Description
Write 1-2 short paragraphs for each article discussing the data collection method used for each. Discuss why each method was chosen and if you think it was effective for the paper that was written. Would you do anything differently than the author? Cite your references in AMA format as appropriate.
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Journal of the American Society of Radiologic Technologists
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Volume 26, Number 1 Spring 2017
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E M O R AT I N G 2
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DIRECTED READING ARTICLES
Surface Imaging in
Radiation Therapy
PAGE 23
Intraoperative
Radiation Therapy
PAGE 45
PEER-REVIEWED ARTICLES
University Student Awareness
of Skin Cancer: Behaviors,
Recognition, and Prevention
PAGE 11
Do Fertility Drugs Increase
Cancer Risk? A Literature
Review
PAGE 16
CE
Directed Reading
Surface Imaging
in Radiation Therapy
Alisha Chlebik, BS, R.T.(T)
Surface imaging is an
emerging radiation therapy
technique that aids in the
setup of patients for treatment
and acts as an intrafraction
monitoring system. Although
the technology offers several
advantages for staff and
patients, it can be challenging
to put into practice. With
appropriate training and
implementation, radiation
oncology staff can use surface
imaging to improve patient
care and comfort while
reducing dose to the patient.
This article describes surface
imaging, its uses, and its
applications for treating
specific anatomy.
This article is a Directed
Reading. To earn
continuing education
credit for this article,
see the instructions on
Page 40.
After completing this article, the reader should be able to:
Summarize surface imaging principles and how the technique can improve patient
setup, positioning, and monitoring of intrafraction movements.
Explain various methods of calibration and quality assurance processes for
surface imaging.
Discuss how to implement surface imaging and identify steps that improve the
technology’s accuracy and effectiveness.
Evaluate the benefits and drawbacks of implementing surface imaging.
Identify strategies for surface imaging use at various treatment sites.
A
s radiation therapy delivery
systems become more complex, the need increases for
greater precision in localization and surveillance of the treatment
area. Many radiation therapy centers use
onboard imaging to localize tumors and
closed-circuit television (TV) for surveillance. Onboard imaging can include
megavoltage imaging, kilovoltage (kV)
imaging, or cone-beam computed
tomography (CBCT). Onboard imaging, although accurate, exposes
patients to additional radiation and
can confirm proper positioning only
at a single time point.
Radiation therapists who rely on
closed-circuit TV to detect motion
typically cannot see patient movements
of less than approximately 1 cm. In
addition, therapists must pay constant
attention to the closed-circuit TV, which
is impractical and might not allow the
beam to be shut off in a timely manner.
RADIATION THERAPIST, Spring 2017, Volume 26, Number 1
To counter these drawbacks, a more
accurate real-time motion detection
system is needed. Surface imaging, a
tool that combines surface localization
and surveillance, is becoming more
widely used for setup and intrafraction monitoring. Radiation therapy
departments can use surface imaging
to improve treatment accuracy and
the speed of workflow while reducing
radiation exposure to the patient from
medical imaging.
The use of surface imaging in radiation therapy gradually has increased
since its introduction in other fields in
the 1940s. Common applications of surface imaging included imaging of large
objects, anthropology studies, and accident scene investigations. However, it
has been available for medical use only
since the late 20th century.1,2 Although
surface imaging is not a common tool in
clinical oncology settings, other medical specialties, such as plastic surgery,
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Surface Imaging in Radiation Therapy
dentistry, sports medicine, and gastroenterology,
routinely use 3-D surface imaging.3-5 Surgeons create
simulations before starting procedures to aid in surgical mapping and planning.5,6 In addition, surgeons can
access 3-D surface imaging data in real time, which can
shorten decision times for complex surgeries. 3,5 Plastic
surgeons specializing in rhinoplasty commonly use 3-D
surface imaging to delineate soft tissue and volumetric
changes before and after surgery. 6 In endoscopic procedures with 3-D surface imaging, physicians can access
quantitative measurements such as size, depth, and
shape of internal anatomy, which can increase the accuracy and precision of an intervention.4 Furthermore,
surface imaging provides the data needed to customize
medical devices, such as ear impressions for hearing
aids and dental molds.5
Surface imaging has evolved greatly since 1944,
when a plotting machine was developed to create 3-D
images of objects using a technique called stereophotogrammetry. In stereophotogrammetry, measurements
from 2 or more photographs are used to estimate the
3-D coordinates on the surface of an object.
