A single isocenter technique using CT-based planning in the treatment of breast cancer

Breast cancer will afflict 1 of every 9 women. With advances in mammography and public awareness, breast cancer is being detected at an earlier stage and is therefore more curable. The combination of lumpectomy and radiotherapy is a standard treatment option for most women with stage I and II invasive breast cancer. Radiotherapy treatment fields are usually tangential to encompass the breast, and in some cases, matched to a supraclavicular field. Due to variation in the size and shape of the breast, dosimetry and treatment planning can be challenging, yet many radiation oncology centers still achieve a treatment plan of the breast by using a single plane hand-generated contour 2-dimensional (2D) through the center of the breast. This type of planning neglects the variations in contours and chest-wall separation superior and inferior to that plane, which significantly impacts dose homogeneity and dosimetry. Computed tomography (CT) images are being utilized more often for planning in radiotherapy and should be considered for breast planning. CT-based treatment planning 3-dimensional (3D) allows the planner and physician to evaluate the dosimetry across the entire breast. Consequently, the plan can be optimized to limit lung volume with selective blocking, and minimize hot spots by using a higher energy and less wedge angle, thus improving dose homogeneity. For a larger breast, when the dosimetry using 6 MV is undesirable, a mix of 6 MV and higher energy may be used. This paper describes a single isocenter treatment technique using CT-based planning for tangents and a supraclavicular field and the advantages our department has found using 3D treatment planning vs. 2D. In addition, the creative planning done for larger breasts and the use of 18 MV combined with 6 MV to optimize a treatment plan will American Association of Medical Dosimetrists.