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principles of radiation therapy in breast cancer
Whole Breast Radiation
Target definition includes the majority of the breast tissue, and is best done by both clinical assessment and CT-based treatment planning. A uniform dose distribution and minimal normal tissue toxicity are the goals. The breast should receive a dose of 45-50 Gy in 23-25 fractions (long course is preferred for patient need regional nodal radiotherapy) or 40-42.5 Gy in 15-16 fractions (short course is preferred for most patients). A boost to the tumor bed is recommended in patients at higher risk (age <50 and high-grade disease). This can be achieved with electron beam or photon fields. Typical doses are 10-15 Gy at 2.5 Gy/fx. All dose schedules are given 5 days per week.
Chest Wall Radiation (including breast reconstruction)
The target includes the ipsilateral chest wall, mastectomy scar, and drain sites where possible. Depending on whether the patient has been reconstructed or not, several techniques using photons and/or electrons are appropriate. CT-based treatment planning is encouraged, in order to identify lung and heart volumes, and minimize exposure of these organs. Special consideration should be given to the use of bolus material when photon fields are used, to ensure the skin dose is adequate. Dose is 50-50.4 Gy, given as 1.8-2.0 Gy fraction size (± scar boost at 2 Gy per fraction to a total dose of approximately 60 Gy), all dose schedules are given 5 days per week.
Regional Nodal Radiation
Target delineation is best achieved by the use of CT-based treatment planning. For the paraclavicular and axillary nodes, prescription depth varies based on the anatomy of the patient. For internal mammary node identification, the internal mammary artery and vein location can be used as a surrogate for the nodal locations, which usually are not visible on imaging. Dose is 50-50.4 Gy, given as 1.8-2.0 Gy fraction size; all dose schedules are given 5 days per week. Based on the modern post-mastectomy radiation randomized trials and other recent studies, consider including the internal mammary lymph nodes when delivering regional nodal irradiation. CT treatment planning should be utilized in all cases where radiation therapy is delivered to the internal mammary lymph node field.
For Patient with Neoadjuvant chemotherapy
Indications for radiation therapy and fields of treatment should be based upon the pretreatment tumor characteristics in patients treated with neoadjuvant chemotherapy.
Axillary Radiotherapy
No axillary irradiation if axillary clearance is adequate. For T1 patients with clinically negative axilla and 1-2 positive sentinel lymph node, axillary radiation may replace axillary dissection level I/II for regional control of disease.