Chapter 12

DELIVERY SYSTEMS
CHENG B. SAW, PHD, KOMANDURI M. AYYANGAR, PHD, KOMANDURI V. KRSIHNA, PHD,
ANDREW WU, PHD, SHALOM KALNICKI, MD

Intensity-modulated radiation therapy (IMRT) is a method readily accessible,6 the MLC is the most common delivery
of radiation treatment planning and delivery that conforms system for IMRT. The goal of this chapter is to review the
the high-dose region to the shape of the target volume.1–5 beam delivery systems used in IMRT. The physical char-
An essential component of any IMRT delivery system is acteristics (Table 12-1) and system integration issues are
the beam intensity modulator. There are three general cat- discussed using examples from the major manufacturers.
egories of intensity modulators: physical modulators, bina- Quality assurance on these systems is discussed in Chapter
ry beam modulators, and multileaf collimators (MLCs). 13, “Commissioning and Dosimetric Quality Assurance.”
Physical intensity modulators are similar to compensators
used in conventional radiation therapy and hence are insert-
ed manually. Binary beam modulators are computer- Physical Beam Modulators
controlled modulators that can operate automatically. These The simplest method of performing IMRT is through the
are either “open” or “closed.” The last type of modulator is use of physical beam intensity modulators.7,8 A physical
the conventional MLC, which is a component of the mod- modulator is similar to a compensator except that the for-
ern linear accelerator. Given that linear accelerators are mer is used to modulate the radiation beam intensity

TABLE 12-1. Summary of Commercially Available Delivery Systems

Vendor Type Delivery No. of Resolution, Thickness, Transmission, Focus Maximum Field Overtravel,
(Web Site) Leaves mm cm % Size, cm cm Speed

BrainLAB Micro-MLC Static or 52 3–5 6.4 2 Single; 10 × 10 5 1 cm/s

<www.brainlab.com> dynamic rounded ends
Elekta Inc. MLC Static 80 10 7.5 1.8–2.5 Single; 40 × 40 12.5 2 cm/s
<www.elekta.com> rounded ends

North American Binary Tomotherapy 40 4, 8, or 16 8 0.5 Double 20 × 30 NA 50 cm/s

Scientific (Nomos)
<www.nasmedical.com>

Southeastern Compensator NA NA Based on 5.1 ~ 65 aluminum; NA 40 × 40 NA NA

Radiation Products planning aluminum ~ 84 brass
<www.seradiation.com> system or brass

Siemens Medical MLC Static 82 10 7.5 0.9–1.25 Double; 40 × 40 10 2 cm/s

Systems flat ends
<www.siemens.com>

TomoTherapy Inc. Binary Tomotherapy 64 6.25 10 0.4 Double 160 (long) × NA < 40 msec
<www.tomotherapy.com> 40 (diameter) transit
time

Varian Medical MLC Static or 120 5–10 6 1.6–1.9 Single; 40 × 40 17 3 cm/s

Systems dynamic rounded ends
<www.varian.com>

MLC = multileaf collimator; NA = not available.