In 1995, Ras et al improved the technique
by using digitized capture to reduce the
amount of time needed for manual analysis.7
Low-cost charge-coupled device (CCD)
cameras replaced the old camera systems
in 1999, which helped speed up automatic
analysis. The first laser scanning system
was used clinically in 1991 to monitor the
growth of children who had facial deformities. Over the next 5 years, measurements
improved, becoming more accurate than
those of previous laser scanning systems.8
treatment fraction. The deltas represent the observed
intrafraction deviations from the starting isocenter.
The 2 most common types of surface imaging are
optical-based video surface imaging and laser scanning.9 Modern video surface imaging uses structured or
unstructured light patterns and stereophotogrammetry
to recreate the surface shape of a 3-D object based on
the distortion of the projected light pattern.1,5,8 The system calculates the geometric shifts from the recorded
surface to a previously recorded reference surface.
Unstructured light is a random light pattern projected
onto the surface of a patient or object.8 Structured light
involves illuminating a target with patterns such as dots
or grids while the video camera photographs the surface
at several frames per second.
Stereophotogrammetry is based on the principle of
taking 2 images of the same object from different angles
to create a stereoscopic pair. These images contain
distance and spatial information about the surface of
the object that can be used to create a 3-D shape.8 For
video-based systems, mounting more than 2 cameras to
Surface Imaging
Surface imaging provides deltas in 6 directions: vertical, longitudinal, lateral, pitch,
roll, and yaw.9-11 Pitch is a rotation along the
horizontal axis, roll is a rotation along the longitudinal axis, and yaw is a rotation along the
vertical axis (see Figure 1). Delta is a common term in radiation therapy that indicates
a real-time tracking change, in 3 translational
and 3 rotational directions, from the initial
isocenter point set at the beginning of the
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Figure 1. The surface imaging system detects 3 translational and 3 rotational
references for patient alignment. Directional variations that affect treatment alignment are measured in the x (laterial), y (longitudinal), and z (verticle) directions.
Rotational variations include pitch, roll, and yaw. © ASRT 2013.
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the ceiling of the treatment room to record the reflected
images increases the 3-D accuracy of the surface image.
Using more than 2 cameras also is helpful should the
rotating linear accelerator obstruct the cameras’ line of
sight during treatment.12,13
Digital speckle photogrammetry is an example of
surface imaging using structured light. A speckle light
pattern is projected onto the curved surface of the target. Stereo cameras receive the reflected pattern, and
the system software triangulates the data, creating a
3-D surface model of the object. The 3-D model can be
registered with a reference surface image, usually from
the treatment planning system (see Figure 2).10
Some surface imaging systems use a near-visible
light-emitting diode projector and a CCD camera.9 The
3 light wavelengths (blue, green, and red) are projected
onto the patient. The reflected blue light received by
the CCD camera is used to determine the skin surface
coordinates. The projected green and red lights show
the mismatch of the reference surface vs the actual captured patient surface.9
Laser imaging systems sweep a laser beam across the
target area, and multiple cameras receive the reflected
light from the region of interest (ROI) to help determine the coordinates of the target object.8-10,12,14,15 An
algorithm then constructs a 3-D model by calculating
the difference between the surface of the object and the
reference surface.10
Setup and Monitoring
The body contours from a computed tomography
(CT) simulation provide the initial reference surface for the patient. Typically, contours are exported
through the Digital Imaging and Communications
in Medicine (DICOM) structure set file. DICOM
data are imported into the surface imaging software
and should be used for the initial treatment. A new,
in-room surface imaging capture can be performed
at the treatment position once imaging demonstrates
accurate patient position. The reference image, either
from DICOM data or an in-room capture, provides
information for daily patient setup for radiation therapy treatments.10,11,13,15,16 An in-room surface imaging
capture does not replace the original DICOM data but
can be used in place of the DICOM reference each day.
The radiation therapist must select the correct type of
RADIATION THERAPIST, Spring 2017, Volume 26, Number 1
Figure 2. Pseudorandom speckle photogrammetry light pattern
projected onto an object or patient. Image courtesy of the author.
reference image when performing patient setup and
alignment analysis. Choosing the wrong reference
could lead to incorrect patient positioning.
Surface imaging also can help monitor patient motion
or position changes during treatment.10,14,16-18 A separate
image is captured and used to determine whether motion
occurs after the patient is in the treatment position;
this monitoring image serves as the baseline for patient
motion. Subsequent delta values are then brought to zero.
