Introduction
Breast cancer is a heterogeneous group of diseases in which cells originating most commonly from the ducts and lobules in the breast tissue, change and divide uncontrollably with the resulting formation of a lump or mass. Breast cancer is the most common cancer in women throughout the world, representing a major public health problem. In the United States, breast cancer is the most frequent cancer in women and the second most frequent cause of cancer death in females. The American Cancer Society estimates that in 2019 in the United States, there will be approximately 268,600 new cancer cases of invasive breast cancer diagnosed in women. An additional 2,670 cases will be diagnosed in men. Approximately 62,930 cases of in situ (pre-invasive) breast cancer will be diagnosed (ductal carcinoma in situ or lobular carcinoma in situ) in women. It is anticipated that 41,760 women and 500 men will die from breast cancer in 2019.
Radiation Therapy in the Treatment of Breast Cancer
Breast cancer is most commonly a disease of women. In the United States, approximately 1 in 8 women (13%) will be diagnosed with invasive breast cancer in their lifetime and 1 in 39 women (3%) will die from the disease. The risk in men is significantly less. Most cases of breast cancer are sporadic. Despite an association between the BRCA 1 and 2 genes and breast cancer, genetically associated breast cancer comprises approximately 10% of all cases. However, with extended genetic testing, newer genes associated with breast cancer are emerging.
The use of screening mammography has greatly changed the outcome of patients with breast cancer where most women are now diagnosed with small, lymph node–negative disease. The cure rate for early stage breast cancer is above 95%.
Radiation is utilized to treat malignant neoplasms and some forms of benign disease marked by an excessive proliferation of cells. Radiation Therapy (RT) therefore is effective in killing cancer cells. Radiation kills cells by damaging DNA strands. There are two primary mechanisms of radiation damage. In the direct action the particle directly affects the clinical target (DNA) inside the cell. The indirect action of radiation is a result of the interaction of the radiation (primarily photons or electrons) with molecules in the cell producing free radicals, which in turn will cause DNA damage ( Fig. 9.1 ). Contrary to normal cells, tumor cells lack repair mechanism that can correct the DNA damage caused by radiation and therefore cell death ensues.
RT is an integral component in the treatment of breast cancer. In patients with early stage disease, surgical options include a lumpectomy and sentinel lymph node biopsy also known as breast conservation. In this setting, RT reduces the local recurrence rates by 50%–70%. RT is also utilized in patients having positive lymph node disease at surgery either after lumpectomy and sentinel lymph node biopsy or mastectomy. In this patient population, radiation is delivered not only to the breast and chest wall regions but also to the regional lymph node basins. In this setting, RT has been shown to not only decrease local recurrence but also improve overall survival.
For breast cancer patients with locally advanced disease and patients with inoperable disease, RT is utilized in the palliative treatment of bleeding, chest wall pain and brachial plexus neuropathy, and for relief of symptoms in patients with metastatic disease. In this chapter, we will discuss primarily the role of RT in the curative setting.
RT is utilized in the majority of patients diagnosed with early stage breast cancer after lumpectomy and in patients with lymph node positive disease after lumpectomy or mastectomy. The majority of patients with breast cancer are eligible for RT. However, in patients who are entertaining the possibility of breast conservation, RT is not indicated for patients with collagen vascular disease, more specifically, scleroderma and patients with active, uncontrolled systemic lupus erythematosus. These patients are at risk for development of severe fibrosis after RT. Another group of patients for whom RT should be used with caution are patients with mutations in the ATM gene. Ataxia telangiectasia is a mostly neurological disease caused by a defect in the ATM gene, which is responsible for recognition of DNA damage and its repair. These patients are at risk of complications from radiation exposure.
Types of Radiation Therapy for Breast Cancer
Patients diagnosed with preinvasive (in situ) disease and those with invasive breast cancer with pathologically negative lymph nodes are candidates for RT to the breast tissue only. In this setting the primary goal of RT is to reduce local recurrence. Radiation is delivered to the whole breast tissue or to the area of tissue surrounding the lumpectomy cavity as most recurrences will occur within 0.5–0.8 cm from the periphery of the lumpectomy cavity.