178
 Delivery Systems / 179

instead of compensating for missing tissue. Use of these thickness of the slice is defined by the leaf size of the spe-
modulators requires mechanical fabrication. During treat- cially designed beam-modulating delivery system, referred
ment, each physical modulator must be manually inserted to as the multileaf intensity-modulating collimator
into the tray mount of the linear accelerator. Entering the (MIMiC). The MIMiC is mounted on the gantry of an exist-
treatment room and inserting these modulators is labori- ing linear accelerator.
ous, especially when multiple gantry angles are used. A Another commercially available binary system is the
recent technical development by Yoda and Aoki reported TomoTherapy system (TomoTherapy Inc., Madison, WI).
the introduction of an automatic tray mount that can hold Many of the dosimetric features were derived based on the
up to six physical modulators, allowing autoinsertion prior assessment of the MIMiC delivery system.15–17 From the
to treatment of a given beam.9 The number of monitor outside, the TomoTherapy Hi-Art machine looks like a
units (MUs) is significantly less with a physical modulator computed tomography scanner. This unit performs IMRT
compared with MLC-based modulation. However, a poten- with a helical (or spiral) dose delivery pattern. A 6 MV lin-
tial disadvantage of physical modulators is the increase in ear accelerator is mounted onto the gantry ring and direct-
photon scatter outside the portal, which can produce a ed toward the center of the gantry. Using slip-ring
higher skin dose. technology, this device is capable of continuously rotat-
ing around a couch, enabling a smooth dose delivery.
Southeastern Radiation Products
Southeastern Radiation Products (Sanford, FL) markets NOMOS MIMIC
the .decimal system for the remote fabrication of physical The MIMiC is a binary beam modulator that has 40 leaves
modulators. The ordering facility creates the filter specifi- (or vanes) divided onto two banks (Figure 12-2).10,11 Each
cation file from the treatment planning software and then leaf projects a beam length of 0.8 cm at the isocenter in the
either e-mails this file or uses a Web site directly linked to 1 cm treatment mode and a 1.6 cm beam length in the 2
the manufacturing process to upload the files. These file cm treatment mode. The thickness of each leaf is approx-
specifications can be in the proprietary .decimal file for- imately 8 cm, resulting in a transmission of ~ 0.5%. Because
mat or any other modulator file format from the various the MIMiC has two banks, the nominal treatment slice
treatment planning systems. Once the filter specifications length is double the leaf size to either 1.6 or 3.3 cm. IMRT
are received, the device is automatically produced to the delivery is achieved by rotating the gantry (equipped with
customer’s specifications. Customized software enables the the MIMiC) around the patient while the beam is on.
order to be processed and ready for shipment in an aver- During the rotation, the binary modulator opens and clos-
age of 1.5 hours or less. es via electropneumatic actions according to the instruc-
The filters (Figure 12-1) are manufactured using indus- tions prescribed by the planning system. The add-on
trial (Mazak, Florence, KY) machining centers that mill the
IMRT modulators out of solid blanks of aluminum or brass.
This process thereby eliminates all porosity issues associat-
ed with pouring individual molds. In addition, it enables
inspection of the filter while on the Mazak CNC milling
machine using five-axis “touch probe” technology. A hard
copy quality control report is sent with each filter. The tol-
erance of each filter is ± 0.25 mm. Southeastern Radiation
Products also provides traceability of the alloy, thereby pro-
viding customers with a consistent attenuation factor (eg,
for a 6 MV linear accelerator, the attenuation coefficient is
0.112/cm for aluminum and 0.359/cm for brass).

Binary Beam Modulators

The first commercially available system that used a bina-
ry beam modulator was the PEACOCK System (North
American Scientific, NOMOS Radiation Oncology Division,
Cranberry Township, PA) introduced in 1996. This system
employs a slice-by-slice beam delivery method and hence
is referred to as serial tomotherapy.10–14 Stacking a series
of slices through a target constitutes a complete single- FIGURE 12-1. An aluminum filter constructed to produce an intensity-
fraction treatment. In principle, such a beam delivery tech- modulated anterior right lung/supraclavicular port. Courtesy of Richard
nique can be used to treat a target of any length. The Sweat, Southeastern Radiation Products, Inc.
180 / Intensity-Modulated Radiation Therapy

components for this delivery system are the MIMiC, a con- The NOMOS CRANE II is used to position the treat-
troller, a dual-computer system for control and continuous ment couch to within 0.1 mm accuracy (a tolerance that is
monitoring of the MIMiC, a radiotherapy table adapter device typically not available on a linear accelerator couch). This
for patient immobilization, and a NOMOS CRANE II (North device is attached to the side of the treatment couch and
American Scientific) for indexing the treatment couch. latched to the handrail. A crank controls the movement of
The treatment planning system CORVUS (originally called the treatment couch. During actual dose delivery, the ther-
PEACOCK PLAN) was developed to support the MIMiC apist must enter the room after each treatment slice to repo-
beam delivery system. The CORVUS system uses an inverse sition or advance the couch to the next index. More recently,
planning algorithm for optimization.10,11 Beam delivery the AutoCrane has been introduced as a method of pro-
instructions are transferred via a floppy disk from CORVUS viding remote, automated table positioning (Figure 12-3).
to a controller connected to the MIMiC. The controller auto-
matically directs the modulation of the leaves as the gantry TomoTherapy
of the linear accelerator rotates around the patient to pro- The TomoTherapy Hi-Art system (Figure 12-4) uses a bina-
duce a narrow highly varying field of 1.6 × 20 cm or 3.3 × ry modulator that has 64 interdigitated tungsten leaves that
20 cm. The dose and gantry rotation rates are kept con- move in a steel guide. The leaves are 10 cm thick in the beam
stant during the delivery. The controller senses faults based direction. The tongue and the groove dimensions are both
on gantry position and halts treatment if necessary. Because 0.30 (± 0.03) mm, with a nominal overlap of 0.15 (± 0.03)
this delivery system supports the slice-by-slice treatment par- mm. This results in an interleaf leakage of 0.5% and an intraleaf
adigm, the abutment of contiguous slices must be precise to leakage of 0.3%. Each leaf projects a 0.625 cm width at the
minimize dose nonuniformity at the slice junction.13,14 center of the gantry (85 cm from the source) and is capable
of opening from 0 to > 5 cm. The leaves are pneumatically
controlled by individual air values so that each leaf can open
and close quickly. The length of opening or closing of each
leaf modulates the intensity of the beam. The transit time
(opening or closing of each leaf) is less than 40 milliseconds.
The length of the treatment beam can be as long as 160 cm,
and the fan beam width can vary from 0.6 to 5.0 cm.

