Similarly, the lumpectomy scar and axillary scar are wired to permit their visualization on x-rays taken within the simulator suite. Suitable beam trajectories are chosen such that the medial and lateral entry points encompass all of the breast tissue and limit the exposure to the lung and, in the case of left-sided lesions, to the heart.
Furthermore, the beam trajectories must be evaluated closely to assure that the medial aspect of the contralateral breast is not being irradiated. Final beam trajectories will satisfy the requirement to treat all breast tissue and minimize the dose to lung, heart and contralateral breast. Permanent tattoo marks are placed to be utilized in coordination with calibrated laser beams, both in the simulator and treatment suites, to assure accurate daily treatment setup.
A customized plan is generated to modify the distribution of radiation dose throughout the breast tissue to enhance dose homogeneity. Without such planning and dose homogenization efforts, undesirably high doses in certain areas of the breast will result. Once the above calculations have been finalized and all appropriate beam-modifying devices have been specified, the patient is ready to start treatment. In the future, technological advances in the planning and delivery of radiation therapy, such as intensity-modulated conformal therapy, will permit even greater sparing of surrounding normal tissues.
Ordinarily, the entire breast is treated to 46-50 Gy in approximately 5 weeks of daily treatment, Monday through Friday. Ordinarily, the primary site is boosted so that it receives a total dose of 60 Gy.
The placement of small surgical clips within the lumpectomy cavity greatly enhances the ability of the radiation oncologist to completely cover the biopsy cavity with the boost. Utilizing the scar as an external landmark and the clips to define the biopsy cavity, a boost field can be designed to assure that the proper dose is being delivered thoroughly to the region that clearly has the highest risk of microscopic residual disease. Investigators have shown that the spatial correlation between the external scar and the biopsy cavity is imperfect and unreliable.
Other investigators have utilized ultrasound to localize the biopsy cavity. The placement of small surgical clips in the biopsy cavity not only enhances the design of radiation therapy treatments. It is very helpful to the breast radiologist in directing attention, once again, to the area that will in the future be the most complicated and most in need of careful mammographic analysis.
Karen D. Schupak
American College of Physicians