If motion causes the patient’s alignment to move outside
the set tolerance range determined by the surface imaging system, the radiation therapist can hold the beam. If
the patient’s position then falls back within the tolerance,
the therapist can continue treatment with confidence
that the patient is aligned correctly.
When treatment equipment can interface with the
surface imaging system, the equipment automatically
holds the beam if the patient moves outside the tolerance parameters. A starting point for tolerance is 2 mm
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Surface Imaging in Radiation Therapy
and 1°, but the actual tolerance range should be based on
the anatomical site. For example, tolerance for a patient
undergoing breast cancer treatment can be wider than for
a patient receiving treatment to the brain, which should
have a much smaller tolerance range.
If the patient moves, the therapist can realign the
patient with surface imaging.10 This ability potentially
improves the therapist’s workflow because less time
is spent checking the patient’s positioning. Without
surface imaging, a therapist has to enter the treatment
room after observing movement on closed-circuit TV
to verify whether the patient is still in the correct position. The radiation therapist also might need to adjust
the patient’s position and take another image, which
adds to the patient’s total ionizing radiation exposure.10
Comparison With Optical Tracking Markers
Marker-based optical tracking in radiation therapy
relies on reflective marker photogrammetry to determine the surface of an object.10,18 This method differs
from surface imaging in that the optical marker is passive and either rests on or is affixed to the patient or to a
device that corresponds to the patient’s positional alignment. Surface imaging captures a patient’s entire skin
surface to determine the correct position relative to the
equipment’s isocenter and to monitor the patient
in real time. Optical tracking primarily assists with
monitoring respiratory motion rather than with
the positioning of a large ROI. Optical tracking
can hold the beam should the patient’s breathing
pattern fall outside the set tolerance when interfaced with the linear accelerator.
Several methods are used for passive marker
attachment. An example of an invasive marker
is a bite block with an attached reflective marker
array.18,19 This method requires creating a customfit bite block for the patient and using the block
during each treatment session. The markers
attached to the mouthpiece help with patient
setup and monitoring. Noninvasive optical tracking includes markers afixed to or resting on the
patient’s skin; the markers have adhesive backings
that adhere to the patient’s skin for gated treatments.18 The markers must be in the same position
each session for the system to provide correct
26
couch shifts. Inconsistent placement can result in
patient misalignment.
Calibration and Quality Assurance
The acceptance period for surface imaging systems
must involve thorough testing and development of
routine quality assurance (QA) procedures. Surface
imaging requires an initial calibration of the system
on installation to ensure that the equipment’s isocenter is aligned with the surface imaging system. A
manufacturer representative performs setup and initial
calibration.15 Additional daily QA tests are required
to maintain the accuracy of the system. To use the
equipment for patient setup and treatment delivery,
appropriate calibration and verification guidelines and
tools must be available to radiation therapy staff. Each
clinical facility can implement more stringent QA protocols and tolerances than are recommended by the
manufacturer.
One method of calibration uses a plate with a printed
grid of circles in contrasting colors. The center of the
plate’s surface is aligned to the isocenter (see Figure 3).
The cameras take images of the plate and process the
images to identify the center of each circle.16,20,21 The set
Figure 3. A model of a daily and monthly calibration plate. Image
courtesy of Vision RT.
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of images then can be used to find the center of the plate,
which is the calibration point for the surface imaging
system. For radiation therapy, the calibration point of
the surface imaging system should correspond to the
isocenter of the treatment equipment.
In addition to the QA and calibration requirements
set forth by the American Association of Physicists in
Medicine (AAPM),22 manufacturers can recommend
other periodic testing to ensure accurate performance
of the equipment.23,24 For instance, monthly calibration
of the system should be performed because it contributes to the system’s accuracy.5 Typically, a medical
physicist performs the monthly calibrations; however,
in some instances, radiation therapists conduct them
under the direction and guidance of a medical physicist. Each morning as part of the equipment warm-up
process, calibration verification should be performed
on the surface imaging system.25 Some systems use the
same calibration plate for monthly and daily QA. These
checks are required to ensure that the isocenter of the
machine and of the surface imager are in alignment.
Surface imaging calibration is based on the isocenter of
the machine. The daily QA verifies system alignment
with the equipment isocenter.
