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High-Dose-Rate Intraoperative Radiation Therapy For Colorectal Cancer

High-Dose-Rate Intraoperative Radiation Therapy For Colorectal Cancer

ABSTRACT: Intraoperative radiation therapy (IORT) has the obvious advantage of maximally irradiating the tumor bed while eliminating surrounding normal organs from the field of radiation. This approach has been especially useful when the required radiation dose exceeds the tolerance dose of the surrounding normal tissues. However, the application of IORT has been significantly limited by cost, logistic issues, and technical problems related to delivering treatment to difficult anatomic areas. We have developed a new approach to IORT that obviates the need for patient transport: In a dedicated, shielded operating room, the surgery is performed and IORT is delivered via HDR remote afterloading. We have found this approach to be cost effective, logistically sound, and suitable for a wide range of anatomic sites. The technical aspects of the procedure, as well our preliminary results in colorectal cancer, will be presented. Lastly, the authors present the technical aspects of delivering HDR intraoperative brachytherapy, their dosimetry atlas, and their results using HDR-IORT in the treatment of patients with colorectal cancer[ONCOLOGY 9(7):679-683, 1995]

Introduction

The efforts of radiation oncologists have long been thwarted by
the therapeutic ratio. This ratio, which is expressed as the required
dose to eradicate tumor divided by the tolerance dose of the surrounding
normal tissues, often dictates the potential for tumor control
with radiation therapy. When the required radiation dose exceeds
the tolerance dose of the surrounding normal tissues, it becomes
either difficult or impossible to control the tumor using conventional
radiation therapy techniques. Such cancers as advanced pelvic
tumors, abdominal and retroperitoneal tumors, liver tumors, certain
pediatric tumors, and selected thoracic tumors frequently pose
this therapeutic dilemma.

Over the years, radiation oncologists have developed numerous
novel strategies to overcome the constraints of the therapeutic
ratio and to increase the biologic effectiveness of radiation.
These include radiation sensitizers, radiation protectors, brachytherapy,
intra-operative radiation therapy (IORT), three-dimensional conformal
external-beam irradiation, heavy-charged-particle irradiation,
and various combinations of these techniques.

At Memorial Sloan-Kettering Cancer Center, we have developed a
new program for intraoperative radiation therapy: high-dose-rate
intraoperative radiation therapy (HDR-IORT), that attempts to
combine the technical and dosimetric advantages of brachytherapy
with the conceptual and logistic advantages of intraoperative
electron-beam irradiation. The entire procedure is performed in
a specially designed operating room. Thus, no intraoperative patient
transportation is required.

For intraoperative radiation therapy delivery, we use an HDR remote
afterloader, a device that advances a cable-mounted radioactive
(iridium-192) source out of its shield into proximity with the
tissue to be treated. The machine permits stopping the source
for prescribed "dwell" times at regularly spaced positions
in one or more catheters. This equipment is far less expensive
than a linear accelerator, allowing the treatment to be given
in a more cost-effective manner. Because the remote after- loader
is portable, it can also be utilized for other procedures in the
outpatient facility when it is not needed for intraoperative cases.
This further enhances the cost effectiveness of the program.

Advantages and Limitations of Novel Strategies

Conventional Brachytherapy

Brachytherapy involves the placement of interstitial or intracavitary
sources of radioactive material either into or against the desired
target region. This permits high doses of radiation to be successfully
and safely delivered to tumors, with acceptable toxicity to the
surrounding normal structures. For this reason, brachytherapy
has become a standard part of the sophisticated management of
a wide variety of tumors, such as cancers of the oral cavity,
oropharynx, nasopharynx, rectum, cervix, vagina, endometrium,
prostate, brain, and eye and soft-tissue sarcoma.

Conventional brachytherapy is not always feasible, however. Advanced
tumors of the pelvis or retroperitoneum require a large surface
area to be irradiated after appropriate tumor resection. Interstitial
techniques are often suboptimal in these anatomic regions, as
they fail to cover the complex surfaces adequately with permanent
or temporary implants. Catheter movement, risk of infection related
to indwelling catheters, risk that normal tissues, such as the
large and small bowel, will fall in close proximity to the implanted
isotopes (increasing complications), and suboptimal implant geometry
are all potential obstacles to adequate conventional brachytherapy.

Intraoperative External-Beam Radiation Therapy

Intraoperative external-beam irradiation has been explored for
most of this decade in an attempt to improve the therapeutic ratio
[1-3]. The concept on which this technique is based is quite simple.
During an operation, the normal organs are physically moved out
of the pathway of the radiation beam. A large, single fraction
of radiation is directed onto the target surface during the operative
procedure, with the normal tissues physically distanced and protected
from the beam.

Although conceptually attractive, intraoperative external-beam
irradiation also has several limitations:

1) The most common technique for administering this treatment,
a linear accelerator, is quite expensive to install in a dedicated
operating room. This expense has seriously limited the number
of medical centers in this country that use this form of therapy.

