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Brachytherapy in the Treatment of Breast Cancer

Brachytherapy in the Treatment of Breast Cancer

ABSTRACT: Whole-breast external-beam radiation therapy (EBRT) involves a 6-week course of fractionated treatments. In contrast, brachytherapy can be completed in a 4- to 5-day treatment course. Because of this shortened time frame, there has been interest in breast brachytherapy as a sole modality after lumpectomy. The American Brachytherapy Society (ABS) has issued guidelines specifically for the use of brachytherapy in breast carcinoma. In these guidelines, the ABS addresses important areas of controversy related to the indications, execution, and evaluation of breast implants when utilized in the following settings: as the sole treatment modality following lumpectomy, as an alternative to a 6-week course of EBRT following lumpectomy, as a boost following whole-breast irradiation, and for the treatment of local recurrences following breast-conservation treatment. The ABS recommends a precise definition and meticulous delineation of the clinical target volume. In addition, the Society recommends the routine use of dose-volume histograms and a dose-homogeneity index as tools to ensure reproducible brachytherapy and to allow interinstitutional comparisons. Brachytherapy as a sole modality is currently considered investigational and should be performed in the context of a controlled clinical trial. Practitioners and cooperative groups are encouraged to use these guidelines to formulate treatment and dose-reporting policies, but responsibility for medical decisions ultimately rests with the treating radiation oncologist. [ONCOLOGY 15(2):195-207, 2001]

Introduction

Breast brachytherapy has been in
use for most of the 20th century.
In the 1920s, Keynes used interstitial radium needles to implant the entire
breast, and frequently, the peripheral lymph nodes, to treat cancer of the
breast.[1] With the advent of megavoltage radiation, external-beam radiation
therapy (EBRT) was used to treat the whole breast, with brachytherapy being
utilized as a boost for unresected tumors. The high total doses resulted in poor
cosmetic results, and therefore, the trend was to perform lumpectomy followed by
EBRT and lower doses of brachytherapy.[2,3]

Published reports, however, showed that lumpectomy (with
biopsy-negative margins) followed by EBRT without an intersitial boost was as
effective as mastectomy.[4] This raised the question of whether boosts were
necessary. In addition to these reports, the widespread availability of the less
invasive electron-beam boost led to a decline in the role of brachytherapy boost
in treating primary breast cancers.

Whole-breast EBRT involves a 6-week course of fractionated
treatments. In contrast, brachytherapy can be completed in a 4- to 5-day
treatment course.[5-7] This feature has renewed interest in breast brachytherapy
as a sole treatment modality after lumpectomy. The American Brachytherapy
Society (ABS) recognizes that EBRT is the standard radiation modality used in
the treatment of breast cancer. Brachytherapy is an alternative that is being
investigated for specific circumstances.

The ABS Guidelines
for Brachytherapy

Breast brachytherapy techniques vary widely, and few radiation
oncologists have extensive experience in this realm. Because limited guidelines
exist for the clinical use of this therapy,[8] the ABS formed a panel to issue
guidelines specifically for the use of brachytherapy in breast carcinoma.

The ABS panel consisted of selected ABS members with expertise
in breast brachytherapy. The panel performed a literature review, and
supplemented with their clinical experience and biomathematical modeling,
formulated specific recommendations and directions for future investigations in
breast brachytherapy. Technical details were also included to benefit readers
who may not be able to find such details in standard textbooks.

Recommendations were made by consensus and supported by evidence
in the literature whenever possible. The ABS’s categories of consensus are
similar to those used by the National Comprehensive Cancer Network.[9] Unless
specifically noted, these recommendations generally reflect a category 2
consensus. Definitions of categories 1 through 3 are as follows:

Category 1: There is uniform panel consensus based on
high-level evidence that the recommendation is appropriate.

Category 2: There is panel consensus based on lower-level
evidence, including nonpublished clinical experience, that the recommendation is
appropriate. There is no major disagreement among panel members.

Category 3: There is major disagreement among panel members
that the recommendation is appropriate.

The initial report was revised due to additional comments of
external experts who were not members of the panel. These reviewers are listed
in the acknowledgments below. The Board of Directors of the ABS approved the
final document.

