the application of this treatment to other fractures in
patients who are either unsuitable for surgical stabilization or
whose radiation-related insuciency fracture does not require
a traditional, more invasive repair. is has been most commonly referred to as osteoplasty with sacral osteoplasty or
sacroplasty, accounting for the second most common percutaneous fracture management procedure.
27,28,29
Sacroplasty
involves the unilateral or bilateral injection of PMMA into
the lateral sacral ala, where sacral insuciency fractures most
commonly occur. Sacral insuciency fractures are most commonly secondary radiation osteitis in pelvic malignancies and
are reported to occur in up to 30% of patients receiving pelvic radiation. is procedure is performed under uoroscopic
or CT guidance with technical success achieved by injecting
PMMA along the fracture lines that is typically oriented vertically just lateral to the neural foramen and medial to the sacroiliac joints. Frequently, there is also a horizontal component,
completing the “Honda sign” on bone scan, that passes through
the S1 or S2 corridor that can be targeted with PMMA aswell.
Pain relief and improvement in function are similar to that
seen in vertebral augmentation with reduction in pain, reduction in narcotic requirements, and improved function. ere
260
Chapter26:Cementoplasty and musculoskeletal interventions
Figure 26.7 Leiomyosarcoma lesions in the pelvis. (A) Axial CT scan illustrating polymer in right iliac bone from past osteoplasty session and the lytic lesion in the
right wing of the sacral bone. (B) P-A fluoroscopic view illustrating needle access through the right sacro-illiac joint. (C) Axial CT scan illustrating polymer in right
iliac bone as well as satisfactory filling of the lesion in the right wing of the sacral bone.
Figure 26.8 HCC lytic metastasis in humeral diaphysis. (A) Trocar is placed within the lesion (contrast medium confirms intralesional placement). (B) Coaxially a
coblation electrode is inserted. Plasma mediated RF ablation is performed for tumor decompression. (C, D) Coaxially, a metallic mesh consisting of 25–50 stainless
steel micro-wires (22 G, 2–6 cm length) is inserted in the lesion of interest under fluoroscopic control followed by PMMA injection.
Table 26.2 Harrington’s definition for impending pathological fractures
of long bones
I More than 50% of the circumferential cortical bone has been
destroyed
II Lesion greater than 2.5 cm in any direction in the proximal femur
III Lytic lesion associated with pathological avulsion fracture of the
lesser trochanter
IV Persisting, increasing, or recurring pain with weight-bearing
postradiation therapy
have been several moderate to large retrospective studies demonstrating the ecacy and safety of sacroplasty.
27,28,29
Metastatic disease in the pelvis with impending or completed
pelvic pathologic fractures has traditionally been treated with
radiation, medical therapy, and surgical xation depending on
severity and risk of fracture, with several classication schemes
utilized. e Harrington classication, described by Harrington
in 1986, is presented in Table 26.2.30 Patients with lesions at
higher risk for fracture are treated with open surgical xation.
Unfortunately, the literature suggests that, in the patient with a
limited prognosis, these highly invasive options require signicant recovery, have a high risk of complications, including infection, bleeding, and hardware failure, and are unable to receive
chemotherapy or radiation.
31,32,33
In one report, average length
of stay was 20days, blood loss was 2,200 cc, and infection rate
was 30%. e authors concluded that surgical repair should be
limited to only those patients with a good prognosis.
In the elderly, debilitated, or patients with limited mobility, several authors have reported the use of osteoplasty in lieu
of surgery. is treatment option appears to have merit as a
minimally invasive option, aording pain relief and some stability despite the load issues discussed previously. Hirsch etal.
reported pain relief and improved mobility with acceptably low
risk of construct failure in a total of 15 patients with osteoplasty
of acetabular lesions from various tumors.
34,35
Ablation has been utilized in several other series. e use of
percutaneous ablation with cryoablation, radiofrequency ablation, or microwave has the ability to relieve pain secondary to
the bone–tumor interface. e need for stabilization is lesion,
location, and to some degree based on operator judgment.
ere have been several reports of fracture aer ablation in
weight-bearing bones, including the femoral neck and sacrum,
and therefore the addition of either osteoplasty alone, or hybrid
screw xation and augmentation, has been employed.