Electron-beam irradiation can also be administered intraoperatively
by transporting the patient from the main operating room to the
radiation therapy facility. Afterward, the patient is either closed
in the radiation therapy facility or transported back to the main
operating room. There are obvious safety and logistic concerns
about subjecting anesthetized patients to this process. It is
also quite disruptive to the outpatient radiation therapy schedule.

2) It can be difficult to target complex surfaces, particularly
in the pelvis, retroperitoneum, or chest, with available electron
cones. Although the use of beveled cones enhances the capability
to treat most anatomic surfaces, in many cases effective intraoperative
orientation can prove quite awkward with the available or appropriate
electron cones.

3) Available electron cones have size limitations. When a large
surface requires treatment, it becomes necessary to use abutting
electron fields. This introduces the potential both for underdosage
and for overdosage at the junction of these fields [4]. Because
relatively large fractions are delivered (1,000 to 2,000 cGy),
the dose in an overlapped region can be substantial, increasing
the risk of toxicity.

4) The electron beam delivers a relatively homogeneous dosimetry.
Although not inherently disadvantageous, homogeneous dosimetry
does not allow for dose intensification within the treatment volume
that can be accomplished with brachytherapy.

All these issues notwithstanding, selected institutions have had
substantial success using the intraoperative electron beam [1-3].

High-Dose-Rate Intraoperative Radiation

At Memorial Sloan-Kettering Cancer Center, we have developed a
new program for intraoperative radiation therapy, high-dose-rate
intraoperative radiation therapy (HDR-IORT), that attempts to
combine the technical and dosimetric advantages of brachytherapy
with the conceptual and logistic advantages of intraoperative
electron-beam irradiation. The entire procedure is performed in
a specially designed OR. Thus, no intraoperative patient transportation
is required.

For radiation therapy delivery, we use an HDR remote afterloader.
This equipment is far less expensive than a linear accelerator,
allowing the treatment to be given in a more cost-effective manner.
Because the remote afterloader is portable, it can also be utilized
for other procedures in the outpatient facility when it is not
needed for intraoperative cases. This further enhances the cost
effectiveness of the program.

We have developed an applicator system that employs flexible,
intraoperative applicators of various sizes designed to contour
to any surface within the body (Figure 1). These applicators are
connected to the HDR remote afterloader using customized source
guide tubes. With this applicator system, a large, single fraction
of radiation therapy can be delivered to any tumor bed during
the surgical procedure.

Our new facility opened in November 1992. In the following sections,
we will describe the treatment facility, surgical procedure, and
HDR-IORT equipment and technique. We will also outline our preliminary
results using HDR-IORT in patients with locally advanced or recurrent
colorectal cancer-the predominant area of investigation to date.
Results of treatment in other tumors under study, including retroperitoneal
sarcoma, selected pediatric tumors, advanced or recurrent gynecologic
malignancies, and malignant pleural mesothelioma, will not be
discussed.

Treatment Facility

As mentioned above, all HDR-IORT procedures take place in an operating
room located in the Brachytherapy Suite in the Department of Radiation
Oncology. This facility was designed and constructed under the
auspices of a multidisciplinary group of radiation oncologists,
surgical oncologists, anesthesiologists, nurses, physicists, and
hospital administration personnel. The operating room is a full-service
facility, allowing for the performance of all major operative
procedures, and has all of the necessary support services of the
main operating room. It is fully shielded for the delivery of
radiation therapy.

During the actual radiation therapy delivery, all personnel obviously
must leave the room, and thus, the anesthetized patient remains
alone in the operating room for an extended period. Our facility
has a remote-control station with a duplicate set of monitors
immediately outside of the operating room in an area where the
radiation oncologist, surgeon, and operating nurse can remain
gowned and gloved. This station allows for identical monitoring
of the patient during the delivery of radiation therapy as is
possible in the operating room.

Video cameras, installed in several strategic locations in the
operating room, can be controlled by the anesthesiologist, who
sits at the monitoring station just outside the operating room.
They provide complete, consistent visual backup to the online
monitoring of the patient's vital signs, ECG tracing, arterial
or central line, endotracheal tube, and face. A remote, computer-controlled
software system regulates the rate of infusion of two intravenous
fluids, three syringes with drugs, and blood products.

Using a separate video system, the radiation oncologist and surgeon
can remain scrubbed and view the operative field and brachytherapy
application. Any malfunction of the remote afterloader, movement
of the applicator or disruption of the source guide tubing, or
obvious bleeding would be immediately observed on the color video
monitor. For any reason, whether related to anesthesia, radiation,
or surgery, the treatment can be instantaneously interrupted by
the press of a button. When the button is pressed, the radioactive
source is immediately retracted, the door to the room opens, and
the patient's needs can be handled literally within seconds. Once
these needs have been satisfied, radiation treatment can be resumed.

Patients who undergo major operations and intraoperative radiation
procedures recover in the main recovery room. They are transported
from the Brachytherapy Suite to the recovery room on a life-support
gurney that allows for full monitoring and resuscitation of the
patient. Total transport time is 5 to 8 minutes.

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