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Radiation Therapy for Breast Conservation

 
 
Radiation Therapy for Breast Conservation: Overview
Chris Rose, MD
Dept. of Radiation Oncology
Providence Saint Joseph Medical Center, Burbank
 
Although radiation had been shown to be effective in the treatment of breast
cancer as far back as 1936 when Sir Geoffrey Keynes first published his
series from England, the randomized controlled studies by surgeons Umberto
Veronese in Italy and Bernard Fisher in the USA in the early 1980's caused
this treatment to be seen to be more widely accepted. Indeed, the most recent
NCI Consensus Conference in 1989 states that conservative management with
radiation and partial mastectomy is the preferred alternative for most women
with early breast cancer.
 
Conservative management is safe and equivalent to mastectomy for most women.
All T1 and T2 tumors can be treated with radiation (up to 5 cm in diameter),
as long as the partial mastectomy does not result in marked asymmetry of
breast size. Also, patients with T3 tumors can be irradiated if the
lumpectomy does not result in significant breast asymmetry. Patients with
multiple gross tumors in the breast widely spread apart in two quadrants
probably are best managed with mastectomy. Patients with associated ductal or
lobular carcinoma in situ can be treated with radiation as long as the
microscopic margins can be cleared surgically, or there is no more than focal
marginal involvement. Even patients with subareolar primaries are acceptable
candidates, but the appropriate surgery sometimes means that the patient will
have a partial or total amputation of the nipple/areolar complex. Patients
with axillary involvement are also acceptable candidates, though the nodal
involvement implies that they will need chemotherapy first, if they are
premenopausal. Patients with involvement of the axillary fat, or patients
with greater than 3 involved lymph nodes will also require supraclavicular
and axillary apical irradiation, though this increases the risk of
significant arm edema to about 10%.
 
The technique of radiation therapy for early breast cancer is conceptually
simple. Prior to initiation of treatment, a unilateral mammogram should be
performed with magnification views to document the complete removal of all
calcifications by the partial mastectomy. The entire breast is radiated to a
dose of between 4600 and 5000 cGy. Depending upon the pathology either the
lower or the higher dose is employed: for patients with significant DCIS, or
lymphatic involvement, the higher dose is used. Then the area of the
tumorectomy is "boosted" with additional focal irradiation (either via
interstitial brachytherapy--tubes of radioactive Iridium-192 which are
inserted into the breast tissue, or via the electron beam which has a well
defined path length of radiation deposition, totally dependent upon the
energy of the incident electrons) so that the total dose to this "cone-down"
volume is between 5600 and 6600 cGy. Again the pathologic findings determine
the dose. For patients with relatively encapsulated tumors, no or little
DCIS, and widely cleared margins, a total dose of 5600 cGy is employed. For
patients with well encapsulated tumors and close margins doses in the range
of 6200-6400 cGy are employed. For tumors with a lot of DCIS, or involved
margins doses of 6600 cGy are employed.
 
The actual treatments are done with the patient lying in the supine position
with her arm abducted over her head in a foam cradle. Medial and lateral
tangential portals are constructed to treat the breast and the underlying
muscle and approximately 1 cm of underlying lung. The latter measurement is
chosen to make sure that the intercostal lymphatics are included in the
treatment volume. The lateral field is usually situated approximately 30
degrees below the horizontal and the opposed medial field is then
approximately 60 degrees beyond the vertical so that the two fields are 180
degrees apart. Actually the fields are usually 184-188 degrees apart so as to
oppose the deep edges of the two beams and limit the dose incident on the
underlying lung. The collimator which defines the rectangular shape of the
beam is also rotated so that the beam parallels the sloping contour of the
sternum, as closely as possible. Sometimes a "tilt table" is placed on the
treatment couch and raised about 10-20 degrees so as to make the sternum
parallel with the couch table. This latter technique is particularly useful
for women with large breasts to prevent cephalad movement of the breasts with
the patient in the straight supine position. It also obviates the need to
rotate the collimators, since the sternum is automatically made parallel to
the collimators in the un-rotated angulation. The boost is critically
dependent upon the radiation oncologist knowing where the original tumor was
removed. This task is made much simpler when the breast surgeon remembers to
place small silver clips at the superior, inferior, medial, lateral, and deep
margins of the breast resection cavity. When clips are not present, the
radiation oncologist is forced to rely upon the site of the incision, the
pre-op mammogram, and the patient's recollection. Studies which have
correlated clip position with the latter methods all show distinct
inferiority of the indirect methods. Another direct method that can be
employed is ultrasound localization of the residual biopsy cavity, or
fat/tissue interface.
 