One consideration for the accuracy of surface imaging is room lighting. The room lighting should be the
same for calibration and verification of the imaging
equipment as the room lighting that is used for each
treatment.19,26 For optimal effectiveness, if patients are
positioned initially with the treatment room lights off,
radiation therapists should continue treating the patient
with the lights off on subsequent days. In addition, the
lighting should be off for all monthly and daily QA procedures of the imaging system.18,23
A radiation therapy center might choose to add extra
QA steps for surface imaging to the morning warm-up
process. Performing a CBCT or a set of kV images on a
phantom can confirm that the surface imaging system
is aligned properly with the treatment machine isocenter. To do this, a QA “patient” is created, and a DICOM
reference surface image of the phantom is acquired and
transferred to the QA “patient.” A reference surface image
of the phantom also can be obtained on the equipment
in the treatment room. A daily CBCT scan or paired kV
images of the phantom are used to match to the reference
RADIATION THERAPIST, Spring 2017, Volume 26, Number 1
surface or digital reconstructed rendering. A phantom
placed at the isocenter should have shifts of less than
1 mm.27 Surface imaging systems have demonstrated
calibration within 1 mm and 1° over several months with
little effect from couch rotation.1,13,15,16,19,28
Implementation
Implementation of surface imaging affects departmental workflow. Any change to workflow in a
radiation therapy department can stress staff and negatively affect implementation.29 As with adoption of any
new technology, it is important that all staff members
are on board with the technology and well trained in its
use. Surface imaging systems involve a steep learning
curve. Training is a vital component of the technology’s
implementation; if the incorrect ROI is used or the
system is used incorrectly, misalignment of the patient
or unnecessary repositioning can occur. The training
should include all personnel involved in the process,
including medical physicists, medical dosimetrists,
radiation therapists, and, when possible, physicians.
Defining the workflow and responsibilities assigned to
personnel can ease the transition.27,30
Several factors should be considered when a clinic
chooses to introduce surface imaging into the workflow. Using the technology on a small group of patients,
such as some patients with breast cancer, is optimal for
initial implementation. 31 This practice allows the users
to become more comfortable using surface imaging
for alignment before increasing the complexity of the
variables associated with other treatment sites. As the
staff of a clinic becomes more comfortable with surface
imaging, the implementation team can add more treatment areas (eg, brain, chest, and pelvis).
To help staff adjust to the new workflow during the
initial implementation period, extra time should be added
to the appointment. Adjusting the appointment time can
ease the stress of maintaining the schedule for therapists
and ensure shorter wait times for patients. After staff feels
confident in the process and workflow, the appointment
time can return to the original timeframe.
Clinical Workflow
The following is a general template of the steps
for incorporating surface imaging into the treatment
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process, which facilities can modify to meet staffing
and equipment needs.
The surface imaging workflow begins with immobilization and patient setup in the treatment position.
The radiation therapist activates the surface imaging
system and notes the areas of mismatch between the
current imaged surface and the referenced surface from
the patient’s CT simulation. Next, the therapist adjusts
the patient and table to correct for the mismatch. After
the patient is aligned based on surface imaging, treatment staff can use standard department protocols to
determine whether radiographic imaging is necessary
for positioning.
Departments and clinics have used several
approaches to determine if radiographs are needed for
positioning. One method involves taking a new monitoring capture after the patient is aligned to eliminate
(zero) any remaining deltas. The patient is then treated
if no daily imaging is needed. For patients requiring
further imaging, the therapist confirms the isocenter
from the additional images and applies the shifts. A
new monitoring capture is taken to detect subsequent
shifts, and the therapist delivers the treatment. Zeroing
the deltas after imaging and before treatment makes it
easier to detect changes in the patient’s position during
the entire treatment.
Another method involves aligning the patient and
continuing with treatment from that point. If a patient
is treated without imaging and the deltas are not taken
to zero, the therapist can determine whether the patient
falls outside the tolerance from initial setup.28,32 To
illustrate this point, if the patient is within tolerance at
3 mm from planned position but then moves 2 mm out
of tolerance, the patient is now 5 mm from the planned
setup. A monitoring surface capture would show only a
2-mm difference from the ideal position. This approach
can be useful if daily imaging is not used and instead
surface imaging alone is used to position the patient.
Each facility must choose the workflow that best suits
its existing processes and workflow (see Figure 4).