FIGURE 12-2. The multileaf intensity-modulating collimator (MIMiC) FIGURE 12-3. Attachment of the multileaf intensity-modulating colli-
delivery system. This binary modulator consists of two banks, each with mator (MIMiC), AutoCrane, and radiotherapy table adapter to a linear
20 leaves. Reproduced with permission. accelerator. The AutoCrane provides a remote, automated table posi-
tioning for serial tomotherapy. The treatment table can be repositioned
from outside the treatment room, eliminating the time associated
with entering the room for manual indexing. (To view a color version
of this image, please refer to the CD-ROM.) Courtesy of Tim Biertempfel,
North American Scientific, NOMOS Radiation Oncology Division.
 Delivery Systems / 181

MLC-Based Delivery
Originally, the MLC was introduced as an autofield shap-
ing device to replace custom blocks. As such, MLCs were
designed with specifications for purposes other than IMRT.
All MLC systems consist of a series of collimating blocks,
vanes, or leaves arranged side by side, as shown in Figure
12-5. These leaves are separated into two banks, and each
leaf is driven independently using microprocessors to facil-
itate autofield beam shaping. The movement of the leaves
is limited to one dimension, either in or out.
Currently, there are two mechanisms of modulating
beam intensity using an MLC. The first mechanism is
termed “segmental IMRT,” in which the collimator’s shape
is constant during irradiation and changes while the beam
is “off.”5 This mechanism is also called the “step-and-shoot”
FIGURE 12-4. The TomoTherapy Hi-Art system. Treatment is delivered
technique or static multileaf collimation (sMLC). The
as the couch advances through the gantry and the beam rotates con-
tinuously around the patient. Courtesy of Sam Jeswani, TomoTherapy, planned intensity-modulated beam at each gantry angle is
Inc. deconvolved into a series of segments (subfields) that are
delivered by the MLC system of a linear accelerator. This
The TomoTherapy unit uses a compact linear accelera- process, known as leaf sequencing, is carried out by a com-
tor for both imaging and treatment. The bremsstrahlung puter algorithm.18,19 By superimposing a series of segments,
target has a unique design: a button of tungsten that is free each with a uniform intensity (but a unique number of
to rotate in a stream of water. The photon beam is unflat- monitor units), a nonuniform fluence pattern is produced.
tened with a maximum dose rate of 8.5 Gy/min at the cen- The linear accelerators from the manufacturers discussed
tral axis. The primary collimator and jaw pair, which define below (BrainLAB, Elekta, Siemens, and Varian) all support
the fan beam width, are immediately downstream from the the sMLC dose delivery mechanism.
target. In the forward direction, the total shielding thick- The second mechanism of dose delivery is termed
ness of the primary collimator and jaw is 23 cm of 94% “dynamic IMRT,” in which the collimator’s shape changes
purity tungsten. This shielding reduces the leakage radia- during irradiation.5 This is different from sMLC, in which
tion for helical IMRT to levels much lower than those of the collimator’s shape remains stationary during irradia-
conventional IMRT. tion. This mechanism is also called the “sliding window”
Treatment is delivered as beam rotation is synchronized technique or dynamic multileaf collimation. In this tech-
with the continuous longitudinal movement of the couch nique, each MLC leaf pair defines a gap or section of a field
through the bore of the gantry, forming a helical beam pat- shape that moves unidirectionally. The leaves move with
tern (sinogram) from the patient’s point of view. various velocities as a function of time to create the nonuni-
Simultaneously, the set of binary collimator leaves rapid- form intensity field. A fast-moving gap creates a low-
ly transitions between open (leaf retracted) and closed (leaf intensity region, whereas a slow-moving gap produces a
blocking) states according to the treatment plan. high-intensity region.