When the axilla and supraclavicular nodal groups require irradiation, the
technique is much more complicated to prevent overdosage or underdosage along
the inferior edge of the supraclavicular/axillary field as it abuts the two
tangential breast fields. Since the superior edges of the two tangential
fields are diverging towards the patient's head, it is impossible to match
any one supraclavicular field oriented in an antero-postero direction to the
tangents. Sometimes the tangent fields are blocked to remove the divergent
edges. Sometimes the treatment couch is rotated 3-5 degrees away from the
beam to make the two medial and lateral superior borders parallel to each
other. Either technique allows the creation of a direct match with the AP
supraclavicular field when its divergence is removed by the use of a block at
its central axis.
 
Previously, patients were subjected to biopsies years after the irradiation
because of the development of a band of linear fibrosis at the superior edge
of the breast. This so-called "match line fibrosis" has been avoided by the
use of the field matching techniques, described above.
 
The long term results from the large cooperative groups and university
centers show survivals absolutely equivalent to those for mastectomy.
Actually the most recent meta-analyses suggest that for node-positive
patients radiation is statistically superior to mastectomy. Whether this is
due to selection factors (paradoxically it is the patients with more
extensive, multi-focal tumors who now have mastectomies) or due to the
potential advantage of irradiating the internal mammary lymph nodes in
patients with a 15-45% probability of internal mammary involvement, cannot be
determined. Nevertheless, looking at all of the published series, for
patients with T1 tumors the 10 year local control rate after radiation and
partial mastectomy is between 90-95%. For patients with T2 tumors the local
control rate is between 82-90%. Note that all of the failures are not local
recurrences. Because the breast is left in place it is at risk for new
tumors. The absolute rate of new tumor formation is approximately 1/2-3/4%
per year. Thus 20 years post radiation, women have a 10-15% chance of
developing a new cancer either in the irradiated or contralateral breast.
This risk does not seem to transform itself into a higher risk of death,
presumably because this cohort of women is followed closely and the new
tumors tend to be small. Side effects from the treatment include: 1)
fatigue, 2) some degree of cosmetic alteration, usually a slight uplifting of
the breast with mild fibrosis, 3) hypopigmentation of the nipple, 4) some
degree of breast muscle tenderness due to pectoral muscle radiation myositis,
and 5) a 2-5% risk of rib fracture which is self-limited. Because the heart
and the lung are not in the tangential portals to any significant degree,
well placed fields should not result in radiation pneumonitis, or carditis. A
meta-analysis from Great Britain disclosed an increased risk of death in
patients radiated post-operatively to the left breast only. Further analysis
demonstrated that the women had excess atherosclerotic morbidity. With the
abandonment of direct, enface, techniques to treat the breast and internal
mammary lymph nodes, the more modern series have not reported this toxicity.
 
Breast preservation techniques demand life-long follow-up to detect
recurrences and new primary tumors which can be salvaged by subsequent
mastectomy. Follow-up regimes usually recommend a visit to the radiation
oncologist alternating with a visit to the surgeon every three months for the
first year, every four months for the second year, every six months for years
three through five and then once a year. Follow-up mammograms should be
performed 3-6 months after the conclusion of the radiation, once the post-op
and post-radiation edema has resolved, and then once a year. The treatment
guidelines document published by the American College of Surgery, the
American College of Radiology, and the American College of Pathology
recommends mammograms every six months for the first five years, but provides
no literature based evidence for this conclusion.