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.