36,37
Kelekis
etal.38 and Deschamps etal.39 have separately reported favorable
results in combination pin or screw and PMMA xation of femoral lesions (Figure 26.8). Further, several authors have utilized
a hybrid minimally invasive ablation and augmented screw xation for impending or completed pathologic fractures.
40
261
Section VIII:Musculoskeletal
e combination of PMMA with its excellent axial
load-bearing properties combined with cannulated screws or
pins capable of bearing bending and shearing forces results in
an ideal structure similar to rebar reinforced concrete, universally employed in highway construction.
While the literature is still lacking for these hybrid interventions, several centers have successfully employed a minimally
invasive strategy to avoid open surgery with its inherent limitations and complications. Ablation followed by augmented
screw xation of fractures that can then be consolidated with
posttreatment radiation has been used in metastatic renal cell,
thyroid, melanoma, lung, and lytic forms of breast and prostate.
Summary
Extended life expectancy of oncologic patients due to advancements in chemotherapy and radiotherapy elds should be
combined with ecient pain control for improved life quality.
Image-guided, percutaneous minimally invasive techniques
such as bone augmentation and newer hybrid techniques combining cement and instrumentation are safe and ecacious
therapies aiming at pain reduction and mobility improvement in
oncologic patients with symptomatic lesions. ese techniques
provide palliative treatment aimed at pain reduction or can be
combined with ablation when local tumor control is thegoal.
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263
Section IX
Organ-specific cancers – prostate
Chapter
Prostate ablations
27
François Cornelis, Jeremy C. Durack, Behfar Ehdaie, Jonathan Coleman,
and Stephen B. Solomon
Introduction
In the last decades, the incidence of prostate cancer tripled
to 152 new cases of prostate cancer per 100,000 men in 2013.
Among cancer in men, it is the third most common cause of
death in men, with 23 per 100,000 men/year. Abetter understanding of prostate cancer biology and earlier detection with
prostate-specic antigen (PSA) screening and imaging
1–3
have
contributed to interest in less invasive alternatives to surgical
resection.
Focal tumor ablation has been increasingly used for local
control or with curative intent in solid-organ tumors such
as kidney, thyroid, breast, liver, and lung.4 While stimulating
thought about ablation application in prostate cancer, clinical application has been limited despite encouraging functional and short-term oncological outcomes.5 Furthermore,
despite evidence that men with low-risk localized prostate
cancer may not benet from treatment in terms of prostate
cancer-specic mortality, many men still elect to undergo radical treatment. For these patients, minimally invasive options
that could provide oncologic ecacy with little impact on quality of life may be attractive. More importantly, focal ablation
of intermediate-risk tumors may enable more men to remain
on active surveillance, thereby sparing them the consequent
harms associated with radical treatment, including sexual, urinary, and bowel complications.
Prostate ablation is an emerging treatment modality oering promise for local cancer control with reduced morbidity
relative to alternatives. e image-guided nature of focal ablation techniques is particularly appealing as preservation of
erectile, urinary, and rectal function can be achieved by minimizing damage to the neurovascular bundles, external sphincter,
bladder neck, and rectum. e reality, however, is that ablation
strategies have not been standardized in the prostate. Atrend
toward targeted treatments in men with smaller tumor volume
and away from whole- or half-gland therapy has been obser
6,7,8,9
ved.
One explanation is that the natural history of the disease is driven by the largest lesion with the highest grade, the
so-called “index lesion,” and not by the presence of multiple foci
of disease observed in surgical series.
10,11,12
Improvements in
imaging techniques, particularly magnetic resonance imaging
(MRI), now enable visualization of small foci of prostate cancer. Whether focal ablation should play an increasing role in
prostate cancer management is a matter of ongoing debate,
though clinical outcomes aer treatment of smaller-volume
disease in other organs have been encouraging. erefore, the
objectives of this chapter are to:(1)review strategies for focal
prostate cancer ablation patient selection; (2)describe current
and future ablation techniques; and (3)assess the current evidence for safety and oncologic ecacy of prostate ablation.