For patients with early stage, lymph node negative breast cancer, two methods of RT can be utilized-partial breast irradiation (PBI) and whole breast irradiation therapy.
Partial Breast Irradiation
A select group of patients with breast cancer who undergo a lumpectomy, are candidates for treatments to the lumpectomy area alone without the necessity of exposing the entire breast tissue to RT. Patients that qualify for PBI include
- •
age ≥40
- •
tumor ≤3 cm
- •
negative margins
- •
ductal carcinoma in situ, invasive ductal carcinoma and invasive lobular carcinoma
- •
any receptor status
- •
focal lymphovascular invasion
- •
negative lymph nodes
This type of radiation is called accelerated PBI (APBI). The early clinical trials that revealed equivalence between breast-conserving surgery followed by RT and mastectomy, utilized traditionally radiation regimens of 1.8–2 Gy per fraction to a total dose of 45–50 Gy to the whole breast and an additional 5–8 fractions to the lumpectomy cavity (usually called boost field). Therefore patients underwent radiation typically for 5–6.5 weeks of treatment. Many patients that underwent breast-conserving surgery ultimately did not receive the necessary RT due to the inconvenience of several weeks of radiation most notably in patients living in rural areas, elderly patients with transportation difficulties as well as younger women for whom the commitment to RT for several weeks created a burden on the daily living schedules with work and care of family and children. Currently, several single institution experiences as well as randomized trials in the United States and Europe have established the effectiveness, safety, and equivalent local control with the utilization of RT to the lumpectomy cavity only (PBI) in qualified patients. In addition, the cosmetic result has been excellent, particularly in patients undergoing partial breast radiation with brachytherapy, which treats a smaller volume of breast tissue.
Brachytherapy is a technique by which RT is delivered to the tissue via radioactive seeds. The most common isotope utilized in brachytherapy for breast cancer is iridium 192 that delivers gamma rays. Usually, a device or several small hollow catheters are placed inside or around the lumpectomy cavity. The radioactive source then will reach the proper location via the catheters. Some methods of delivering this type of radiation are illustrated next ( Fig. 9.2 ).
Radiation Dose in Accelerated Partial Breast Irradiation
From its early inception until recently, patients undergoing APBI would be treated twice a day at a dose of 3.4 Gy to the planning target volume (PTV) corresponding to the lumpectomy cavity with an added 1 cm margin deeming the PTV. This dose was delivered for a total of 10 fractions culminating with a total dose of 34 Gy to the PCV and five treatment days. A recently multiinstitutional clinical trial was published reporting on a three fraction regimen of 7.5 Gy per fraction to a total dose of 22.5 Gy delivered over 2–3 days. The triumph–T trial reported excellent cosmetic outcomes and comparable recurrence rates to the experience with whole breast radiation and accelerated partial breast radiation from multiple single institutional trials, registry trials, and randomized phase 3 clinical trial.
Whole Breast Irradiation
The majority of patients with early stage breast cancer who may not be eligible for PBI receive RT to the whole breast tissue. Traditionally, patients have been treated in the supine position with the arms raised above the head. Merchant and McCormick were pioneers in introducing prone positioning for patients receiving radiation to the whole breast. In their early experience, patient selection was limited to women who had large, pendulous breasts. Given the benefits of a reduced dose to the chest wall and to lungs and heart, most radiation oncology departments that treat a large volume of breast cancer patients have embraced prone positioning for early-stage breast cancer.
Fig. 9.3 demonstrates the prone breast radiation treatment setup. Fig. 9.4 illustrates the advantages of the prone position in minimizing the exposure to radiation dose to the lung, heart, and the contralateral breast. In Fig. 9.5 the supine position is demonstrated for comparison. It is important that for each of these positions, the patient needs to have an adequate range of motion for both shoulders to be able to tolerate lying in the required treatment position during the RT session. Figs. 9.6–9.9 demonstrate the radiation fields as they correlate with important muscles for shoulder function, including the pectoralis major, pectoralis minor, serratus anterior, infraspinatus and subscapularis, and brachial plexus ( Fig. 9.10 ).
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