FIGURE 12-5. Side view (A) and a beam’s-

eye-view (B) of a Siemens’ multileaf collima-
tor (MLC). In general, MLCs are constructed
with two banks of leaves. Each leaf has its
own motor, allowing it to move independently.
182 / Intensity-Modulated Radiation Therapy

MLC designs differ from one manufacturer to anoth- 10 × 10 cm. An mMLC is installed under the primary colli-
er. Thus, leaf sequencing algorithms must take into con- mators as an integrated component of the treatment unit.
sideration the design and mechanical limitations of each The m3 mMLC is also available as an add-on system, which
MLC system. As an example, one such design charac- can be adapted to an existing linear accelerator. There are 26
teristic is known as interdigitation. This is the property pairs of leaves: 14 pairs with a leaf width of 3 mm at the
whereby the tips of neighboring leaves on opposed MLC isocenter, 6 pairs with a leaf width of 4.5 mm at the isocen-
banks are allowed to pass one another. Figure 12-6 shows ter, and 6 pairs with a leaf width of 5.5 mm at the isocenter.
interdigitation limits based on existing MLC designs. The single-focused mMLC has a special tongue-and-groove
Depending on the MLC design, full interdigitation, no design, full over-center travel, a low leakage of (1.5–2%), and
interdigitation, or no interdigitation with a gap may be a maximum speed of 1 cm/s.21 The leaves have rounded ends
allowed. Consequently, a deliverable segment for one to minimize the penumbra size. Circular cones with differ-
MLC may not be deliverable on a different manufactur- ent diameters can also be mounted below the mMLC.
er’s MLC. Other features, such as leaf width, leaf diver- Novalis can operate in different treatment modes, includ-
gence, leaf motion, leaf travel, and tongue-and-groove ing conventional circular arc SRS, conformal SRS (multi-
design, are also different for each MLC. Each vendor has ple static shaped beams), dynamic conformal arc SRS (arc
provided its MLC design specification to the treatment delivery combined with mMLC field shaping that contin-
planning systems so that these characteristics can be mod- uously conforms to the beam’s eye view projection of the
eled during the planning process. target), and dynamic or step-and-shoot IMRT. The pri-
The design and dosimetric characteristics of three mary components of the system—linac, MLC, treatment
commercially available conventional MLCs are described planning system, infrared and x-ray tracking and position-
by Xia and Verhey and Arnfield and colleagues.19,20 These ing system—are fully integrated through a record and ver-
MLCs and a specialized micro–multileaf collimator ify system, which is a patient information management
(mMLC)21 for stereotactic radiosurgery (SRS) are briefly system. All treatment planning parameters, including the
presented here. gantry, couch, collimator position, monitor units, and leaf
position, are automatically transferred from the treatment
BrainLAB planning system to Novalis through this information man-
The Novalis dedicated Shaped Beam Surgery System agement system.
(BrainLAB, Heimstetten, Germany) is a megavoltage treat-
ment unit (Figure 12-7). It has a single 6 MV photon beam Elekta
with an output range of 0.3 to 20 cGy/deg (arc mode) and The Elekta Precise (Elekta, Stockholm, Sweden) MLC deliv-
up to 800 cGy/min (fixed mode). This allows efficient deliv- ery system replaces the upper movable jaws inside the lin-
ery of a high-dose single fraction and conventional frac- ear accelerator head (Figure 12-8). The close proximity to
tionation schemes. The maximum field size of the unit is the target results in a minimal range of motion required for

A B

1 cm

FIGURE 12-6. Schematic diagram illustrating the interdigitation restric-

tions for various multileaf collimators (MLCs) based on their design
specifications. (A) Full interdigitation is allowed; (B) leaf tips from oppos-
ing MLC banks are allowed to meet, but not pass, each other; (C) leaf FIGURE 12-7. Novalis Shaped Beam Surgery System with the infrared
tips from opposing leaf banks must remain 1 cm apart. Adapted from and x-ray tracking and positoning system. (To view a color version of
Xia P and Verhey LJ.19 this image, please refer to the CD-ROM.) Courtesy of Franz Gum, BrainLAB.
 Delivery Systems / 183