Advantages
Surface imaging offers numerous benefits for radiation
therapy staff and patients, the primary one being that it
is noninvasive and uses no ionizing radiation for image
capture. These advantages mean the system does not add
to treatment risk or discomfort for the patient.17,23,24 The
ALARA (as low as reasonably achievable) principle is an
important concept in radiation therapy. Although radiation is administered for therapeutic purposes according
to a prescription, the radiation therapist still must limit
unnecessary radiation exposure to the patient. Using
B
A
Setup
Monitoring
Reference
Figure 4. A. Patient reference position using only the setup coordinates for intrafraction monitoring. B. Patient reference position taken after setup
constituting a “zero” position. Submillimeter changes are seen subsequent to this new capture. Images courtesy of the author.
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surface imaging reduces the radiation dose from imaging
because it limits the number of radiographs or in-room
scans needed to ensure correct patient position. A surface
imaging system performs 2 different steps in the treatment process, setup and monitoring, without exposing
the patient to additional ionizing radiation.33 The dose
reduction is possible because of the decreased need for
repeated imaging.17,23,24 Dose reduction is an especially
important concern in the pediatric population.33 Other
benefits include fewer repeated images, the ability to
monitor a patient during treatment, a decrease in the
amount of immobilization necessary, and reduced need
to mark the patient.
In addition to facilitating patient alignment before
radiologic imaging, surface imaging can limit the number
of large shifts or rotations found after radiographic verification. Rotations (ie, pitch, roll, and yaw) are especially
difficult to correct without the real-time interactive data
provided by surface imaging software.11 Even if CBCT
shows rotations, these rotations cannot be corrected easily without a couch capable of 6 degrees of freedom, and
the radiation therapist must manually manipulate the
patient to make adjustments. Manual adjustment can be
a laborious and inaccurate approach. Modifications must
be confirmed by additional imaging, and repeating this
process means incurring extra time and radiation dose.
Even with a couch capable of moving in 6 directions, the
range of rotations that can be applied is limited.34 When
used in conjunction with radiologic imaging for patient
setup, surface imaging facilitates manual adjustments
and reduces the number of repeat images, thus limiting
unnecessary radiation exposure.
Surface imaging also can be used as a surveillance
tool to monitor patient movement and reduce the need
for repeat imaging during treatment. It can be difficult
for the therapist to observe and quantify small patient
movements on closed-circuit TV, even if the patient has
reference marks or lines. Surface imaging shows submillimeter movements that can indicate when a patient has
moved out of tolerance or has returned to the planned
setup. When a patient has returned to the desired position, the radiation therapist can continue treatment
without additional imaging. If a patient moves outside
the tolerance, the therapist can realign the patient using
surface imaging and continue treatment.28
RADIATION THERAPIST, Spring 2017, Volume 26, Number 1
Surface imaging systems automatically can interrupt
the beam during treatment if the patient moves outside
the tolerance set by the system.9,23,24 The ability to hold
the beam can be advantageous for all treatment cases,
not just gated treatments. The radiation therapist also
can set a threshold to define when a surface imaging
system should hold the beam by adding a time limit or
increasing the tolerance for a particular patient.23,24 A
time threshold can be helpful for volumetric arc therapy
treatments in which a camera can be blocked for a short
time during equipment rotation. The possibility of a
limited visual field is especially of concern for facilities
that have only 1 or 2 cameras.28,35 Thus, the therapist
might choose a threshold of 1 to 2 seconds to account
for potential times the camera is blocked. This particular feature is vendor specific and must be compatible
with the treatment equipment.23,25
Respiratory gating and deep inspiration breath-hold
techniques can be performed with surface imaging and
4-D CT.23,24 Gating is a strategy to decrease the dose to
surrounding healthy structures, such as the heart, when
treating left-sided breast cancer.36,37 Respiratory gating
or deep inspiration breath hold helps decrease irradiated lung volume and thus limits unnecessary radiation
dose to critical structures. The advantage of using surface imaging to hold the beam during treatment is that
no extra devices, such as markers, are attached to the
patient. Optical tracking requires passive markers to
be placed on the patient, which can be uncomfortable.
Surface imaging can monitor whole-body movement
for an entire ROI and motion in a smaller area such as
breathing motion of the chest.
Surface imaging can enhance patient comfort by
decreasing the need for immobilization devices, especially for patients with brain cancer.16 In particular, patients
receiving palliative treatment are more comfortable when
there is less or no need for immobilization. Patients are
less restricted because the system can detect minute
changes in positioning and indicate when the patient is
out of tolerance. In addition, because the skin surface,
rather than external markers on the patient, is used as a
reference, surface imaging is not subject to registration
errors from a misplaced marker.
Surface imaging allows a radiation therapist to position the patient without the use of skin markings, which
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can be advantageous for the patient and the therapist.