Please note: These guidelines represent a
consensus of the authors regarding a currently accepted treatment. These
guidelines will be updated as significant new outcome data are available. Any
clinician following these guidelines is expected to use clinical judgment to
determine an individual patient’s treatment. The American Brachytherapy
Society makes no warranties of any kind regarding the use of these guidelines
and disclaims any responsibility for their application in any way.

General Considerations Regarding Technique

Clinical Target Volume

The ABS recommends precise definition and meticulous delineation
of the clinical target volume. There are various methods of identifying this
parameter, including the use of surgical clips, computed tomography (CT),
magnetic resonance imaging (MRI), ultrasound, nonionic radio-opaque contrast
material, and/or direct visualization at the time of surgery.[8,10-12] Patients
should be seen by both a surgeon and radiation oncologist before treatment.

The optimum volume to be treated by breast brachytherapy is
controversial; treating too small a volume would result in high recurrence
rates.[13,14] The ABS currently recommends a 2-cm margin around the lumpectomy
cavity. This results in the irradiation of a large volume, but reduces local
recurrence. Only controlled clinical trials will be able to demonstrate whether
it is possible to treat a smaller volume and still obtain good local control.

The clinical target volume is defined as the volume encompassed
by an irregularly shaped surface approximately 2 cm outside of the excision
cavity, unless extending the margin would go beyond the breast tissue.[8] If the
skin restricts the superficial margin, then the superficial target margin is
redefined as 0.5 cm below the skin surface. Similarly, if the chest wall
restricts the deep margin, the new deep-target margin boundary would be
redefined as the surface of the chest wall.

The margin can be modified under special circumstances,
depending on the tumor size and extent of surgical resection (consensus category
3). For brachytherapy, the clinical target volume is the same as the
planning-target volume. In order to guarantee adequate coverage, the treated
volume is ideally larger than the target volume.[8]

Treatment Planes

The ABS recommends using a minimum of two planes, unless the
amount of breast tissue limits the target volume to less than a 2-cm thickness.
For a larger target volume (> 2.5- to 3-cm thickness), additional planes
should be considered.

Optimized values of interplanar spacing for a range of biplanar
implant sizes are available.[15-17] Within a given plane, the separation between
catheters is 1.0 to 1.5 cm. Ideally, the catheters should extend 1 to 2 cm
beyond the edge of the clinical target volume. Coverage of the target volume
along the length of the catheters is determined by the length of the active
sources or dwell positions along each catheter. They should also extend 1 to 2
cm beyond the target volume.

To allow for this, skin entry and exit points should extend 2 to
4 cm beyond the edge of the target volume. This will allow a "dead
space" of 1 to 2 cm from the last radioactive sources to the skin, which
minimizes the risk of skin hyperpigmentation and telangiectasia.[8] To minimize
the risk of a high dose to the ribs, a minimum distance of 0.5 cm between
catheters in the deep plane and the ribs is suggested.

If a wide separation between catheters or planes is noted, or if
a peripheral edge at the clinical target volume is not covered by the
prescription isodose curve, it is preferable to insert additional catheters to
avoid underdosage. Similarly, if the target volume is thicker on one side,
additional crossing catheters may be required to adequately cover the thicker
side. A less desirable alternative would be a higher weighting (increased dwell
times) on the thicker side. However, this may lead to problematic local
high-dose regions surrounding these catheters.

Catheter Concerns

The ABS deems the use of rigid templates as optional. The
advantage of templates is that they effect precise geometric source
distributions. However, this strategy may produce coverage problems in cases of
curved, irregularly shaped target volumes. The freehand technique, especially
with an open wound, permits catheter placement that conforms to the shape of the
lumpectomy cavity. Nonetheless, this may result in less uniform isodose
distributions.

The ABS recommends the appropriate use of dose optimization in
high-dose-rate therapy. However, optimization should not be used to compensate
for inadequate or improper catheter placement. It is preferable to have too many
catheters implanted rather than too few. Since the catheters are commonly left
in place for 1 to 2 weeks when brachytherapy is used as a sole modality, the ABS
recommends appropriate catheter care to reduce the risk of infection and
minimize discomfort.[8]

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