precise field shaping. There are several benefits to this design, display of leaf position via charge injection device camera
placing less wear and tear on the leaf positioning mecha- technology on color monitors in both the treatment room
nism, and it allows the head size to be very compact at only and the control room. It also offers beam’s eye view veri-
62 cm in diameter. A smaller head size reduces the poten- fication of the actual leaf setup, with the precision of the
tial for gantry and table collisions when noncoplanar beams individual leaf position being ± 0.6 mm.
are used. The system is capable of delivering a dose at 0.1
MU resolution, allowing for the accurate delivery of small- Siemens Medical Solutions
dose segments common to IMRT prescriptions. In the Siemens (Siemens Medical Solutions, Malvern, PA)
The Elekta MLC consists of 40 pairs of tungsten alloy PRIMUS and ONCOR linear accelerators, the MLC deliv-
leaves with a 7.5 cm thickness and each leaf projecting a 1.0 ery system replaces the lower movable jaws inside the lin-
cm width at the isocenter. The average leakage through ear accelerator head (Figure 12-9). The OPTIFOCUS MLC
the MLC system is 1.8 to 2.5%.20 Transmission is reduced for the ONCOR linear accelerators has 39 pairs of inner
to less than 0.5% by 3 cm thick backup jaws directly under- leaves with a 1.0 cm width and two pairs of outer leaves
neath the leaves. Because of the integrated nature of Elekta’s with a 0.5 cm width. This provides coverage of a full 40 cm
design, the same computer controls the MLC, the leaves, IMRT field length. The three-dimensional MLC on the
and the backup jaws. Therefore, the backup jaws automat- PRIMUS linear accelerators consists of 27 pairs of inner
ically follow to the edge position of the outermost with- leaves with a 1.0 cm width at the isocenter and two pairs
drawn leaf. Each leaf has a length of 32.5 cm at the isocenter of outer leaves with a 6.5 cm width. The leaf length for both
and is single focus, with a rounded end. The maximum field systems is 31 cm at the isocenter, with a straight edge fac-
size for conventional treatment is 40 × 40 cm. Each leaf can ing toward the center of the beam. A double-focus leaf
travel 12.5 cm over the beam central axis, allowing an IMRT design follows the beam divergence so that the end and side
field of 25 × 40 cm. The maximum leaf speed is 2.0 cm/s, of the leaves follow the beam divergence in both directions
defined at the isocenter. IMRT is delivered using the step-
and-shoot technique. The Precise linear accelerator is capa-
ble of delivering each segment automatically through an
autofield sequencer available either with the PreciseBEAM
software or an external record and verification system.
Elekta’s PreciseBEAM IMRT interface adheres to an
open-systems philosophy using the Digitial Imaging and
Communication in Medicine (DICOM) radiation thera-
py standard for communications with other systems, allow-
ing an interface to all major record and verification systems.
Unique to Elekta’s PreciseBEAM IMRT design is the option
to receive prescriptions directly from the treatment plan-
ning system without passing through an external record
and verification system. Elekta’s MLC provides real-time

FIGURE 12-8. The Elekta Synergy (registered) uses Cone-beam kilo-

voltage computed tomography (KVCT) to guide IMRT treatments. (To FIGURE 12-9. Siemens ONCOR linear accelerator. Courtesy of Sandi
view a color version of this image, please refer to the CD-ROM.) Courtesy Lotter, Siemens Medical Solutions.
of Timothy Prosser, Elekta.
184 / Intensity-Modulated Radiation Therapy