Patient selection
Cancer detection and treatment guidance
To be an eective focal therapy, target visualization and selective treatment are essential. Template biopsies have to date
served as the primary mechanism for prostate cancer localization, with variable use of adjunctive imaging to better delineate organ-conned and extraprostatic spread of disease.8
Studies have shown that conventional template transrectal
ultrasound (TRUS) biopsy alone is insucient for identifying candidates with localized disease that may be treated
with focal therapy.
sound (CEUS) has been proposed to increase the sensitivity of
TRUS-guided biopsies, as early enhancement in cancer foci can
be detected in 23–31% of patients.
tumor enhancement has limited the utility of this technique.
As a result, consensus statements have recommended transperineal template-mapping biopsies (TTMBs) as the standard for
disease localization prior to prostate ablation.10 While TTMB
is more invasive, the risk of complications, such as infection,
appears negligible.10 A recent study reported TTMB using a
5-mm sampling frame, missing only one lesion from a total
of 64 that had a volume of <0.5mL and/or had elements of
Gleason pattern 4 on subsequent whole-mount radical prostatectomy specimens.23 However, for both TRUS-guided and
TTMB, there is no consensus regarding how many biopsies are
sucient to detect the most clinically signicant cancers.
To improve the sensitivity of biopsies for prostate cancer
detection and localization of index lesions, a multiparametric MRI (mpMRI) examination can be used.24 MRI is able
13,14,15,16,17,18,19,20
Contrast-enhanced ultra-
21,22
e transient nature of
Interventional Oncology, Second Edition, ed. Jean-François H.Geschwind and Michael C.Soulen. Published by Cambridge University Press.
©Cambridge University Press2016
265
Section IX:Prostate
to identify and localize areas of suspected adenocarcinoma
greater than 3mm25 and enables whole-gland assessment. In
recently published reports, multiparametric MRI with contrast
injection of gadolinium is sensitive for the detection and characterization of both anterior and posterior tumors.
2,26,27,28
At
this time, most prostate ablation studies rely on multiparametric MRI before ablation in addition to biopsy results for patient
selection.29 MRI-guided biopsy can also be useful, although it
is an expensive and time-consuming solution that is still limited to only a few academic centers30 (Figure27.1). Using the
MR-guided technique, Hoeks etal.30 recently reported a cancer
detection rate of 41% in a series of 265 patients (108/265) with
PSA >4.0ng/mL, with 87% of these patients presenting with
a clinically signicant cancer according to D’Amico scores.
Image fusion algorithms have been developed to superimpose
MR images and real-time TRUS imaging for targeting biopsies.31 Arecent study of patients undergoing MR/ultrasound
(US) fusion-guided biopsies32 reported an overall detection
rate of prostate cancer of 54.4% (55 of 101 patients). Combined
with MRI, CEUS-targeted biopsies1 have a reported overall
diagnostic accuracy close (48.9%) to that reported for in-bore
of early treatment failure, making it dicult to fully interpret
treatment ecacy.
A meta-analysis by Valerio etal. in 2013 summarized these
results:among all ablation studies performed, 1,109 men with
low-risk disease were treated with focal therapy (56%), 704
men with intermediate-risk disease (36%), and 164 men with
high-risk disease (8%).10 Among all the studies discussed, the
PSA level was 3.76–24 ng/mL (overall range: 0.01–82.2 ng/
mL) and the median age ranged from 56.5 to 73years (overall
range:47–80years). Individual Gleason attribution was available in 20 series, with 1,503 men with Gleason score <6, 521
with Gleason score 7, and 82 men with Gleason score >8. ese
results show that prostate ablation is being applied in a wide
range of men. But, as this population eligible for focal therapy
is heterogeneous, the interpretation of results may be dicult.
However, these characteristics dier from salvage series,
where patients are older, with the median age ranging from 65
to 77years. Valerio etal.10 reported 88 men (76%) with failure
following radiotherapy, 17 (15%) aer brachytherapy, 2 (2%)
aer brachytherapy combined with radiotherapy, and 8 (7%)
aer proton beam therapy.
targeted MR-guided biopsies or MRI/US fusion techniques in
patients with visualized cancer foci on MRI and previous negative biopsies (Figure27.2). ese technologies are promising
and warrant further investigation.