The patient does not have to worry about preserving
marks applied during treatment or experience anxiety
about having permanent tattoos. For the therapist,
surface imaging can mitigate inherent challenges associated with using lasers for patient setup, such as laser
inaccuracies, setup subjectivity, and the unpredictability of patient skin movement. When a clinic moves to
eliminate skin markings from the setup process, therapists can be hesitant. However, slowly decreasing the
use of skin marks on the patient and relying more on
surface imaging can help to alleviate concerns during
the transition.
Studies have shown that surface imaging improves
workflow. For example, Batin et al found setup time
decreased 45% for breast treatments when changing
from a standard workflow using tattoos to a surface
imaging workflow.11 The ability to monitor the patient
at all treatment couch angles as well as gantry positions
further enhances workflow by decreasing the amount
of time needed to verify patient positioning during
treatment.16 With real-time imaging during treatment,
the therapist might not need to bring the couch back to
zero to verify correct positioning between couch angles,
which speeds treatment delivery. Workflow improvements after implementing surface imaging are different
for each radiation therapy clinic. The change in amount
of time for patient treatment depends on the existing
workflow and treatment process.
Challenges
Surface imaging has limitations that could impede
adoption or use of this technology in radiation therapy
clinics. Some limitations, such as workflow or the
additional difficulty for patients who have a large body
habitus, can be overcome relatively easily. However,
equipment cost can be a main barrier to some clinics
adopting the technology.
One of the drawbacks of surface imaging is that the
system uses the surface contours to align the patient
and cannot match surface images to the patient’s internal anatomy.10,38,39 For rigid structures, such as cranial
sites, the difference between external and internal
anatomy is less important than for other sites.10 For sites
such as the pelvis, the mismatch of surface and internal
30
contours can be a large obstacle to overcome. Tumors
that are located posteriorly are less accurately represented by surface imaging on the anterior skin surface,
which can lead to a suboptimal setup if treating with
smaller margins.
Surface imaging requires a patient’s skin in the area
of concern to be uncovered during the entire treatment
process.28 For some anatomical sites such as the breast
or chest, leaving the patient uncovered might be the
standard procedure. However, for some areas of interest, particularly the pelvis, the patient might have to
be uncovered for longer periods than with treatment
protocols not using surface imaging. Patients might feel
uncomfortable being exposed, which could decrease
patient compliance and increase movement during
treatment. The radiation therapist can help preserve
some of the patient’s modesty by keeping the patient’s
genitals or other private areas covered with a washcloth or similar covering that does not interfere with
the ROI. Accidental placement of a blanket or clothing
item within the ROI is detected as skin surface by the
system and leads to inaccurate results. Therefore, it is
important that therapists check for any items that might
interfere with the ROI.27,30
A multidisciplinary team is required to implement
surface imaging. Each radiation oncology center might
differ in how it chooses to divide tasks among team
members. A medical physicist or medical dosimetrist
can export the initial data set while a radiation therapist
imports the structure set into the surface imaging system.
One clinic might choose to have the medical physicist
or medical dosimetrist create the ROI, whereas another
site might have the radiation therapist create the ROI.
The radiation oncologist typically is involved in deciding whether surface imaging is appropriate for treatment
use. The distribution of tasks should be outlined clearly
before implementation, and changes should be discussed
as they occur. Over time, staff roles can evolve and lead to
redistribution of tasks. If implementing surface imaging
causes modifications to departmental workflow, the team
should discuss the changes with all staff to avoid role
confusion or overlap.27,30
Body habitus of patients can affect the accuracy of
surface imaging and how it is implemented. Setup can
be more difficult with patients who have a larger than
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average body habitus. Excess adipose tissue and skin
are highly mobile and can decrease the accuracy of the
surface imaging system. Adjusting the ROI to exclude
extra tissue can help alleviate the problem but will not
solve it completely. Radiation therapy staff should take
extra care to ensure that the setup for larger patients
falls within the expected tolerance.
Setup also can be challenging for patients who have
no peaks or valleys in their anatomy, such as those with
a flat chest, because there is little topographic variation to help the system detect angular and positional
changes.16 One solution is to set the ROI on the surface
imaging system to follow, or wrap around, the patients’
body laterally from the anterior surface for treatment
sites within the thorax, abdomen, or pelvis. This gives
the surface imaging system more area to use for its algorithm and should lead to a more accurate calculation.
Weight fluctuations can occur in patients during
their course of treatment and affect the surface imaging
registration.