(along and perpendicular to the leaf motion). This con-

figuration produces a relatively narrow beam penumbra.
Because of the complex design for an arc trajectory, the leaf
position is accurate only to within 2 mm.
The average leakage through the Siemens MLC is 0.9 to
1.25%.20 Each leaf can travel a maximum distance of 15
cm over the beam central axis, which may limit the IMRT
field width in some cases to 27 cm. The maximum speed
of the leaf is 2 cm/s, defined at the isocenter. The upper
jaws must be positioned no more than 0.5 cm beyond the
boundary of the MLC shape. Siemens linear accelerators
provide a maximum field size for conventional treatment
of 40 × 40 cm.
The MLC-based IMRT is designed for the automated FIGURE 12-10. Varian Clinac with On-Board Imager. The On-Board
segmental treatment technique, also known as CINEMATIC Imager is used to fine-tune patient setups before delivery of intensity-
IMRT. Siemens linear accelerators are capable of deliver- modulated radiation therapy begins. (To view a color version of this
ing each segment automatically through an autofield image, please refer to the CD-ROM.) Courtesy of L. Scott Johnson, Varian
sequencer available on the LANTIS record and verification Medical Systems.
system. To efficiently deliver IMRT, a delivery module known
as SIMTEC (Siemens Intensity Modulation Technology)
has been developed. This delivery module contains an auto- ter to 17 cm beyond the isocenter as long as multiple car-
field sequencer that automatically delivers all fields with- riage positions are used. There is no restriction in the upper
out human intervention provided that all fields are coplanar. and lower movable jaw location relative to the MLC shape.
In addition, IM-MAXX is a software package from Siemens However, the recommended jaw position is 0.5 cm distal
designed for efficient IMRT dose delivery. These opti- to the boundary of the MLC shape for conventional treat-
mization tools can provide the user with faster IMRT deliv- ment. Because the leaf length is 16 cm, the distance between
ery times, keeping all of the verification elements intact. the most leading and the most retracted leaves from the
same bank is limited to 14.5 cm to avoid radiation leak-
Varian Medical Systems age through the tail of the most leading leaf or the tip of
The Varian (Varian Medical Systems, Palo Alto, CA) Clinac the most retracted leaf.22 The MLC system supports all
MLC delivery system is a tertiary system mounted below types of IMRT delivery: segmental, dynamic, combined
the lower movable jaws inside the linear accelerator head dynamic and segmental in the same field, and conformal
(Figure 12-10). The MLC consists of 26, 40, or 60 pairs arc.
of tungsten alloy leaves with 6 cm thickness and each pro- The dynamic IMRT delivery module is called the dose
jecting a 0.5 or 1.0 cm width at the isocenter. For the newer mode in the Varian system. In this mode, an intensity-
delivery system, the Millennium 120 MLC, there are 40 modulated MLC file is executed, consisting of a sequence of
inner pairs of leaves, with each leaf projecting a 0.5 cm all leaf positions as a function of a dose index, starting from
width, and 20 outer pairs of leaves, with a 1.0 cm width at 0.0 to 1.0. This dose index is a percentage of the total MU for
the isocenter. The average leakage through the Varian MLC this intensity-modulated field. During the delivery, the MLC
is 1.6 to 1.9%.20 Each leaf has a length of 16 cm measured leaf positions are controlled by the MLC control computer,
at the isocenter and is single focus, with a rounded end. whereas the total MU is controlled by console computer. The
In the single-focused MLC, the leaf motion is along a MLC control computer and the MU console computer com-
straight line in a plane perpendicular to the beam central municate with each other every 50 milliseconds to establish
axis. The mechanical design is therefore simpler, with a the correspondence between the leaf position and the cumu-
leaf positional accuracy of 1 mm at the isocenter. The lative MU, as described in the intensity-modulated file.23
rounded end is used to ensure that leaf end transmission
is nearly independent of the leaf position. The maximum
leaf speed is 3 cm/s. Summary
With two MLC leaf carriages, the maximum conven- The intensity beam modulator is the primary component
tional field size is 40 × 40 (26) cm, depending on the num- of the treatment machine that allows for the delivery of
ber of leaf pairs available on the MLC. The travel range of IMRT. Each of the modulation systems described here
each leaf is 15 cm from the end of the carriage.22 The car- has its advantages and disadvantages. The choice of a par-
riage can be retracted up to 20 cm from the beam axis ticular manufacturer’s system depends on a number of fac-
and can travel up to 2 cm beyond the axis. Therefore, the tors, including available hardware and software, the scope
leaf positions can vary between 20 cm away from the isocen- of the IMRT program, and cost. IMRT delivery systems are
 Delivery Systems / 185

continually evolving. Future systems will improve on the investigation in quality assurance. Z Med Phys 2001;11:15–22.
features of existing technologies by reducing radiation trans- 9. Yoda K, Aoki Y. A multiportal compensator system for IMRT
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10. Curran B.“Where goest the peacock?” Med Dosim 2001;26:3–9.
hardware, and increasing delivery efficiency to reduce over-
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all treatment times. of Peacock system for intensity-modulated radiation
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uals for contributing to this chapter: Tim Biertempfel (North 14. Salter BJ, Helvezi JM, et al. An oblique arc capable positioning
American Scientific, Nomos Radiation Oncology Division), s ys tem for s e qu ent ial tomo ther apy. Me d P hys
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L. Scott Johnson (Varian Medical Systems), Sandi Lotter 15. Balog JP, Mackie TR, Reckwerdt P, et al. Characterization of the
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Richard Sweat (Southeastern Radiation Productions). Med Phys 1999;26:55–64.
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