In addition to these techniques, new positron emission tomography (PET) tracers have been shown to provide greater sensitivity and specicity compared with the
uorine-18-labeled glucose analog (FDG-PET) for prostate
cancer detection.33 Compared to FDG-PET, the carbon-11
or uorine-18 cholines may be more accurate but are limited to recurrent local disease or the detection of early nodal
involvement,
34,35,36
although a signicant correlation was found
between sections with the highest uorine-18 choline uptake
and tumor inltration (r=0.68; P=0.0001).
36
Patient selection
At this time, no consensus exists regarding ideal candidacy for
prostate ablation, though several guiding principles may be
considered. First, patients with low-risk disease may represent
the best initial candidates for focal therapy. Dened criteria
include a PSA level <10ng/mL, the absence of Gleason grade 4
or 5 foci in biopsied tissues, maximum length of cancer in each
core of 7mm, maximum percentage of total cores with cancer
of 33%, and the use of extended or targeted biopsy schemes.
In addition, an MRI-detectable lesion that is concordant with
the biopsy pathology would be important. However, increasing
numbers of low-risk prostate cancer patients are managed by
active surveillance, and may not benet from treatment of their
indolent tumor.37 Secondly, more consensus is being achieved
for proposing focal ablation of low-volume intermediate-risk
and few higher-risk prostate cancer as an alternative strategy
for those men who would normally be advised to undergo
radical therapy.9 A concern of including intermediate- and
high-risk men is their higher rate of micrometastases and disease progression, even aer radical therapy,38 which means that
including them in a focal therapy trial may increase the risk
Targeting strategies
Tempering arguments in favor of focal prostate cancer treatment is evidence that up to 80% of cases demonstrate multifocality on whole-gland pathology mounts.39 Countering these
concerns, studies suggest that dominant index lesions drive
the natural history of the disease.
studies reveal that a single tumor focus is frequently responsible for metastasis and disease progression.12 Furthermore,
lesions smaller than 0.5mL or with a Gleason score less than
7 may not contribute to disease progression over a 10–20-year
period. It must be pointed out that the 0.5-mL tumor volume
represents the lower limit of detection sensitivity for current
imaging techniques.
29
is concept is related to the data that all prostate tumors
do not have similar outcomes
cal disease is also present in many other cancers in which
tissue-preserving therapy is now standard care.
of prostate ablation strategies have been used (Figure27.3).
In general, dierences relate to whether specic cancer foci
(lesion-targeted therapy) or whole regions (region-targeted
therapy) are ablated.56 Depending on experience and protocols, some investigators treat one-half of the prostate, whereas
others limit the ablation to index lesions even when multifocal
disease is present.10 Some proponents of hemi-gland ablation
point out that unilateral disease is present in up to one-third
of men who have surgery.
ment of all known signicant areas of cancer, even in case of
multifocal lesions, though another strategy involves treating
only the largest and highest-grade tumor, sparing smaller foci.
Reconciliation of these multiple treatment strategies with outcome studies may ultimately expand the proportion of men
eligible for focal therapy treatment. Some estimates suggest
that between one-half and two-thirds of men with localized prostate cancer may benet from some form of prostate
ablation.
40,42
40,41,42,43,44,45
44,46,47,48,49,50,51,52
57,58,59,60,61
Molecular genetic
and multifo-
53,54,55
Avariety
Most series report treat-
266
Chapter27:Prostate ablations
AB
ABC
Figure 27.1 Magnetic resonance (MR)-guided prostate biopsy in a 67-year-old man. (A) Axial T2-weighted MR image showing heterogeneous transitional zone
with non-specific hypointensity (arrow). (B) Corresponding focal area of restricted diffusion on axial apparent diffusion coefficient (ADC) image. (C) Transgluteal
MR-guided biopsy (dashed arrow – coaxial needle; arrowhead – core needle tray extended into prostate).
Figure 27.2 Transrectal
ultrasound-guided prostate biopsies in a
65-year-old man with a prostate-specific
antigen of 7 and 2 previous negative
transrectal ultrasound non-targeted
biopsies. (A) Unrevealing transrectal
ultrasound of the prostate. (B) Axial
T2-weighted magnetic resonance
(MR) image showing non-specific
heterogeneous signal of the prostatic
transitional zone. (C) Axial T1-weighted
postcontrast MR image showing a focal
enhancement in the anterior zone of
the prostate (arrow). (D) Corresponding
contrast-enhanced ultrasound showed
an early enhancement (dashed arrow).
Targeted biopsies confirmed the diagnosis
of prostate carcinoma Gleason 7 (3 + 4)
C
D
(dashed arrow). (Courtesy of Dr. Nicolas
Grenier and Dr. Yann Le Bras.)
Retreatment of tumors with prostate ablation is possible,6 as well with radical therapy, although it may be technically more challenging.62 Salvage therapy aer surgery and/or
external-beam radiotherapy has also been proposed.
63,64,65,66
to safety and ecacy. Anumber of imaging techniques can be
used for this purpose, but most studies report the use of US or
MR guidance. While more ecient and less costly than MR,
cancer localization and treatment monitoring by US alone
can be challenging. For example, acoustic shadowing during
Image guidance for prostate ablation
Ultrasound guidance
Once clinically signicant index tumors in the prostate are
identied, accurate targeting of the ablation energy is essential
cryoablation can impair visualization. Lesion detection and
targeting by US may be improved by MR fusion soware or
contrast-enhanced US techniques. CEUS allows a real-time
feedback of tissue destruction with most focal therapy technologies.
future to target more specically the tumor by targeting the
67,68,69
Targeted microbubbles may also be used in the
267
Section IX:Prostate
AB
CD
Figure 27.3 Different prostate therapy
strategies. (A) Lesion-targeted unifocal
ablation. (B) Lesion-targeted multifocal
ablation. (C) Lesion-targeted index
lesion ablation only. (D) Region-targeted
hemiablation.
vascular endothelial growth factor receptors, for example, as
recently shown.
22,70,71,72
MR guidance
MR-guided prostate ablation may obviate many of the limitation of US guidance, though at a cost of longer procedure time
and expense. Early studies suggest that real-time MR monitoring is promising73 but limited to only a few centers with the
required resources. Potential advantages of MR guidance are
improved target visualization and real-time MR thermometry74
to monitor the distribution of cytotoxic temperatures. For
example, isotherms
73,75
may be visualized in tumor foci as well
as around critical structures such as the urethra, rectal wall,
and neurovascular bundle to mitigate ablation complications.
Computed tomography guidance
CT-guided percutaneous transgluteal ablation, most commonly cryoablation, has been described and may oer several
advantages. Namely, the cost and complexity of the procedure
may be reduced by use of fewer cryoprobes.76 e risk of rectourethral stulas may be lower with this approach, though
carbon dioxide dissection may be required through another
interventions seem particularly promising. Early eorts to
fuse previously acquired PET or PET-CT images to intraprocedural CT have evolved to enable real-time PET-CT-guided
interventions. However, these procedures depend upon tracer
specicity. e most common tracer, FDG, is non-specic2 and
suers from low-level, heterogeneous utilization of glucose,
especially in slow-growing prostate cancer foci. As a result, the
role of FDG-PET guidance is limited. Additional PET tracers
with unique biological specicities, such as 11C- or 18F-choline,
deserve further investigation in the prostate cancer setting.
Prostate ablation techniques
As in other organs,5 many types of thermal and non-thermal
ablative techniques have been tried in the prostate gland.
To date, predominantly cryotherapy in North America and
high-intensity focused ultrasound (HIFU) in Europe have been
used and midterm outcomes have been reported. However, as
no randomized controlled trials comparing the ablative technologies have been performed at this time, experience and
accessibility of particular devices continue to drive selection of
ablation technique. e potential advantages and challenges of
the most common ablation techniques deserve consideration.
needle. Multiplanar CT reconstructions may be useful for
monitoring the volume and extent of ice-ball margins, though
index lesions are dicult to visualizeonCT.
Positron emission tomography guidance
Molecular imaging has become an area of intense interventional oncology research to enhance lesion identication,
targeting, and early evaluation of therapeutic response.77
Among the dierent techniques available, PET-CT-guided
High-intensity focused ultrasound
HIFU destroys tissue by focusing acoustic waves through a
transducer to generate heat. e size and location of the ablated
region (“focal zone”) depend on the shape of the piezo-ceramic
element and its focusing system, the US frequency and duration
of sonication, the absorption coecient of the incident tissues,
and the site intensity achieved (Figure27.4). Two mechanisms
are primarily responsible for tissue destruction. First, US waves
78,79
268